Field of the Invention

The present invention relates to a loudspeaker assembly for producing sounds at bass frequencies.

Background

Among the frequencies in the audible spectrum, lower frequencies are the ones that tend to carry most over large distances and are the ones difficult to keep inside a room. For example, nuisance from neighbouring loud music has mostly a low frequency spectrum. “Low” frequencies can also be referred to as “bass” frequencies and these terms may be used interchangeably throughout this document.

Many cars today are equipped with a main audio system, which typically consists of a central user interface console with internal or external audio amplifiers, and one or more loudspeakers placed in the doors. This type of audio system is used to ensure enough loudness of the same content (e.g. radio) for all passengers.

Some cares include personal entertainment systems (music, games & television) which are typically equipped with headphones to ensure individual passengers receive personalised sound, without disturbing (or being disturbed by) other passengers who are enjoying a different audio-visual content.

However, although the usage of headphones ensures a good sound quality and a very effective personal sound cocoon (little sound leakage), the use of headphones has safety, ergonomic and comfort problems. Similar considerations apply in other environments such as home, studio, and public areas where individual entertainment is needed without disturbing neighbours.

Some cars include loudspeakers placed very close to an individual passenger, so that sound having an adequately high sound pressure level (“SPL”) can be obtained at the ears of that individual passenger, whilst having a much lower SPL at the positions of other passengers.

The present inventor has observed that the concept of a personal sound cocoon is a useful way to understand the approach of having a loudspeaker placed close to a user, wherein the personal sound cocoon is a region in which a user is able to experience sound having an SPL deemed to be acceptably high for their enjoyment, whereas outside the personal sound cocoon the sound is deemed to have an SPL which is lower than it is within the personal sound cocoon.

It is known that the use of a highly directive loudspeaker positioned close to an individual passenger I user can bring an effective solution for medium and high frequencies. However, it is generally impractical in most situations to make a loudspeaker directive at bass frequencies, since in order to provide a highly directive loudspeaker for bass frequencies, the dimensions of the radiating surface must be of the same order as the wavelength, and wavelengths are typically very long for bass frequency content (e.g. A =3.4m for f = 100Hz). Loudspeakers with radiating surfaces of this scale for producing bass frequency content are impractical in many situations, such as in a car. Nonetheless, bass frequency content is a very important part of the audio spectrum and in most music this spectrum represents half or more of the total sound power.

It is known from WO2019/121266A1 that dipole loudspeakers can provide an effective personal sound cocoon at bass frequencies, thereby effectively providing a personal subwoofer. In particular, WO2019/121266A1 explains how sound produced by a first radiating surface of a diaphragm of such a dipole loudspeaker interferes with the sound produced by a second radiating surface of the diaphragm, and this interference results in beneficial effects that may help to create a personal sound cocoon at bass frequencies. In particular, for a suitably dimensioned diaphragm, from a listening position that is 40cm or less from the first radiating surface of such a loudspeaker (e.g. measured along a principal radiating axis of the first radiating surface), a user can experience bass sound that is highly localised, in the sense that the sound pressure level (SPL) experienced by a user will quickly attenuate with increasing distance from the loudspeaker.

Figs. and Fig. 17of WO2019/121266A1 show example dipole loudspeakers in which a diaphragm is suspended from a drive unit frame via drive unit suspensions, and the drive unit frame is itself suspended from a mounting frame via mounting frame suspensions.

The purpose of these mounting frame suspensions (referred to in WO2019/121266A1 as “secondary suspension elements) is given by WO2019/121266A1 as “to reduce vibrations passing from the loudspeaker into the environment”, see page 9 lines 3-4. WO2019/121266A1 further teaches an embodiment in which the mounting frame suspensions are tuned to have a resonance frequency that is well below the frequency spectrum over which the loudspeaker is intended to operate, thereby limiting the transmitted force on the ‘application’ (i.e. the car seat frame to which the mounting frame would in practice be connected), see page 24 lines 5-7.

WO2019/121266A1 acknowledges that in some cases, someone may want to use residual vibrations from the loudspeaker, but indicates in most cases the residual vibrations from the loudspeaker are unwanted since .they could distract from a “pure bass” experience, see page 21 line 36 - page 22 line.

The present inventor has found that space inside a car headrest for integrating a bass dipole loudspeaker may be limited, due to design aspects, mechatronics, and the further inclusion of comfort elements and safety features, for example. The present inventor has thus found that providing a mounting frame suspension adjacent to, and around the periphery of, the diaphragm, as illustrated in Fig. 10 of WO2019/121266A1 can be an inefficient use of the space available inside the car headrest for obtaining a desired SPL at the listening position. The present inventor has also found that suspending a drive frame from mounting legs of a car headrest as shown in Fig. 17 of WO2019/121266A1 can, if the loudspeaker is mounted in an aperture inside a headrest, result in the acoustic output being diminished due to sound interference from the first and second radiating surfaces of the diaphragm of the loudspeaker (caused by an acoustic output short circuit) at the listening position of the user. The present inventor has observed that the amount of vibrations transmitted to a seat to which the loudspeaker of WO2019/121266A1 is fixed in the implementations considered so far, with this amount being defined by the design of the mounting frame suspension, which in general will be tuned so that as little as possible vibrations are transmitted during operation.

The present inventor has also observed that the amount of vibrations conveyed to a seat that are perceived as annoying or pleasant (contributing to the experience) are strongly dependent on: the situation in which one is listening to sound produced by the loudspeaker (e.g. noisy environment versus silent environment, driving or standing still); the content of the sound (e.g. speech vs music, dance music vs classical music); the listener’s mood; and the listener’s personal taste.

It is known to the inventors for a car to include active shaking devices in a car seat for enhancing the listening experience, but the present inventors observe that active shaking devices are often perceived by users as annoying due to the lack of correlation between the active shaking and the audio, and also due to their location in the seat.

The present invention has been devised in light of the above considerations.

Summary of the Invention

A first aspect of the present invention may provide:

A loudspeaker assembly for producing sound at bass frequencies, the loudspeaker assembly including: a loudspeaker, including: a diaphragm having a first radiating surface and a second radiating surface, wherein the first radiating surface and the second radiating surface are located on opposite faces of the diaphragm; a drive unit configured to move the diaphragm along a movement axis at bass frequencies such that the first and second radiating surfaces produce sound at bass frequencies, wherein the sound produced by the first radiating surface is in antiphase with sound produced by the second radiating surface; a drive unit frame, wherein the diaphragm is suspended from the drive unit frame via at least one drive unit suspension; and a mounting frame, wherein the drive unit frame is suspended from the mounting frame via a mounting frame suspension system that includes at least one mounting frame suspension; an adjustment mechanism configured to adjust the mounting frame suspension system so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

The adjustment mechanism thus permits a user to adjust the extent to which vibrations generated naturally by the action-reaction forces of the loudspeaker, when the loudspeaker is in use, are passed on to the mounting frame and thus on to a user sat in a seat which incorporates the loudspeaker (via a seat frame or other application to which the mounting frame is attached/part of).

Note that the vibrations generated naturally by the action-reaction forces of the loudspeaker are perceived as being “one” with the music, without the need for synchronisation between the music and active shaking devices, and thus the vibrations generated naturally by the action-reaction forces of the loudspeaker are much better integrated as compared with artificially generated vibrations, yet the amplitude of these vibrations can be adjusted by the user via the adjustment mechanism.

The extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use may be measured by operating the loudspeaker in a fixed way (e.g. to produce sound having a fixed frequency in the range 30Hz-60Hz, and to have a fixed amplitude at a defined measuring location) and measuring the magnitude of the resulting accelerations at the mounting frame, e.g. using an accelerometer attached to the mounting frame. If the acceleration measurements change following an adjustment of the mounting frame suspension system by the adjustment mechanism, this would indicate a change in the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system. If the maximum acceleration as measured by the accelerometer attached to the mounting frame increases following an adjustment of the mounting frame suspension system by the adjustment mechanism, this would indicate an increase in the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system.

Of course, the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use may be measured in other ways. For example, a user sat in a seat incorporating the loudspeaker assembly could subjectively evaluate whether the vibrations generated by the loudspeaker changed following an adjustment of the mounting frame suspension system by the adjustment mechanism, when the loudspeaker is operated in a fixed way (e.g. to produce sound having a fixed frequency in the range 30Hz-60Hz, and to have a fixed amplitude at a defined measuring location).

Preferably, the adjustment mechanism is configured to adjust a stiffness and/or resistance of the mounting frame suspension system via which the drive unit is suspended from the mounting frame.

A theoretical explanation showing why and how adjusting a stiffness and/or resistance of the mounting frame suspension system can affect the vibrations passed onto a user is provided below.

For avoidance of any doubt, a stiffness and/or resistance of the mounting frame suspension system may be adjusted by modifying a stiffness and/or resistance of one or more existing mounting frame suspensions (not necessarily all mounting frame suspensions, if there is more than one mounting frame suspension), or by introducing a new mounting frame suspension (having its own stiffness and/or resistance) which newly interconnects the loudspeaker frame and mounting frame. In some examples, a stiffness and/or resistance of the mounting frame suspension system may be adjusted “homogenously”, by modifying a stiffness and/or resistance of an existing mounting frame suspension in a manner that is homogenous along a path which extends along the existing mounting frame suspension and around the movement axis. See for example Fig. 2A and Fig. 4A, discussed below.

In some examples, a stiffness and/or resistance of the mounting frame suspension system may be adjusted “locally”, by modifying a stiffness and/or resistance of the mounting frame suspension system at only one or more predetermined locations. This might be achieved e.g. by modifying a stiffness and/or resistance of an existing mounting frame suspension at only one or more predetermined locations, or by introducing a new mounting frame suspension element which interconnects the loudspeaker frame and mounting frame at only one or more predetermined locations. See for example Figs. 3A-G, discussed below.

In the present application, the mounting frame suspension system may be referred to as having a “first configuration” and a “second configuration”. Preferably, the “first configuration” of the mounting frame suspension system is a configuration in which vibrations (caused by movement of the diaphragm) reaching a user in a seat which incorporates the loudspeaker are significantly inhibited compared with a “second configuration” of the mounting frame suspension system. The first configuration of the mounting frame suspension system may therefore be referred to herein as a “low vibration” configuration (these terms may be used interchangeably), and the second configuration of the mounting frame suspension system may therefore be referred to herein as a “high vibration” configuration (these terms may also be used interchangeably). For avoidance of any doubt, the mounting frame suspension system have other configurations in addition to a “first configuration” and a “second configuration”.

The mounting frame suspension system may be configured to have a first (e.g. “low vibration”) configuration.

In the first configuration, the mounting frame suspension system may have a resonant frequency in the range 10Hz-30Hz (inclusive), more preferably in the range 10Hz-20Hz (inclusive). In a first configuration having such a resonant frequency, relatively little of the vibrations produced by a moving diaphragm of the loudspeaker will reach the mounting frame via the mounting frame suspension(s), when the loudspeaker is in use to produce sound at bass frequencies. However, the resonance frequency is preferably not below 10Hz, since a resonance frequency below 10Hz can cause problems with static deflection (“Xstat”) as discussed below.

