Headrest-mounted speaker for producing bass frequencies

Abstract

A headrest is provided that houses a dipole speaker for producing bass frequency sound in a forward direction and a rearward direction and 180 degree out of phase response from respective front and rear resonant surfaces. The headrest includes a waveguide forming member to block sound from propagating through the headrest between the front and rear surfaces. The headrest also includes an attachment forming member and the attachment forming member suspends a first frame of the dipole speaker and acts as a secondary suspension system. By including the waveguide forming member, sound from the front surface of the dipole speaker can be directed to the exterior of the headrest where the shortest path from the front surface to the rear surface extends around the exterior of the headrest. By directing the sound path to the exterior of the headrest, internal sound guiding compresses the expected path length. Furthermore, since the structure of the headrest is formed from a resilient material to provide comfort to the listener, the attachment forming member can be integrally formed from the resilient material, the resilient nature of which provides suspension for the first frame.

Description

[0001] This application claims priority from GB2008724.3 filed on 9th June 2020. TECHNICAL FIELD

[0002] The present invention relates to a loudspeaker for producing bass frequencies when installed in a headrest to provide a personal sound enclosure, and in particular, although not exclusively, to an audio system comprising a headrest and a dipole loudspeaker installed therein, wherein the dipole loudspeaker emits bass frequency sound in a forward direction and in a second direction 180 degrees out of phase response. BACKGROUND

[0003] Recently, various efforts have been made in order to provide an audio system for producing a personal sound enclosure. Here, the personal sound enclosure is an area in which a user can experience sound having a relatively high sound pressure level (SPL) considered to be acceptable for sound appreciation, while outside the personal sound enclosure, the SPL of the sound is considered to be much lower than the SPL within the volume defined by the personal sound enclosure.

[0004] For mid and high frequencies, an effective solution is to employ high directivity loudspeakers positioned close to the position where the listener is likely to position his head. However, in most cases, it is generally impractical to make a loudspeaker directional at bass frequencies, because in order to provide a high directivity loudspeaker for bass frequencies, the size of the radiating surface must be of the same order as the wavelength, and for low frequency content, the wavelength is typically long. For example, for a frequency of 100 Hz, a typical bass frequency content has a wavelength of 3.4m.

[0005] WO2019 / 121266 discloses a dipole loudspeaker for producing bass frequencies, which is particularly suitable for use in an audio system designed to produce a personal sound enclosure. Here, the dipole loudspeaker provides a personal loudspeaker which is designed by interfering sound produced by a first radiating surface of the dipole loudspeaker with sound produced by a second radiating surface of the dipole loudspeaker. It is conceivable that the first and second radiating surfaces will be the front and back surfaces of a diaphragm, wherein the two sounds are produced in anti-phase. It is disclosed that the interference has a beneficial effect in that sound propagating outside the personal sound enclosure is effectively cancelled where the two anti-phase sounds meet. The operation and construction of the dipole loudspeaker disclosed in WO2019 / 121266 is specifically incorporated herein by reference, and therefore a detailed explanation is omitted. However, in brief, the dipole loudspeaker comprises a diaphragm having a first radiating surface and a second radiating surface, which is suspended to a first frame via a primary suspension element. The first frame in turn is suspended to a second frame via a secondary suspension element. The second frame can then be rigidly fixed in a headrest. Suitable suspension elements for the primary and secondary suspension elements are known, such as a roll suspension, metal springs or rubber bands.

[0006] An audio system incorporating the dipole loudspeaker for producing bass frequencies (e.g. in the range of 20 Hz to 2000 Hz) disclosed in WO2019 / 121266 can be incorporated into a headrest to provide a personal sound enclosure which forms a volume in the vicinity of the headrest where a listener wants to rest his head. Such a headrest can be applied in various audio applications, such as cars, aviation, gaming, studio monitoring, home entertainment, etc. Furthermore, in a noisy environment, the headrest can be used to cancel noise at bass frequencies.

[0007] In developing such a headrest, it is an object to further improve the implementation and mounting of the dipole loudspeaker so as to produce a personal sound enclosure which has a higher SPL in the volume of the personal sound enclosure, and additionally or alternatively, a lower SPL outside the personal sound enclosure. It is a further object to limit the propagation of vibrations from the dipole loudspeaker through the headrest and the connected seat.

[0008] In view of the above considerations or other considerations, the present invention is conceived. SUMMARY

[0009] According to example embodiments, there is provided a headrest housing a dipole loudspeaker, wherein the headrest comprises a waveguide forming member to block sound propagating through the headrest between a front surface and a rear surface. It has been found here that if the dipole loudspeaker is suspended within the headrest in a manner that provides an open space through which sound can propagate, then the sound-impervious portions of the headrest (i.e. portions having acoustic resistance to prevent or substantially prevent sound propagating through) can act to direct sound and shorten the path length, which reduces the effective output of the loudspeaker. That is, without the waveguide forming member, the sound opening through the headrest between the front surface and the rear surface of the dipole diaphragm can provide a cavity in the headrest through which sound can be directed, resulting in a reduction in efficiency of the loudspeaker due to a partially enhanced acoustic short circuit. Advantageously, due to the inclusion of the waveguide forming member, sound from the front surface can be directed to the exterior of the headrest, with the shortest path from the front surface to the rear surface extending around the exterior of the headrest. By directing the sound path to the exterior of the headrest, internal sound direction compression of the intended path length is prevented.

[0010] Herein, the sound-impervious material can have a specific airflow resistance (Rs) higher than 30 Pa.s / m or more preferably higher than 60 Pa.s / m. Suitably, the sound-impervious material is a suitable foam. In use, the sound-transmissive or acoustically transparent material can be a material having a specific airflow resistance (Rs) lower than 20 Pa.s / m (more preferably lower than 10 Pa.s / m).

[0011] Further, according to example embodiments, there is provided a headrest housing a dipole loudspeaker, wherein the headrest comprises an attachment forming member and the attachment forming member suspends a first frame of the dipole loudspeaker and acts as a secondary suspension system. Here, the dipole loudspeaker comprises a diaphragm providing a first radiating surface (which can suitably be a front surface) and a second radiating surface (which can be a rear surface). The diaphragm is suspended to the first frame via a primary suspension system. Here, the first frame is suspended directly from the headrest, rather than the first frame being suspended to a second frame via a secondary suspension system and the second frame being rigidly attached to the headrest. In particular, the attachment forming member can be integral with the structure of the headrest. Advantageously, as the structure of the headrest is formed from a resilient material to provide comfort to a listener, the attachment forming member can be integrally formed from this resilient material, the resilient properties of which provide suspension for the first frame. Further, by removing the second frame and secondary suspension system from the dipole loudspeaker, the number of components of the dipole loudspeaker can be reduced. As the structure of the headrest is necessary to provide the functionality of the headrest (i.e. the functionality of providing a rest for the head), there is no or limited increase in complexity or cost in combining the functionality of the headrest structure with the functionality of the secondary suspension system.

[0012] In a particular suitable exemplary embodiment, a headrest is provided that houses a dipole loudspeaker, wherein the headrest comprises an attachment formation for suspending a first frame of the dipole loudspeaker, and the attachment formation also acts as a waveguide formation to block sound from propagating through the headrest between a front surface and a rear surface.

[0013] Exemplary embodiments provide an audio system comprising a headrest and a dipole loudspeaker. Although in some exemplary embodiments the headrest is formed as a separate headrest that is attachable to a backrest to form a seat or chair or the like, it is conceivable that the headrest can also be integral with the backrest. Furthermore, it is conceivable that the headrest can take any structural form that a listener wants or causes him to rest his head against. For example, the headrest is typically a dedicated structure that is provided at a location where a listener's head can be located. When the listener is in a position to carry out an activity, the user's head can rest against this structure or at least be located in its vicinity. Thus, the headrest can take the form of a conventional seat headrest, but also other suitable structures that a user wants to position his head in the vicinity of. For example, it is appropriate that in exemplary embodiments the headrest is configured for use with a seat. Here, the seat is configured to position a user (also referred to as a listener) sitting on the seat such that the user's ears are located in a listening position relative to the dipole loudspeaker. It will be appreciated that the headrest is thus optimally arranged relative to the seat as is known in the art. Here, the listening position is a position in which the ear (preferably each ear of the user is located in a respective listening position) is located at a distance of 40 cm or less (more preferably 30 cm or less, more preferably 25 cm or less, more preferably 20 cm or less or more preferably 15 cm or less) from the first radiating surface of the loudspeaker. It will be appreciated that the headrest can be shaped and configured as is known in the art, since the headrest is typically configured to position a user sitting on the seat such that the user's ears are located in a listening position at a small distance (e.g. 30 cm or less) from the first radiating surface of the loudspeaker. Here, the seat headrest typically has a front surface configured to face the head of a user sitting on the seat and a rear surface configured to face away from the head of a user sitting on 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 the main axis of the first radiating surface extending through the front surface of the headrest.

