GB2586959A

GB2586959A - Distributed mode loudspeaker

Info

Publication number: GB2586959A
Application number: GB1911348.9A
Authority: GB
Inventors: Mikalauskas Egidijus; Newlove Richard
Original assignee: Amina Technologies Ltd
Current assignee: Amina Technologies Ltd
Priority date: 2019-08-08
Filing date: 2019-08-08
Publication date: 2021-03-17
Anticipated expiration: 2039-08-08
Also published as: GB201911348D0; CN111918181A; GB2586959B; CN213126444U

Abstract

The distributed mode loudspeaker comprises a planar diaphragm 12 having at least one exciter 24 coupled to the rear of the diaphragm and causing the diaphragm to vibrate to generate sound. The periphery of the diaphragm 12 is fixedly mounted to a support frame (38, fig 4). The rear of the planar diaphragm 12 has at least one groove 30 defining a thinned region of the diaphragm 12 relative to a region 36 of the planar panel away from the at least one groove. The grooves are said to facilitate flexing of the diaphragm and to increase the area of the diaphragm that is subject to flexibility. This is said to improve the low frequency response of the loudspeaker when it is mounted within a structure such as a wall.

Description

Distributed Mode Loudspeaker [0001] This disclosure relates to a distributed mode loudspeaker for mounting inside a structure, and a method of manufacture thereof.

BACKGROUND

[0002] It is often desirable to mount devices that would otherwise be taking up space within rooms in the walls or in other surfaces such as ceilings in those rooms so as to be flush with, or substantially not protruding from the surfaces. Distributed mode loudspeakers (sometimes referred to as flat panel loudspeakers) are particularly suited to this application, because they can be mounted in an opening defined in a surface of a building, such as a surface of a wall, a floor, or a ceiling. Such distributed mode loudspeakers include a planar panel having a front surface that is arranged to be substantially flush with, for example, the surface of the wall. One general appeal of distributed mode loudspeakers installed in this way is that the loudspeaker can be made to look invisible. Once such a distributed mode loudspeaker is mounted in the opening of the surface, the loudspeaker can be made "invisible" by blending the surface with a boundary of the loudspeaker insofar as it is generally not apparent that the flat panel of the loudspeaker forms part of the surface (or that the surface defines an opening therein). For example, a thin plaster coat can be applied over at least a boundary of the front surface of the flat panel loudspeaker to make it difficult, if not impossible, to visually identify the location or even presence of the flat panel loudspeaker in the wall.

[0003] Distributed mode loudspeakers typically comprise a resonant panel having a front surface to face outwardly from the distributed mode loudspeaker in use, and a rear surface opposite the front surface. An exciter is generally provided mounted to the rear surface of the resonant panel via a coupler to cause the resonant panel to vibrate, whereby the vibrations cause the resonant panel to generate sound. In this way, the placement of the exciter and the coupler does not interfere with the blending of the front surface of the resonant panel and the surface in which the distributed mode loudspeaker is to be mounted. The exciter and other components of the flat panel loudspeaker can be protected by being mounted within a mounting box or similar.

[0004] Where flat panel loudspeakers are mounted inside a structure, such as a wall, there may be structural features, or other components, also provided within the structure. Therefore, the space available for mounting the flat panel loudspeaker may be restricted. Typically, the low frequency audio performance of a flat panel speaker can be detrimentally affected by any restrictions in the size of the resonant panel of the flat panel speaker.

[0005] It is in this context that the present disclosure has been devised. BRIEF SUMMARY OF THE DISCLOSURE [0006] In accordance with a first aspect of the present disclosure, there is provided a distributed mode loudspeaker for mounting inside a structure, the distributed mode loudspeaker comprising: a planar panel having a front to face outwardly when mounted inside a structure and a rear opposite the front; an exciter coupled to the rear of the planar panel and configured to cause the planar panel to vibrate to generate sound; and a support frame having the rear of the planar panel fixedly mounted thereto about a periphery of the rear of the planar panel, such that the periphery of the planar panel is configured to be fixedly mounted relative to the structure, when mounted inside the structure, wherein the rear of the planar panel has defined therein at least one groove defining a thinned region of the planar panel relative to a region of the planar panel away from the at least one groove.

[0007] A groove defines a thinned region of the panel, such that the groove has a depth penetrating into the rear of the panel relative to a region of the panel away from the groove. By providing one or more grooves in the planar panel, the inventors have found that the loudspeaker described herein can reproduce sound that is a more accurate replication of the input audio signal, as compared with conventional flat panel loudspeakers of the same size. In particular, the present loudspeaker can improve the sound quality of reproduced audio up to and substantially including 10 kHz, and more particularly with respect to low to mid frequency sound, as follows: In conventional flat panel loudspeakers for mounting in a structure, the periphery of the panel is, in use, fixedly mounted relative to a structure in which it is mounted, such that displacement of the planar panel away from its equilibrium position as a result of low frequency excitation by the exciter is opposed by the fixed mounting of the planar panel relative to the structure; this can impede the low frequency audio performance of the flat panel loudspeaker. A cause of this phenomenon has been found to be the relative rigidity of the planar panel. Relatively rigid planar panels are nevertheless required for accurate high frequency audio reproduction. In other words, panels with a reduced area of flexibility generally reduce the quality of audio reproduced, since low to mid frequency vibrations cannot be efficiently generated as the panel cannot be optimally displaced to reproduce the corresponding audio. The inventors have found that grooves in the planar panel of the present loudspeaker provide thinned regions less resistant to the flexibility necessary for displacement from the equilibrium state; indeed, it will be understood that any thinned region of the panel facilitates greater flexibility of the panel, as compared with relatively thicker regions of the panel. In doing so, the panel can displace sufficiently from its equilibrium position so that sound waves, and more particularly those with low to mid frequencies, can be generated by efficiently displacing the panel from its equilibrium position, without having to increase the area of the panel to do so. Of course, it will be understood that whilst the present disclosure describes a thinned region provided by a groove, a substantially similar effect may be achieved by substantially any planar panel having localised regions in the same location(s) and configuration(s) as the at least one groove, which increase the local flexibility of the planar panel without thinning the panel in that region.

[0008] The planar panel may be fixedly mounted to the support frame around a periphery of the rear of the planar panel. When the support frame is mounted to the structure during mounting of the flat panel loudspeaker in the structure, it will be understood that the planar panel will come to be fixedly mounted relative to the structure.

[0009] The planar panel may comprise a plurality of layers. The plurality of layers of the planar panel may include a first layer forming the front of the planar panel, a second layer forming the rear of the planar panel, and one or more intermediate layers interposed between the first layer and the second layer. The at least one groove may have a depth extending through the second layer. The at least one groove may have a depth extending into the one or more intermediate layers.