References herein to a “resonant frequency” of the at least one mounting frame suspension refer to a frequency at which, in use, the mass suspended from the mounting frame by the at least one mounting frame suspension is caused to resonate.

Preferably, in its first configuration, the stiffness and resistance of the/each mounting frame suspension is homogenous along a path which extends along the mounting frame suspension and around the movement axis. This helps to achieve a clearly defined resonant frequency (which as noted above is preferably in the range 10Hz-30Hz, more preferably 10Hz-20Hz), which can help to suppress vibrations. The at least one mounting frame suspension may be configured such that the static deflection of the at least one mounting frame suspension in the first configuration, at an angle a of 90°, is 2.5mm or less, more preferably 1 ,5mm or less. The at least one mounting frame suspension may be configured such that the static deflection of the at least one mounting frame suspension in the first configuration, at an angle a of 90°, is 0.5mm or higher. This corresponds to an arrangement in which there is a resonant frequency in the range 10Hz-30Hz.

Herein, a is an angle between a plane perpendicular to the principal radiating axis and a vertical direction, and “static deflection” of the at least one mounting frame suspension is the distance by which the mass suspended from the mounting frame by the mounting frame suspension system deviates from a rest position, where the rest position is defined as the position of the mass at a = 0°.

The mounting frame suspension system may be configured to have a second (e.g. “high vibration”) configuration.

Preferably, the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use is greater when the mounting frame suspension system is in the second configuration, compared with in the first configuration.

For example, the first and second configurations of the mounting frame suspension system may be such that, when the mounting frame suspension system is in the second configuration and the loudspeaker is operated at a frequency in the range 30Hz to 60Hz, the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system is greater than when the mounting frame suspension system is in the first configuration and the loudspeaker is operated at the same frequency.

Preferably, the mounting frame suspension system, in the second configuration, has a resonant frequency that is in the range 20Hz-60Hz (inclusive), more preferably in the range 30Hz-60Hz (inclusive). In this way, the extent to which vibrations generated by the loudspeaker, when the loudspeaker is operated at typical bass frequencies in the range 30-60Hz, is increased for the second configuration compared with the first configuration.

By way of example, the mounting frame suspension system, in the first configuration has a resonant frequency in the range 10-20Hz (inclusive), and in the second configuration has a frequency that is in the range 20Hz-60Hz (inclusive).

The adjustment mechanism may be configured to adjust the mounting frame suspension system so that the mounting frame suspension system changes from the first configuration to the second configuration.

If the adjustment mechanism adjusts the mounting frame suspension system to change from the first configuration to the second configuration by adjusting a stiffness and/or resistance of the mounting frame suspension system “homogenously” (see comments above), then the mounting frame suspension system may have a clearly defined resonant frequency in the range 20Hz-60Hz. If, on the other hand, the adjustment mechanism adjusts the mounting frame suspension system to change from the first configuration to the second configuration by adjusting a stiffness and/or resistance of the mounting frame suspension system “locally” (see comments above), then the mounting frame suspension system may have a less clearly defined resonant frequency in the range 20Hz-60Hz, for examples the resonant frequency in the range 20Hz-60Hz may be one of several resonant frequencies introduced by the locally adjusted stiffness and/or resistance.

A resonant frequency of the mounting frame suspension system may be referred to herein as a “tuning frequency” of the mounting frame suspension. The term “tuning frequency” would typically be used where the mounting frame suspension system has one clearly defined resonance (as is preferably the case in the first configuration, see above). However, the term “tuning frequency” is less useful if there are multiple or less clearly defined resonances (as may be the case in the second configuration, see above).

The at least one mounting frame suspension may be configured such that the static deflection of the at least one mounting frame suspension in the second configuration, at an angle a of 90°, is 1 mm or less, more preferably 0.5mm or less. The at least one mounting frame suspension may be configured such that the static deflection of the at least one mounting frame suspension in the first configuration, at an angle a of 90°, is 0.1 mm or higher. This corresponds to an arrangement in which there is a resonant frequency in the range 20Hz-60Hz.

For reasons explained below with reference to Figs. 9A-E, the adjustment mechanism is preferably configured to increase both the stiffness and resistance of the mounting frame suspension system in the second configuration, compared with in the first configuration. The stiffness [N/m] of the mounting frame suspension system in the second configuration is preferably increased by at least 50% (i.e. at least 1 .5x), more preferably at least 100%, compared with the first configuration. The resistance [Ns/m] of the mounting frame suspension system in the second configuration is preferably increased by at least 100% higher (i.e. at least double) compared with the first configuration.

A skilled person would appreciate there are a number of ways in which the adjustment mechanism may be configured to adjust the stiffness and/or resistance of the mounting frame suspension system.

In a first set of examples, the adjustment mechanism may be configured to mechanically adjust the mounting frame suspension system (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system).

For example, the adjustment mechanism may be configured to mechanically adjust mounting frame suspension system by deforming one or more mounting frame suspensions (not necessary each mounting frame suspension, if there is more than one mounting frame suspension), e.g. by bringing an additional (e.g. rigid) element of the mounting frame suspension into contact with one or more mounting frame suspensions.

For example, the adjustment mechanism may be configured to mechanically adjust the mounting frame suspension system by introducing a new mounting frame suspension (having its own stiffness and/or resistance) which newly interconnects the drive unit frame and mounting frame at one or more predetermined locations, thereby creating a new path for vibrations to pass from drive unit frame to mounting frame.

The introduction of a new mounting frame suspension may be achieved, for example, by bringing an additional element attached to a first one of the drive unit frame and mounting frame into contact with the other one of the drive unit frame and mounting frame at one or more predetermined locations. Preferably, such implementations would avoid hard contact between two rigid materials since that can cause “rattling” sounds. Accordingly, if the additional element is a rigid element, the contact between the additional element and the other one of the drive unit frame and mounting frame is preferably indirect contact, via a soft element (e.g. friction pad) which may formed on the additional element or the other one of the drive unit frame and mounting frame.

The introduction of a new mounting frame suspension may be achieved, for example, by bringing a first one of the drive unit frame and mounting frame into contact with the other one of the drive unit frame and mounting frame at one or more predetermined locations. Preferably, such implementations would avoid hard contact between two rigid materials since that can cause “rattling” sounds. Accordingly, the contact between the drive unit frame and mounting frame is preferably indirect contact, via a soft element (e.g. friction pad) which may formed on the drive unit frame or the mounting frame.

In some examples, the adjustment mechanism configured to mechanically adjust the mounting frame suspension system may include a pulling device configured to pull the drive unit towards a grille positioned in front of the second radiating surface of the diaphragm. The grille positioned in front of the second radiating surface of the diaphragm may be the second grille of the loudspeaker-mounting frame unit discussed below.

The pulling device may be configured to, by pulling of the drive unit towards the grille positioned in front of the second radiating surface of the diaphragm, cause the at least one mounting frame suspension to stiffen, thereby changing the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

The pulling device may be configured to, by pulling of the drive unit towards the grille positioned in front of the second radiating surface of the diaphragm, cause the drive unit to come into contact with at least one soft element (e.g. a soft pad) on the grille positioned in front of the second radiating surface of the diaphragm, thereby changing the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use (here, the at least one soft pad can be considered as a new mounting frame suspension which newly interconnects the drive unit frame and mounting frame at one or more predetermined locations).

The pulling device may be configured to pull the drive unit frame towards the grille via a length of flexible material (e.g. a rope, string or cable) attached to the drive unit or the drive unit frame. The length of flexible material may pass through a gap in the grille in order to reach the pulling device. This arrangement may allow the pulling device to be located laterally with respect to the grille and drive unit, e.g. with the pulling device being located in a position that, when projected onto a plane perpendicular to the movement axis, is outside of the portion of that plane taken up by the grille and drive unit, when projected onto that plane.

The pulling device may, for example, be a rotary motor or manual rotary knob, optionally with an asymmetric pulley.

In a second set of examples, the mounting frame suspension system may include at least one portion of flexible (preferably elastic) material which defines a hollow region, and the adjustment mechanism may include an air pressure control unit (which may be referred to as a pneumatic control unit) configured to adjust the air pressure inside the hollow region so as to (“pneumatically”) adjust the mounting frame suspension system (so as to change in the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system).

In some examples, the drive unit frame may be suspended from the mounting frame via a portion of flexible material, in which case the portion of flexible material may be viewed as a mounting frame suspension (see e.g. Figs. 4A, 4B).

In other examples, a portion of flexible material may be attached to a first one of the drive unit frame and the mounting frame, and configured to contact the other one of the drive unit frame and the mounting frame (preferably via a friction pad, e.g. formed on the other one of the drive unit frame and the mounting frame) when inflated so as to adjust the mounting frame suspension system (see e.g. Fig. 4D). In these examples, the portion of flexible material introduces a new mounting frame suspension which newly interconnects the loudspeaker frame and mounting frame, when the portion of flexible material contacts the other one of the drive unit frame and the mounting frame. In such examples, it should be appreciated that the portion of flexible material is not always in contact with both the drive unit frame and mounting frame, so would not always be acting as a mounting frame suspension.

The/each portion of flexible material may be elastic (e.g. rubber).

The at least one portion of flexible material may include a portion of flexible material that forms a hollow band which includes a hollow region which extends continuously around the drive unit frame. Thus, if the portion of flexible material is acting as a mounting frame suspension (see e.g. Figs. 4A, 4B), the stiffness and/or resistance of the mounting frame suspension system may be adjusted “homogenously” by inflating and/or deflating the hollow region.

In other examples, a portion of flexible material may include a hollow region which only partly extends around the drive unit frame.

In a third set of examples, the mounting frame suspension system may include an electroactive polymer, and the adjustment mechanism may be configured to adjust the mounting frame suspension system by applying an electric field to the electroactive polymer so as to alter the shape of the electroactive polymer (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system).

Electroactive polymers are polymers that exhibit a large change in size or shape when stimulated by an electric field. The adjustment mechanism may be configured to adjust the mounting frame suspension system to have a plurality of discrete configurations in which the stiffness and/or resistance of the at least one mounting frame suspension system is different.

Alternatively, the adjustment mechanism may be configured to adjust the mounting frame suspension system to have a continuum of different configurations in which the stiffness and/or resistance of the at least one mounting frame suspension system can gradually be adjusted, e.g. based on user input.

In some examples, the electroactive polymer may be attached to a first one of the drive unit frame and the mounting frame, and configured to contact the other one of the drive unit frame and the mounting frame (preferably via a friction pad, e.g. formed on the other one of the drive unit frame and the mounting frame) when an electric field is applied thereto so as to adjust the mounting frame suspension system.