[0014] The dipole loudspeaker of the example embodiment is configured to produce bass frequencies. Here, the dipole loudspeaker comprises a driver unit configured to move a diaphragm at bass frequencies. Thus, the driver unit is suitably configured to move the diaphragm in a bass frequency range. For example, the bass frequency range can be 60Hz to 80Hz (more preferably the range can be 50Hz to 100Hz, or more preferably the range can be 40Hz to 100Hz), and can include frequencies in the range 40Hz to 160Hz. At these frequencies, the loudspeaker is able to produce a particularly useful personal sound enclosure.

[0015] Moving the diaphragm at frequencies below 40Hz can be beneficial for some applications, but not for others (e.g. in a car, background noise below 40Hz tends to be too loud). At frequencies above 160Hz, the “enclosure” effect can disappear. Thus, the driver unit can be configured to move the diaphragm at frequencies not exceeding 250Hz, 200Hz, or even 160Hz. This can help to ensure that the loudspeaker achieves a suitable SPL within the personal sound enclosure and also outside of the personal sound enclosure.

[0016] In view of the above considerations, the dipole loudspeaker is preferably configured as a bass bin. A bass bin can be understood as a loudspeaker that is specifically designed (rather than adapted) to produce bass frequencies.

[0017] In view of the considerations explained in more detail in WO 2019 / 121266, the first and / or second radiating surface of the diaphragm can each have a relatively large surface area. For example, in the example embodiment, the dipole loudspeaker has a diaphragm with a first and second radiating surface having an area of at least 100cm 2 , more preferably at least 150cm 2 , more preferably at least 200cm 2 , or more preferably at least 250cm 2 . In some cases, the first and / or second radiating surface can each have a surface area of at least 300cm 2 or at least 400cm 2 . To maximise the surface area of the first and second radiating surface under other design constraints (e.g. incorporating the loudspeaker into a car headrest), the diaphragm can have a shape that is non-circular (e.g. rectangular or square). Thus, in the example embodiment, it is conceivable that the diaphragm, and thus the first and second radiating surface, can be circular, rectangular, rectangular with rounded corners, or indeed have a more freeform shape.

[0018] The dipole loudspeaker of the example embodiment is configured to suspend the diaphragm from the frame by a first suspension system. As the dipole loudspeaker is configured to suspend directly from the headrest by a second suspension system, the dipole loudspeaker only comprises the first frame of the dipole loudspeaker disclosed in WO2019 / 121266. Thus, in the present text, the first frame is referred to as the “frame” for simplicity. Further, in the context of the present disclosure, the frame is intended to comprise any substantially rigid structure from which the diaphragm can be suspended. For example, the frame from which the diaphragm is suspended can comprise one or more mounting legs extending into one or more (respective) cavities in the diaphragm, wherein the diaphragm is suspended from the one or more mounting legs via one or more suspension elements of the first suspension system. The first frame can comprise a rigid body extending around a diaphragm axis along which the drive unit is configured to move the diaphragm. The first frame is preferably located radially outside the diaphragm with respect to the diaphragm axis. Suitably, the frame can comprise one or more rigid support elements (e.g. arms) configured to hold the magnet unit of the drive unit in front of the first and / or second radiating surface of the diaphragm (preferably in front of the second radiating surface of the diaphragm). Alternatively, in some examples, the magnet unit can be suspended from the diaphragm via a resilient member. The one or more magnet unit resilient members can comprise for example one or more (preferably two or more) speaker spider rings, wherein a speaker spider ring can be understood as a fabric ring with a circumferentially extending wave (which can facilitate motion along a longitudinal axis while preventing motion perpendicular to that axis), as known in the art. It can be conceived that the skilled person can consider other forms of resilient members, for example springs such as metal springs.

[0019] The first suspension system and the second suspension system can be supplemented by a third suspension system or another suspension system. Here, the third suspension system or the other suspension system suspends one part of the assembly from another part. For example, the loudspeaker can comprise an intermediate frame between the diaphragm and the loudspeaker frame (e.g. outer frame), and the third suspension system can suspend the intermediate frame from the outer frame, while the first suspension system suspends the diaphragm from the intermediate frame.

[0020] The diaphragm can take various forms known in the art. For example, in one example embodiment, the diaphragm can be a single piece (monolithic) of material. The material forming the diaphragm is suitably light and thin, for example the material suitably has a mass of 0.1 g / cm 3or lower. In example embodiments, the material is extruded polystyrene, extruded polypropylene, or similar material. In some examples, the diaphragm is covered by a skin, for example to protect the diaphragm. Suitably, the skin is formed from paper, carbon fibre, or a plastic foil, or the like. In some example embodiments, the diaphragm comprises a number of pieces of material attached together. For example, the diaphragm comprises a number of pieces of material attached to each other by glue. Here, the diaphragm can comprise first and second cones as first and second pieces attached together, wherein the first and second cones are suitably bonded back to back to attach each cone to the other. Here, the front surface of one of the cones forms the first radiating surface (e.g. front surface), while the back surface of the other cone provides the second radiating surface (e.g. back surface). In one example embodiment, the first and second cones are formed from paper. The diaphragm can also comprise one or more cut-outs on one of the radiating surfaces (preferably the second radiating surface), wherein each cut-out is configured to have a respective rigid support element extending through the cut-out when the loudspeaker is in use. This can allow the loudspeaker to have a low profile in the thickness direction of the diaphragm.

[0021] The dipole loudspeaker of example embodiments is configured to suspend the diaphragm from the frame by a first suspension system. Here, suitably, the first suspension system comprises a plurality of first suspension elements. That is, the first suspension system comprises one or more suspension elements via which the diaphragm is suspended from the frame. For example, the first suspension system via which the diaphragm is suspended from the first frame can comprise one or more suspension elements (e.g. one or more roll suspensions) attached between the first radiating surface and the frame and one or more suspension elements (e.g. one or more roll suspensions) attached between the second radiating surface and the frame. Preferably, the one or more suspension elements (e.g. one or more roll suspensions) attached between the first radiating surface and the frame correspond to (e.g. match, such as in position, number, and length) the one or more suspension elements attached between the second radiating surface and the frame. This matching of suspension elements is particularly beneficial if the diaphragm is non-circular, as it can help to remove any asymmetry in the performance of the suspension elements attached to one radiating surface of the diaphragm. The one or more suspension elements can be tuned to have a resonant frequency lower than the frequency spectrum at which the loudspeaker is configured to operate, for example to maximise the efficiency of the loudspeaker in the frequency spectrum of interest.

[0022] In an exemplary embodiment, the dipole loudspeaker is configured to comprise a drive unit. Here, the drive unit suitably comprises an electromagnetic drive unit comprising a magnet unit configured to generate a magnetic field and a voice coil attached to the diaphragm. In use, the voice coil can be energized (current is made to flow through the voice coil) to generate a magnetic field that interacts with the magnetic field generated by the magnet unit and causes the voice coil (and thus the diaphragm) to move relative to the magnet unit. The magnet unit can comprise a permanent magnet. The magnet unit can be configured to provide an air gap and can be configured to provide the magnetic field in the air gap. The voice coil can be configured to be located in the air gap when the diaphragm is at rest. Such drive units are well known. The magnet unit can be located in front of the second radiating surface of the diaphragm.

[0023] The dipole loudspeaker of an exemplary embodiment can comprise a safety element located between the magnet unit and the second radiating surface of the diaphragm. The safety element can be configured to prevent the magnet unit from passing through the diaphragm, for example in a crash event or another event involving a sudden deceleration of the loudspeaker (e.g. the loudspeaker has been moved in the direction of the main radiation axis of the first radiating surface). The safety element is preferably rigid. The safety element can be a voice coil coupler. Such a safety element can be especially beneficial if the loudspeaker is installed in a headrest of a seat of a vehicle, as it can help to provide protection for a person sitting in such a seat in the event of a crash of the vehicle. Here, the voice coil can be attached to the diaphragm, e.g. to the second radiating surface of the diaphragm. The voice coil can be attached to the diaphragm (e.g. the second radiating surface of the diaphragm) via the voice coil coupler. As mentioned above, the voice coil coupler can also be the safety element.

[0024] In another exemplary embodiment, the safety element can comprise or further comprise a rigid restraint in a cavity in which the dipole loudspeaker is disposed. For example, the rigid restraint can be part of a base frame of the headrest, in particular an inner flange formed in the cavity in which the loudspeaker is disposed. Here, a rigid portion of the dipole loudspeaker is configured to be sized to overlap with the rigid restraint in a forward direction. For example, the rigid portion of the dipole loudspeaker is suitably a frame. In one embodiment, the rigid portion of the dipole loudspeaker is a protruding flange of the loudspeaker frame. Thus, in the event of a crash of the vehicle for example, the abutment between the rigid portion of the frame and the rigid restraint in the cavity can provide a safety feature that limits or prevents the dipole loudspeaker from bouncing forward through the stiffest portion. In embodiments in which a rigid restraint is included in the cavity, the dipole loudspeaker can be directly connected to the rigid restraint, e.g. via a flexible member (e.g. a foam member or the like), to provide a second suspension system.

