Field of Invention

The present invention relates to transducer units that house transducers such as microphones and more particularly to a transducer unit for substantially reducing or eliminating entirely the pickup of vibrational noise by a transducer.

Background Microphones are ubiquitous in modern technology. Many devices such as cameras, mobile telephones, PDA's, video cameras and other electronic devices routinely incorporate microphones. Many of these devices are designed to be hand held and portable, introducing significant constraints on their weight and size.

A problem with microphones incorporated into such devices is that they pick up vibrations transmitted through the casing or body of the device. These vibrations typically have a number of causes. One example is through user interaction with the device (e.g. pressing a key). Another example is where the operation of the device itself can cause vibrations that are picked up by the microphone. In the case of a still or video camera, or a mobile phone incorporating camera functionality, the vibrations generated by a motor used to focus or zoom the lens of the device during picture taking/video recording can be picked up by the microphone.

It is desirable to eliminate as much as possible the unintentional pickup by the microphone of vibrations transmitted through the body of a device, as preventing these vibrations from being picked up results in an audio signal that does not suffer from a high degree of unwanted vibration noise. The noise free audio signal may then be streamed as a live feed, or it may be saved on internal or external storage means such as a solid-state drive, memory card or hard drive for later playback. Existing solutions for removing unwanted microphone noise involve postprocessing audio data obtained from a microphone, in order to remove unwanted noise from the audio signal. These systems may require additional microphones to determine the characteristics of the noise that is to be removed, as well as hardware to carry out the time consuming and computationally costly post-processing algorithms that perform the noise removal.

Japanese patent application JP 2005-354581 discloses a microphone arrangement in which the transmission of vibrations is apparently reduced.

Summary

From a first aspect, the present invention provides a transducer unit for an electronic device capable of capturing audio, the unit comprising:

a transducer; and

a support means for supporting the transducer, the support means being located between the transducer and a body of the electronic device; the unit further comprising a vibration damping material located between the transducer and the body of the electronic device, wherein the vibration damping material is arranged to decouple the transducer from the body.

This transducer unit effectively decouples a transducer from its surroundings, greatly reducing or eliminating entirely the transducer's pickup of unwanted vibrational noise and enables the unit to be secured to a suitable electronic device.

From a second aspect, the present invention provides an electronic device capable of capturing audio, the electronic device having a body, wherein the transducer unit of the first aspect is installed within said body. The electronic device further comprises at least one vibration generating component coupled to the body. Brief Description of Drawings

Embodiments of the invention are described below in more detail, by way of example, with reference to the accompanying drawings in which:

Fig. 1 is a schematic drawing of a transducer unit according to a first embodiment of the present invention; Fig. 1A is a schematic drawing of a transducer unit according to an alternative embodiment of the present invention;

Fig. 2 is a schematic drawing of a layering arrangement of vibration absorbing materials according to a second embodiment of the present invention, which may be used in the transducer unit shown in Fig. 1 or Fig. 1 A;

Fig. 3 is a schematic drawing of a video camera incorporating a transducer unit according the present invention within its body; Description of Embodiments

Embodiments of the present invention will be described primarily using the example of a video camera containing a microphone, but it will be appreciated that the present invention is applicable to any device having a transducer housed within its body where it is desirable to avoid the pickup of vibrational noise.

In the context of the present specification, 'vibration noise' is understood to mean pressure waves transmitted to a microphone via a non-gaseous medium. This should be understood to be clearly distinct from 'sound', which in the context of the present specification is understood to mean pressure waves propagating via a gaseous medium (e.g. air). In the case of a microphone, the former is an unwanted source of noise and the latter is the desired signal. Fig. 1 is a schematic of a transducer unit 10 according to a first embodiment of the present invention. Unit 10 has a body 15 formed typically of a lightweight, durable material such as plastic. A vibrational noise source 16 is included within body 15. This may be any component that generates vibrations, such as a motor to focus or zoom the lens of a video camera. Vibrational noise source 16 may itself be comprised of multiple individual components, some or all of which generate vibrational noise. Body 15 includes a recess 20, in which a transducer is inset. In the present embodiment the transducer is a microphone 25, although other types of transducer may be used. Microphone 25 may be any type of microphone known to the skilled person (e.g. an Electret Condenser Microphones (ECM) or a Micro Electrical-Mechanical System microphone (MEMS microphone), or other sensor) and would be readily chosen by the skilled person according to the nature of the device in which it is to be installed. The microphone may face any direction appropriate to pick up sound. .