In a fourth set of examples, the mounting frame suspension system may include a magnet attached to one of the drive unit frame and the mounting frame, and a magnetic element attached to the other one of the drive unit frame and the mounting frame, wherein the magnet is configured to magnetically interact with the magnetic element so as to influence relative movement between the drive unit frame and the mounting frame, wherein the adjustment mechanism is configured to adjust the magnetic interaction between the magnet and the magnetic element (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system).

The magnetic element may be a second magnet, but this is not a requirement, since it is also possible for the magnetic element to be a paramagnetic, ferromagnetic, or diamagnetic material, for example.

The adjustment mechanism may be configured to adjust the magnetic interaction between the magnet and the magnetic element in a number of ways. For example, if the magnet includes a permanent magnet, the adjustment mechanism may be configured to adjust the magnetic interaction between the magnet and the magnetic element by moving one of the magnet and magnetic element relative to the other of the magnet and magnetic element (as in the example of Figs. 6A-B) or by rotating the magnet relative to the magnet element. As another example, if the magnet is an electromagnet, the adjustment mechanism may be configured to adjust the magnetic interaction between the magnet and the magnetic element by changing the strength of the electromagnet (e.g. by increasing the current through the electromagnet). As another example, if the magnet is a magnetic switch (capable of being in an on state or an off state), the adjustment mechanism may be configured to adjust the magnetic interaction between the magnet and the magnetic element by changing the state of the magnetic switch from an off state to an on state (and vice versa). A skilled person would appreciate the different ways in which the adjustment mechanism may be configured to adjust the stiffness and/or resistance of the mounting frame suspension system discussed above, can be combined (see e.g. the example of Figs. 6A-B discussed below).

The loudspeaker assembly may include a control interface configured to control the adjustment mechanism so as to adjust the mounting frame suspension system (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system) based on user input at the control interface, e.g. so that the user can adjust the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system by providing an input at the control interface.

The control interface may be a moveable element, e.g. a rotatable knob, wherein the user can adjust the extent to which vibrations generated by the loudspeaker reach the mounting frame by moving the moveable element (e.g. by rotating the knob). Such a moveable element is preferably located on the headrest of a seat, if the loudspeaker is mounted within a headrest of a seat (see below).

The control interface may be a part of a graphical user interface, “GUI”, wherein the user can adjust the mounting frame suspension system by manipulating the GUI. Such a graphical user interface is preferably part of a graphical user interface displayed by an entertainment system of a vehicle having a seat assembly that includes the loudspeaker (see below).

Preferably, the/each mounting frame suspension, as projected onto a plane perpendicular to the movement axis, at least partially overlaps with one or more elements selected from the diaphragm and the at least one drive unit suspension as projected onto the same plane, wherein at least one mounting frame suspension is formed in a gap between the drive unit frame and the mounting frame and extends substantially continuously around the drive unit frame.

By extending substantially continuously around the drive unit frame, the at least one mounting frame is able to inhibit sound produced by the first radiating surface from reaching the second radiating surface via the gap. Accordingly, unwanted interference of the sound produced by the first radiating surface with the antiphase sound produced by the second radiating surface, at a listening position, is reduced at positions close to the first radiating surface (at larger distances, such interference will still take place, as is desired for a personal sound cocoon).

By forming the at least one mounting frame suspension in the gap between the drive unit frame and the mounting frame, it is possible to provide an effective baffle without necessarily increasing a maximum height of the dipole loudspeaker (e.g. the dimension of the dipole loudspeaker in a direction parallel to the movement axis).

By having the/each mounting frame suspension, as projected onto a plane perpendicular to the movement axis, at least partially overlap one or more elements selected from the diaphragm and the at least one drive unit suspension as projected onto the same plane, the effective radiating surface area of the diaphragm can be increased within a given space, e.g. within a mounting frame for accommodating a loudspeaker which may be part of the chassis of a headrest, e.g. in a car.

Moreover, by having the mounting frame suspension extend substantially continuously around the drive unit frame, the mounting frame suspension is able to reduce lateral rocking of the diaphragm/drive unit frame in any direction other than parallel to the movement axis, compared e.g. with a configuration as shown in Fig. 17 of WO2019/121266A1 .

For avoidance of any doubt, the/each mounting frame suspension, as projected onto a plane perpendicular to the movement axis, may at least partially overlap with the diaphragm only, one or more drive unit suspensions only, or both the diaphragm and one or more drive unit suspensions, as projected onto the same plane. If there are two or more drive unit suspensions, the mounting frame suspension may at least partially overlap with one of the drive unit suspensions, or with multiple (e.g. all) drive unit suspensions. If there are two mounting frame suspensions, each mounting frame suspension may at least partially overlap with the same one or more elements, or different one or more elements, selected from the diaphragm and the at least one drive unit suspension as projected onto the same plane.

Preferably, the phrase “extends substantially continuously around the drive unit frame” is intended to mean that the/each mounting frame suspension extends around the drive unit frame with no, few or small interruptions/discontinuities, preferably such that sound produced by the first radiating surface is inhibited, more preferably significantly inhibited, from reaching the second radiating surface via the gap. For example, large interruptions/discontinuities in a mounting frame suspension may mean that the mounting frame suspension provides virtually no inhibiting effect on sound produced by the first radiating surface from reaching the second radiating surface via the gap, whereas small or few discontinuities may still allow for a significant inhibiting effect to be provided.

The substantially continuously-extending mounting frame suspension may thus provide a baffle configured to inhibit sound produced by the first radiating surface from reaching the second radiating surface via the gap.

The present inventor has found that the gap between the drive unit frame and the mounting frame is preferably minimized in order to maximise the effective radiating surface area of the diaphragm. A gap of some extent is required in order to allow the drive unit to move the diaphragm along the movement axis at bass frequencies, whilst having the drive unit frame suspended from the mounting frame by the at least one mounting frame suspension.

Accordingly, in some examples, a gap between the drive unit frame and the mounting frame, as measured in a plane perpendicular to the movement axis, may be 5mm or less (more preferably, 4mm or less, more preferably 3mm or less, more preferably 2mm or less) at one or more locations at a periphery of the drive unit frame. A gap of less than 1 mm is difficult to achieve in practice because of production tolerances, as contact between rigid elements of the drive unit frame and mounting frame should generally be avoided. In some examples, a gap between the drive unit frame and the mounting frame, as measured in a plane perpendicular to the movement axis, may be 5mm or less, more preferably 3mm or less, more preferably 2mm or less, for at least 50% (more preferably at least 80%, more preferably at least 90%, more preferably at least 95%) of a path which extends around the drive unit frame at a periphery of the drive unit frame).

In some examples, a gap between the drive unit frame and the mounting frame, as measured in a plane perpendicular to the movement axis, may be 5mm or less, more preferably 3mm or less, more preferably 2mm or less, for substantially the entirety of a path which extends around the drive unit frame at a periphery of the drive unit frame. However, larger gaps may be required at certain regions of a periphery of the drive unit frame, particularly where the mounting frame and/or diaphragm has a non-circular shape (such as diaphragms having an oval or race-track shape, for example).

In some embodiments, the loudspeaker may be a dipole loudspeaker, wherein the loudspeaker is configured to, in use, allow sound produced by the first radiating surface to propagate out from a first side of the dipole loudspeaker and to allow sound produced by the second radiating surface to propagate out from a second side of the dipole loudspeaker.

If the loudspeaker is a dipole loudspeaker, the dipole loudspeaker may be for use (e.g. configured to be used) with an ear of a user being located at a listening position (preferably each ear of a user being located at a respective listening position) that is in front of the first radiating surface and is 50cm or less (more preferably 40cm or less, more preferably 30cm or less, more preferably 25cm or less, more preferably 20cm or less, more preferably 15cm or less) from the first radiating surface. The terms “user” and “listener” may be used interchangeably in this disclosure.

The present inventor has observed that, at such a listening position(s), increasing the effective radiating surface area of the diaphragm results in an improved SPL for the user, whilst providing a much reduced SPL for users further away from the loudspeaker, see WO2019/121266A1 for details.

Here it is to be noted that although the(/each) listening position has been defined with respect to the front of the first radiating surface, this does not rule out the possibility of a similar effect being achievable in front of the second radiating surface. Indeed, it is expected that a similar effect could be achieved in front of the second radiating surface.

The dipole loudspeaker assembly may be configured (e.g. by appropriately arranging and sizing the diaphragm, drive unit suspension(s) and mounting frame) such that the SPL of sound produced by the loudspeaker at a bass frequency of 60Hz as measured at 80cm from the first radiating surface along a principal radiating axis of the first radiating surface is at least 25dB (more preferably at least 30dB) lower than the SPL of the same sound as measured at 10cm from the first radiating surface along the principal radiating axis of the first radiating surface in a free field condition.

Herein, a free field condition may be understood as anechoic conditions, e.g. as might be measured in an anechoic chamber. Herein, a principal radiating axis of a radiating surface may be understood as an axis along which the radiating surface produces direct sound at maximum amplitude (sound pressure level). Typically, the principal radiating axis will extend outwardly from a central location on the radiating surface. The principal radiating axes of the first and second radiating surfaces will in general extend in opposite directions, since they are located on opposite faces of the diaphragm.

In other embodiments, the loudspeaker may be a monopole loudspeaker, in which the loudspeaker is configured to substantially inhibit sound produced by the second radiating surface.

The drive unit may be configured to move the diaphragm at bass frequencies. The bass frequencies at which the drive unit is configured to move the diaphragm preferably include frequencies across the range 60-80Hz, more preferably frequencies across the range 50-100 Hz, more preferably frequencies across the range 40-100Hz, and may include frequencies across the range 40-160Hz. The drive unit may be configured to move the diaphragm at frequencies that do not exceed 250Hz, 200Hz, or even 160Hz, in order to ensure (if the loudspeaker is a monopole loudspeaker) the loudspeaker achieves a desired level of “cocooning”, as described in WO2019/121266A1 .

Moving the diaphragm at frequencies below 40Hz may be useful for some applications, but not for others (such as in a car, where below 40Hz background noise tends to be too loud).

The loudspeaker may thus be (configured as) a subwoofer. A subwoofer can be understood as a loudspeaker dedicated to (rather than suitable for) producing sound at bass frequencies.

The loudspeaker assembly may include multiple loudspeakers, wherein a drive unit frame of each loudspeaker is suspended from the mounting frame via one or more mounting frame suspensions. Each loudspeaker may have features according to the definition of a loudspeaker provided herein. For example, each loudspeaker may include: a diaphragm having a first radiating surface and a second radiating surface, wherein the first radiating surface and the second radiating surface are located on opposite faces of the diaphragm; a drive unit configured to move the diaphragm along a movement axis at bass frequencies such that the first and second radiating surfaces produce sound at bass frequencies, wherein the sound produced by the first radiating surface is in antiphase with sound produced by the second radiating surface; a drive unit frame, wherein the diaphragm is suspended from the drive unit frame via at least one drive unit suspension. Each loudspeaker may be a dipole loudspeaker..