[0025] The loudspeaker can be configured to perform noise cancellation, for example, at low frequencies. For example, the drive unit can be configured to drive the diaphragm (e.g., at low frequencies) such that the first radiating surface produces sound configured to cancel ambient sound detected by the one or more microphones. This can be useful in a noisy environment (e.g., in a car or airplane), for example, where the loudspeaker is part of a seat assembly including a vehicle seat. Noise cancellation techniques are well known.

[0026] Accordingly, in one aspect, a dipole loudspeaker is provided. The dipole loudspeaker includes a diaphragm and a frame. The diaphragm is suspended from the frame by a primary suspension system. The diaphragm has a first radiating surface and a second radiating surface on opposite faces of the diaphragm. The dipole loudspeaker also includes a drive unit configured to move the diaphragm at low frequencies. Because the first radiating surface and the second radiating surface are driven to move at low frequencies, the first radiating surface and the second radiating surface produce sound at low frequencies. Moreover, because the first radiating surface and the second radiating surface are opposite surfaces of the same diaphragm, the sound produced by the first radiating surface is out of phase with the sound produced by the second radiating surface. Furthermore, in exemplary embodiments, the dipole loudspeaker is not configured to have a second frame suspended from a secondary suspension system. Rather, the dipole loudspeaker of this aspect is specifically configured to attach to an attachment formation of a headrest. Here, the dipole loudspeaker includes a corresponding attachment formation. In one exemplary embodiment, the corresponding attachment formation is directly connected to the frame. That is, the corresponding attachment formation is not connected to the frame via a secondary suspension system. In an alternative exemplary embodiment, the corresponding attachment formation is attached to the frame via a secondary suspension system

[0027] In one exemplary embodiment, the dipole loudspeaker with the corresponding attachment formations attached to the frame is configured such that the corresponding attachment formations on the dipole loudspeaker snap into the attachment formations on the headrest. Here, the dipole loudspeaker can be installed in the headrest without additional fixing means. Furthermore, advantageously, the dipole loudspeaker is securely fixed in the headrest due to the snap-in interference of the attachment formations on the headrest with the corresponding attachment formations on the frame. The snap-in interference of the two attachment formations can be achieved in various ways. For example, in one embodiment, one of the attachment formations comprises a semi-enclosed cavity for receiving a portion of the corresponding attachment formation. Here, the semi-enclosed cavity receives and clamps the corresponding portion. For example, one of the portions is elastic such that it deforms when the dipole loudspeaker is assembled for installation in the headrest. The deformation opens the cavity and / or compresses the corresponding portion such that the corresponding portion can be pushed or moved into the cavity by relative movement in a first direction. After the one or more elastic portions return to their original shape, the semi-enclosed cavity clamps the corresponding portion. Here, clamping means that the semi-enclosed cavity has an opening in the first direction, wherein the opening is smaller than the size of the corresponding portion. Thus, when the corresponding portion is pushed into the semi-enclosed cavity and is located therein, the corresponding portion is clamped, the size of the opening is smaller than the corresponding portion, and thus prevents relative movement of the two portions to separate the portions in a direction opposite to the first direction. Thus, the dipole loudspeaker comprises corresponding attachment formations, wherein the corresponding attachment formations comprise a semi-enclosed cavity or a portion to be received by a semi-enclosed cavity.

[0028] In one embodiment, the dipole loudspeaker comprises corresponding attachment formations for engaging with attachment formations of the headrest. Suitably, the corresponding attachment formations comprise a semi-enclosed cavity. The semi-enclosed cavity has an opening. The opening is configured to receive a portion of the attachment formation on the headrest when the headrest is moved in an assembly direction. Although the semi-enclosed cavity can be elastically deformable to open when receiving the corresponding portion and to close around the portion when the force causing the deformation is removed, in one embodiment, the semi-enclosed cavity is relatively rigid or at least relatively rigid compared to the corresponding portion such that the corresponding portion is configured to deform when forced through the opening. For example, the corresponding portion of the attachment formation on the headrest can be formed of foam. Here, the foam is compressed during being pushed into the semi-enclosed cavity when the loudspeaker is moved relative to the headrest in the assembly direction. Advantageously, a snap-in connection is thus formed to connect the dipole loudspeaker to the headrest.

[0029] In an alternative embodiment, the dipole loudspeaker comprises a corresponding attachment formation for engaging with the attachment formation of the headrest. Suitably, the corresponding attachment formation comprises a protruding portion for being received by a semi-enclosed cavity of the attachment formation on the headrest. Although the semi-enclosed cavity can be provided to be elastically deformable to open and close the opening of the semi-enclosed cavity, additionally or alternatively, according to an exemplary embodiment, the protruding portion of the frame of the dipole loudspeaker is provided to be deformed during being pushed into the semi-enclosed cavity. For example, the protruding portion is deformed during being pushed into the semi-enclosed cavity in the assembly direction. Here, the protruding portion suitably comprises a bent plate, wherein the bend provides a suitable hinge for deforming the protruding portion. Suitably, the protruding portion of the attachment formation of the headrest can be formed by foam. Advantageously, a snap-fit connection is thus formed to connect the dipole loudspeaker to the headrest.

[0030] As an alternative to the snap-fit connection between the attachment formation on the headrest and the corresponding attachment formation extending from the frame of the dipole loudspeaker, a push-fit can be employed. In embodiments comprising a push-fit, one of the portions is provided to surround the other portion around at least two opposite sides. The portion surrounding the other portion does not clamp the other portion as in the case of a snap-fit. Instead, the portions are held firmly together by the length of the surrounding portion. For example, one of the portions comprises an open cavity, while the other portion is configured to fit within the open cavity. The portion fitting within the cavity can be configured to have sufficient length to remain in the cavity over the range of relative motion of the portions expected in use. In an exemplary embodiment, the portion remaining in the cavity can be compressed into the open cavity and held in the compressed arrangement. Here, the portion remaining in the cavity is larger or slightly larger in size than the cavity. However, it is conceivable that the push-fit can also be configured with the portions being the same size or the portion being held being slightly smaller in size than the cavity. By the push-fit, the dipole loudspeaker can be slid onto the attachment formation on the headrest. Here, the direction of the sliding can be along an axis of the attachment formation. For example, along an axis parallel to the plane of the frame. An alternative to the sliding push-fit connection is that one of the portions can be substantially elastically deformable, such that the other portion can be pushed into the cavity. For example, one of the portions and preferably the attachment formation on the headrest can be formed by foam. Here, the foam is compressed to deform to allow the corresponding attachment formation to be pushed into the cavity formed in the foam attachment formation. Once positioned, the attachment formation can be reshaped around the protruding portion extending from the frame. Here, the protruding portion can be substantially rigid. Alternatively, at least the attachment formation forming the cavity is substantially rigid. Advantageously, here, the dipole loudspeaker can be mounted in the headrest without additional securing means.

[0031] In one embodiment, the dipole speaker includes a corresponding attachment formation for engaging with the attachment formation of the headrest. Suitably, the corresponding attachment formation includes an open cavity. The open cavity has an opening. Here, the opening is sized greater than or equal to the size of the cavity. The opening is configured to receive a portion of the attachment formation on the headrest when the headrest is assembled to the dipole speaker. In one embodiment, the open cavity is relatively rigid or at least relatively rigid compared to the corresponding portion of the attachment formation on the headrest. For example, the corresponding portion of the attachment formation on the headrest can be formed of foam. The attachment formation attached to the frame of the dipole speaker and forming the open cavity can have a similar rigidity as the frame. Advantageously, a push-fit connection is thus formed to connect the dipole speaker to the headrest.

[0032] In an alternative embodiment, the dipole speaker includes a corresponding attachment formation for engaging with the attachment formation of the headrest. Suitably, the corresponding attachment formation includes a protruding portion for being received by an open cavity of the attachment formation on the headrest. Although the open cavity can be configured to elastically deform to receive the protruding portion, additionally or alternatively, according to one exemplary embodiment, the protruding portion of the frame of the dipole speaker suitably includes a flexing tab. Advantageously, a snap-fit connection is thus formed to connect the dipole speaker to the headrest.

[0033] In exemplary embodiments in which one of the attachment formation on the headrest or the corresponding attachment formation on the dipole speaker includes an open cavity for push-fitting or a semi-enclosed cavity for snap-fitting, the protruding portion can suitably extend around a major perimeter of the frame. For example, the protruding portion can form a continuous protruding portion around the outer periphery of the frame. Here, the corresponding cavity can also extend around the major perimeter of the frame, that is, the cavity can also be substantially continuous. Alternatively, the cavity can be discontinuous, forming one or more cavity portions around the periphery.

[0034] Alternatively, in exemplary embodiments in which one of the attachment formation on the headrest or the corresponding attachment formation on the dipole speaker includes an open cavity for push-fitting or a semi-enclosed cavity for snap-fitting, the protruding portion can suitably extend discontinuously around the perimeter of the frame. That is, the protruding portion forms one or more protruding portions, each protruding portion extending a distance around the perimeter of the frame. Here, the corresponding cavity can extend around the major perimeter of the frame, that is, the cavity can be substantially continuous. Alternatively, the cavity can be discontinuous, forming one or more cavity portions around the periphery, where the cavity portions correspond to the portions of the protruding portion.

