TECHNICAL FIELD

[0001] The disclosure relates to a device and a method for generating tactile feedback, in particular for generating tactile feedback for bass enhancement of loudspeaker devices, in particular for wearable loudspeaker devices.

BACKGROUND

[0002] It is known that tactile sound devices for producing vibrations that can be felt on the body enhance the sound perception, in particular the bass sound perception. A tactile sound device, also known as tactile transducer or bass shaker, for example, is designed to allow people to not only hear low bass frequencies, but also feel the low bass frequencies by transmitting low-frequency vibrations into various surfaces such as a chair on which a user is seated, for example.

SUMMARY

[0003] A device for generating tactile feedback comprises an enclosure, at least one loudspeaker mounted in a wall of the enclosure between the inside and the outside of the enclosure and configured to produce sound waves, and at least one membrane mounted in a wall of the enclosure between the inside and the outside of the enclosure, wherein the pressure inside the enclosure changes depending on the sound waves, and wherein the at least one membrane is configured to be stimulated to vibrate depending on the pressure inside the enclosure and to be brought in contact with an object to provide tactile feedback.

[0004] A method for generating tactile feedback comprises generating sound waves within an enclosure using at least one loudspeaker that is mounted in a wall of the enclosure between the inside and the outside of the enclosure, wherein the pressure inside the enclosure changes depending on the sound waves, generating vibrations of at least one membrane mounted in a wall of the enclosure between the inside and the outside of the enclosure, wherein the vibrations of the at least one membrane are dependent on the pressure inside the enclosure, and providing tactile feedback by transferring the vibrations of the membrane to an object.

[0005] Other devices, systems, methods, features and advantages will be or will become apparent to one with skill in the art upon examination of the following detailed description and figures. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The method may be better understood with reference to the following description and drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.

[0007] Figure 1 is a schematic diagram of a tactile loudspeaker device.

[0008] Figure 2 is a schematic diagram illustrating an exemplary wearable loudspeaker device and a user wearing the wearable loudspeaker device.

[0009] Figure 3 is a schematic diagram illustrating a wearable loudspeaker device including a device for tactile feedback that is worn by a user.

[0010] Figure 4 illustrates in a flow chart a method for generating tactile feedback in a loudspeaker device. [0011] Figure 5 illustrates in diagrams different relative sound pressure levels for a loudspeaker with and without a device for tactile feedback.

[0012] Figure 6 illustrates in diagrams the total harmonic distortion and the relative sound pressure level during the measurement of the total harmonic distortion of a loudspeaker with and without a device for tactile feedback. [0013] Figure 7 illustrates in diagrams an impedance curve of a loudspeaker under different conditions. [0014] Figure 8 is a schematic diagram of another tactile loudspeaker device.

DETAILED DESCRIPTION

[0015] Referring to Figure 1, a loudspeaker device 100 is illustrated. The loudspeaker device 100 includes a closed enclosure 110. The enclosure 110 is illustrated having a rectangular cross section in Figure 1. However, this is only an example. The enclosure 110 may have any cross section and any shape. A loudspeaker 120 is mounted in a front panel of the enclosure 110 between the inside and the outside of the enclosure 110. This is, however, only an example. The loudspeaker 120 may also be mounted in a back panel, sidewall or any other wall or baffle of the enclosure 110. The loudspeaker 120 may be any transducer configured to convert electrical signals into sound waves. For example, the loudspeaker 120 may include a diaphragm attached to and driven by a voice coil, such as in a dynamic driver setup, a balanced armature setup, etc. When an electrical signal is applied to the loudspeaker 120, a mechanical force causes the diaphragm to move back and forth, thereby reproducing sound under the control of the applied electrical signal. [0016] When moving back and forth, the outward-facing surface of the diaphragm generates sound waves at the front of the loudspeaker 120 outside of the enclosure 110, and the inward- facing surface of the diaphragm generates sound waves at the back of the loudspeaker 120 inside the enclosure 110. The primary role of the enclosure 110 is to prevent the sound waves generated by the inward-facing surface of the diaphragm to interact with the sound waves generated by the outward-facing surface of the diaphragm. The outward and inward generated sounds are usually out of phase with each other and an interaction between them generally results in cancellation of at least parts of the wanted sound signal. The enclosure 110 may further prevent echo and reverberation effects.