If the loudspeaker is a dipole loudspeaker, the effective radiating area of the first radiating surface (or the combined effective radiating areas of the first radiating surfaces, if there is more than one dipole loudspeaker included in the loudspeaker assembly) may be 60cm ² or more, more preferably 80cm ² or more, more preferably 100 cm ² or more. For reasons that can be understood from WO2019/121266A1 , an effective radiating area in this range can provide an effective personal sound cocoon at bass frequencies.

As is known in the art, for a diaphragm having a circular perimeter which is suspended from a loudspeaker support structure by a roll suspension having an outer diameter do and an inner diameter di, the effective radiating surface area of the diaphragm may be estimated as S here d is the half-diameter of the roll suspension, (do + di)/2.

Alternatively, or for more complex diaphragm geometries, the effective radiating area of the diaphragm SD may be measured using known techniques, see e.g. “Dynamical Measurement of the Effective Radiating area SD”, Klippel GmbH (https://www.klippel.de/fileadmin/klippel/Files/Know_How/App lication_Notes/AN_32_Effective_Radiation_ Area.pdf).

To avoid complex calculations regarding effective radiating area, the surface area of the first radiating surface of the dipole loudspeaker (or the combined surface area of the first radiating surfaces, if there is more than one dipole loudspeaker included in the loudspeaker assembly) may be 50cm ² or more, 60cm ² or more, more preferably 80cm ² or more, more preferably 90 cm ² or more. With surface areas in these ranges, an effective personal sound cocoon at bass frequencies can be achieved for reasons that can be understood from WO2019/121266A1 (noting that the effective radiating area is generally only a few % larger than the actual surface area).

The diaphragm may take various forms.

For example, the diaphragm could be of paper, or another sheet material.

For example, the diaphragm may be a single (monolithic) piece of material. Such a material is preferably light-weight, e.g. having a density of 0.1g/cm ³ or less. The material may be extruded polystyrene or similar. In some examples, the diaphragm may be covered by a skin, e.g. to protect the diaphragm. The skin could be of paper, carbon fibre, plastic foil, for example.

For example, the diaphragm may include several pieces of material attached together, e.g. by glue. For example, the diaphragm may include a first cone and a second cone, wherein the first and second cone are glued back to back. The first and second cones may e.g. be made of paper.

The diaphragm may comprise a one or more (e.g. a pattern of) folds (most appropriate if the diaphragm is of a sheet material, such as paper). This may help to reduce the height of the dipole loudspeaker (e.g. in a direction parallel to the movement axis), whilst still maintaining a stable dipole loudspeaker. The/each fold may, when viewed in a circumferential direction, radially extend between an inner circumferential edge and an outer circumferential edge of the diaphragm. The/each fold may have a depth which increases from the outer circumferential edge, and the inner circumferential edge, of the diaphragm towards a base region positioned between (e.g. approximately mid-way between) the outer circumferential edge and the inner circumferential edge of the diaphragm. Accordingly, a maximum depth of the/each fold may be located at the base region. The/each fold may be provided with a respective face in the base region. Examples of possible patterns of folds are described in W02005/015950A1 .

The at least one drive unit suspension may include a roll suspension. The roll suspension may interconnect the drive unit frame and an outer circumferential edge of the diaphragm. The at least one drive unit suspension may include a spider. The spider may be secured at its inner rim to the drive unit frame, and at its outer rim to the diaphragm. Alternatively, the spider may be secured at its outer rim to the drive unit frame, and at its inner rim to the diaphragm. A spider may be understood as a textile ring having circumferentially extending corrugations. A spider may facilitate movement of the diaphragm along the movement axis whilst inhibiting, preferably substantially preventing, movement of the diaphragm perpendicular to the movement axis.

If the diaphragm comprises one or more folds (see above), the spider may be secured at its inner rim to the drive unit frame, and at its outer rim to the faces of the folds at the base regions of the diaphragm, preferably by an adhesive such as glue. Alternatively, the spider may be secured at its outer rim to the drive unit frame, and at its inner rim to the faces of the folds at the base regions of the diaphragm, preferably by an adhesive such as glue. Optionally, the diaphragm may be suspended from the drive unit frame by a plurality of spiders.

If the diaphragm comprises one or more folds (see above), the dipole loudspeaker may include a stiffening element which extends around a magnet unit of the drive unit and stiffens the diaphragm at the base region(s) of the diaphragm, so as to reinforce the diaphragm against deformation in the base region(s). The stiffening element may be circular, and may, when viewed in cross-section, include a corrugation to stiffen the base region. The stiffening element may be made from a material selected from paper, aluminium, titanium, polypropylene, polycarbonate, acrylonitrile butadiene styrene or Kevlar ™, for example. The stiffening element may be attached (directly or preferably via the spider) to the mid-region of the diaphragm, preferably by an adhesive. Examples of possible stiffening elements are described in WO2008/135857A1.

The/each mounting frame suspension may interconnect the drive unit frame and the mounting frame.

The drive unit frame may be suspended from the mounting frame via at least two mounting frame suspensions, wherein the at least two mounting frame suspensions are separated in a direction parallel to the movement axis.

Providing two mounting frame suspensions in this manner, each extending substantially continuously around the drive unit frame, may improve the stability of the dipole loudspeaker.

One or more mounting frame suspensions (optionally the/each mounting frame suspension) may comprise a roll suspension.

One or more mounting frame suspensions (optionally the/each mounting frame suspension) may comprise one or more pieces of elastic material held taut between the mounting frame and the drive unit frame.

One or more mounting frame suspensions (optionally the/each mounting frame suspension) may comprise a block of elastic material.

For avoidance of any doubt, if the loudspeaker comprises a plurality of mounting frame suspensions, each of the mounting frame suspensions may be a same type of mounting frame suspension as described above. Alternatively each, or some, or the mounting frame suspensions may be a different type of mounting frame suspension as described above.

In some examples, the first and second radiating surfaces of the diaphragm may have a circular shape.

In other examples, the first and second radiating surfaces of the diaphragm may have a non-circular shape, e.g. an oval, rectangular, square, rounded rectangular or race-track shape. This may help to maximize the effective radiating surface area of the diaphragm within other design constraints (e.g. incorporating the loudspeaker into a car headrest).

The present inventor has found that the dimension and shape of the mounting frame may vary depending on the shape and size of the space available, e.g. space available in the headrest, in which the loudspeaker is to be mounted. The shape of the diaphragm (and in particular the first and second radiating surfaces of the diaphragm) may therefore be chosen to closely match the shape of the space provided by the mounting frame, e.g. so that the gap between the mounting frame and the drive unit frame is minimised along a path which extends around the drive unit frame at a periphery of the drive unit frame.

Even if the first and second radiating surfaces of the diaphragm have a non-circular shape, the loudspeaker may include a circular drive unit suspension (e.g. spider) which attaches to a circular portion of the diaphragm. For example, the loudspeaker may include a circular drive unit suspension (e.g. spider) which attaches to a circular base region of the diaphragm, wherein the circular base region of the diaphragm is positioned between (e.g. approximately mid-way between) the outer circumferential edge and the inner circumferential edge of the diaphragm. Such a base region has already been discussed, above.

In the context of this disclosure, the term “drive unit frame” is intended to encompass any substantially rigid structure from which a diaphragm can be suspended.

In the context of this disclosure, the term “mounting frame” is intended to encompass any substantially rigid structure from which a drive unit frame of a loudspeaker can be suspended.

The mounting frame may define a waveguide which at least partially (preferably entirely) surrounds the diaphragm and is configured to guide sound produced by the first and/or second radiating surface of the diaphragm out of opposite sides of the mounting frame. The waveguide may optionally be formed (partly, or entirely) of foam. The waveguide may be located in a headrest of a seat, if the loudspeaker assembly is a seat assembly (see below).

The drive unit may be an electromagnetic drive unit that includes a magnet unit configured to produce a magnetic field, and a voice coil attached to the diaphragm. The magnet unit may be rigidly attached to the drive unit frame. In use, the voice coil may be energized (have a current passed through it) to produce a magnetic field which interacts with the magnetic field produced by the magnet unit and which causes the voice coil (and therefore the diaphragm) to move relative to the magnet unit. The magnet unit may include a permanent magnet. The magnet unit may additional include a yoke, e.g. a U-yoke. The magnet unit may be configured to provide an air gap, and may be configured to provide a magnetic field in the air gap. In particular, the air gap may be provided between a top part (e.g. “washer”) of the magnet unit located radially inwards of the air gap with respect to a direction parallel to the movement axis, and the yoke located radially outwards of the air gap with respect to a direction parallel to the movement axis. The voice coil may be configured to sit in the air gap when the diaphragm is at rest. Such drive units are well known.

In this disclosure, a voice coil can be understood as a coiled length of wire that is attached to the diaphragm. The voice coil may be considered to be distinct from any of the (typically non-coiled) electrical connections (e.g. wires) used to supply electrical energy to the voice coil.

The magnet unit may be located in front of the second radiating surface of the diaphragm. The loudspeaker may include a safety element which is located between the magnet unit and the second radiating surface of the diaphragm. The safety element may be configured to prevent the magnet unit from passing through the diaphragm, e.g. in a crash event or another event that involves a sudden deceleration of the loudspeaker (e.g. where the loudspeaker has been moving in the direction of the principal radiating axis of the first radiating surface). The safety element is preferably rigid. The safety element may also serve as a voice coil coupler as described below.

Such a safety element may be particularly useful if the loudspeaker is mounted in a headrest of a vehicle seat, since it may help to provide protection for a person sat in such a seat in the event of a vehicle crash.

The loudspeaker may include a voice coil coupler attached to the diaphragm, preferably to the second radiating surface of the diaphragm, optionally at an inner circumferential edge of the diaphragm. The voice coil coupler may comprise a tubular element. The voice coil may be attached to the diaphragm by being wrapped around a tubular element of the voice coil coupler. The voice coil coupler may also serve as a safety element, as described above.

Optionally, a top-part of the magnet unit and the magnetic yoke of the magnet unit are configured such that the magnetic flux density in the air gap reaches a first local maximum peak location along a direction parallel to the movement axis and a second local maximum peak location along a direction parallel to the movement axis, wherein the first peak and the second peak location are separated spatially in a direction parallel to the movement axis by a valley region in which the magnetic flux density is lower than both the first local maximum and the second local maximum, wherein the voice coil is configured to be positioned in the valley region when the diaphragm is at rest. This may allow for a large real application excursion whilst using a magnet unit with a small height.