[0035] In some example embodiments, the attachment formations of the headrest are secured to corresponding attachment formations on the frame of the dipole loudspeaker. For example, the attachment formations can be secured together with an adhesive or the like. Alternatively, a mechanical securing can be employed. For example, the mechanical securing can be a nut and bolt or the like. In these example embodiments, the dipole loudspeaker comprises corresponding attachment formations extending from the frame, and the corresponding attachment formations are protrusion sites configured to cooperate with the mechanical securing. For example, the protrusion sites can comprise through-holes through which the mechanical securing passes. Suitably, the protrusion sites are substantially rigid. That is, the rigidity of the protrusion sites is similar to the rigidity of the frame. The protrusion sites can be continuous around the periphery of the frame, or can be discontinuous to form a plurality of protrusion portions. In any case, the mechanical securing can be applied at discrete points around the periphery. In example embodiments which utilise a mechanical securing, the attachment formations on the headrest are also suitably relatively rigid, for example having a rigidity similar to that of the protrusion sites of the dipole loudspeaker and / or the rigidity of the frame.

[0036] Accordingly, in a second aspect there is provided an audio system comprising a dipole loudspeaker and a headrest. The dipole loudspeaker is mounted within the headrest. The headrest comprises a main body assembly. The main body assembly is shaped to comprise a through-hole in which the dipole loudspeaker is mounted. For example, the through-hole extends from a front face of the main body assembly to a rear surface of the main body assembly. When the dipole loudspeaker is mounted in the through-hole, a first opening is formed between a front face of the dipole loudspeaker and a front portion of the headrest. The first opening can be formed by one or more first opening portions. Suitably, the first opening is configured to allow sound generated from a first radiating surface (e.g. a front surface) of the dipole loudspeaker to propagate out of a first side (e.g. a front portion) of the headrest. Furthermore, when the dipole loudspeaker is mounted in the through-hole, a second opening is formed between a back face of the dipole loudspeaker and a back portion of the headrest. The second opening can be formed by one or more second opening portions. Suitably, the second opening is configured to allow sound generated from a second radiating surface (e.g. a rear surface) of the dipole loudspeaker to propagate out of the first side (e.g. the front portion) of the headrest. Here, the first and second sides of the headrest are opposite sides, for example a front side and a rear side of the headrest.

[0037] In exemplary embodiments, the first opening and the second opening are acoustic openings. That is, the through hole through the headrest body assembly in which the dipole loudspeaker is mounted can be covered by, for example, a sound-transmissive material. For example, the headrest body assembly can comprise a foam structure forming the hole, and the body assembly can further comprise a cover. The cover encloses the foam structure and provides an aesthetic function. The cover is sound-transmissive, meaning that it does not or substantially not inhibit sound propagation through the material. Furthermore, the body assembly can comprise additional foam parts cooperating with the foam structure to provide the shape of the headrest. For example, instead of closing the openings, substantially sound-transmissive open-cell foam parts can be employed to provide the headrest structure as needed. Since the sound-transmissive foam provides less compression resistance compared to the sound- resistant foam used to form the foam structure, optionally, other sound-resistant foam blocks can be employed where needed to provide support for the listener’s head.

[0038] According to exemplary embodiments, the second aspect comprises a waveguide formation configured to guide sound produced by the first radiating surface out of the first opening and to guide sound produced by the second radiating surface out of the second opening. The waveguide formation is formed on a surface of the headrest body assembly, and suitably on an inner surface of the through hole. The waveguide formation is formed of a sound-resistant material. For example, the waveguide formation can be formed of foam. Suitably, a plurality of waveguide protrusions form the waveguide formation. Here, one or more of the waveguide protrusions act to guide sound out of the first opening. The waveguide protrusions act to close the main gap between the headrest body assembly and the frame of the dipole loudspeaker. Thus, sound from the first radiating surface is isolated from the second opening, and the shortest sound path between the first radiating surface and the second radiating surface is directed out of the headrest. Furthermore, sound from the second radiating surface is isolated from the first opening, and the shortest sound path between the second radiating surface and the first radiating surface is directed out of the headrest. In preferred embodiments, the waveguide formation closes any gap of the frame, such that the waveguide formation and the frame in combination form a baffle that inhibits sound propagation through the through hole of the headrest between the first radiating surface and the second radiating surface. Preferably, the waveguide formation is integrally formed with a component of the body assembly. For example, the body assembly comprises a foam structure that provides the through hole, and the waveguide formation is integral with the foam structure.

[0039] According to exemplary embodiments, the second aspect comprises an attachment formation on the headrest for attaching to the dipole loudspeaker. The attachment formation suspends the frame of the dipole loudspeaker from the body assembly of the headrest. For example, the attachment formation suspends the frame from the inside of the hole through the headrest body assembly. Here, the attachment formation forms a secondary suspension system. Suitably, the secondary suspension system is one or more secondary suspension elements.

[0040] One or more secondary suspension elements can be tuned to have a resonant frequency lower than the frequency spectrum for which the loudspeaker is configured to work on, for example in order to limit the forces on the support structure. One or more secondary suspension elements can be tuned to have a resonant frequency lower than the resonant frequency that one or more primary suspension elements have after tuning. In exemplary embodiments, one or more secondary suspension elements are tuned to have a predetermined resonant frequency. While the predetermined resonant frequency can be 20 Hz or lower (more preferably 10 Hz or lower or more preferably 5 Hz or lower) for a static backrest that is essentially vertically arranged with respect to the loudspeaker, the preferred tuning frequency of the second suspension for a reclining backrest is between 10 Hz and 20 Hz. This is because the static deflection of the second suspension at frequencies lower than 10 Hz can become unreasonably large when the seat is reclined. Thus, the predetermined resonant frequency is preferably lower than 20 Hz, and for some embodiments, preferably higher than 10 Hz.

[0041] In some exemplary embodiments, the attachment formation comprises one or more attachment protrusions on which the frame is attached. Here, the plurality of attachment protrusions can be resilient, such that the resilient nature of the attachment protrusions provides the secondary suspension element. For example, the one or more attachment protrusions can be formed from foam. The one or more attachment protrusions can be integral with a component of the body assembly. As an example, the body assembly comprises a foam structure that provides a through hole in which the dipole loudspeaker is mounted, and the attachment formation is integral with the foam structure.

[0042] Suitably, the attachment formation and each attachment protrusion provided to form the attachment formation can be formed from foam (e.g. acoustically resistive foam). As described above, the attachment formation can be a protrusion to cooperate with a corresponding attachment formation of the dipole loudspeaker. For example, the attachment formation can be one or more protrusions that cooperate with an open cavity (or a closed cavity), or be one protrusion and further secured to the frame of the dipole loudspeaker. Here, the protrusion of the headrest suitably comprises a distal end that is spaced from the headrest by a resilient portion. The resilient portion provides at least some resilience for the secondary suspension system. Here, the resilient portion can be controlled to provide a tuning stiffness profile that is optimised for the desired secondary suspension system characteristics. For example, the stiffness and progression of the resilient portion can be selected by optimising the material properties, the length and cross-sectional area of the resilient portion, and the number and size of any cavities inside and around the portion of the headrest from which the protrusion extends. Furthermore, reinforcing elements can be embedded within the foam. Thus, in some embodiments, the protrusion forming the attachment formation can comprise an embedded component. The embedded component can be a corrugated suspension element, a monolithic sheet or segmented or a reinforcing plastics or metal component. Furthermore, a plurality of protrusions can also be used to control and optimise the stiffness profile for performance.

[0043] In particularly suitable example embodiments, the attachment formations and waveguide formations are common. That is, the headrest body assembly includes protrusions that extend from the interior side of the through hole. These protrusions include attachment formations at the end portions for coupling with corresponding attachment formations on the dipole speaker. These protrusions are resilient to provide a secondary suspension system, and they act as waveguide formations by coupling closely around the frame to acoustically isolate each side of the through hole from the other by directing the respective sound through the respective openings.

[0044] In another aspect, there is provided a method of assembling an audio system of the aforementioned aspect, the method comprising attaching a dipole speaker of the aforementioned aspect to a headrest, wherein the method comprises connecting the frame of the dipole speaker to the attachment formations of the headrest. In example embodiments, the method can comprise urging the corresponding attachment formations together with the attachment formations of the headrest. Here, one of the attachment formations is deformed to allow the two parts to be urged together and held in place.

[0045] According to some embodiments, the method suitably comprises optimising the stiffness of the attachment formations so as to provide a secondary suspension system for the frame. Here, the method comprises inserting a component into the foam, and / or forming a cavity in the attachment formations, and / or forming a cavity in the body assembly of the headrest in the region from which the attachment formations extend.