[0017] A membrane 130 is mounted in a back panel of the enclosure 110 between the inside and the outside of the enclosure 110. This is, however, only an example. The membrane 130 may also be mounted in a front panel, sidewall or any other wall or baffle of the enclosure 110. The membrane 130 includes a passive membrane. A passive membrane is a membrane that is stimulated through changes in the surrounding pressure only. No actuators are used for its stimulation. Therefore, when the pressure in the enclosure 110 changes due to the movement of the diaphragm of the loudspeaker 120, the membrane 130 is stimulated depending on the pressure inside the enclosure 110. This means that the membrane 130 moves around a resting position by a certain distance x. The distance x may be variable depending on a current pressure inside the enclosure 110. The distance x may further be dependent on the material, the thickness, the mass or the surface area of the membrane 130 and on how the membrane 130 is fixed to the enclosure 110. The distance x may vary for different parts of the membrane.

[0018] The membrane 130 may include an elastic material such as rubber, latex, polypropylene, textile fabric or woven fabric, for example. The membrane 130 may also include a material that is, at least virtually, not stretchable in one or multiple dimensions, but is still bendable such as glass fibre or carbon, for example. The membrane 130 may be fixed to the enclosure 110 using a glue or an adhesive which may optionally also be flexible. The fixation of the membrane to the enclosure may also include a flexible surrounding that supports movements, especially movements of membrane materials that are not or only slightly flexible or stretchable along their main dimensions (width and length). These are, however, only examples. The membrane 130 may be fixed to the enclosure 110 in any other way that allows a vibration of the membrane 130 in response to a change of pressure within the enclosure 110. Such membrane vibrations may include a movement of the whole membrane or only parts of the membrane. The membrane weight may optionally be adjusted in combination with the stiffness and/or flexibility of the membrane and/or surrounding, to promote movement below certain frequencies or within certain frequency ranges by controlling inertia and/or a resonance frequency of the membrane. To adjust the membrane weight, flexibility and/or stiffness, the material or material mix of the membrane and/or surrounding may be chosen accordingly. Furthermore, the thickness of at least parts of the membrane may be adjusted to control the membrane weight, flexibility and/or stiffness. Adjustments of thickness may induce thickness patterns that control the flexibility of the membrane. Flexibility, shape, size and weight of the membrane may further be adjusted to control the distance x that the membrane moves out of its resting position at a given sound pressure level produced by the loudspeaker. This may be required in order to adjust the intensity of the tactile feedback to a level preferred by the majority of potential users. The size and shape of the membrane may be adjusted to match parts of the human body for which tactile feedback shall be provided. [0019] When the membrane 130 is brought in contact with a user or the clothing of a user, for example, the user can feel the vibrations of the membrane 130. In this way, a tactile feedback can be provided to the user. This tactile feedback is dependent on the sound or music that is currently playing over the loudspeaker 120. This can improve the listening experience of the user while listening to a sound or music that is generated by the loudspeaker 120. The loudspeaker 120 may be configured to reproduce low or very low frequencies, for example. Loudspeakers that are configured to reproduce low frequencies are generally known as woofers, whereas loudspeakers that are configured to generate very low frequencies are generally known as subwoofers, for example. Especially the low frequency perception can be greatly increased by providing tactile feedback to the user. When playing sound or music, it is generally necessary to also reproduce middle and high frequencies. Additional loudspeakers may be integrated in the same enclosure 110 or in different enclosures that are arranged adjacent or in close proximity to the enclosure 110. Loudspeakers that are configured to generate middle frequencies are generally known as mid-range speakers and loudspeakers that are configured to generate high frequencies are also known as tweeters. However, in general the perception of the lowest frequency range that a loudspeaker can support may be improved by providing tactile feedback. In many cases, maximum sound pressure levels that a loudspeaker is able to produce are reduced with a decreasing frequency of the sound signal. At some frequencies the loudspeaker may no longer produce considerable sound pressure, but may still provide enough air pressure inside the enclosure to induce motion to the passive membrane. In this way, tactile feedback may enhance the perception of these frequencies. The proposed method, therefore, is not restricted to loudspeakers producing low frequencies, but may also be used for small fullrange loudspeakers, for example, which cover large parts of the audible frequency range and which are optionally used without any additional loudspeakers that could support frequency ranges outside the frequency range of the fullrange loudspeaker.