To achieve such a magnetic flux density, the top-part of the magnet unit may comprise a recess (e.g. a cut out) at a location along a direction parallel to the movement axis adjacent, e.g. near to the position of, the voice coil when the diaphragm is at rest. The cut out may accommodate a shorting ring (e.g. an electrically conducting ring configured to dissipate eddy currents). The shorting ring may comprise copper, for example. Examples are provided in PCT/EP2020/064577. Preferably, the loudspeaker assembly includes a loudspeaker-mounting frame unit configured to be mounted in an application (e.g. a headrest of a seat), wherein the loudspeaker-mounting frame unit includes: the loudspeaker; the mounting frame; and one or more attachment formations on the mounting frame, wherein the attachment formations are configured to facilitate attachment of the loudspeaker-mounting frame unit to the application (e.g. a headrest of a seat). The one or more attachment formations may, for example, include wings (e.g. with screw holes) configured to facilitate attachment of the loudspeaker-mounting frame unit to the application (e.g. via passing one or more screws via screw-holes in one or more wings, see e.g. Fig. 11 A).

If the loudspeaker assembly includes a loudspeaker-mounting frame unit, then the mounting frame may include a first grille positioned in front of the first radiating surface of the diaphragm, and a second grille positioned in front of the second radiating surface of the diaphragm. Such grilles can help to protect the diaphragm, e.g. when attaching the loudspeaker-mounting frame unit to an application (e.g. a headrest of a seat).

Preferably, the loudspeaker assembly is a seat assembly including a seat for seating a user, wherein the mounting frame is a rigid frame of the seat.

The loudspeaker may be mounted within a headrest of the seat (“seat headrest”).

In some examples, the mounting frame may be part of the headrest. In other examples, the loudspeaker and mounting frame may be included in a loudspeaker-mounting frame unit, wherein the loudspeakermounting frame unit is attached to the headrest via one or more attachment formations on the mounting frame (see above)..

It has surprisingly been found that the headrest is a particularly good location to transmit vibrations homogeneously into the complete backrest of a car seat. The vibrations are nicely spread and reach to the bottom of the backrest. This applies if the seat includes a stiff chassis of the backrest onto which the headrest is mounted via the headrest pins. But it also applies if the headrest is integral with a backrest of the seat.

The seat assembly may include a control interface configured to control the adjustment mechanism so as to adjust the stiffness and/or resistance of the mounting frame suspension system based on user input at the control interface. For example, the control interface may be a graphical user interface incorporated in the seat assembly in a manner accessible by a user (e.g. on an armrest of the seat).

The headrest may include a control interface configured to control the adjustment mechanism so as to adjust the mounting frame suspension system (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system) based on user input at the control interface. For example, the control interface may be a rotatable knob incorporated in the headrest in a manner accessible by a user (e.g. on a side wall of the headrest). The headrest could include mounting pins which are part of the rigid frame of the seat, but are configured to allow the headrest to be detached from the remainder of the rigid frame of the seat (such mounting pins are common in most cars). Alternatively, the headrest may be integral with the remainder of the seat.

Preferably, the seat is configured to position a user who is sat down in the seat such that the at least one ear of the user is located at a listening position (preferably each ear of a user is located at a respective listening position) that is 40cm or less (more preferably 30cm or less, more preferably 25cm or less, more preferably 20cm or less, more preferably 15cm or less) from the first radiating surface of the loudspeaker.

This can conveniently be achieved by mounting the loudspeaker within a headrest of the seat, since a typical headrest is configured to be a small distance (e.g. 30cm or less) from the ear(s) of a user who is sat down in a seat.

A seat headrest typically has a front surface configured to face towards the head of a user sat in the seat, and a back surface configured to face away from the head of a user sat in the seat. The loudspeaker is preferably mounted within the headrest of the seat e.g. with the first radiating surface of the loudspeaker facing the front surface of the headrest, e.g. with a principal axis of the first radiating surface extending out through the front surface of the headrest.

If the loudspeaker is a dipole loudspeaker, the loudspeaker may be mounted in the seat headrest so that the seat headrest is configured to allow sound produced by the first radiating surface of the diaphragm to propagate out through the front surface of the headrest and to allow sound produced by a second radiating surface of the acoustic radiator to propagate out from the back surface of the headrest. The seat headrest may include acoustically transparent regions (e.g. acoustically transparent foam) for this purpose.

A skilled person would appreciate that the extent to which the seat headrest is configured to allow sound produced by the first radiating surface of the diaphragm to propagate out through the front surface of the headrest and to allow sound produced by a second radiating surface of the acoustic radiator to propagate out from the back surface of the headrest will depend on a number of factors such as the level of person sound cocooning desired, the size of personal sound cocoon desired, and other design considerations (e.g. implementing the loudspeaker in a car headrest may require some of the frame or other structure to be located in front of the first and/or second radiating surfaces). Accordingly, the degree to which the seat headrest should be open to both the first and second radiating surfaces cannot readily be defined in a precise manner.

The seat assembly may include one or more additional loudspeakers, for example one or more, preferably two or more, directional mid-high frequency loudspeakers, e.g. operating over a frequency band that includes 300Hz-3kHz, more preferably 150Hz-20kHz. In particular, the headrest may include one or more dipole loudspeakers according to the first aspect (i.e. for producing bass frequencies), and one or more, preferably two or more, directional mid-high frequency loudspeakers included in forwardprotruding wings of the headrest. The one or more directional mid-high frequency loudspeakers may be of a cardioid types, e.g. as described in GB2004076.2, although other forms of directional loudspeaker are of course possible.

The seat may be a vehicle seat, for use in a vehicle such as a car (“car seat”) or an aeroplane (“plane seat”).

The seat could be a seat for use outside of a vehicle. For example, the seat could be a seat for a computer game player, a seat for use in studio monitoring or home entertainment.

In a second aspect, there is provided a vehicle (e.g. a car or an aeroplane) having a one or more seat assemblies as described in connection with the first aspect of the invention.

The vehicle may include a control interface configured to control the adjustment mechanism so as to adjust the mounting frame suspension system (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system) based on user input at the control interface. For example, the control interface may be part of a graphical user interface displayed by (e.g. an entertainment system of) the vehicle in a manner accessible by a user (e.g. a car entertainment system).

The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

Summary of the Figures

Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

Figs. 1 A and 1B are a schematic drawings of an example loudspeaker assembly for producing sound at bass frequencies.

Fig. 1C shows a schematic drawing of another example loudspeaker assembly.

Fig. 2A is a cross-sectional view of another example loudspeaker for producing sound at bass frequencies.

Fig. 2B shows the magnet unit of the example loudspeaker of Fig. 2A in more detail.

Figs. 3A-G show a first set of examples in which an adjustment mechanism is configured to mechanically adjust the mounting frame suspension system.

Figs. 4A-D show a second set of examples in which an adjustment mechanism is configured to pneumatically adjust the mounting frame suspension system.

Fig. 5 shows a further example in which the adjustment mechanism is configured to adjust the mounting frame suspension system by applying an electric field to an electroactive polymer so as to alter the shape of the electroactive polymer. Figs. 6A(i)-(iii) and 6B(i)-(iii) show a further example in which the mounting frame suspension system includes a first permanent magnet attached to the mounting frame, and a second permanent magnet attached to the drive unit frame.

Figs. 6C(i)-(ii) shows an example magnetic switch.

Figs. 7A-C show a loudspeaker assembly in which the loudspeaker is mounted in the headrest of a seat.

Fig. 7D shows the interior of a car that includes a seat which incorporates the headrest of Fig. 7A-C.

Figs. 8A-B show another loudspeaker assembly in which the loudspeaker is mounted in the headrest of a seat.

Figs. 9A and 9B show a model of the loudspeaker shown in Fig 2A.

Figs. 9C-E show simulation data obtained using the model of Figs. 9A-B.

Figs. 10A-B show the influence of tuning frequency of the mounting frame suspension on static deflection.

Fig. 11 A shows another loudspeaker assembly in which the loudspeaker is mounted in the headrest of a seat.

Fig. 11 B is a schematic drawing showing a potential implementation of the asymmetric pulley of Fig. 11A.

Detailed Description of the Invention

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

Figs. 1 A and 1 B are a schematic drawings of an example loudspeaker assembly 100 for producing sound at bass frequencies.

Fig. 1 A shows the loudspeaker assembly 100 from above, and Fig. 1 B shows the loudspeaker assembly 100 from the side.

As shown, the loudspeaker 1 includes a mounting frame 140 from which a loudspeaker 101 is suspended by a mounting frame suspension system that includes at least one mounting frame suspension 142, which in this case is the only mounting frame suspension. The mounting frame suspension 142 is formed in a gap between a drive unit frame of the loudspeaker 101 and the mounting frame 140 and extends substantially continuously around the drive unit frame 130, as can be seen most clearly from Fig. 1 B.

As shown schematically by an arrow in Figs. 1 A and 1 B, the mounting frame suspension 142 can be adjusted by an adjustment mechanism (not shown) so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use. In particular, the adjustment mechanism is configured to adjust a stiffness and/or resistance of the mounting frame suspension system that include the mounting frame suspension 142. Various examples of adjustment mechanisms configured to adjust a mounting frame suspension are provided below.

Fig. 1C shows a schematic drawing of another example loudspeaker assembly 100’.

In the loudspeaker 100’ of Fig. 1 C, the loudspeaker 100’ has a mounting frame suspension system that includes two mounting frame suspensions 142, 143 which do not extend substantially continuously around a drive unit frame of the loudspeaker 101 . In this example, an adjustment mechanism is configured to adjust a stiffness and/or resistance of each of the two mounting frame suspensions 142, 143. Note that even a change in a stiffness and/or resistance of just one of the mounting frame suspensions 142, 143 would have an impact on extent to which vibrations from the loudspeaker 101 reach the mounting frame 140.

Fig. 2A is a cross-sectional view of an example loudspeaker assembly 200 for producing sound at bass frequencies.

The loudspeaker assembly 200 comprises a loudspeaker 201 , the loudspeaker 201 including diaphragm 210, a drive unit 220, a drive unit frame 230. The loudspeaker also includes a mounting frame 240, wherein the drive unit frame 230 of the loudspeaker 201 is suspended from the mounting frame 240 via a mounting frame suspension system that includes at least one mounting frame suspension.

The diaphragm 210 has a first radiating surface 212 and a second radiating surface 214, wherein the first radiating surface 112 and the second radiating surface 214 are located on opposite faces of the diaphragm 210.

The drive unit 220 is configured to move the diaphragm 210 along a movement axis 202 at bass frequencies such that the first and second radiating surfaces 212, 214 produce sound at bass frequencies. The sound produced by the first radiating surface 212 is in antiphase with sound produced by the second radiating surface 214.

In this example, the loudspeaker 201 is a dipole loudspeaker wherein the loudspeaker 201 is configured to, in use, allow sound produced by the first radiating surface 212 of the diaphragm 210 to propagate out from a first side of the dipole loudspeaker 201 and to allow sound produced by the second radiating surface 214 to propagate out from a second side of the dipole loudspeaker 201 .

The diaphragm 210 is suspended from the drive unit frame 230 via (in this example) two drive unit suspensions 232, 233.

The first drive unit suspension 232 is a roll suspension extending substantially continuously around the periphery (outer edge) of the diaphragm 110. The second drive unit suspension 233 is a spider.