[0046] The dipole speaker according to the foregoing, and the audio system comprising the dipole speaker and a headrest that houses the dipole speaker, can be used in any application where it can be desirable to provide a personal sound enclosure. Particularly suitable environments can be headrests for vehicle seats, such as car seats or aircraft seats. Here, the seat can be reclining (reclinable) such that the backrest of the seat can be positioned at different reclinations relative to a generally horizontal seat portion. Because the headrest is typically attached or indeed integrated to the backrest, the dipole speaker can need to be optimised to work over a range of reclinations. As mentioned above, the stiffness of the attachment formations can be controlled by a number of factors to ensure optimal performance.

[0047] In another aspect, there is provided a seat assembly comprising an audio system of the aforementioned aspect. The seat can be a vehicle seat for use in a vehicle, such as a car (“car seat”) or an aircraft (“aircraft seat”). The seat can also be a seat for use outside of a vehicle. For example, the seat can be a seat for a computer game player or a seat for studio monitoring or home entertainment. In another aspect, there is provided a vehicle (e.g. a car or an aircraft) having a plurality of seat assemblies according to the aforementioned aspect.

[0048] The application includes combinations of the described aspects and preferred features unless such combinations are clearly impermissible or should be explicitly avoided. Attached Figure Description

[0049] The embodiments and experiments illustrating the principles of the present invention will now be discussed in conjunction with the accompanying drawings, wherein:

[0050] Figure 1 A top view of a simplified audio system based on a first model is shown, which has dipole speakers suspended in a hypothetical acoustically transparent headrest.

[0051] Figure 2 The second model is shown. Figure 1 A top view of the audio system, depicting a headrest with more realistic acoustic properties;

[0052] Figure 3 A top view of the audio system according to the first embodiment is shown;

[0053] Figure 4 The relationship between the SPL and the distance from the resonant surface for the first model and the exemplary embodiment is plotted.

[0054] Figure 5 A top view of the audio system according to the second embodiment is shown;

[0055] Figure 6 A front view of the audio system of the second embodiment is shown;

[0056] Figure 7 A front view and a top view of the audio system of the second embodiment are shown, including a depiction of the listener's position;

[0057] Figure 8a and Figure 8b The forces acting on the headrest and diaphragm within the frequency range are plotted at upright and tilted seat angles.

[0058] Figure 9a The progressive design choices for the two-stage suspension system are described, and Figure 9b The graphs depicting the static deflection of the secondary suspension system at different headrest tilt angles are shown.

[0059] Figure 10 Options for controlling the stiffness and progressiveness of the attachment form are described;

[0060] Figure 11 A top view of an audio system according to a third embodiment is shown;

[0061] Figure 12 A top view of the audio system according to the fourth embodiment is shown;

[0062] Figure 13 Figures a through l show top views depicting an alternative design for the audio system;

[0063] Figure 14 a top view of an alternative design of an audio system is shown;

[0064] Figure 15 a front view of variants a to d of an audio system is shown; and

[0065] Figure 16 a schematic diagram showing the assembly process of an audio system is shown. DETAILED DESCRIPTION

[0066] Various aspects and embodiments of the present application will now be discussed with reference to the accompanying drawings. Other aspects and embodiments will be apparent to those of ordinary skill in the art. All documents mentioned herein are hereby incorporated by reference.

[0067] Referring to Figure 1 , an audio system 1 is shown, comprising a dipole loudspeaker 100 mounted in a headrest 200. The dipole loudspeaker 100 comprises a diaphragm 110 having a first radiating surface 112 and a second radiating surface 114. The first surface 112 is shown as a front surface, facing towards a passenger seated in a seat incorporating the headrest; while the second surface 114 is shown as an opposing rear surface, facing away from a passenger seated in a seat incorporating the headrest. Suitably, the diaphragm is made of extruded polystyrene foam or similar material, and can optionally be reinforced with a skin. The diaphragm 110 is suspended from a frame 120 by a primary suspension system 130. The dipole loudspeaker 100 further comprises a drive unit 140, configured to drive the diaphragm 110 to produce bass frequencies, as is known in the art. Thus, in operation, the dipole loudspeaker 100 works to drive the first radiating surface 112 to emit sound at bass frequencies and to drive the second surface 114 to emit a 180 degree out of phase response. This out of phase response is anti-phase sound, and will interfere with the sound from the first surface to act to cancel that sound. The shortest path length of sound from the first surface 112 to the second surface 114 (and vice versa) is depicted by arrow P in Figure 1 . The general structure and operation of a dipole loudspeaker is described above and in more detail in WO2019 / 121266, and the description of the dipole loudspeaker therein is incorporated herein by reference.

[0068] Figure 1 is a simplified top view prepared for modelling purposes, and shows the operation of a low frequency dipole loudspeaker 100 suspended directly from a headrest 200. It is determined here that by mounting the frame 120 directly to the headrest via a secondary suspension system (shown in Figure 1 as a resilient spring element 150), the second frame required for the dipole loudspeaker of WO2019 / 121266 can be omitted from the audio system 1.Figure 1 In this model, the headrest is assumed to be acoustically transparent. Here, the shortest path length P is primarily defined by the dimensions of the dipole loudspeaker 100. The path length P is schematically shown by a circular arrow, but it should be recognized that a more realistic representation of the actual path will follow the contours of the vibrating surface and surrounding obstacles.

[0069] Figure 2 The same dipole speaker mounted in a headrest is depicted, shown to include a more realistic foam representation. For example, headrest 200 is formed of foam structure 210, which forms the main structure of the headrest to provide support to the listener, and dipole speaker 100 is mounted in cavity 212 of this foam structure. The foam structure is formed of foam selected to provide support to the listener and may have a density of approximately 20 kg / m³. 3 and 150kg / m 3 (More typically at 50kg / m 3 and 100kg / m 3 The density is between (between). For example, the foam structure can be formed from open-cell PU foam with high flow resistance and therefore high acoustic resistance. The foam structure can be ground to produce open surfaces, or it can be molded to produce closed-cell surfaces and very high or infinite flow resistance. A front opening 214 leading to the cavity 212 and a rear opening 216 leading to the cavity are formed through the foam structure. These openings are acoustic openings and are shown as being filled with acoustically permeable foam. For example, a headrest 200 is formed from a body assembly 202, which includes a foam structure 210 and multiple blocks of acoustically permeable foam 230. Here, the acoustically permeable foam is shown as blocks 232, 234 constructed to substantially close the openings 214, 216. Although the openings 212, 214 may be structurally closed, they remain acoustically open, that is, open for sound propagation through them. The acoustically permeable foam 230 may be an open-cell foam chosen for sound permeability, wherein the material is chosen to have very low flow resistance. For example, the acoustically permeable foam 230 may be a material with an airflow resistance (Rs) of less than 20 Pa·s / m (more preferably less than 10 Pa·s / m).

[0070] It can be observed that, with Figure 1 Compared to the acoustically modeled headrest shown, Figure 2 The path length P formed by the model is shortened. The presence of the foam structure is thought to serve to guide the sound and shorten the path length. That is, by closing the path length and allowing it to be guided within the cavity, the path length P is shortened, which reduces the effective output of audio system 1 through partially enhanced acoustic short-circuiting.

[0071] According to an exemplary embodiment, Figure 3 Describing the modelingFigure 1 and Figure 2 The same dipole loudspeaker 100 is installed in an exemplary headrest 200. Here, the headrest 100 has been adapted to mount the frame 120 directly to the headrest 200 via protruding elements 220. The protruding elements 220 extend from the inner walls of the cavity 212 of the headrest. As explained herein, the protruding elements 220 can take a variety of forms, but are shown in Figure 3 as first and second protrusions 221, 222 extending around the periphery of the frame. Further, as explained further herein, the frame can be connected to the protruding elements in a variety of ways, but are shown in Figure 3 as being secured with glue or the like.

[0072] It has been found that by providing the protruding elements 220 to extend between the acoustically resistive headrest foam structure and the frame 220 of the dipole loudspeaker to substantially close off the first or front side of the cavity 212 from the second or rear side of the cavity 212, the front radiating surface of the dipole loudspeaker can be acoustically isolated from the rear radiating surface. Suitably, the protruding elements can be integrally formed from the structural foam, thus they are acoustically resistive, and also provide a convenient manufacturing process for the protruding elements 220 without the need for additional processes or special additional costs. Here, the protruding elements 220 act as waveguide formers to direct sound. Thus, the protruding elements 220 act as waveguide formers to direct sound propagating from the first or front resonating surface out of the first or front opening 214. The protruding elements 220 also act as waveguide formers to direct sound propagating from the second or rear resonating surface out of the second or rear opening 216. In acting as waveguide formers, the protruding elements 220 direct the path length outwardly to the headrest, as depicted by the arrows P. Advantageously, by directing the path length outwardly to the headrest, acoustic shorting within the headrest is prevented, and a greater acoustic path length is achieved compared to the arrangements shown in Figure 1 and Figure 2 both. As mentioned above, the headrest foam and the protruding elements (e.g. attachment formers and waveguide formers) are acoustically resistive. Suitably, the material is a suitable foam, in particular a foam or other material with a Specific Airflow Resistance (Rs) higher than 30 Pa.s / m or more preferably higher than 60 Pa.s / m.