[0010] In other words, the one or more intermediate layers may provide the planar panel with a core having a boundary provided by the first and second layers. The first layer and the second layer may be provided by a skin, for example a paper skin. The one or more intermediate layers may be formed with one or more pre-preg layers. A pre-preg layer will be understood to be a layer of woven or non-woven fibres provided in a resin. The resin may be semi-cured. Typically, the pre-preg layer can cure fully under application of heat and/or pressure during manufacture of the planar panel. Any grooves in the planar panel may be formed before, during or after curing of the planar panel during manufacture.

[0011] A depth of the planar panel may extend from the rear to the front of the planar panel, away from the at least one groove. A depth of the at least one groove may be less than two thirds of the depth of the planar panel. The depth of the at least one groove may be less than half the depth of the planar panel.

[0012] A width of the at least one groove may be defined between a first edge of the at least one groove and a second edge of the at least one groove. The second edge may be spaced from the first edge. The width of the at least one groove may be greater than 1 mm. The width of the at least one groove may be greater than 2 mm. The width of the at least one groove may be less than 10 mm. The width of the at least one groove may be less than 5 mm.

[0013] The at least one groove may be at least one elongate groove having a groove length greater than a width of the at least one elongate groove. The elongate groove may be arranged to extend substantially parallel to a length of the planar panel. The length of the planar panel may be greater than a width of the planar panel. The groove length of the at least one groove may be greater than 50% of the length of the planar panel. The groove length of the at least one groove may be less than 90% of the length of the planar panel. However, the orientation of the groove is not limited; the length of the at least one groove may extend substantially perpendicularly to a direction of the length of the planar panel. In other words, the groove may extend in a direction defined by the shortest axis of the planar panel. In some examples, the at least one groove may be a plurality of grooves, extending in a plurality of different directions.

[0014] By providing elongate grooves in this manner, the grooves may facilitate displacement of the panel by flexing of the planar panel substantially along its long edges, and therefore increase the area of the panel that is subject to flexibility. However, the arrangement of the grooves is not limited to this, and the grooves may instead or additionally be provided parallel to a shorter side of the planar panel. The grooves may be substantially straight, so as to make for efficient manufacture. However, the grooves are not limited to this configuration, and may be non-straight, for example curved, or any other

suitable shape.

[0015] In other words, the grooves may have one or more of the above dimensions i.e. the above depth, width and/or length. Moreover, the grooves are not limited to all the grooves having identical dimensions, but may for example have differing depths, widths and lengths from groove to groove. By providing grooves with such dimensions (i.e. having the above depth, width and/or length), the grooves increase the flexibility of the panel, while maintaining the structural integrity of both the panel and any skim applied thereto. In particular, such groove dimensions reduce the risk of the thinned region of the panel from becoming too weak and breaking, thereby maintaining the structural integrity of the panel.

Moreover, when the loudspeaker is mounted inside a structure such as a wall or the like and a skim is applied thereto so as to make the loudspeaker look "invisible", the skim, which is typically plaster or the like, is prone to cracking when displaced excessively. Hence, by providing the present groove dimensions, the structural integrity of the skim can also be maintained in use, by reducing the effect of the displacement of the panel on the applied skim.

[0016] The at least one groove may be defined by at least one wall. The at least one groove may be defined by at least two side walls. The at least two side walls may extent substantially straight, towards a base. The at least two side walls may extend substantially parallelly towards the base. The at least two side walls may extend in an inclined arrangement towards the base. The at least two side walls may be inclined substantially inwardly, such that a region of the at least two side walls at the rear of the planar panel is further apart than a region of the at least two side walls further within the panar panel, towards the base. Such configurations of the at least one groove, which define a cross-section of the at least one groove, can allow the at least one grooves to be manufactured efficiently. However, the groove is not limited to the shapes described hereinbefore. The at least two side walls may together meet to form a curved or pointed base. In doing so, the cross section of the groove may be substantially U-shaped or V-shaped. Such inclined walls can provide the advantage of increasing the flexibility of the panel, as compared with parallel facing walls, by virtue of providing groove walls that are obtuse with the rear surface of the panel.

[0017] The rear of the planar panel may comprise at least one groove region and a non-groove region. The at least one groove may be defined within the at least one groove region. The non-groove region may be substantially devoid of grooves. In other words, there may be no grooves in the planar panel outside the at least one groove region. To put this another way, all of the grooves in the planar panel can be contained within the at least one groove region. The at least one groove region may include a first groove region and a second groove region. The second groove region may be spaced from the first groove region. The non-groove region may be interposed between the first groove region and the second groove region. In other words, the first groove region, the non-groove region and the second groove region are arranged adjacent to one another. The non-groove region can provide a central region of the panel, with the grooves provided outside of the central region and towards the edges of the panel.

[0018] By dividing the panel into such an arrangement of at least one groove region and a non-groove region, the audio performance of the distributed mode loudspeaker can be further improved. In particular, by providing the groove regions towards the edges of the panel in this manner, the flexibility of the panel is further increased. As discussed above, the periphery of the panel is fixedly mounted to the structure in use. In conventional loudspeakers, this causes the regions of the panel near its periphery to oppose flexing of the panel by virtue of being proximal to the fixedly mounted periphery. By contrast, providing groove regions towards the edges of the panel locally reduces the rigidity of the panel, thereby giving rise to an increased flexibility in the local region. Accordingly, the non-groove region of the panel is capable of greater displacements in response to a given low frequency audio input signal to the exciter. Therefore, the panel can vibrate, particularly with low to mid frequencies, to a greater extent, thereby improving the audio performance of the distributed mode loudspeaker. Furthermore, by providing a non-groove region that is interposed between the groove regions so as to be substantially centrally disposed, the structural integrity of the panel is maintained in regions that may be maximally displaced from its equilibrium state, since the panel is relatively sturdier therein and hence less prone to snapping or breaking, by virtue of being relatively thicker than the grooves.

[0019] The first groove region may include a plurality of first grooves and the second groove region may include a plurality of second grooves. By providing multiple grooves in the first and second groove regions in this manner, the first and second groove regions facilitate displacing the panel from its equilibrium state, while maintaining the structural integrity of the panel. The number of first grooves in the plurality of first grooves in the first groove region may be equal, for example exactly equal, to the number of second grooves in the plurality of second grooves in the second groove region.