[0020] The enclosure 110 may be mounted on or may be part of a wearable loudspeaker device. Different wearable loudspeaker devices are known. Referring to Figure 2, a wearable loudspeaker device 240 is illustrated that is configured to be worn around the neck of a user 200. The wearable loudspeaker device 240, therefore, may have a U-shape as is illustrated in Figure 2. Any other shape, however, is also possible. The wearable loudspeaker device 240, for example, may be flexible such that it can be brought into any desirable shape. The wearable loudspeaker device 240 may rest on the neck and the shoulders of the user 200, as is illustrated in Figure 2. This, however, is only an example. The wearable loudspeaker device 240 may also be configured to only rest on the shoulders of the user 200 or may be clamped around the neck of the user 200 without even touching the shoulders. Any other location or implementation of the wearable loudspeaker device 240 is also possible. To allow the wearable loudspeaker device 240 to be located in close proximity of the ears of the user 200, the wearable loudspeaker device 240 may be located anywhere on or close to the neck, chest, back, shoulders, upper arm or any other part of the upper body of the user 200. Any implementation is possible that attaches the wearable loudspeaker device 240 in close proximity of the ears of the user 200. I.e., the wearable loudspeaker device 240 may be attached to the clothing of the user 200. Still referring to Figure 2, the wearable loudspeaker device 240 is implemented as one piece. However, the wearable loudspeaker device 240 may also include two parts (not illustrated), wherein one part is arranged to provide sound to the left ear and the other part is arranged to provide sound to the right ear. Each part may rest on one shoulder of the user 200, for example. In other embodiments the wearable loudspeaker device 240 may include even more than two parts.

[0021] The wearable loudspeaker device 240 may include at least one loudspeaker 220. The wearable loudspeaker device 240, for example, may include two loudspeakers 220R, 220L, one loudspeaker for each ear of the user 200. The at least one loudspeaker 220 may be arranged at a first side of the wearable loudspeaker device 240. The at least one loudspeaker 220 may be arranged to be in close proximity to the ear of a user 200. When the wearable loudspeaker device 240 is worn around the neck or shoulders, the at least one loudspeaker 220 may, for example, be arranged on an upper side of the wearable loudspeaker device 240 which is closest to the ears of the user 200. In this way, the sound or music may be provided to the user 200 without interference from the clothes or any parts of the body of the user 200. This is exemplarily illustrated in Figure 3. The membrane 130, on the other hand, may be arranged on the wearable loudspeaker device 240 such that it comes into contact with the user or the clothing of the user, for example, in order to provide tactile feedback. As is illustrated in Figure 3, the membrane 130 may be arranged at a bottom wall or a side surface of the wearable loudspeaker device 240, for example. The exact location of both the loudspeaker 120 and the membrane 130, however, depends on the form and implementation of the wearable loudspeaker device 240 and the part of the user's body to which tactile feedback should be provided. One advantage of the proposed method compared to methods that cause vibration of the whole wearable device (i.e. by using a shaker) is that by adjusting the size, shape and position of the membrane 130, the parts of the human body to which the tactile feedback is provided may be chosen deterministically. For example, vibrations to the neck may be perceived as unpleasant by some users, especially near the carotid artery, while vibrations in the region of the collarbone may be perceived as pleasant and may enhance the listening experience. Therefore, the membrane 130 may be positioned such that it touches or avoids certain regions of the user's body. Furthermore, the membrane may reduce vibrations of the enclosure walls by reduction of the air pressure inside the enclosure. This can reduce vibrations that are felt on parts of the user's body where they are perceived as unpleasant. Reduced enclosure vibrations may also improve the sound quality of the wearable loudspeaker device, as magnification and cancellation effects between the sound radiated by the loudspeaker membrane and the enclosure walls may be reduced. More than one membrane 130 may be provided within one enclosure 110 to intensify the tactile feedback. More than one loudspeaker 120 may be used to improve the listening experience of the user 200.

[0022] The wearable loudspeaker device 240 that is illustrated in Figure 3 has a rounded cross section. This, however, is only an example. Any other cross section such as rectangular, for example, is also possible. The cross section can also be irregular and uneven and may be adapted to align with the relevant parts of the user's body. [0023] Now referring to Figure 4, a method for providing tactile feedback is illustrated. First, using a loudspeaker 120, sound waves are generated (step 401). The sound waves are primarily generated at the outside of an enclosure 110, however, sound waves are also generated at the rear side of a loudspeaker 120 inside the enclosure 110. The sound waves inside the enclosure 110 effect a change of pressure inside the enclosure 110. This change of pressure inside the enclosure 110 causes a vibration of a membrane 130 that is mounted in the same enclosure as the loudspeaker 120 (step 402). Tactile feedback may be generated by transferring the vibrations of the membrane 130 to the body of a user (step 403).