In the example shown in Fig. 2A, the diaphragm 210 has a folded paper structure, explained in more detail below. The drive unit frame 230 is suspended from the mounting frame 240 via a mounting frame suspension system that (in this example) includes a single mounting frame suspension 242 formed in a gap between the drive unit frame 230 and the mounting frame 240.

The mounting frame 240 defines a waveguide (in the form of an aperture in the mounting frame) which surrounds the diaphragm 210 and is configured to guide sound produced by the first and/or second radiating surface of the diaphragm out of opposite sides of the loudspeaker 200.

The mounting frame suspension 242, as projected onto a plane perpendicular to the movement axis 202, at least partially overlaps with the at least one drive unit suspension 232 as projected onto the same plane.

The mounting frame 240 includes a supplementary frame 246. The supplementary frame 246 of the mounting frame 240 is configured to snap-fit to the remainder of the mounting frame 240 via snap-fit feature(s) 248 on the remainder of the mounting frame. This may help simplify assembly of the loudspeaker 200.

In this example, the mounting frame suspension 242 is a portion of elastic material that forms a hollow band, which includes a hollow region that extends continuously around the drive unit frame 230.

The mounting frame suspension 242 is attached to the supplementary frame 246 of the mounting frame 240 (e.g. by an adhesive), and is also attached to the drive unit frame 230 (e.g. by an adhesive).

A gap 250 is provided between the drive unit frame 230 and the mounting frame 240 in order to allow the drive unit 220 to move the diaphragm 210 along the movement axis 202, whilst having the drive unit frame 230 suspended from the mounting frame 240 by the mounting frame suspension 242. However, the gap 250 is preferably minimized in order to maximise the effective radiating surface area 254 of the first radiating surface 212 within the mounting frame 240. Accordingly, the gap 250 is preferably 2mm or less, as measured in a plane perpendicular to the movement axis, at one or more locations (and preferably for substantially the entirety of a path which extends around the drive unit frame) at a periphery of the drive unit frame 230.

The effective radiating surface area 254 of the first radiating surface 212 is preferably 60cm ² or more.

Ideally, a shape of the diaphragm 210 is chosen to closely match the shape of the space provided by the mounting frame 240. In this example, the diaphragm 210 has an oval or racetrack shape. This is shown figuratively in the cross-section view of Fig. 2A, by the diaphragm 210 having different dimensions to the right and left of the drive unit 220.

However, the shape of the diaphragm 210 may not completely correspond to the shape of the space provided by the mounting frame 240. As such, the gap 250 between the drive unit frame 230 and the mounting frame 240 may have a different size, as measured in a plane perpendicular to the movement axis, at different locations around the periphery of the drive unit frame 230. In this example, the diaphragm 210 is a paper diaphragm which comprises a pattern of folds 260 similar to those described in W02005/015950A1 . When viewed in a circumferential direction, each fold 260 radially extends between the inner circumferential edge and the outer circumferential edge of the diaphragm 210, and has a depth that increases from the outer circumferential edge, and the inner circumferential edge of the diaphragm 210, towards a base region 262. A maximum depth of each fold 260 is located at the base region 262 and the folds 260 are provided with faces at the base region 262 (these faces are part of the second radiating surface 214).

The spider 233 is secured (e.g. by an adhesive) at its inner rim to the drive unit frame 230, and at its outer rim to the faces of the folds 260 at the base region 262 of the diaphragm 210.

Attached to the outer rim of the spider 233 is a stiffening element 268 with a corrugation, similar to that described in WO2008/135857A1 , which extends around a magnet unit of the drive unit 220, and which stiffens the diaphragm at the base region 262 of the diaphragm 210, so as to reinforce the diaphragm 210 against deformation in the base region 262. The stiffening element 268 may be made from a material selected from paper, aluminium, titanium, polypropylene, polycarbonate, acrylonitrile butadiene styrene or Kevlar ™, for example.

The mounting frame 240 is only partly shown in Fig. 2A, and is a support foam region of a car headrest. The complete headrest is not shown in Fig. 2A, but may be similar to that shown in Fig. 7A, below.

The drive unit 220 is an electromagnetic drive unit including a magnet unit 270 and a voice coil 222. The voice coil 222 is attached to the inner circumferential edge of the diaphragm 210 by a tubular element 224 of a voice coil coupler. In particular the voice coil 222 is wrapped around the tubular element 224 and is configured to be energized by having a current passed through it (via lead wires 282).

A dustcap 280 is attached to the tubular element 224 of the voice coil coupler.

The magnet unit 270 is located in front of the second radiating surface 214 of the diaphragm 210. The magnet unit 270 comprises a permanent magnet 272, a top part 273, and a U-yoke 274 (e.g. of steel). The top part 273 is formed here by a first (bottom) washer 273a (e.g. of steel) and a second (top) washer 273b (e.g. of steel). The magnet unit 270 provides an air gap 228 in which the voice coil 222 is configured to sit when the diaphragm 210 is at rest. In particular, the air gap 228 is between the top part 273 and the U-yoke 274.

The top part 273 comprises a cut-out at a location along a direction parallel to the movement axis 202, adjacent to the voice coil 222 when the diaphragm 210 is at rest. A shorting ring 278 is positioned in the cut-out. The shorting ring 278 may comprise copper, for example.

In use, the voice coil 222 may be energized (have a current passed through it) to produce a magnetic field that interacts with a magnetic field produced by the magnet unit 270 in the air gap 228, and which causes the voice coil 222 (and therefore the diaphragm 210) to move relative to the magnet unit 270.

The permanent magnet 272, top part and the U-yoke 274 are configured such that the magnetic flux density in the air gap 228 reaches a first local maximum peak location along a direction parallel to the movement axis 202 and a second local maximum peak location along a direction parallel to the movement axis 202. The first peak and the second peak location are separated spatially in a direction parallel to the movement axis 202 by a valley region in which the magnetic flux density is lower than both the first local maximum and the second local maximum. The voice coil 222 is configured to be positioned in the valley region when the diaphragm 210 is at rest. The shorting ring 278 described above may help to achieve such a magnetic flux density. Analogous examples are provided in PCT/EP2020/064577.

In use, the drive unit 220 may be configured to move the diaphragm 210 at bass frequencies across the range 40-100Hz, for example.

The loudspeaker 200 additionally includes an adjustment mechanism 285 configured to adjust the mounting frame suspension 242 (which in this example is the only element included in the mounting frame suspension system) so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In this example, the adjustment mechanism 285 is an air pressure control unit (which may be referred to as a pneumatic control unit) configured to adjust the air pressure inside the hollow band mounting frame suspension 242 so as to (“pneumatically”) adjust the mounting frame suspension system so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system.

In particular, by inflating the hollow band, both the stiffness and resistance of the mounting frame suspension system will be increased, which will in turn affect the extent to which vibrations from the moving diaphragm 210 reach the mounting frame 240.

The mounting frame suspension system may be configured to have a first (e.g. “low vibration”) configuration in which the mounting frame suspension system has a resonant frequency in the range 10Hz-30Hz (inclusive), more preferably in the range 10Hz-20Hz (inclusive). In a first configuration having such a resonant frequency, relatively little of the vibrations produced by a moving diaphragm 210 of the loudspeaker 201 will reach the mounting frame 240 via the mounting frame suspension 242, when the loudspeaker 201 is in use to produce sound at bass frequencies.

The adjustment mechanism may be configured to adjust the mounting frame suspension system so that the mounting frame suspension system changes from the first configuration to a second (e.g. “high vibration”) configuration.

Preferably, the mounting frame suspension system, in the second configuration, has a resonant frequency that is in the range 20Hz-60Hz (inclusive), more preferably in the range 30Hz-60Hz (inclusive). In this way, the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system, when the loudspeaker is operated at typical bass frequencies in the range 30-60Hz, is increased for the second configuration compared with the first configuration.

In the second configuration, the mounting frame suspension 242 may be more inflated than it is in the first configuration, thereby increasing the stiffness and resistance of the mounting frame suspension system (and therefore increasing the frequency at which the mounting frame 240 of the loudspeaker assembly 200 is caused to resonate, and therefore increasing the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use).

Of course, there may be yet further (e.g. intervening) configurations in which the stiffness and resistance of the mounting frame suspension system is different from that in the first and second configurations.

A skilled person would appreciate that the adjustment mechanism shown in Fig. 2A is just one example of how an adjustment mechanism may be configured to adjust the stiffness and/or resistance of a mounting frame suspension system.

We will now describe a variety of alternative ways in which an adjustment mechanism may be configured to change the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use. Each of these alternative mechanisms could be incorporated into the loudspeaker 200 of Fig. 2A, instead of the particular mechanism shown in Fig. 2A. Alike reference numerals have thus been used to refer to alike features.

Figs. 3A-G show a first set of examples in which an adjustment mechanism is configured to mechanically adjust the mounting frame suspension system.

In the example of Fig. 3A, the mounting frame 240 includes a fixed part 240a and a moveable part 240b, and the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a threaded additional rigid element 244 which passes through a threaded hole in the fixed part 240a of the mounting frame 240. The adjustment mechanism 285 is a rotary motor or manual rotary knob connected to the threaded additional rigid element 244. In use, the adjustment mechanism 285 rotates the threaded additional rigid element 244 which acts to pull the movable part 240b away from the drive frame 230, thereby stretching the roll suspensions 242, 243 and increasing the stiffness provided by the roll suspensions 242, 243, thereby adjusting the stiffness of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3B, the mounting frame 240 includes a fixed part 240a and a moveable part 240b, and the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a threaded additional rigid element 244 which passes through a threaded hole in the fixed part 240a of the mounting frame 240. The adjustment mechanism 285 is a rotary motor 285 or manual rotary knob connected to the threaded additional rigid element 244. In use, the adjustment mechanism 285 rotates the threaded additional rigid element 244 so that the movable part 240b of the mounting frame 240 is brought into contact with a friction pad 296 (e.g. of rubber, foam, felt or textile) on the drive frame 230, thereby adjusting the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3C, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a threaded additional rigid element 244 which passes through a threaded hole in the mounting frame 240. The adjustment mechanism 285 is a rotary motor or manual rotary knob connected to the threaded additional rigid element 244. In use, the adjustment mechanism 285 rotates the threaded additional rigid element 244 so that a friction pad 245 (e.g. of rubber, foam, felt or textile) on a head of the additional rigid element 244 is brought into contact with the drive frame 230, thereby adjusting the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3D, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a threaded additional rigid element 244 which passes through a threaded hole in the mounting frame 240. The threaded additional rigid element 244 includes a non-circular (e.g. oval) head 245. The adjustment mechanism 285 is a rotary motor or manual rotary knob connected to the threaded additional rigid element 244. In use, the adjustment mechanism 285 rotates the threaded additional rigid element 244 whose non-circular head is caused to contact and then stretch the roll suspensions 242, 2423 locally, so as to adjust the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3E, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes an additional rigid element 244. The adjustment mechanism (not shown) is a motor or manual rotary knob connected to the additional rigid element 244. In use, the adjustment mechanism moves the additional rigid element into contact with one of the roll suspensions 243 so as to adjust the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3F, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes an additional rigid element 244 attached to the mounting frame 240 via a friction fit. The adjustment mechanism (not shown) is a motor or manual rotary knob connected to the additional rigid element 244. In use, the adjustment mechanism moves the additional rigid element 244 into contact with the drive unit frame 230 so as to adjust the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 3G, the mounting frame suspension system includes two mounting frame suspensions in the form of elastic blocks 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes an additional rigid element 244 attached to the mounting frame 240 via a friction fit. The adjustment mechanism (not shown) is a motor or manual sliding element connected to the additional rigid element 244. In use, the additional rigid element 244 is moved to extend by a different amount between the elastic blocks 242, 243 so as to change the proportion of the elastic blocks which is permitted to bend so as to adjust the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

Figs. 4A-D show a second set of examples in which an adjustment mechanism is configured to pneumatically adjust the mounting frame suspension system.