[0020] The at least one groove may include at least two grooves spaced apart from each other by a predetermined spacing distance. The predetermined spacing distance may be greater than 1 mm. The predetermined spacing distance may be greater than 2 mm. The predetermined spacing distance may be less than 10 mm. The predetermined spacing distance may be less than 5 mm. The predetermined spacing distance may be substantially equal to a width of the at least one groove. By providing multiple grooves with such spacing distances, the grooves can together facilitate displacing the panel from its equilibrium state, while maintaining the structural integrity of the panel, and the structural integrity of the surface in which the loudspeaker is installed. This is because the arrangement of multiple grooves ensures that the change in the angle of any two adjacent portions of the front surface of the planar panel is reduced, the total change in the angle of the front surface being spread out across all of the grooves. In other words, if the grooves are sized and/or spaced as described hereinbefore, the inventors have found that the risk of plaster cracking is reduced, because the stresses imposed on the plaster on the panel are spread out over multiple discrete regions on the panel, and not focused on only a single area, which reduces the risk of the panel deforming to such an extent that the panel and/or any covering plaster would fail (by deforming to a non-recoverable level).

[0021] The at least one groove may comprise a plurality of grooves distributed symmetrically about a central axis of the planar panel. In providing the panel with a symmetrical profile of thinned and thicker regions, the weight of the panel may be evenly distributed when mounted in use. In doing so, the loudspeaker may be more supported more sturdily in the structure in which it is mounted, as compared to panels with asymmetrically distributed weight. Furthermore, the audio performance of the distributed mode loudspeaker may be modelled more easily due to the symmetric form of the planar panel. This is because the panel is less prone to a "rocking" effect, which can occur when the panel is not balanced. In particular, such rocking effects can cause the corners of the panel to displace unevenly, which in turn may cause the exciter to bend such that some of its constituent components can rub against one another. For example, a voice coil of a driver of the exciter may rub against metal parts of the exciter, which can cause audio distortion, particularly at high amplification. By contrast, providing the panel with the above symmetrical profile of grooves facilitates the panel to displacing substantially symmetrically in response to an input audio signal to the exciter. For example, if the force is applied in a substantially central region of the panel, the displacement of the panel in each of opposing corners is substantially similar, if not the same. However, the skilled person will understand that at least some of the technical effects of the present disclosure may still be achieved with non-symmetrical grooves.

[0022] The at least one groove may be disposed away from the periphery of the rear of the planar panel. In doing so, the periphery of the planar panel may be used for fixedly mounting the loudspeaker to a surface. Furthermore, in examples where the front of the planar panel comprises a depression region surrounding a periphery of the front of the planar panel, the at least one groove may be disposed away from the depression region, in a region bounded by the depression region. It will be understood that the use of a depression region allows a front surface of the planar panel to be depressed around the periphery, facilitating application of plaster skim over the boundary of the planar panel and the front surface of the structure in which the planar panel is installed.

[0023] In some examples, the at least one groove may comprise a first groove, extending in a first direction over the panel, and then snaking back over the panel in a second direction substantially opposite the first direction. In this way, a single groove can function in a similar way to a plurality of spaced grooves. In some examples this can be considered to provide a plurality of grooves, at least because a notional line across the rear of the planar panel, substantially transverse to a portion of the first groove, will cross several different, spaced portions of the first groove.

[0024] In accordance with another aspect of the present disclosure, there is provided a method of manufacturing a distributed mode loudspeaker for mounting inside a structure.

The method comprises: providing a planar panel having a front to face outwardly when mounted inside a structure and a rear opposite the front. The planar panel is to be provided fixedly mounted to a support frame about a periphery of the rear of the planar panel when the distributed mode loudspeaker is manufactured. The method further comprises forming at least one groove in the rear of the planar panel, the at least one groove defining a thinned region of the planar panel relative to a region of the planar panel away from the at least one groove; and coupling an exciter to the rear of the planar panel.

The exciter is configured to cause the planar panel to vibrate to generate sound.

[0025] Thus, there is provided a method of forming the distributed mode loudspeaker disclosed herein. It will be understood that the planar panel can be fixedly mounted to the support frame before or after the forming of the at least one groove. Similarly, the excited can be coupled to the rear of the planar panel before or after forming the at least one groove. In some examples, the at least one groove may be formed during the manufacture of the planar panel, for example in a pressing operation.

[0026] Forming the at least one groove may comprise using a groove forming tool. The groove forming tool may include a saw. The groove forming tool may include a routing tool, for example a drill. Accordingly, the grooves may be routed efficiently through the rear of the panel.

[0027] Forming the at least one groove may comprise cutting into at least a portion of the rear of the planar panel.

[0028] Forming the at least one groove may comprise tearing at least a portion of the rear of the planar panel. The tearing may be performed in addition to the cutting, which is particularly advantageous for reducing the amount of precision required to form the groove. Accordingly, the amount of time and resources required during the manufacturing process may be reduced. Tearing is particularly applicable where the planar panel is formed from a plurality of layers, including a first layer and a second layer, providing a front and a rear of the planar panel respectively, wherein the first layer and the second layer are each formed from paper, and wherein the paper of the second layer is torn as part of forming the groove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the present disclosure are further described hereinafter with reference to the accompanying drawings, in which: Fig. 1 is a schematic rear view of a speaker according to an example of the disclosure; Fig. 2 is a perspective cross-sectional view of a second groove region of a panel of the speaker according to the example of the disclosure; Fig. 3 is a graph plotting the audio performance of the speaker of the example of the disclosure compared with a speaker without grooves; Fig. 4 is a schematic rear view of a speaker according to a further example of the disclosure; Fig. 5 a perspective rear view of a support frame of the speaker of the further

example of the disclosure; and

Fig. 6 is a flow chart of a method of manufacturing a speaker according to a third example of the disclosure.

DETAILED DESCRIPTION

[0030] The present inventors have realised that distributed mode loudspeakers or flat panel loudspeakers of the prior art, of the type described in the background section hereinbefore, suffer from suboptimal audio performance because at least some low to mid frequency sounds are not accurately reproduced between the audio input received by the exciter and the audio output generated by the planar panel. In particular, the inventors have noticed that, by virtue of distributed mode loudspeakers being fixedly mounted at a periphery of the panel in use, a periphery region of the panel remains substantially rigid and therefore cannot be displaced sufficiently to vibrate to generate sounds of mid to low frequencies in panels of relatively small sizes. This is particularly disruptive to accurately reproducing audio with low to mid frequency tones, since such reproduction requires the panel to have an area that can displace sufficiently at these lower frequencies corresponding to the input audio. In particular, panels with smaller areas of flexibility reduce the efficiency with which lower frequency vibrations can be generated, since the panel cannot be optimally displaced to reproduce the corresponding audio. Accordingly, this can result in poorer audio performance by the speaker compared to larger distributed mode loudspeakers, such that the reproduced sound may not be an accurate replication of the original signal received by the speaker.