[0024] When the membrane 130 vibrates, it also produces some additional sound pressure outside the enclosure 110. This additional sound pressure is out of phase compared to the sound pressure that is generated outside the enclosure 110 by the at least one loudspeaker 120. The additional sound pressure generated by the membrane 130 may reduce sound pressure that is produced by the loudspeaker 120. Therefore, the total sound pressure of the device may be slightly reduced when a passive membrane 130 is included in the device. Furthermore, the movement of the passive membrane caused by the air pressure inside the enclosure that is generated by the active loudspeaker 120 may induce mechanical losses to the complete system, thereby reducing the total sound pressure generated by the device. This is illustrated in the diagrams in Figure 5. In the left diagram in Figure 5, graph A illustrates the relative sound pressure level that is produced by the loudspeaker 120 when a sound is played and no additional membrane 130 is arranged in the enclosure 110. Graph B illustrates the relative sound pressure level inside the enclosure when a membrane 130 is mounted in the same enclosure 110 and produces additional out-of-phase sound pressure. The left diagram shows the case in which the membrane 130 is not in contact with a person, meaning that the membrane 130 can vibrate freely without any restrictions. The sound pressure loss in this example is about 2 - 3dB. Sound pressure loss can vary depending on the size and geometry of the enclosure 110, the size of the loudspeaker and the size, flexibility or weight of the membrane, for example.

[0025] In the right diagram in Figure 5, additional graph C illustrates the sound pressure loss when the membrane 130 is in contact with an object such as a human body, for example. When the membrane 130 is in contact with an object it cannot vibrate freely because its movement is restricted by the object. Therefore, the distance x (see Figure 1) is generally smaller when the membrane 130 is brought into contact with an object. The membrane 130 can move out of its resting position to a full extent when it is not in contact with an object, but is prevented to move out of its resting position to its full extent when it is in contact with an object because the object forms a barrier for the membrane 130. When the membrane movement is decreased, this also decreases the generation of additional sound pressure by the membrane 130. The sound pressure loss decreases noticeably when the membrane 130 is brought into contact with an object. In the example of Figure 5, the sound pressure loss decreases to about only ldB.

[0026] When the diaphragm of the loudspeaker 120 moves to produce sound waves, the pressure in the enclosure 110 may change in a nonlinear way over the excursion range of the loudspeaker 120. This may lead to distortions in the sound produced by the loudspeaker 120. The membrane 130 may have a certain nonlinear stiffness over its excursion range which may cause additional nonlinear air pressure changes inside the enclosure, thereby inducing additional distortion of the sound produced by the loudspeaker 120. In the left diagram in Figure 6, graph D illustrates the total harmonic distortion of the loudspeaker 120 for different frequencies when only the loudspeaker 120 is mounted in the enclosure 110. Graph E illustrates the total harmonic distortion when a membrane 130 is additionally mounted in the enclosure 110. As can be seen, the total harmonic content increases when a membrane 130 is mounted in the enclosure 110 in addition to the loudspeaker 120. In the given example, however, this increase of total harmonic distortion is moderate compared to the already rather high distortion of the loudspeaker 120. Furthermore, in the given example, distortion is actually reduced between 400Hz and 500Hz when including an additional membrane 130 into the device. This may be caused by damping of standing sound pressure waves inside the enclosure by the passive membrane 130 or the reduction of enclosure wall vibrations by air pressure reduction inside the enclosure caused by the passive membrane. As explained above, the loudspeaker 120 may be configured to produce low or very low frequencies. At low frequencies, the increase of total harmonic distortion may be greater than at high frequencies. However, the harmonics generated by the distortion process may actually support bass perception, as known from techniques that enhance bass perception through generation of harmonics. Therefore, harmonic distortion at low frequencies may at least be tolerable or even beneficial. The total harmonic distortion may be reduced by motional or sound pressure feedback methods or by forward distortion reduction techniques, if desired. Such methods are known in the art and will not be explained in further detail. In the right diagram of Figure 6, graph F illustrates the relative sound pressure level during the total harmonic distortion measurement when there is only a loudspeaker 120 mounted in the enclosure 110. Graph G illustrates the relative sound pressure level during the total harmonic distortion measurement when there is an additional membrane 130 mounted in the enclosure 110. As can be seen, the relative sound pressure level decreases when an additional membrane 130 is mounted in the enclosure 110.