In the example of Fig. 4A, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The two roll suspensions 242, 243 are portions of flexible (e.g. elastic material) which partly (along with the drive unit frame and mounting frame) define a hollow region. The adjustment mechanism is an air pressure control unit 285. In use, the air pressure control unit 285 adjusts the air pressure in the hollow region, thereby changing the stiffness of the roll suspensions 242, 243, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 4B, the mounting frame suspension system includes a single mounting frame suspension 242 in the form of a portion of elastic material that forms a hollow band, which includes a hollow region that extends continuously around the drive unit frame 230. The adjustment mechanism is an air pressure control unit 285. In use, the air pressure control unit 285 adjusts the air pressure in the hollow region, thereby changing the size of the hollow band 242, the area of contact between the hollow band 242 and the frames 230, 240, and hence the stiffness and resistance of the overall mounting frame suspension system, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

In the example of Fig. 4C, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a portion of elastic material that forms a hollow band 244, which includes a hollow region that extends continuously around the drive unit frame 230. The adjustment mechanism is an air pressure control unit 285. In use, the air pressure control unit 285 adjusts the air pressure in the hollow region, thereby changing the stiffness and resistance of the hollow band 242, and thus the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use. In this example, the mounting frame 240 and/or the drive unit frame 230 include vents 249, 239 which serve to equalize the air pressure in the volume enclosed by the roll suspensions 242, 243 with the surrounding air pressure.

In the example of Fig. 4D, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a portion of elastic material 244 that defines a hollow region and is attached to the mounting frame 240. In this example the portion of elastic material 244 does not extend continuously around the drive unit frame 230 (but could in other embodiments). The adjustment mechanism is an air pressure control unit 285. In use, the air pressure control unit 285 adjusts the air pressure in the hollow region defined by the portion of elastic material 244 thereby inflating or deflating the portion of elastic material 244, and which brings the hollow band 242c into contact with a friction pad 245 (e.g. of foam, felt, textile or rubbed) on the drive unit frame 230, so as to increase the resistance of the mounting frame suspension system, and thus increasing the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use. In this example, the drive unit frame 230 includes vents 239 which serve to equalize the air pressure in the volume enclosed by the roll suspensions 242, 243 with the surrounding air pressure.

Fig. 5 shows a further example in which the mounting frame suspension system includes an electroactive polymer, and the adjustment mechanism is configured to adjust the stiffness and/or resistance of the mounting frame suspension system by applying an electric field to the electroactive polymer so as to alter the shape of the electroactive polymer.

In the example of Fig. 5, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. The mounting frame suspension system also includes a portion of an electroactive polymer 244 that is attached to the mounting frame 240. The adjustment mechanism is an electric field generating unit (not shown) for applying an electric field to the portion of electroactive polymer 244. In use, the electric field generating unit applies an electric field to the portion of electroactive polymer 244 which causes the portion of electroactive polymer 244 to change shape so as to bring the portion of electroactive polymer 244 into contact with the drive unit frame 230, so as to increase the resistance of the mounting frame suspension system, and thus increase the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

Figs. 6A-B, in which Figs. 6A(i)-(iii) provide a side view, and Figs. 6B(i)-(iii) provide a top view, show a further example in which the mounting frame suspension system includes a first permanent magnet 244a attached to the mounting frame 240, and a second permanent magnet 235 attached to the drive unit frame 230. The first permanent magnet 244a is mounted on a rigid element 244, and is attached to the mounting frame by the composite element formed from the rigid element 244 and first permanent magnet 244a being held by a friction fit in a hole in the mounting frame 240. The second permanent magnet 235 is fixedly mounted in a hole in the drive unit frame 230.

In the example of Figs. 6A-B, the mounting frame suspension system includes two mounting frame suspensions in the form of roll suspensions 242, 243 separated in a direction parallel to the movement axis. An additional suspension is provided by the two permanent magnets 235, 244a. In particular, the first permanent magnet 244a is configured to magnetically interact with the second permanent magnet 235 so as to influence relative movement between the drive unit frame 230 and the mounting frame 240.

In this example, the adjustment mechanism (not shown) is configured to adjust the magnetic interaction between the first permanent magnet 244a and the second permanent magnet 235 by moving the first permanent magnet 244a relative to the second permanent magnet 235, in this case by sliding the first permanent magnet 244a (via the rigid element 244) towards and away from the second permanent magnet 235.

It can be seen by comparing Figs. 6A(i) and 6B(i) with Figs. 6A(ii) and 6B(ii) that changing the distance between the permanent magnets 244a, 235 alters the amount of interaction between them, thereby changing the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system.

In this example, the orientation and polarity of the permanent magnets 244a, 235 is chosen to have a strong resistance force against relative movement of the magnets (and therefore between the mounting frame 240 and the drive unit frame 230) in the direction of the movement axis (as shown by the double ended arrow labelled ‘z’ in Fig. 6A(ii)). In a perpendicular direction (as shown by the double ended arrow labelled ‘x’ in Fig. 6A(ii)) there is far less resistance force against relative movement of the magnets.

As the magnets get closer (Figs. 6A(ii) and 6B(ii)), the greater the resistance to relative movement along the movement axis can be observed, hence changing the properties of the mounting frame suspension system, and thus changing the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

When the magnets are in contact via a friction pad 244b mounted on the first permanent magnet 244a (Figs. 6A(iii) and 6B(iii)), the resistance caused by magnetic interaction is at its maximum, plus the magnets are now in physical contact (via the friction pad 244b), further increasing the resistance.

In further examples (not shown), one of the magnets 244a, 235 could be replaced by an electromagnet, with both magnets being fixed in place (no need to vary the distance between them), and with the magnetic interaction between the magnets being altered by changing the strength of the electromagnet (e.g. by increasing the current through the electromagnet).

In further examples (not shown), one of the magnets 244a, 235 could be replaced by a magnetic switch (capable of being in an on state or an off state), with the adjustment mechanism being configured to adjust the magnetic interaction between the magnet and the magnetic switch by changing the state of the magnetic switch from an off state to an on state (and vice versa). Here, there would be no need to vary the distance between the magnet and the magnetic switch.

Figs. 6C(i)-(ii) show an example magnetic switch that could be used in the example described in the previous paragraph. In the example magnetic switch of Figs. 6C(i)-(ii), a rotatable round magnet 255 is mounted in a shell comprising two steel shoes 256a, 256b, and a non-ferrous material 257.

In an off state shown in Fig. 6C(i) , the magnet switch produces minimal magnetic field outside the switch, because the north and south poles of the magnet 255 are shorted within the steel shoes 256a, 256b.

In an on state shown in Fig. 6C(ii), the magnet switch produces a significant magnetic field outside the switch, because the north and south poles of the magnet 255 are guided outside of the switch by the steel shoes 256a, 256b. Another example magnetic switch is described e.g. in https://en.wikipedia.org/wiki/Magnetic_switchable_device.Fig s. 7A-C show a loudspeaker assembly 300 in which the loudspeaker 301 has been mounted in the headrest 390 of a seat.

The loudspeaker 301 is essentially the same as the loudspeaker 201 of Fig. 2A, except that it uses an adjustment mechanism analogous to that shown in Fig. 5D (described below).

The seat (not shown) which incorporates the headrest 390 is configured to position a user who is sat down in the seat such that each ear of a user is located at a respective listening position that is 40cm or less (more preferably 30cm or less, more preferably 25cm or less, more preferably 20cm or less, more preferably 15cm or less) from the first radiating surface of the loudspeaker 200.

The headrest 390 includes two directional mid-high frequency loudspeakers 391 configured to operate over a frequency band that includes 300Hz-3kHz, more preferably 150Hz-20kHz. The one or more directional mid-high frequency loudspeakers may be of a cardioid types, e.g. as described in GB2004076.2, although other forms of directional loudspeaker are of course possible.

The headrest 390 comprises rigid mounting pins 392 and rigid framework 392a, support foam 393 (which may be acoustically opaque) and acoustically transparent foam 393a.

The support foam 393 forms a waveguide which surrounds the diaphragm of the loudspeaker 301 (in a place perpendicular to the movement axis) and is configured to guide sound produced by the first and/or second radiating surface of the diaphragm out of opposite sides of the headrest 390.

The regions of acoustically transparent foam 393a are positioned in front of the first and second radiating surfaces of the loudspeaker 300, as well as in front of the mid-high frequency loudspeakers 391 , to allow sound produced thereby to reach a user sat as shown in Figs. 7B-C.

The rigid mounting pins 392 and rigid framework 392a form part of a rigid seat frame of the seat. The rigid seat frame permits vibrations generated by the moving diaphragm 210 of the loudspeaker 200 to propagate into the body of a user sat in the seat.

In this example, the entire rigid seat frame can be viewed as the mounting frame of the loudspeaker assembly 300, though it is also possible to view any structure from which the drive unit frame of the loudspeaker 301 is suspended as being the mounting frame (e.g. it would be possible for just the supplementary frame 346b to be viewed as the mounting frame).

The drive unit frame of the loudspeaker 301 is suspended from this mounting frame by the roll suspensions 342, 343.

Fig. 6D shows the interior of a car that includes a seat 395 which incorporates the headrest 390.

The headrest 390 includes a first control interface 294 configured to control the adjustment mechanism so as to adjust the mounting frame suspension system based on user input at the control interface, so that the user can adjust the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system by providing an input at the control interface. The first control interface 294 is a manual rotatable knob.

The car includes a second control interface 396 configured to control the adjustment mechanism so as to adjust the mounting frame suspension system based on user input at the control interface, so that the user can adjust the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system. The second control interface 396 is a graphical user interface which is part of a graphical user interface displayed by a car entertainment system.

Figs. 8A-B shows another loudspeaker assembly 400 in which the loudspeaker 401 has been mounted in the headrest 490 of a seat.

The loudspeaker assembly 400 and headrest 490 of Fig. 8A are similar to those shown in Fig. 7A.