[0031] Conventional methods address this problem simply by increasing the size of the panel of the loudspeaker, so that these low frequency vibrations can be generated in the panel, to generate corresponding sound. Without doing so, the quality of low to mid frequency audio can be reduced. Accordingly, many conventional loudspeakers have to be produced at large sizes to achieve high quality audio, but this is not always practical for mounting in structures, and particularly in domestic structures such as walls, ceilings, etc. In some examples, by requiring accommodation in a large cavity of such structures, this can reduce the structural integrity of the that structure in which it is mounted.

[0032] The present inventors have thus sought a way to improve the audio performance of such distributed mode loudspeakers.

[0033] Fig. 1 shows a speaker 10 according to an example of the disclosure. In particular, Fig. 1 illustrates a rear view of the speaker 10. The speaker 10 is a distributed mode loudspeaker, otherwise called a flat panel speaker, which comprises a panel 12. The panel 12 has a front that is substantially flat or planar. The panel 12 has a rear opposite the front, such that the front and rear of the panel 12 are arranged substantially parallel to one another. The panel 12 is substantially cuboid in shape having a width W, a length L and a depth D, whereby the width W, length L and depth D each extend perpendicularly to one another, as shown in Figs. 1 and 2 (Fig. 2 is discussed in detail below). As shown in Fig. 1, the length L of the panel 12 in this particular example is longer than the width W of the panel 12, but the present disclosure is not limited to this shape or orientation, and may have a different shape, such as a circular shape or an oval shape.

[0034] The panel 12 comprises a plurality of layers, so as to provide a multi-layer panel.

A front layer defines the front of the panel 12, a rear layer defines the rear of the panel 12, and one or more intermediate layers are interposed between the front layer and the rear layer. The intermediate layers provide the panel 12 with an interior or a core having a boundary defined by the front and rear layers of the panel 12. However, the disclosure is not limited to this form of construction of the planar panel, and the panel may be formed of a uniform composition, rather than split into different composite layers. Typically, the front layer and the rear layer are provided by a skin, for example a paper skin. The one or more intermediate layers are formed from one or more layers of pre-preg material. Pre-preg material will be understood to be a layer of woven or non-woven fibres embedded in a resin, which hardens when cured. The planar panel 12 is typically formed by curing under heat and/or pressure where the resin of the one or more intermediate layers impregnates into the skin layers to form a strong, lightweight, planar panel, highly suited for use in distributed mode loudspeakers of the type described herein. A number of options for the materials used to form the layers of the panel will be apparent to those skilled in the art. Furthermore, it will be understood that alternative constructions can be used to provide the planar panel, providing that the resulting panel is stiff enough to cause emission of sound output when vibrated by an exciter coupled thereto, as described further hereinafter.

[0035] The speaker 10 further includes at least one exciter 24, which is coupled to the panel 12. As shown in Fig. 1, the exciter 24 is provided at the rear of the panel 12, and may be coupled to the panel 12 via any suitable means, such as a coupler (not shown).

The exciter 24 is a transducer, which, in practice, causes the panel 12 to vibrate to generate sound by virtue of an input audio signal applied to the exciter 24. Typically, the exciter 24 is an electromagnetic exciter, of any of the types commonly used in distributed mode loudspeakers. When caused to vibrate by the exciter 24, the panel 12 acts by resonance to output the applied displacements in a similar manner to a soundboard of a violin or piano such that the speaker 10 produces sound. The above description of the operation of the exciter 24 and the panel 12 is provided merely for the convenience of the reader. The skilled person will understand the typical operation of distributed mode loudspeakers. The exciter 24 comprises circuitry, an input and an output (not shown). The input of the exciter 24 is in wired or wireless communication with a transmitting device (not shown) for receiving the input audio signal therefrom, and the output of the exciter 24 is mechanically coupled to the panel 12.

[0036] The transmitting device is for transmitting a signal to the exciter 24, whereby the signal includes audio data corresponding to audio for being reproduced by the speaker 10, such as music, etc. The transmitting device can be disposed externally of the speaker 10 as shown in Fig. 1, and may include any suitable device for transmitting the signal to the exciter 24. For example, the transmitting device may include a smart phone, tablet, computer, and any other suitable portable and/or non-portable computing devices. Furthermore, the transmitting device may transmit the signal to the exciter 24 using any suitable transmission means. For example, the exciter 24 may include a wireless communication module to enable wireless communication (e.g. Bluetoothe, W-Fi, etc. communication) with a suitable transmitting device that has a counterpart wireless communication module. Such wireless communication configurations are particularly advantageous for enabling the exciter 24 to receive audio input from portable devices. The exciter 24 may otherwise, or additionally, be in wired communication with the transmitting device.

[0037] The circuitry of the exciter 24 is configured to process the received input signal to generate a mechanical output for causing the panel 12 to vibrate. In particular, the vibrations generated by the mechanical output of the exciter 24 have frequencies corresponding to the received input signal. It will be understood by the person skilled in the art that the circuitry of the exciter 24 can have any suitable topology for processing the signal. Once the signal has been processed, the exciter 24 outputs the mechanical output to the panel 12. It will be understood by the skilled person that more than one exciter may be provided for the panel 12, whereby each exciter is tailored for causing the panel to vibrate at a predetermined set of frequencies. For example, one exciter from among the exciters may cause the panel to vibrate at high frequencies, while another exciter from among the exciters may cause the panel to vibrate at low frequencies. The person skilled in the art will understand where to dispose the exciters across the rear of the panel for optimal sound output, and/or will understand how to determine how to tune the audio response of the panel for given placement location(s) of the one or more exciters.

[0038] The speaker 10 further comprises a plurality of grooves 30 provided in the rear of the panel 12. Each groove 30 defines a thinned portion of the panel 12 relative to a region of the panel 12 away from the groove 30. In other words, the groove 30 provides a depression in the rear 16 of the panel 12 having a depth extending into the panel 12. Fig. 2 is a detailed cross-sectional perspective view of the rear 16 of the panel, detailing the grooves 30. In particular, Fig. 2 shows the groove 30 as a cutaway region in the rear 16 of the panel 12. The groove 30 may also be referred to as a channel or a slot in the rear 16 of the panel 12.