[0073] Here, Figure 4 the Sound Pressure Level (SPL) at a distance from the first resonating surface of the diaphragm is plotted at a frequency of 60 Hz. The diaphragm produces a 5 mm peak excursion. The solid line Sd50P5 depicts the expected result for the arrangement of the audio system shown in Figure 1 where the headrest is modelled as being acoustically transparent. The dashed line Sp50P10 depicts the expected result for the arrangement shown in Figure 3 where the headrest is modelled as being acoustically transparent, thisFigure 3 The arrangement shown employs an exemplary headrest including a protruding element 220, which acts as a waveguide forming element to guide the path length P outwards into the headrest, and in the modeled embodiment, with Figure 1 Compared to the previous model, the path length P was increased from 5cm to 10cm. No specific... Figure 2 The relationship between the SPL and the distance from the diaphragm in the embodiment is modeled, but because the path length is longer than... Figure 1 The path length needs to be short, so if in Figure 4 The curve shown is plotted on Figure 2 Then the curve will be in Figure 1 Below the solid line in the model. It should be recognized that... Figure 4 The graph illustrates how increasing the path length P improves the SPL (Sound Proportion) of an exemplary headrest incorporating a waveguide forming element at a given distance to guide sound from the same dipole speaker 100 and extends the path length to the outside of the headrest. Suitablely, in the exemplary embodiment where the waveguide structure extends the path length to the outside of the headrest 200, the formed path length is preferably set between 5 cm and 20 cm (more preferably between 7.5 cm and 15 cm).

[0074] See you again Figure 3 The protruding element 220 also provides functionality for a secondary suspension system. Here, the protruding element provides an attachment forming element for attaching the dipole speaker to the headrest (specifically, attaching the structural foam 210 directly to the frame 120). That is, the protruding element has elasticity and stiffness characteristics optimized for a secondary suspension system. Advantageously, the secondary suspension system can be easily formed by forming the secondary suspension system from the protruding element 220, which is integrally formed with the structural foam 210. Further explanation of the formation of the secondary suspension system from the protruding element 220 will be described below.

[0075] exist Figure 3 An exemplary headrest is shown, in which the protrusion element 220 combines the functions of a waveguide forming element and an attachment forming element. However, in some embodiments, these functions are separate, and the protrusion element 220 provides only one of the functions, while the other function is provided by a separate element.

[0076] Figure 5 A second exemplary embodiment of the audio system 1 is shown. The dipole loudspeaker 100 is shown having a different configuration from the dipole loudspeaker 100 of the aforementioned embodiment. However, the main components and functions remain the diaphragm 110 suspended from the frame 120 by a primary suspension system 130, and include a drive unit 140 for driving the diaphragm to vibrate at a low-frequency range. Figure 5In this configuration, the dipole loudspeaker 100 is adapted to include a corresponding attachment forming 160. The attachment forming 160 connects to the attachment forming of the headrest to secure the frame 120 to the headrest 200. The corresponding attachment forming is shown as an open cavity defined by parallel fins 161, 162. The fins 161, 162 house the attachment forming of the headrest. As shown, it is suitable that the attachment forming is a spherical head 222 of the protruding element 220. The size of the spherical head may be excessive relative to the open cavity between the fins 161, 162, such that the corresponding attachment forming can be pushed onto the attachment forming of the headrest while the spherical head is pressed between the fins. Alternatively, the spherical head 222 may be appropriately sized or set to a slightly smaller size to be pushed into and fitted therein.

[0077] exist Figure 5 In the illustrated embodiment, the protruding element 220 extends from the structural foam 210 and around the center of the cavity 212 formed therein. A rear opening 216 and a front opening 214 are formed. Here, the central foam block 218 of the foam structure divides the front opening 212 into a first through-hole and a second through-hole. The central foam block 218 is configured to support the listener's head 2 (see [link]). Figure 7 This is because the sound-permeable foam may be too soft to provide sufficient support for the user. Furthermore, the headrest is formed of a main body assembly 202, which includes a foam structure 210 and a sound-permeable material 230. The sound-permeable material 230 is shown as a rear block 232 and a first front block and second front blocks 235, 236.

[0078] The headrest 200 is formed of a body assembly 202, which includes a foam structure 210 and an acoustically permeable filling block 230. The acoustically permeable block maintains acoustic openings 214, 216, but physically closes the body assembly 202 to enclose the cavity 212 in which the dipole speaker 100 is mounted. The body assembly 202 of the headrest 200 also includes a base frame 204, which is configured to provide structural and safety features to the headrest, as known in the field of headrest design. The base frame may include a cage-like portion surrounding the dipole speaker to provide a safety aspect that prevents the dipole speaker from being dislodged from the headrest in the event of a collision. The base frame also includes a rod 205 (see...). Figure 6 It provides attachment points for attaching the headrest to the chair back, as is known.

[0079] While this application primarily relates to providing a dipole loudspeaker for generating low-frequency frequencies, it should be understood that the audio system will also include directional loudspeakers ranging from mid-frequency to high-frequency. The mid-high frequency loudspeaker 206... Figure 5are shown attached to the chassis 204 on the sides of the headrest to direct sound into the personal sound enclosure in which the listener's head is disposed. It will be appreciated that the sound transparent front blocks 235, 236 are extended as shown to provide an opening between the mid-high frequency speaker 206 and the front of the headrest. See Figure 6 The body assembly is shown from the front with the sound transparent front blocks assembled into the foam structure 210 before and after the sound transparent trim material 207 is applied. The trim material has a lower flow resistance and can be a low flow resistance textile or perforated leather. Figure 7 A user 2 is shown in the intended position relative to the headrest 200. Here, the audio system 1 provides a personal sound enclosure around the user with better (high) SPL within the personal sound enclosure and better (low) SPL outside the personal sound enclosure.

[0080] Again, see Figure 5 In the second embodiment, the protruding element 220 provides both the waveguide forming function and the attachment forming function. For example, the protruding element 220 works with the frame 120 to provide the partitions that isolate the front and back of the cavity. In addition, the protruding element 220 includes the ball head 222 and together form the attachment forming piece that attaches the dipole speaker to the headrest and provides a secondary suspension system. Here, the elastic portion 224 between the sides of the cavity and the ball head can be adjusted to provide the desired stiffness. For example, a corrugated structure is shown and the corrugated structure can be sized to provide the desired stiffness to the elastic portion 224.

[0081] Various methods of controlling the stiffness of the protruding element 220 to match the desired stiffness will be discussed below. Known dynamic and static adjustment calculations can be used to calculate the optimal stiffness. For example, by plotting the force applied to the headrest from the working dipole speaker and the force applied to the diaphragm, the stiffness of the secondary suspension can be optimized. Here, see Figure 8a and Figure 8b , the solid line represents the force acting on the headrest that, if too high, will cause undesirable vibrations through the headrest; while the dashed line represents the force acting on the diaphragm that produces the SPL. Here, within the working frequency range of the dipole speaker (typically in the range of 40 Hz to 200 Hz), the stiffness of the secondary suspension system can be optimized to reduce the force acting on the headrest. For reclined seats, the optimization needs to take into account the change in suspension system due to the change in angle (relative to vertical). In Figure 8a and Figure 8b , Figure 8a a seat is shown in the upright (vertical) position, while Figure 8b shows the change in force within the frequency range due to the change in stiffness of the secondary suspension system due to the change in angle (plotted at a 45° angle relative to vertical). In Figure 8a andFigure 8b In this context, Mms is the mass of the moving diaphragm, Bl is the force generated by the dipole loudspeaker driver unit, Kms is the combined stiffness of the diaphragm suspension to the dipole loudspeaker frame, Ml is the mass of the loudspeaker frame and driver, and Ks2 is the stiffness of the secondary suspension system.

[0082] To optimize the stiffness of the secondary suspension system within the tilt angle range, the progressiveness of the secondary suspension system can also be optimized. Figure 9a and Figure 9b An optimized force distribution diagram relative to deflection is shown. Taking into account the mass of the dipole speaker and the second suspension adjustment frequency, the first and second suspension regions will be defined by the vibration requirements during audio playback. The maximum seat angle and the second suspension adjustment frequency will define their static deflection. See, for example, [link to relevant documentation]. Figure 9b The diagram shows graphs illustrating the static deflection of the second suspension system at different seat tilt angles. The graphs indicate that the preferred adjustment frequency for the second suspension is between 10Hz and 20Hz. Below 10Hz, the static deflection of the second suspension becomes excessively large rapidly when the seat is tilted. Furthermore, above 20Hz, the vibrations transmitted to the seat become excessively large rapidly, as seen from… Figure 8b It is evident. In Figure 8b In this configuration, due to the highly progressive nature of the second suspension, its adjustment frequency rises to 20Hz. Therefore, it is recommended to anticipate the essentially linear first suspension region so that the static deflection occurring when the seat is tilted has a smaller impact on the second suspension's adjustment frequency, thereby better maintaining good seat damping. Anticipated mechanical shocks from external vibrations will preferably be used to define the suspension's progressiveness and limiting region.