[0027] Figure 7 illustrates different impedance curves over frequency. The top diagram of Figure 7 illustrates the impedance curve of the original loudspeaker 120 (no additional membrane 130 mounted in the enclosure). The middle curve illustrates the impedance curve when an additional membrane 130 is mounted in the enclosure 110. The bottom curve illustrates the impedance curve when weight is added to the membrane 130. The effect of the membrane 130 on the resonance frequency and resonance quality factor of the loudspeaker 120 within the enclosure 110 can be evaluated, for example, by means of the impedance curve measurement. As can be seen, the resonance frequency is not affected. The resonance quality in this example is slightly reduced by the membrane 130. Added mass on the membrane 130 further increases this effect, as can be seen by means of the bottom diagram. Added mass may also further reduce sound pressure. However, the additional mass that was added in the given example is not required for the function of the loudspeaker device 100.

[0028] The diagrams that are illustrated in Figures 5, 6 and 7 indicate that it is possible to add passive tactile feedback (without the use of actuators or similar) to wearable loudspeaker devices that are worn in close contact to a user's body without causing an excessive reduction of sound pressure level and without causing an excessive increase of total harmonic distortion. Sound pressure level reduction can generally only be partly compensated by an increased loudspeaker input power. In particular, by increasing the loudspeaker input power only sound pressure losses caused by mechanical losses induced by the additional membrane 130 may be at least partly compensated. Distortion may theoretically be reduced below the level of the loudspeaker 120 without an additional membrane within the same enclosure 110 by employing motional or sound pressure feedback methods as well as feed forward distortion reduction techniques. Whether such methods are required or viable greatly depends on the exact implementation of the device.

[0029] Tactile feedback may be provided to any part of the user's body. For example, the membrane 130 may be in contact with the neck, shoulders, chest, back or upper arms of the user. These, however, are only examples. The membrane 130 may provide tactile feedback to any other part of the user's body.

[0030] In another embodiment, the loudspeaker device 100 includes more than one enclosure. One example of such a loudspeaker device 100 is schematically illustrated in Figure 8. A second enclosure 111 is arranged such that the loudspeaker 120 is mounted between the first enclosure 110 and the second enclosure 111. When moving back and forth, a first surface of the loudspeaker diaphragm generates sound waves at the front of the loudspeaker 120 inside the second enclosure 110, and a second surface of the loudspeaker diaphragm generates sound waves at the back of the loudspeaker 120 inside the first enclosure 110. At the outside of the enclosures 110, 111, the loudspeaker 120 and the associated membrane 130 may generate sound waves at sound pressure levels that are not audible to the user. The loudspeaker 120 may, additionally or alternatively, generate sound waves at frequencies which are not audible to the user. For example, very low frequencies are not audible to human ears. The second enclosure 111 includes at least one second membrane 131 arranged between the inside and the outside of the second enclosure 111. The at least one second membrane 131 may be mounted in a front panel, sidewall or any other wall or baffle of the second enclosure 111. The at least one second membrane 130 includes a passive membrane. When the pressure in the second enclosure 111 changes due to the movement of the diaphragm of the loudspeaker 120, the second membrane 131 is stimulated depending on the pressure inside the second enclosure 111. This means that the second membrane 131 moves around a resting position by a certain distance y. The distance y may be variable depending on a current pressure inside the second enclosure 111. The distance y may further be dependent on the material, the thickness, the mass or the surface area of the second membrane 131 and on how the membrane 131 is fixed to the enclosure 110. The distance y may vary for different parts of the membrane. [0031] Each enclosure 110, 111 may be used to provide tactile feedback to different parts of the user's body. For example, the first enclosure 110 with the first membrane 130 may be configured to provide tactile feedback to the right shoulder of the user 200, whereas the second enclosure 111 with the second membrane 131 may be configured to provide tactile feedback to the left shoulder of the user 200. This is, however, only one example. Tactile feedback may be provided to any other part of the user's body. Such a device may include further enclosures and loudspeakers that are configured to generate sound that is audible for the user.

[0032] While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.