[0039] By providing grooves in the planar panel, the loudspeaker can reproduce sound that is a more accurate replication of the input audio signal, as compared with conventional loudspeakers of the same size. In particular, the present loudspeaker can improve the sound quality of reproduced audio up to and substantially including 10 kHz, and more particularly with respect to low to mid frequency sound, particularly in the range of approximately 20 to 500 Hz. In conventional distributed mode loudspeakers for mounting in a structure to be made substantially invisible, the periphery of the panel is, in use, fixedly mounted to relative to a structure in which it is mounted, such that only a relatively small area of the panel away from the fixed region may be sufficiently flexible to displace substantially from its equilibrium position. However, panels with such a small area of flexibility generally reduce the quality of audio reproduced, since low to mid frequency vibrations cannot be efficiently generated as the panel cannot be optimally displaced to reproduce the corresponding audio. By contrast, the grooves in the planar panel of the present loudspeaker provide thinner regions less resistant to displacement from the equilibrium state; indeed, it will be understood that any thinned region of the panel facilitates greater flexibility of the panel, as compared with thicker regions of the panel. In doing so, the panel can displace sufficiently from its equilibrium position so that sound waves, and more particularly those with low to mid frequencies, can be generated by efficiently displacing the panel from its equilibrium position, without having to increase the area of the panel to do so. Accordingly, the skilled person will understand that the disclosure is not limited to having a plurality of grooves. Indeed, providing just one groove in the rear of the panel will improve the accuracy of audio reproduced, as compared with panels without any grooves disposed therein.

[0040] In the first example of the disclosure, the rear 16 of the panel 12 is divided into groove and non-groove regions, whereby groove regions define areas of the panel where the grooves 30 are provided, and non-groove regions define an area of the panel substantially devoid of grooves 30. More particularly, as shown in Fig. 1, the rear 16 of the panel 12 includes a first groove region 32, a second groove region 34 and a non-groove region 36 interposed between the first and second groove regions 32, 34, each positioned in parallel with one another. In doing so, the rear of the panel includes a substantially central region within which grooves are absent, with the grooves 30 disposed substantially outside the centralised non-groove region 36 towards the edges of the panel 12. As shown in Fig. 1, the plurality of grooves 30 are disposed in and evenly split between the first and second groove regions 32, 34. In this example, the first groove region 32 includes approximately five grooves 30, and the second groove region 34 includes approximately five grooves 30. In doing so, the grooves 30 are distributed substantially symmetrically about a central elongate axis of the planar panel 12, thereby providing the panel 12 with a symmetrical profile of relatively thin and thick regions. Accordingly, the weight of the panel may be evenly distributed when mounted in use, so that the speaker 10 may be more supported more sturdily in the structure in which it is mounted, as compared to panels with non-symmetrically distributed weight.

[0041] By dividing the panel 12 into such an arrangement of groove and non-groove regions, the quality of audio reproduced is further improved. In particular, by providing the groove regions 32, 34 towards the edges of the panel in this manner, the flexibility of the panel is further increased. However, as shown in Fig. 2, while being disposed towards the edges of the panel 12, the grooves 30 and accordingly groove regions 32, 34 are disposed away from the periphery of the rear 16 of the panel 12. As discussed above, the periphery or outer boundary of the panel 12 is fixedly mounted to the structure in use, for example by being adhesively or mechanically affixed thereto. In conventional loudspeakers, this causes the regions of the panel near its periphery to also be rigid by virtue of being proximal to the fixedly mounted periphery. By contrast, providing groove regions towards the edges of the panel reduces the rigidity of the panel, thereby giving rise to an increased flexibility. Accordingly, the panel can vibrate, particularly with low to mid frequencies, to accurately reproduce audio. Furthermore, by interposing the non-groove region 36 between the groove regions so as to be substantially centrally disposed, the structural integrity of the panel is maintained in regions that may be maximally displaced from its equilibrium state, since the panel is relatively sturdier therein and hence less prone to snapping or breaking, by virtue of being relatively thicker.

[0042] Furthermore, the audio performance of the distributed mode loudspeaker may be modelled more easily due to the symmetric form of the planar panel. This is because the panel is less prone to a "rocking" effect, which can occur when the panel is not balanced.

In particular, such rocking effects can cause the corners of the panel to displace unevenly, which in turn may cause the exciter to bend such that its constituent components rub against one another. For example, a voice coil of a driver of the exciter may rub against metal parts of the exciter, which can cause audio distortion, particularly at high amplification. By contrast, providing the panel with the above symmetrical profile of grooves facilitates the panel in displacing symmetrically. For example, if the force is applied in a substantially central region of the panel, the panel is displaced by substantially the same amount in each of opposing corners. However, the skilled person will understand that at least some of the technical effects of the present disclosure may still be achieved with non-symmetrical grooves.

[0043] In this example of the disclosure, the grooves 30 are defined with predetermined dimensions, which are particularly illustrated in Figs. 1 and 2. As shown in Fig. 2, the grooves 30 of the first example of the disclosure have depths extending into the intermediate layers 22 of the panel 12, which are approximately half the depth D of the panel 12. Here, the depth D of the panel 12 is defined between the rear 16 and the front of the panel 12. The grooves 30 also have widths that extend substantially orthogonally to the depth in the width W direction of the panel 12, and are predetermined to be approximately 3 mm. The grooves 30 also have a length extending in the length L direction of the panel 12 that is predetermined to be approximately 70 to 80 % of the length L of the panel 12, as shown in Fig. 1. In doing so, the grooves 30 are substantially elongate and narrow, and arranged to be parallel with the long edges of the panel 12, i.e. arranged in the elongate axis of the panel 12. In this example, the length L of the panel is approximately 300 millimetres, the width W of the panel is approximately 200 millimetres and the depth D of the panel is approximately 5 millimetres.

[0044] The grooves 30 having the dimensions as described hereinbefore are particularly advantageous by increasing the flexibility of the panel, while maintaining the structural integrity of both the panel and any skim applied thereto. In particular, such groove dimensions reduce the risk of the thinned region of the panel from becoming too weak and breaking, thereby maintaining the structural integrity of the panel. Moreover, when the loudspeaker is mounted inside a structure such as a wall or the like and a skim is applied thereto so as to make the loudspeaker look "invisible", the skim, which is typically plaster or the like, is prone to cracking when displaced excessively. Hence, by providing the present groove dimensions, the structural integrity of the skim can also be maintained in use, by reducing the effect of the displacement of the panel on the applied skim. Moreover, by providing elongate grooves 30 that are parallel with an elongate axis of the panel 12, the grooves may facilitate flexing of the panel substantially about an axis parallel to its long edges, and therefore increase the flexing of the panel for a given input force from the exciter 24.