[0083] As described herein, the stiffness of the protruding element 220 can be adjusted in a variety of ways, such as by changing the size of the protruding element. Figure 10 As shown, in Figure 10 Figure a illustrates a foam protrusion element. Here, stiffness can be controlled by varying the free length X, thickness, density, or insertion length Y of the foam (the insertion length Y is the length by which the protrusion element is inserted into the corresponding attachment forming of the frame). Furthermore, the protrusion element can be combined with other elements. For example, a secondary suspension system, either attached to or as a replacement for the foam protrusion element, may include, for instance... Figure 10 The wavy material shown in b, or such as Figure 10 The integral strip or sheet shown in c. Regarding corrugated materials, stiffness can also be controlled by the corrugated material, its thickness or size, and the corrugation form. In an integral strip or sheet, stiffness can be controlled by the material or its thickness and size. When the foam protrusion element 220 includes additional elements, the foam can be molded or shaped around these additional elements.

[0084] Other example embodiments will now be described. These other example embodiments describe alternative configurations of waveguide-forming members and attachment-forming members and structures of the dipole loudspeaker 100 without describing in detail the general configuration of the headrest 200.

[0085] Figure 11 A third embodiment of the example audio system 1 is shown. The dipole loudspeaker 100 is mechanically attached to the headrest. The mechanical attachment is shown as a screw, but other forms such as a nut and bolt can also be employed. The attachment-forming member on the headrest is shown as a protruding element 220 that includes an insert member 260 (or insert) molded therein. The protruding element 220 is formed by creating a slot in the side of a cavity in the headrest. It will be appreciated that the size of the slot can be controlled to control the stiffness of the foam protruding element. Here, the cavity is shaped as a through-hole through the headrest from the front to the back that forms a cavity, a front opening, and a back opening. The insert 260 extends from the protruding element 220 to provide a fixed location (e.g., a hole or a threaded portion, or a threaded portion) for receiving a mechanical fastening. The protruding element in combination with the insert 260 provides a secondary suspension system. The corresponding attachment-forming member on the frame 110 is shown as a flange that extends around the periphery of the frame, but can also be intermittent, such as tabs at fixed locations. Multiple fixed locations can be needed to accommodate the suspension of the frame.

[0086] In Figure 11 the waveguide-forming member function is provided by the combination of the frame and the protruding element 220.

[0087] Figure 12 Another embodiment is shown in which the audio system 1 includes a first dipole loudspeaker 100 and a second dipole loudspeaker 100a. The second dipole loudspeaker 100a is substantially the same as the dipole loudspeaker 100 described herein. In addition, the headrest provides a first cavity and a second cavity for mounting the first and second dipole loudspeakers as described herein. Each cavity includes a protruding element 220 that provides a waveguide-forming member and an attachment-forming member. Here, the attachment-forming member is shown as a flange 263 on the frame. The flange 263 is inserted into an open cavity formed distal to the protruding element 220. The flange 263 can be held in the cavity by an adhesive or can be held by the length of the insertion distance of the flange. For example, the protruding element can compress or deform to push the flange into the cavity, thereby eliminating the need for further fastening. In addition, the stiffness of the protruding element 220 is controlled by the combination of parallel slots that extend out from the protruding element. In Figure 12 the waveguide-forming member is provided by the protruding element 220. The protruding element 220 in combination with the frame 110 provides a baffle to direct the sound.

[0088] Figure 13a shows a protrusion element 220 formed by two protrusions 226, 228. The protrusions 226, 228 combine to form a partially enclosed cavity into which a corresponding attachment formation on the frame is inserted to mount the dipole speaker in the headrest. Here, the corresponding attachment formation is shown as a molded plate forming the protrusion site 170. The protrusion site is pushed into the partially enclosed cavity between the protrusions 226, 228. In this case, the protrusions 226, 228 are designed to deflect to open the cavity to allow the protrusion site 170 to enter. The attachment formation provides a snap fit when the protrusions 226, 228 snap back and close around the protrusion site 170. Furthermore, the stiffness of the protrusion element 220 is controlled by incorporating the cavity 262 into the structural foam of the headrest. On the front side, the protrusion 228 provides a waveguide formation. Here, the surface of the protrusion is curved to provide a smooth waveguide. On the back side, the protrusion 226 provides a waveguide formation. Here, the waveguide formation combines with the frame, specifically the molded plate 170, to form a baffle.

[0089] Figure 13 b shows a protrusion element 220 formed by a first protrusion and a second protrusion 226, 228. These protrusions are spaced apart by a distance to improve stability of the motion. The protrusions 226, 228 form an attachment formation. Here, the distal ends of the protrusions are adapted to be inserted into an open cavity formed in the frame of the dipole speaker 100. Here, the corresponding attachment formation on the speaker 100 includes a pair of first and second parallel flanges with an open cavity formed between the first and second flanges. The foam protrusions 226, 228 can be pushed into the open cavity. For example, the foam protrusions will deflect or deform to snap into the open cavity. The dipole speaker is secured to the protrusions by the length of insertion. The protrusions 226 and 228 form waveguide formations on the back and front sides, respectively, of the cavity in which the dipole speaker is mounted and formed through the headrest. Figure 13 e shows a similar embodiment including a chassis and acoustically transparent inserts 232, 234.

[0090] Referring to Figure 13 c, the protrusion element 220 forms an attachment formation similar to that of Figure 11 However, another foam brace is provided as a strut 264, 265 on the front and / or back of the frame. Here, the frame extends towards the front and back of the headrest and is supported by the struts. These struts provide further suspension to assist in designing the suspension characteristics of a secondary suspension system. Furthermore, in the event of a crash, the struts provide some resistance to the motion of the dipole speaker. The protrusion element 220 combines with the frame of the speaker to provide a baffle to direct sound from the respective vibrating surface out of the front and back through holes.

[0091] In Figure 13In d, the cavities and slots are used to define the stiffness of the protruding element 220. As shown, the corresponding attachment formations on the frame and the attachment formations on the headrest are formed by a shaped plate and a pair of protrusions similar to those of Figure 13 a The attachment formations of a are formed by a shaped plate and a pair of protrusions. However, the shaped plate extends on the front and back sides to extend over and cover the protruding element 220. The extended portions of the shaped plate are curved to provide a smooth waveguide formation and provide a baffle through the combination of the protruding element and the frame.

[0092] Figure 13 f Depicts an audio system 1 in which the protruding element 220 is reinforced with an insert. The insert is shown as a contoured insert 260. The contoured insert can be used to adjust the stiffness of the protruding element 220.

[0093] Figure 13 g Shows an example in which the waveguide formation is provided by a separate component from the component that provides the baffle. Here, the dipole speaker is attached to the headrest by a suspension element 268 shown as a unitary sheet. The suspension element 268 is separate from the foam protruding element 220 and is attached to the chassis 204. The foam protrusions 226, 228 extend near the dipole speaker to provide the waveguide formation function.

[0094] Figure 13 h Provides another example of using an insert 260 in the foam structure 210 to control the stiffness of the foam protruding element 220. The insert 260 can be attached to the chassis or float within the encapsulating foam.

[0095] Figure 13 I Shows an example of using cavities to adjust the foam density and thereby adjust the tuning frequency of the secondary suspension system. For example, circular cavities are provided in the foam structure around the attachment formations to which the dipole speakers are attached. The dipole speaker 100 is also adapted to include a flexible attachment between the frame and the inner frame. Here, the diaphragm is attached to the inner frame by a first suspension system, and the frame is attached to the headrest as described herein. The flexible attachment, shown as a third suspension system 131, suspends the inner frame on the frame. Providing a third suspension system (or another suspension system) can help increase the design options for seat dampening.

[0096] In Figure 13 j In which the attachment portion is shown as a foam protruding element 220 in which the foam structure 210 is formed from two pieces that are fixed or glued together after the dipole speakers are assembled. The two pieces each include a portion of the protruding element so that the protruding element can sandwich the flanges on the frame of the dipole speakers when assembled.

[0097] Figure 13k illustrates an example in which the protruding element forming the waveguide is configured to extend in front of one or both radiating surfaces. For example, foam protrusion 220 is configured to provide an opening that is more limited in area than the resonant surface, either forward or backward. Thus, an overlap 269 is formed between the resonant surface and the corresponding forward or backward opening.

[0098] Figure 13 The illustration depicts an embodiment in which the foam structure 210 has a graded or variable density profile (represented by grayscale variations). For example, the material forming the foam structure can have variable stiffness by changing the material density at specific locations. For instance, the distal ends of the protruding elements (shown as spaced-apart first and second protrusions) can have different densities from the protrusions in the foam structure 210.

