Electrostatic speaker for a vehicle

Abstract

The electrostatic speaker 210 is configured to be disposed within a vehicle interior component. The electrostatic speaker comprises an electrostatic transducer 220 and a speaker grille 230 configured

Description

TECHNICAL FIELD The present disclosure relates to a speaker, and particularly to an electrostatic speaker in an audio system for a vehicle. Aspects of the invention relate to an electrostatic speaker, to a vehicle audio system, and to a vehicle. BACKGROUND Vehicle systems undergo continuous improvements, particularly at the present time where there is a need to evolve and adapt vehicle system designs based on the ever-changing requirements of consumers as well as the vehicle industry as a whole. For example, consumers desire improvements to be made in the sound quality of their vehicle audio systems. As another example, in recent years, there has been a drive to adopt an increasingly sustainable and eco-friendly approach to vehicle design. It is desirable for this sustainable design approach to be applied to as many aspects of vehicle design as possible, particularly vehicle interior design, such that an increasing proportion of vehicle interior components are made from more sustainable materials and products. As a further example, there is also a drive for vehicle interior designs to more seamlessly integrate accessories, such as the vehicle audio system and its constituent speakers, with the vehicle interior components in which such accessories are installed. It is an aim of the present invention to address one or more disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an electrostaticspeaker, a vehicle audio system comprising the electrostatic speaker, and a vehicle comprising the vehicle audio system, as claimed in the appended claims. According to an aspect of the present invention there is provided an electrostatic speaker, for a vehicle, that is configured to be disposed within a vehicle interior component. The electrostatic speaker comprises an electrostatic transducer and a (speaker) grille configured to protect the electrostatic transducer. The electrostatic transducer is configured to convert an audio signal into sound waves for output. The grille is made of a material that matches or is visually compatible with a material of the vehicle interior component. The grille is configured to protect, and therefore serves as a cover for, the electrostatic transducer. As such, the material used to form the grille typically needs to be of an ‘acoustic grade’ - i.e., substantially acoustically transparent to allow output of the sound waves that are generated by the electrostatic transducer. Examples of such typical ‘acoustic grade’ material that would be used in for grilles in existing vehicle audio systems would be a metallic and / or plastic mesh or grill material. However, such materials would not necessarily match or be visually compatible with the material of the vehicle interior component in which the speaker grille would be installed, since these components are typically made of panelling or softer fabric material. The present Applicant has appreciated that the use of an electrostatic transducer in the speaker means that materials that have not typically been considered to be of ‘acoustic grade’ could be used for the speaker grilles. This allows for a wide range of materials to be used for the speaker grilles, including non-typical but sustainable materials that are intended to be used to make the vehicle interior components in which the speaker is installed. In such cases, the speaker grille materials used can more easily be made compatible (visually) with the materials of the corresponding vehicle interior component, and a seamless integration of speakers within vehicle interiors is thereby made much easier. According to another aspect of the present invention there is provided an electrostatic speaker system comprising an electrostatic speaker, and a vehicle interior component within which the electrostatic speaker is configured to be disposed. The electrostatic speaker comprises an electrostatic transducer and a (speaker) grille configured to protect the electrostatic transducer. The electrostatic transducer is configured to convert an audio signal into sound waves for output. The grille is made of a material that matches or is visually compatible with a material of the vehicle interior component. In some instances, the material of the grille may be the same as the material of the vehicle interior component. It is noted that in this case, the use of the term ‘same’ could be considered to be a ‘continuation of the material of the vehicle interior components, which would further improve the seamless blending of the electrostatic speaker into the vehicle interior design. The resulting design would also likely be more robust, as it would not require the joining of different types of materials having different properties. In some instances, the material used to make the grille may correspond to a breathable fabric. In this context, the term ‘breathable’ is being used to indicate that the material in question is a porous, perforated or loosely woven material. Optionally, the breathable fabric corresponds to any of the following: (i) a woven textile material; (ii) a