However, in the example loudspeaker assembly 400 of Figs. 8A-B, there is a rotatable rod 444 on which is mounted a steel sleeve 444a and a layer 444b of compressible material (e.g. foam) of variable thickness.

Initially, the part of the steel sleeve 444a with no compressible material on it faces the U-yoke 474 of the loudspeaker 401 , and there is no engagement between the steel sleeve 444a and the U-yoke 474 of the loudspeaker 401 .

Turning the rod 444 will bring the layer of compressible material 444b into contact with the U-yoke 474, and as it continues to turn, a progressively thicker layer of compressible material 444b will be brought into contact with the U-yoke 474, causing more stiffness to be mechanically added to the mounting frame suspension. The rod 444, sleeve 444a and layer of compressible material 444b together form an additional element which acts as a new mounting frame suspension which newly interconnects the drive unit frame 430 and mounting frame 440 at one or more predetermined locations, thereby mechanically adjusting the mounting frame suspension system (so as to change the extent to which vibrations generated by the loudspeaker reach the mounting frame suspension system).

A side effect of the thickness of the layer of compressible material 444b between the steel sleeve 444a and the U-yoke 474 increasing is that the loudspeaker 401 will be progressively more pushed forwards. This can be compensated for in part by embedding different sized magnets 444di, 444dii, 444diii in the steel sleeve 444a, which pull the U-yoke 474 to compress the layer of compressible material 444b to a larger extent, as the thickness of the layer of compressible material 444b increases, thereby helping to obtain better control over the additional stiffness provided by the rod 444, sleeve 444a and layer of compressible material 444b. The adjustment mechanism here is a rotatable knob, accessible outside of the headrest 490.

Figs. 9A and 9B show a model of the loudspeaker 200 shown in Fig 2A, in which:

• Re = voice coil electrical resistance [ohm]

• Bli = motor force [N]

• Kms = stiffness of drive unit suspension [N/m]

• Rms = mechanical losses (friction) of drive unit suspension [Ns/m]

• Mms = moving mass of loudspeaker: diaphragm + air load + voice coil + part of drive unit suspension [kg]

• Mf = mass of drive unit frame of loudspeaker + magnet circuit + part of drive unit suspension [kg]

• Ml = mass of loudspeaker = Mf + Mms [kg]

• Ma = mass of headrest ‘application’ [kg]

• Ks2 = total stiffness of mounting frame suspension [N/m]

• Rs2 = mechanical losses of mounting frame suspension [Ns/m]

Here, the ‘application’ is the mass of a body which comprises the mounting frame. Typically this would be the seat frame of a car seat.

The following example values were used in all simulations described below (only Ks2, Rs2 were varied for these simulations):

• Re = 3.4 ohm

• BL = 2.5 Tm

• Kms = 0.5 N/mm

• Rms = 1 Ns/m

• Mms = 10 g

• Mf = 250 g

• Ma = 5 kg

Figs. 9C-E show the force acting on the ‘application’ (Ma) and the force acting on the moving mass of the loudspeaker (Mms) with an electrical input of 2Vrms for the differing values of Ks2 [N/mm], Rs2 [Ns/m], wherein the bold curves show the force acting on the ‘application’ (Ma) and thin curves show the force acting on the moving mass of the loudspeaker (Mms). In more detail, Fig. 9C shows increasing the stiffness (Ks2 = 1 [N/mm], 4 [N/mm], 16 [N/mm]) whilst holding the resistance constant (Rs2 = 1 [Ns/m]).

As shown by Fig. 9C, at a high stiffness (Ks2 = 16 [N/mm]) there is an increased force acting on the application as indicated by the resonance of the mounting frame suspension at a resonant frequency of around 40Hz (see label ‘X’) which may be desirable where a user wants vibrations to reach them, albeit this comes at the expense of a discontinuity in the frequency response of the diaphragm which is not a desirable property (see label ‘Y’). At a lower stiffness (Ks2 = 1 [N/mm]) there is much less force acting on the application, and the resonant frequency of the mounting frame suspension is lower (~10Hz), meaning vibrations reach a user sat in a seat incorporating the loudspeaker to a much reduced extent (see label Z’).

Fig. 9D shows increasing the resistance (Rs2 = 1 [Ns/m], 10 [Ns/m], 100 [Ns/m]) whilst holding the stiffness constant (Ks2 = 1 [N/mm]).

As shown by Fig. 9D, at a high resistance (Rs2 = 100 [Ns/m]) there is an increased force acting on the application and at a higher resonant frequency (~50Hz) of the mounting frame suspension (see label ‘A’), and with a smoother frequency response of the diaphragm (see label ‘B’), albeit the loudspeaker resonance has a less intense amplitude compared with that shown in Fig. 9C (caused by an increase in stiffness) and there is some force leakage at higher frequencies.

Fig. 9E shows increasing the resistance and stiffness (Ks2 = 2 [N/mm] Rs2 = 2 [Ns/m]; and also Ks2 = 16 [N/mm]; Rs2 = 20 [Ns/m]).

As shown by Fig. 9E, increasing both the resistance and stiffness together, causes increased force combined with a smooth frequency response, whilst increasing the resonance frequency (see labels T and ‘J’). So the combination of Ks2 = 16 [N/mm]; Rs2 = 20 [Ns/m] seems to provide a particularly desirable combination for transmitting vibrations to a user sat in a seat which incorporates the loudspeaker.

Fig. 9E therefore shows that there is a benefit in having an adjustment mechanism configured to increase both the stiffness and resistance of the mounting frame suspension system, rather than having an adjustment mechanism configured to increase only the stiffness or resistance of the mounting frame suspension system.

The amount by which the stiffness and/or resistance (preferably the stiffness and resistance) of the mounting frame suspension system is increased to provide increased vibrations is a matter of design choice.

Fig. 10A shows a car seat, wherein an axis extending through the backrest and headrest forms an angle a with a vertical direction [deg].

Fig. 10B shows a plot of the static deflection, Xstatt of the mounting frame suspension [m] against the tuning frequency Fs2 [Hz] of the mounting frame suspension. Here, the static deflection, Xstat, is the amount by which the mounting frame suspension is deflected from its centre position under the effect of gravity. The tuning frequency of the mounting frame suspension is a resonant frequency of the loudspeaker at which the force acting on the ‘application’ (Ma) is at a maximum.

Fs2 and Xstat are defined by the following equations, where g= 9.81 [m/s ² ]:

As shown by Fig. 10B, at all values of a, if the tuning frequency of the mounting frame suspension is below 10Hz, then the required size of Xstat becomes excessively large to be accommodated by a practical loudspeaker.

A preferred tuning frequency for a “first configuration” of the mounting frame suspension system (in which few vibrations reach a user sat in a seat) is therefore between 10Hz-30Hz, more preferably 10Hz-20Hz.

Increasing Ks2 beyond 30Hz will increase Fs2 and will therefore transfer more vibrations to the application and consequently diminish Xstat.

Fig. 11 A shows another loudspeaker assembly 500 in which the loudspeaker 501 has been mounted in the headrest of a seat, albeit that only support foam 593 (which may be acoustically opaque) and acoustically transparent foam 593a of the headrest can be seen in this particular drawing.

The loudspeaker assembly 500 is similar to those shown in Fig. 7A, except that in this example, the loudspeaker assembly 500 includes a loudspeaker-mounting frame unit 547 configured to be mounted in the headrest, wherein the loudspeaker-mounting frame unit 547 includes: the loudspeaker 501 ; the mounting frame 540; and one or more attachment formations 541c on the mounting frame, wherein the attachment formations 541c are configured to facilitate attachment of the loudspeaker-mounting frame unit 547 to the headrest.

The one or more attachment formations 541c, in this example, have the form of wings with screw holes, configured to facilitate attachment of the loudspeaker-mounting frame unit 547 to the headrest via passing one or more screws 541 d via a respective screw-hole in each wing into the support foam 593 of the headrest.

In this example, the mounting frame include a first grille 541a positioned in front of the first radiating surface 512 of the diaphragm 510, and a second grille 541b positioned in front of the second radiating surface 514 of the diaphragm 510.

In this example, the adjustment mechanism includes a pulling device, which here has the form of a manual rotary knob 585 with an asymmetric pulley 585a. The pulling device is configured to pull the drive unit 520 towards the second grille 541 b via a length of flexible material 585b (e.g. a rope) attached to the drive unit 520 or the drive unit frame 530. The length of flexible material 585b passes through a gap in the second grille 541 b in order to reach the pulling device.

In use, the pulling device (through turning of the knob 585) pulls on the length of flexible material 585b, which in turn, pulls the drive unit 520 towards the second grille 541 b, thereby causing:

• the mounting frame suspensions 542, 543 to stiffen, thereby changing the extent to which vibrations generated by the loudspeaker 501 reach the mounting frame 540 via the mounting frame suspension system when the loudspeaker 501 is in use.

• the drive unit 520 to come into contact with at least one soft element (here, two soft pads 545) on the second grille 541 b, thereby changing the extent to which vibrations generated by the loudspeaker 501 reach the mounting frame 540 via the mounting frame suspension system when the loudspeaker 501 is in use (here, the soft pads 545 can be considered as a new mounting frame suspension which newly (and indirectly) interconnects the drive unit frame 530 and mounting frame 540 at one or more predetermined locations).

Note that if the flexible material 585b is a rope that makes a closed loop around the pulley 585a, one can keep rotating the knob 585 while the rope glides over the pulley 585a. In such case the asymmetry of the pulley 585a will make the rope be tensioned or released as the knob 585 is turned. This also allows for a blocking mechanism that prevents the wheel to turn back when the rope is tensioned, which could for example be implemented via a ratchet mechanism as shown in Fig. 11 B, for example.

Note that because the length of flexible material 585b passes through a gap in the second grille 541 b in order to reach the pulling device, the grille 541 b is effectively used as an anchor which allows the length of flexible material to pull the drive unit 520 in a direction parallel to the movement axis 502, even though the pulling device is located laterally with respect to the grille 541 b and drive unit 520, here with the pulling device being located in a position that, when projected onto a plane perpendicular to the movement axis 502, is outside of the portion of that plane taken up by the grille 541 b and drive unit 520, when projected onto that plane. This allows for the manual rotary knob to conveniently be located on the side of the headrest, for example.

A rotary motor or manual rotary knob, with an asymmetric pulley 585a as shown in Fig. 11 A, has been found to be a particularly compact and simple way to permit a user to control the extent to which vibrations generated by the loudspeaker reach the mounting frame via the mounting frame suspension system when the loudspeaker is in use.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/- 10%.

References

A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

W02005/015950A1

WO2008/135857A1

WO2019/121266A1

PCT/EP2020/064577

“Dynamical Measurement of the Effective Radiating area SD”, Klippel GmbH (https://www.klippel.de/fileadmin/klippel/Files/Know_How/App lication_Notes/AN_32_Effective_Radiation_ Area.pdf