[0099] Figure 14 Another embodiment of an audio system according to another exemplary embodiment is shown. In this exemplary embodiment, a waveguide forming element is formed by a base 204 of a headrest. The base 204 is rigid because it provides structure for the headrest. As shown, the distal end of the base extends into the cavity where the speaker is located. For example, the distal end extends partially through the cavity to limit the cavity size between the front and rear portions. The distal end is shown extending substantially perpendicular to the front-rear direction of the headrest. It is conceivable that the distal end of the base can be a continuous flange or a discontinuous flange, as described herein. Here, the waveguide forming element includes a flexible member 205 that connects the base to the frame of the speaker. Thus, the flexible member 205 provides a second suspension system. Furthermore, the frame of the speaker extends to overlap the base 204 in the direction of the headrest (i.e., the forward direction of the headrest). Here, the base provides a mechanical abutment against which the speaker impacts when it is pushed forward through the headrest. For example, in the vehicle example, in the event of a collision, the impact force of the speaker may cause the speaker to be pushed forward, and the abutment between the speaker frame and the base provides substantial restraint to prevent the speaker from popping out of the headrest.

[0100] In addition, such as Figure 14 As shown, although the flexible member 205 can be integral with the headrest foam as previously described, the flexible member is suitably shown as a foam element, such as a separate foam strip. While the foam strip can be one or more separate strips, it can also be formed continuously to extend around the periphery of the cavity, as illustrated herein with reference to examples of integral foam. The foam strip can be glued or adhered to one side of the speaker or headrest. For example, in Figure 14 In the diagram, foam strips are shown glued or adhered to the base frame. Another adhesive can be activated to adhere the other side of the speaker 100 or headrest 200 to it. For example, as...Figure 14 As shown in FIG. 1 1 1, another adhesive (such as an adhesive strip) can be applied on the other side of the foam strip, and the speaker frame can be pushed into contact with the adhesive to secure the speaker to the foam strip. Because the speaker frame and the chassis overlap in the forward direction, the rigid frame provides a convenient element to press together to activate the adhesive or glue during assembly.

[0101] In Figure 14 the distal end of the chassis is curved from the portion of the chassis that forms the inner surface of the cavity. Here, the chassis provides the majority of the waveguide-forming member. The flexible member 205 also helps to form the waveguide-forming member. It is also contemplated that where the distal end of the chassis extends from the headrest foam, the headrest foam can also form part of the waveguide-forming member described herein.

[0102] Referring to Figure 15 , a front portion of the headrest is shown to depict different options for arranging the attachment-forming member and the corresponding attachment-forming member of the dipole speaker. For example, each attachment-forming member extends around the periphery of the frame and the cavity. However, the attachment-forming member can extend substantially continuously around the periphery, or alternatively can extend discontinuously. As Figure 15 b shows that both the attachment-forming member and the corresponding attachment-forming member extend continuously. In Figure 15 a, the foam protruding element 220 forming the attachment-forming member is continuous, while the corresponding attachment-forming member on the dipole speaker is discontinuous. Figure 15 c shows the opposite arrangement, where the foam protrusion is discontinuous, while the corresponding attachment feature on the dipole speaker is continuous. Figure 15 d depicts a possible arrangement of additional insert components 260 extending radially from approximately the center of the dipole speaker. The additional components are equidistantly disposed around the dipole speaker 100.

[0103] Various aspects of the embodiments can be assembled by various assembly methods. However, see for example Figure 16The dipole speaker 100 is pushed into the headrest 200. The dipole speaker is shown as being pushed through the rear opening 216, but this is not limiting, the dipole speaker can also be pushed through the front opening 214. The attachment formations engage or mate with the attachment formations on the headrest, for example by pushing a protrusion on one of the components (shown as a protrusion formed by a molded plate on the frame of the dipole speaker) into a cavity (shown as a partially enclosed cavity formed between two foam protrusions on the foam structure 210) on the other component. In one embodiment, the protrusion deforms or deflects as the dipole speaker 100 is pushed into the headrest 200. Once the protrusion is inserted, the protrusion springs back to snap the dipole speaker into the headrest. Once the dipole speaker is installed in the foam structure 210, other components of the main body assembly can be installed, such as the sound transparent fill blocks 232, 234. Some of the other components of the headrest, such as the chassis and other inserts and / or any other acoustic components, can be installed prior to assembly of the dipole speaker.

[0104] The audio system 1 described herein provides a dipole speaker for producing low frequency sound in a personal sound enclosure around a headrest. Advantageously, the path length of the dipole speaker between the two vibrating surfaces can be extended to increase the SPL within the personal sound enclosure. Furthermore, by incorporating the functionality of a secondary suspension system into the foam protrusions, the audio system can be assembled with fewer components without having to significantly increase the number or cost of headrest components. The audio system 1 can be incorporated into a seat, and in turn, the seat can be incorporated into a vehicle or the like.

[0105] The features disclosed in the foregoing description, 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 result, may, separately, or in any combination of one or more of the features, be used in the practice or implementation of the present application in its various embodiments.

[0106] While this application has been described in connection with the exemplary embodiments thereof, as contemplated by the inventor, it is to be understood that many equivalents, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the exemplary embodiments of the application as set forth above are intended to be illustrative not limiting. Various changes can be made without departing from the spirit and scope of the application.

[0107] To avoid any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of the reader regarding the application. The inventors do not wish to be bound by any of these theoretical explanations.

[0108] Any section headings herein are used for organizational purposes only and are not to be construed as limiting the subject matter described.

[0109] Throughout this specification (including any claims) the word "comprise", and variations such as "comprises" and "comprising", 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.

[0110] It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Ranges can 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 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%.

Claims

1. An audio system comprising a dipole loudspeaker and a headrest; The dipole loudspeaker includes: 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 surfaces of the diaphragm; a drive unit configured to move the diaphragm at a low frequency such that the first radiating surface and the second radiating surface produce a low-frequency sound, wherein the sound produced by the first radiating surface is out of phase with the sound produced by the second radiating surface; and a loudspeaker frame from which the diaphragm is suspended via a primary suspension system; and The headrest includes: A main body component, formed to include: a first opening configured to allow sound generated by the first radiating surface to propagate out of a first side of the headrest; and a second opening configured to allow sound generated by the second radiating surface to propagate out of a second side of the headrest; wherein the main body component includes a foam structure, wherein the foam structure is acoustically resistive; and A protruding element, formed of acoustically damping foam, extends between the foam structure of the headrest and the speaker frame, wherein the protruding element provides: A waveguide forming element configured to guide sound generated by a first radiating surface through a first opening and to guide sound generated by a second radiating surface through a second opening, as a result of the protruding element being combined with the speaker frame to form a sound insulation panel; and An attachment forming member for attaching the speaker frame to the headrest, wherein the attachment forming member provides a secondary suspension system via which the speaker frame is suspended.

2. The audio system according to claim 1, wherein, The headrest includes a plurality of protruding elements that extend between the foam structure of the headrest and the speaker frame, wherein one or more protruding elements close any gap between the main body assembly of the headrest and the speaker frame of the dipole speaker to suppress sound propagation through the headrest between the first radiating surface and the second radiating surface.

3. The audio system of claim 1, wherein the protruding element is integrally formed with the foam structure.

4. The audio system of claim 1, wherein the attachment forming is the protruding element, the protruding element including a distal end for attachment to a corresponding attachment forming on the speaker frame, and the stiffness of the protruding element is adapted to provide a secondary suspension system for suspending the speaker frame.

5. The audio system of claim 4, wherein the dipole loudspeaker includes an open cavity receiving the protruding element integrally formed with the foam structure of the headrest.

6. The audio system of claim 1, wherein the protruding element is attached to the speaker frame.

7. The audio system of claim 6, wherein the protruding element includes an insertion member that extends at least partially along the length of the protruding element to change the stiffness of the protruding element.

8. The audio system of claim 7, wherein the insertion member extends from the distal end of the protruding element, and the speaker frame is attached to the insertion member.

9. The audio system according to any one of claims 1 to 8, wherein the speaker frame is specifically adapted to include a corresponding attachment forming for attaching the speaker frame to the headrest.

10. The audio system of claim 9, wherein the corresponding attachment forming member is a protrusion formed on the speaker frame.

11. The audio system of claim 9, wherein the corresponding attachment forming element is a cavity formed on the frame.

12. A method of assembling an audio system according to any one of claims 1 to 11, wherein the method comprises assembling a dipole loudspeaker onto a headrest, the headrest comprising: A main body component, shaped to include: a first opening configured to allow sound generated by the first radiating surface to propagate out of a first side of the headrest; and a second opening configured to allow sound generated by the second radiating surface to propagate out of a second side of the headrest; a waveguide forming configured to guide sound generated by the first radiating surface through the first opening and to guide sound generated by the second radiating surface through the second opening; and an attachment forming for attaching the speaker frame to the headrest, wherein the attachment forming provides a secondary suspension system via which the speaker frame is suspended; and the method includes: The dipole speaker is moved relative to the headrest so that the attachment forming is coupled to the speaker frame.

13. A seat comprising an audio system according to any one of claims 1 to 11.

14. A means of transport comprising the seat according to claim 13.

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