[0045] In this example, neighbouring grooves 30 are spaced apart from one another by a spacing distance that is substantially equal to the width of the grooves 30, i.e. approximately 3 mm. This is particularly shown in Fig. 2, whereby the grooves 30 in the second groove region 34 are consecutively arranged in parallel, with each being separated by a spacing distance, or a separation. The separations separating each groove 30 are thus provided as thickened regions as compared to the thinned regions of the grooves, so as to provide a cross-sectional profile that is substantially castellated, or otherwise undulated. Here, the cross-sectional profile is taken along the elongate axis of the second groove region 34, so as to be defined in the length L plane. The grooves 30 in the first groove region 32 are similarly arranged with the above separations. By providing multiple grooves 30 with such spacing distances, the grooves together facilitate displacing the panel from its equilibrium state, while maintaining the structural integrity of the panel and/or any plaster covering of the front surface of the panel. This is because the arrangement of the multiple grooves acts to reduce the risk of the panel deforming to such an extent that there is failure of the panel and/or any plaster, such that the panel and/or plaster becomes permanently distorted. In other words, providing multiple grooves with such spacings improves the ability of the panel and any plaster skim applied thereon to return to the equilibrium state for a given displacement, as described hereinbefore.

[0046] However, the disclosure is not limited to the above orientation and dimensions of the first example of the disclosure. For example, the skilled person will appreciate that panels that do not include such intermediate layers (for example if the panel is formed with a uniform composition), the grooves merely extend into the rear of the panel. Moreover, the dimensions are not limited to the above, and are preferably as follows: the grooves may have depths up to and including two thirds of the depth of the panel. The widths may be equal to or greater than 1 mm, preferably equal to or greater than 2 mm, equal to or less than 10 mm, and preferably equal to or less than 5 mm. The lengths of the grooves may be in the range of 50 to 90% of the length of the panel. Moreover, the spacing distances are not limited to the above disclosure: the spacing distance may be predetermined to be equal to or greater than 1 mm, and preferably equal to or greater than 2 mm. The predetermined spacing distance may be equal to or less than 10 mm, and preferably equal to or less than 5 mm.

[0047] Furthermore, the orientation of the grooves is not limited to the above, such that the grooves may be instead or additionally arranged to extend along a shorter axis of the panel, rather than the elongate axis of the panel. For example, the grooves may be arranged to be parallel with the shorter sides of the panel rather than the long elongate sides as in the first example shown in Figs. 1 and 2. The grooves are also not limited to being substantially straight, but may take other configurations, such as being wavy.

[0048] The benefit provided to the audio quality by virtue of the grooves is particularly demonstrated in Fig. 3, which shows audio results of the sound reproduced by the loudspeaker described hereinbefore including five grooves in each of the first and second groove regions (solid line) compared to a conventional loudspeaker without grooves (dashed line). More particularly, the audio results are plotted in a graph showing the sound level (i.e. volume) against the reproduced audio frequency for the above respective loudspeakers. As shown in Fig. 3, the audio quality of the loudspeaker without grooves includes a plurality of sharp spikes in volume at given frequencies throughout the audio spectrum. This causes the resulting audio to differ from the original input signal, with some frequencies being amplified more than they should be, and conversely other frequencies being quieter than they should be. By contrast, the loudspeaker including the grooves in the panel improves the overall sound quality by providing a smoother volume profile across the audio frequency spectrum, by reducing the number of volume spikes and troughs, as compared with the loudspeaker without grooves. Accordingly, the resulting audio is more accurately representative of the input audio signal across the whole frequency spectrum up to and including approximately 10 kHz, and hence improves the resulting audio quality.

As can be particularly seen in Fig. 3, the spectra from approximately 20 Hz to approximately 500 Hz is particularly improved with a smoother volume profile, and thus results in a better sound quality for corresponding low-to mid-range audio. Moreover, the volume of low frequency audio (under 100 Hz) is particularly increased in volume. It can also be seen in the low frequency region from 20 Hz to around 100 Hz that the output sound level is increased relative to the conventional distributed mode loudspeaker, meaning that the low frequency audio performance of the disclosed distributed mode loudspeaker is more similar in level to the audio performance at higher frequencies.

[0049] Fig. 2 illustrates a cross sectional profile that the grooves 30 may take. The grooves 30 are defined by side walls and a base, which together give rise to the cross-sectional profile. As shown herein, each groove 30 has two side walls that are parallel with one another so as to be oppositely facing. The two side walls meet at a base that is substantially planar. Together, the side walls and base define a cross-sectional profile that is substantially quadrilateral-shaped, such as square-or rectangular-shaped. This is particularly beneficial during the manufacturing process, since the grooves with such oppositely facing grooves can be formed efficiently.

[0050] However, the disclosure is not limited to such grooves, and may be provided with different cross-sectional profiles. In some embodiments, a groove 30 may have two side walls that are substantially inclined towards one another and meet at a substantially planar base, to provide a substantially V-shaped cross-sectional profile. In other embodiments, the side walls may be inclined to meet one another to form a curved or pointed base, rather than a planar base. By providing inclined side walls, an obtuse angle is defined where the side walls meet the rear surface of the panel. This acts to increase the flexibility of the panel, since the obtusely inclined walls provide a generally smoother rear surface profile that facilitates bending.

[0051] In further embodiments, a groove may include a single wall that is curved to provide a substantially U-shaped cross-sectional profile. However, the disclosure is not limited to this, and the grooves could give rise to a similarly shaped profile, by providing two oppositely facing parallel side walls that meet with a curved base.

[0052] As shown in Fig. 2, the grooves 30 are all provided with the same cross-sectional profile, which can make for an efficient manufacturing process, without requiring different techniques to form the grooves. However, the disclosure is not limited to this, and the grooves may be formed with different cross-sectional profiles.

[0053] Fig. 4 illustrates a speaker 10' according to a further example of the present disclosure. The speaker 10' includes a panel 12' and an exciter 24' corresponding to those of the speaker 10 of the first example of the disclosure. The speaker 10' further includes a support frame 38 to which the panel 12' can be fixedly mounted about a periphery of the panel 12'. The support frame 38 is also used to facilitate mounting of the speaker 10' in a structure, such as a wall. In some examples, the support frame 38 is additionally for supporting the exciter 24'.

[0054] Fig. 5 shows a perspective view of the support frame 38 of the further example of the disclosure, which comprises a frame portion that is substantially planar and has approximately the same dimensions as the panel 12'. The mounting frame is arranged parallel to and rearward of the panel 12'. The frame further includes sides that extend perpendicularly from a periphery or outer boundary of the rear of the frame to a periphery or outer boundary of the panel 12'.

[0055] Typically, the support frame is attached to the rear 16' of the panel 12' by any suitable attachment means, such as by applying an adhesive coating between an abutting surface of the support frame and the rear of the panel to bond together.