Microphone 25 is supported in recess 20 by a support structure. In the present embodiment the support structure comprises two layers 30 and 40. Sandwiched between these two layers is an intermediate layer 35. As shown in Fig. 1 , in the present embodiment innermost layer 30 comprises a side wall forming a ring-type structure that surrounds the sides of microphone 25. The side wall may be one continuous unbroken piece of material or may have one or more gaps in its structure (not shown). The gaps may be arranged at regular or irregular intervals.

In an alternative embodiment, shown in Fig. 1A, in addition to a side wall, innermost layer 30 additionally includes a base portion 32 covering the base of microphone 25. In a further alternative embodiment, innermost layer 30 fully covers microphone 25. In all of these embodiments holes may be provided in one or more portions of innermost layer 30 to allow sound waves to propagate through it. It will be appreciated that the shape of innermost layer is not limited to a ring shape and other shapes selected on the basis of the shape of microphone 25 can be used in all embodiments of the present invention. It should be appreciated that the present invention is not limited to the particular support structure shown in Fig. 1. In an alternative embodiment, the support structure only includes a single layer located between microphone 25 and intermediate layer 35 (i.e. layer 30 of Fig. 1). In a further alternative embodiment, the support structure only includes a single layer located between intermediate layer 35 and body 15 (i.e. layer 40 of Fig. 1). As described later on in this specification, further alternative support structures having at least one layer disposed between microphone 25 and body 15 are also within the scope of the present invention. As shown in Fig. 1 , intermediate layer 35 comprises a base portion, two pairs of opposing side portions and an upper portion 35a. Intermediate layer 35 is arranged to surround microphone 25 and innermost layer 30. In an alternative embodiment, upper portion 35a of intermediate layer 35 is not present, such that intermediate layer 35 comprises only a base portion and two opposing pairs of side portions.

In the present embodiment the upper edge of upper portion 35a is flush with body 15. In an alternative embodiment, microphone 25 is housed fully within body 15; i.e. the upper edge of upper portion 35a is not flush with body 15. In this alternative embodiment, one or more air channels are provided through body 15 to allow sound waves to propagate to microphone 25.

Outermost layer 40 is composed of a base portion and two pairs of opposing side portions. Outermost layer 40 lines recess 20 such that it is in direct contact with body 15 and is considered to be coupled to the body 15. The contact does not necessarily need to be provided by a further material such as adhesive but can be through friction. Outermost layer 40 is dimensioned such that it is flush with the outer edges of recess 20 in camera body 15, so that it will not slide about in recess 20 if transducer unit 10 is shaken or otherwise set into motion.

It will be appreciated that the present invention is not limited to the particular shaped structure shown in Figs. 1 and 1A and that other shaped structures, such as cylindrical or cuboid structures, may also be used for layers 30, 35 and 40.

The arrangement is such that the intermediate layer 35 is sandwiched between the support structure comprising outermost layer 40 and innermost layer 30. If present, the upper portion 35a of intermediate layer 35 forms a protective layer and is exposed to the air. Optionally upper portion 35a contains a strengthening member within it (not shown), which serves to increase the degree of protection the protective layer offers. The strengthening member is air permeable. One example of a suitable strengthening member is a sheet of plastic having holes extending through its thickness spaced across its surface. If a strengthening member is used, it is embedded within upper portion 35a such that it does not come into direct physical contact with microphone 25 or innermost layer 30.

An external support or cover (not shown) may also be provided for additional protection of transducer unit 10. One example of a suitable external cover is a layer of mesh arranged above upper portion 35a. Innermost layer 30 and outermost layer 40, which form the support structure, are made of a pliable, malleable material such as rubber or a silicone based material. The material is pliable and malleable to the extent that suitable support for the microphone is provided by the innermost layer 30 and suitable support is provided by the outermost layer 40 for the intermediate layer 35 and innermost layer 30. The microphone is typically metallic and the body of the camera is typically plastic which are both rigid and the material for the innermost and outermost layers is chosen to ensure sufficient flexibility when supporting the microphone in the plastic body of the camera. Innermost layer 30 may be partially or fully covered with an adhesive material such as rubber glue. In an alternative embodiment, innermost layer 30 is itself formed of rubber glue. The total thickness of the support structure is chosen to be much less than the thickness of intermediate layer 35. In the present embodiment, the thickness of each of layers 30 and 40 is much less than the thickness of intermediate layer 35.

Innermost layer 30 is in direct contact with microphone 25 and is dimensioned such that microphone 25 fits snugly into innermost layer 30. Preferably innermost layer 30 is slightly smaller than microphone 25, such that once microphone 25 in inserted in innermost layer 30 friction between these two components will prevent microphone 25 from substantially moving within and falling out of innermost layer 30. This type of arrangement is commonly known as an interference fit. This ensures that microphone 25 will not fall out of innermost layer 30 under gravity if transducer unit 10 is inverted. Optionally innermost layer 30 may be covered in or formed from an adhesive material, such as rubber glue, that will secure innermost layer 30 to intermediate layer 35.

Intermediate layer 35 is a vibration damping layer formed of a material having a low vibration transmission coefficient. The material is selected such that microphone 25 has acoustic access to the desired sound source.

The vibration transmission coefficient of a material is defined by equation 1 as: where Pj is the transmitted vibration power and is the incident vibration power. The inventors of the present invention have discovered that it is desirable to form intermediate layer 35 of a material (or composition of materials) that has a transmission coefficient T as close to zero as possible.

Upper portion 35a of intermediate layer 35 is substantially acoustically transparent, in order for microphone 25 to function as intended; that is, the transmission coefficient of upper portion 35a of intermediate layer 35 for sound waves should be as close to one as possible. This allows sound waves to permeate upper portion 35a and impact upon the diaphragm of microphone 25, such that a signal is received by microphone 25. It has been found that rubber on its own is not an adequate material for the intermediate layer since it does not achieve the above purpose. Although it provides some elasticity, its density and high vibration transmission coefficient (close to 1) results in it transmitting vibrations with little attenuation. It will be appreciated that some or all of intermediate layer 35 (i.e. not just upper portion 35a) may also be made of a material that is substantially acoustically transparent.

The inventors of the present invention have discovered that a tightly packed monofilament fabric and particularly a tightly packed woven monofilament fabric is a particularly good choice of material for upper portion 35a and/or intermediate layer 35. In addition, the inventors of the present invention have determined that tightly packed cloth is another particularly good class of material for upper portion 35a and/or intermediate layer 35, although other vibration damping materials such as foam may be used. This is because monofilament fabric and cloth is formed of a series of interwoven threads which form a mesh structure, so any mechanical vibrations pass through the structure of the weave of the material, but will not pass through the channels of air filled holes formed in the gaps between the weave. This is because strands of the weave present a reduced cross-sectional surface area for vibrations to pass through. In addition, adjacent strands rub against each other as vibrations are transmitted, resulting in additional attenuation of the vibrations as they travel through the material. Vibrations therefore do not pass well through the material, but are instead absorbed by the weave of the material.

Sound, on the other hand, passes very easily through the material, even when it is tightly packed. This is because airborne vibrations can travel via the network of interconnecting air channels formed by the gaps between successive layers of the packed material. This means that it is possible to completely cover microphone 25 with intermediate layer 35 without having to provide a hole in upper portion 35a for sound to travel through (as would be necessary with a rubber covering, for example). Therefore, upper layer 35a does not compromise the sound pickup of microphone 25.

In the case of a woven cloth or woven monofilament fabric, transmission of sound may also occur via air channels that are formed by the gaps in the weave of the material.

The above arrangements provide a plurality of channels that allow sound to travel from the side of intermediate layer 35 that is distal the microphone 25 to the side of intermediate layer 35 that is proximal the microphone 25.

One particular example of a cloth that is preferably used in the embodiments of the present invention is wool felt. One particular example of a monofilament fabric that is preferably used in the embodiments of the present invention is a woven monofilament fabric.

Movement of microphone 25 within recess 20 is minimised by the arrangement of innermost layer 30 and intermediate layer 35. As discussed earlier, microphone 25 is secured tightly in innermost layer 30, such that microphone 25 cannot move in any direction within innermost layer 30. Thus, microphone 25 and innermost layer 30 can be considered as a single unit. As shown in Fig. 1 , innermost layer 30 sits in direct physical contact with intermediate layer 35. The tightly packed cloth that forms intermediate layer 35 acts to cushion any motion of the microphone/innermost layer unit, so that microphone housing may be shaken, inverted or otherwise subjected to vigorous motion without microphone 25 becoming dislodged or impacting on any of the walls of recess 20. As a result noise caused by such motion, which ordinarily would be picked up by microphone 25 as it impacted against the walls of recess 20, is greatly reduced and, in some cases, eliminated entirely.