[0056] The support frame 38 as attached to the panel 12' defines a cavity or space that is enclosed by the frame and the rear 16' of the panel 12'. The space of the frame is dimensioned to accommodate the exciter 24', and supports the exciter 24' and the panel 12' together. Wien the speaker 10' includes the above described support frame 38, the front 14' of the panel 12' defines a front of the speaker 10', the rear of the mounting frame defines a rear of the speaker 10', and the sides of the frame define sides of the speaker 10'. The exciter 24' is typically a two-part electromagnetic exciter 24', having a first part (not shown separately) secured to the support frame 38 and a second part (not shown separately) secured to the panel 12', for example via a coupler (not shown). The first part is caused to move relative to the second part by activation of an electromagnet on one of the first part and the second part (to act on a ferromagnetic component on the other of the first part and the second part) in dependence on the input audio signal to the exciter 24'.

[0057] The support frame 38 may be formed from metal, for example steel, or from another material, such as carbon fibre.

[0058] Of course, the skilled person will understand that the support frame, when used, need not be exactly as described hereinbefore, providing the support frame supports the exciter 24' and the panel 12'. For example, the frame may include sides in the absence of a rear. In some examples, the exciter 24 can be inertially mounted to the panel 12 without being mounted to a support frame. In such examples, the panel 12 is caused to vibrate by movement of the exciter 24 which is inertially braced by the mass of the exciter itself.

[0059] The speaker 10' can be mounted inside a structure, in use. More specifically, the speaker 10' can be mounted in a mounting surface. The mounting surface can be provided with an opening in an exposed surface of a structural component of a building, such as a wall, floor, ceiling, air conditioning unit, or the like. In examples of the disclosure, the opening in the mounting surface is defined by one or more cuts in the mounting surface, resulting in the opening in the mounting surface which is sufficiently deep to contain the speaker 10'. The opening is typically of the same shape and slightly larger than the planar panel 12' to accommodate the panel 12' therein when mounted in the surface. Alternatively, the opening can be provided by means of the construction of the mounting surface. In other words, the mounting surface can be formed to have the opening defined therein, and its dimensions are predetermined to accommodate the speaker 10'. In examples where the speaker is not rectangular-shaped, but is of another polygonal shape, the mounting surface is tailored such that its dimensions substantially match the speaker. In doing so, when the speaker 10' is mounted inside the structure, such as within the opening of a wall, the front of the panel 12' is disposed substantially flush with the surface of the structure, such as the wall surface that is facing outwards into a room, so as to face outwardly from the room.

[0060] Prior to mounting the speaker 10 inside the mounting surface, a box (not shown) having an open front may be firstly disposed in the mounting surface, whereby the box is dimensioned to the speaker 10'. The speaker 10' may then be mounted into the box by via its support frame 38. In other examples, the speaker 10' may be provided in the box and the box may be mounted into the mounting surface with the speaker 10' already provided therein.

[0061] In examples where the structure is a plastered wall, once the speaker 10' is mounted inside the structure so as to be substantially flush or not protruding therewith, a skim (not shown) can then advantageously be applied thereto. In particular, the skim that is applied to finish the plastered wall is also applied over the panel 12' of the speaker 10', thereby giving it substantially the same finish as the wall with which it is flush. This means that the speaker 10' can advantageously be made to look "invisible", by virtue of its being accommodated and substantially hidden from view inside the structure, such that the speaker 10' is flush with, or not substantially protruding from the surfaces. It is however understood by the skilled person that applying a skim may not always be necessary, particularly when other forms of wall construction are used, such as drywall lining, in which drywall gypsum boards are attached to stud walls to form the wall surface. The drywall boards themselves provide the wall finish, and so no plastering or finishing skim is applied.

[0062] The support frame 38 as provided in the mounting surface of the wall provides the speaker 10' with greater structural integrity, as well as a protective casing for the exciter 24', particularly for the rear of the exciter 24' during installation in the mounting surface. In particular, the support frame 38 ensures that when the panel 12' is mounted in the mounting surface, and when an operation of an exciter 24' is causing the panel 12' to vibrate, the outer boundary of the panel 12' is fixed relative to the mounting surface. This helps to prevent any plaster layers covering the mounted speaker 10' from cracking or distorting. In this way, the speaker 10' can remain invisible in the mounting surface. However, the disclosure is not limited to this. For example, the speaker may be provided in the absence of a support frame as described hereinbefore. In such examples, exciters may be inertially mounted to the panel. More specifically, the exciters may be arranged to brace against the panel using their own mass/inertia to cause the panel to vibrate and generate sound.

[0063] The present disclosure further provides a method of manufacturing a speaker. Fig. 6 shows a flow chart of the steps of a method 100 of manufacturing a speaker, which will now be described.

[0064] The method 100 comprises a first step 110 of providing a planar panel. The panel has a front, opposite the rear, and to face outwardly of the speaker in use, whereby a periphery of the rear of the panel is configured to be fixedly mounted relative to a structure, in use. The planar panel may be as described hereinbefore. In some examples, the first step 110 of providing the planar panel can comprise forming the panel, as follows. A plurality of layers having predetermined compositions are provided and stacked to dispose a front layer to form the front 14 of the panel 12, a rear layer to form the rear 16 of the panel 12, and one or more intermediate layers interposed between the front layer and the rear layer. The plurality of layers are then secured to one another in the predetermined stacked order to form the panel 12 of the first example of the disclosure. The one or more intermediate layers can be one or more pre-preg layers. The plurality of layers can be bonded together by pressing and curing, through the application of appropriate heat and pressure, sometimes referred to as autoclaving.

[0065] The method 100 further comprises a second step 120 of forming a least one groove in the rear of the planar panel. The groove may be as described hereinbefore, and may be formed by any suitable means. For example, the grooves may be formed using a groove forming tool, such as using a saw, a cutting tool or the like. In doing so, the grooves may be routed efficiently and accurately through the rear of the panel. However, the disclosure is not limited to this. In some examples of the disclosure, the grooves are formed by tearing the rear of the panel, which may be performed in addition to, or instead of, using the groove forming tool. For example, a cutting tool or the like may be used to make an initial incision into the panel, from which the panel can subsequently be torn to provide grooves. In doing so, the precision required to form the groove is relatively low, thereby reducing the amount of resources and time required during the manufacturing process. The grooves may formed with the same arrangements in the panel as described hereinbefore, for example as shown in Figs. 1 and 2. The order with which the steps are performed is not particularly limited, for example any grooves in the planar panel may be formed before, during or after pressing and curing of the planar panel during manufacture.

[0066] The method 100 also includes step 130 of coupling an exciter to the rear of the panel. The exciter may be as described hereinbefore. This coupling of the exciter and the panel may be achieved by any suitable means. For example, the method 100 may further include additional steps (not shown), such as providing a coupler configured to couple to the exciter, coupling the coupler to the exciter, and coupling the coupler to the rear of the panel, which may be performed in any order. Therefore, the method can be used to manufacture the distributed mode loudspeaker as described herein.