Microphone 25 is electrically connected to other devices or components via wire 45, through which the signal generated by microphone 25 is sent. Wire 45 may also supply power to microphone 25. Wire 45 is preferably a small diameter wire. Wire 45 may be a single-strand wire or it may be a multi-strand cable such as a Litz wire. Wire 45 passes through outermost layer 40 and intermediate layer 35 via appropriately sized openings in these layers. If a base portion (not shown) is included in innermost layer 30, wire 45 passes through this in a similar fashion to the other layers. It is preferable that the portion of wire 45 that passes through intermediate layer 35 is not pulled taught, such that a small amount of slack exists in this region. Providing this slack minimises the transmission of vibrations via wire 45.

It will be appreciated after consideration of the teaching herein that more than the three layers described above in the first embodiment may be used in a microphone housing according to the present invention. In a second embodiment of the present invention, as shown in Fig. 2, n intermediate layers 205a, 205b... 205n are used. These intermediate layers are sandwiched between a first layer 200 and a last layer 210. The first layer 200 and the last layer 210 (the innermost and outermost layers, respectively) are thin compared to the total thickness of the n intermediate layers 205a, 205b... 205n. The first 200 and last 210 layers are formed of a pliable, malleable material such as rubber or a silicone based material. First layer 200 is in contact with microphone 25 in a manner similar to innermost layer 30 described earlier in the first embodiment.

. ^. ,

The n intermediate layers 205a, 205b... 205n are formed of a vibration damping material. Preferably these layers are formed of tightly packed cloth, although other materials such as foam may be used. The n intermediate layers 205a, 205b... 205n may be each made of a different material. A repeating pattern of materials, such as the A, B, A, B... repeating pattern shown in Fig. 2 may also be used. In some embodiments the repeating pattern of materials used in the n intermediate layers may include a rubber or silicone based layer R, resulting in a repeating pattern such as A, B, R, A, B, R... Other regular or irregular repeating patterns incorporating any number of different materials may be provided.

Each layer of the layered arrangement has different decoupling and vibration damping characteristics which are considered non-overlapping damping characteristics. For example, rubber, preferably soft rubber and a silicone based layer which is preferably stiff, will have different decoupling characteristics so could be used in the layered arrangement. On the other hand, tightly; packed cloth and felt layers would have similar decoupling characteristics which would not provide improved decoupling. It will be appreciated that the invention is not limited to these materials and similar materials with similar effects may be used although the combination of rubber and silicone based layer is particularly desirable. The layered arrangement of this embodiment is placed in recess 20 in camera body 15 in a manner similar to that described above in respect of the first embodiment to form a transducer unit that substantially reduces or eliminates entirely the transmission of vibrational noise to the microphone. Moving on to Fig. 3, a schematic diagram of a video camera 300 having a transducer unit 310 according to the first or second embodiments of the present invention is shown. Included within the body of video camera 300 is a motor 320 for focusing the lens 330 of video camera 300. Motor 320 emits vibrations during operation, which travel through the body of video camera 300. Transducer unit 310 prevents these vibrations from reaching the microphone housed therein, such that an audio signal produced by video camera 300 does not suffer from vibrational noise.

It has been discovered that arrangements according to those described in the first and second embodiments significantly reduce, and in some cases entirely eliminate, pickup of vibrational noise by a microphone housed in the body of a video camera. However the present invention is not so limited and the skilled person will readily appreciate, after consideration of the teaching contained herein, that the present invention is equally applicable to any device incorporating a transducer where it is desirable to acoustically decouple the transducer from vibration sources.

Further, the present invention provides a transducer unit that is effectively decoupled from vibrational noise sources without requiring the installation of additional computing hardware. Furthermore, the present invention provides a transducer unit that is readily installed in a device where it is desirable to keep size, weight and manufacturing complexity and costs low. In addition to the embodiments of the invention described in detail above, the skilled person will recognize that various features described herein can be modified and combined with additional features, and the resulting additional embodiments of the invention are also within the scope of the accompanying claims.