[0067] In some examples of the disclosure, the method may include an additional step of installing a support frame configured to fixedly mount the speaker to a structure in use. In particular, the support frame may include the frame having the rear and sides as described hereinbefore. The installing of the support frame may include attaching the support frame to a periphery of the panel, for example by applying adhesive to a periphery of the support frame and enclosing the exciter within the frame by abutting the periphery of the support frame to the periphery of the panel as described hereinbefore. In other words, the exciter is enclosed in the space defined between the support frame and the rear of the panel so as to support the exciter and the panel together. In some examples of the method, a rear of the exciter is also attached to the support frame so as to provide further structural integrity in supporting the exciter to the panel. However, the disclosure is not limited to the mounting of the exciter and the panel in the support frame in this way. For example, in examples of the disclosure whereby the exciter is inertially mounted to the panel (see above), the exciter and the panel may be inserted within the mounting surface of the wall receiving the speaker, such that the exciter is braced against the panel by its own inertia/mass.

[0068] In summary, there is provided a distributed mode loudspeaker (10) for mounting inside a structure. The distributed mode loudspeaker (10) comprises a planar panel (12) having a front to face outwardly when mounted inside a structure and a rear (16) opposite the front. An exciter (24) is coupled to the rear of the planar panel (12) and configured to cause the planar panel (12) to vibrate to generate sound. A support frame (38) has the rear of the planar panel (12) fixedly mounted thereto about a periphery of the rear of the planar panel (12), such that the periphery of the planar panel (12) is configured to be fixedly mounted relative to the structure, when mounted inside the structure. At least one groove (30) is defined in the rear (16) of the planar panel (12), and defines a thinned region of the planar panel (12) relative to a region of the planar panel (12) away from the at least one groove (30).

[0069] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0070] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the disclosure are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The disclosure is not restricted to the details of any foregoing embodiments. The disclosure extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A distributed mode loudspeaker for mounting inside a structure, the distributed mode loudspeaker comprising: a planar panel having a front to face outwardly when mounted inside a structure and a rear opposite the front,; an exciter coupled to the rear of the planar panel and configured to cause the planar panel to vibrate to generate sound; and a support frame having the rear of the planar panel fixedly mounted thereto about a periphery of the rear of the planar panel, such that the periphery of the planar panel is configured to be fixedly mounted relative to the structure, when mounted inside the structure, wherein the rear of the planar panel has defined therein at least one groove defining a thinned region of the planar panel relative to a region of the planar panel away from the at least one groove.
2. The distributed mode loudspeaker of claim 1, wherein the planar panel comprises a plurality of layers, wherein the plurality of layers of the planar panel includes a first layer forming the front of the planar panel, a second layer forming the rear of the planar panel, and one or more intermediate layers interposed between the first layer and the second layer, and wherein the at least one groove has a depth extending into the one or more intermediate layers.
3. The distributed mode loudspeaker of claim 1 or claim 2, wherein a depth of the planar panel extends from the rear to the front of the planar panel, away from the at least one groove, and a depth of the at least one groove is less than 70% of the depth of the planar panel, and preferably, the depth of the at least one groove is less than 60% of the depth of the planar panel.
4. The distributed mode loudspeaker of any one of the preceding claims, wherein a width of the at least one groove is defined between a first edge and a second edge, spaced from the first edge, and wherein the width of the at least one groove is greater than 1 mm, and preferably greater than 2 mm.
5. The distributed mode loudspeaker of any one of the preceding claims, wherein a width of the at least one groove is defined between a first edge and a second edge, spaced from the first edge, and wherein the width of the at least one groove is less than 10 mm, and preferably less than 5 mm.
6. The distributed mode loudspeaker any of the preceding claims, wherein the at least one groove is defined by at least two side walls extending substantially straight, towards a base.
7. The distributed mode loudspeaker of claim 6, wherein the at least two side walls extend substantially parallel towards the base.
8. The distributed mode loudspeaker of any one of the preceding claims, wherein the rear of the planar panel comprises at least one groove region and a non-groove region, wherein the at least one groove is defined within the at least one groove region, and wherein the non-groove region is substantially devoid of grooves.
9. The distributed mode loudspeaker of claim 8, wherein the at least one groove region includes a first groove region and a second groove region, spaced from the first groove region and wherein the non-groove region is interposed between the first groove region and the second groove region.
10. The distributed mode loudspeaker of claim 9, wherein the first groove region includes a plurality of first grooves and the second groove region includes a plurality of second grooves, wherein the number of first grooves is equal to the number of second grooves.
11. The distributed mode loudspeaker of any one of the preceding claims, wherein the at least one groove includes at least two grooves spaced apart from each other by a predetermined spacing distance greater than 1 mm, and preferably more than 2 mm.
12. The distributed mode loudspeaker of any one of the preceding claims, wherein the at least one groove includes at least two grooves spaced apart from each other by a predetermined spacing distance less than 10 mm, and preferably less than 5 mm.
13. The distributed mode loudspeaker of claim 11 or claim 12, wherein the predetermined spacing distance is substantially equal to a width of the at least one groove.
14. The distributed mode loudspeaker of any one of the preceding claims, wherein the at least one groove comprises a plurality of grooves distributed symmetrically about a central axis of the planar panel.
15. The distributed mode loudspeaker of any one of the preceding claims, wherein the at least one groove is at least one elongate groove having a groove length along the planar panel greater than a width of the at least one elongate groove.
16. The distributed mode loudspeaker of claim 15, wherein the planar panel has a panel length greater than a panel width, and wherein the elongate groove extends in a direction of the groove length substantially parallel to a direction of the panel length.
17. The distributed mode loudspeaker of any one of the preceding claims, wherein the at least one groove is disposed away from the periphery of the rear of the planar panel.
18. A method of manufacturing a distributed mode loudspeaker for mounting inside a structure, the method comprising: providing a planar panel having a front to face outwardly when mounted inside a structure and a rear opposite the front, the planar panel to be provided fixedly mounted to a support frame about a periphery of the rear of the planar panel when the distributed mode loudspeaker is manufactured; forming at least one groove in the rear of the planar panel, the at least one groove defining a thinned region of the planar panel relative to a region of the planar panel away from the at least one groove; and coupling an exciter to the rear of the planar panel, the exciter being configured to cause the planar panel to vibrate to generate sound.
19. The method of claim 18, wherein forming the at least one groove comprises using a groove forming tool.
20. The method of claim 19, wherein the groove forming tool includes a saw.
21. The method of any one of claims 18 to 20, wherein forming the at least one groove comprises cutting into at least a portion of the rear of the planar panel.