perforated or porous leather; or (iii) perforated or porous leather-substitute material. For example, the perforated leather or leather-substitute material could correspond to the typical leather material that has typically been used to make the interior trim of a vehicle or in certain vehicle interior components, such as a head restraint or in the seat bases of the vehicle. The woven textile material may correspond to a new textile material that is being used in the vehicle interior trim to replace the more typical leather I leather substitute materials mentioned above, to achieve a more sustainable and environmentally friendly design. For example, the textile and woven materials manufactured by the company Kvadrat. Additionally or alternatively, the material may be constituted from recycled materials. In some instances, the audio signal may lie in a frequency range between 125 Hz to 50 kHz. Optionally, the audio signal includes the frequency range between 20 Hz and 20 kHz; between 500 Hz to 50 kHz, more particularly between 1 kHz to 20 kHz, and still more particularly between 1 kHz to 2 kHz. The electrostatic speaker (transducer) provides particularly good performance and sound quality at those lattermost range of frequencies, and is therefore especially beneficial for replacing existing speakers in vehicle audio systems which operate at such frequencies. Additionally, the Applicant has uncovered that there is a further unexpected advantage achieved by certain ones of the materials used for speaker grilles according to some aspects of the invention: natural damping or suppression results from using those certain materials at certain ones of these frequencies (e.g., between 1 kHz and 2 kHz), such that no additional (separate) processing needs to be carried out to achieve the necessary damping, suppression and / or attenuation around that range of frequencies. Optionally, the vehicle interior component corresponds to any one of the following: (a) a head restraint of a vehicle seat; (b) an interior trim component of the vehicle; and (c) a base portion of a vehicle seat. In such cases, the interior trim component could be a door panel, a dashboard panel, etc. The base portion may correspond to the portion of the seat upon which the driver / passenger sits. According to another aspect of the present invention, there is provided a vehicle audio system comprising a plurality of electrostatic speakers as set out hereinabove. In some instances, the plurality of electrostatic speakers may be of different sizes and / or disposed in different locations within the vehicle, such that they may be incorporated into a wide variety of (combinations of) vehicle interior components. According to another aspect of the present invention, there is provided a vehicle comprising the electrostatic speaker and / or the vehicle audio system as described hereinabove. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures 1A and 1B show a perspective schematic illustration, and a top plan view, respectively of vehicles implementing a vehicle audio system in accordance with an embodiment of the present invention; Figure 2 shows a schematic illustration of a vehicle audio system comprising an electrostaticspeaker system in accordance with an embodiment of the present invention which may be used in the vehicles of Figures 1A and 1B; Figure 3 illustrates graphically a simulated performance of a variety of materials proposed to be used in the vehicle audio system of Figure 3; and Figure 4 illustrates graphically a simulated performance of a specific textile material proposed to be used in the vehicle audio system of Figure 3. DETAILED DESCRIPTION A vehicle audio system comprising an electrostatic speaker in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 2. As shown in Figures 1A and 1E3, the vehicle audio system may comprise a plurality of electrostatic speakers, and may be installed in a vehicle. Figure 1A illustrates a generic vehicle 100 in which a vehicle audio system according to an embodiment of the present invention may be installed. The vehicle 100 comprises a vehicle audio source 105, a plurality of electrostatic speakers 110a, 110b, 110c (indicated using dashed lines) and a corresponding plurality of (different) vehicle interior components 115a, 115b, 115c. As will be discussed in more detail subsequently with reference to Figure 1B, these vehicle interior components may include one or more of the following: an interior trim component of the vehicle which may include a front interior trim component 115a (such as a dashboard panel) or a side interior trim component 115c (such as a door panel); or a vehicle seat component 115b (such as a head restraint or a base portion of a vehicle seat upon which the driver I passenger sits). Each vehicle component 115a, 115b, 115c is configured to have installed within it at least one of the plurality of electrostatic speakers 110a, 110b, 110c. Each electrostaticspeaker 110a, 110b, 110c comprises a corresponding electrostatic transducer 120a, 120b, 120c which is configured to convert an audio signal into sound waves for output; and a speaker grille 125a, 125b, 125c which is configured to protect its corresponding electrostatic transducer 120a, 120b, 120c. A material that is used to manufacture some or all of each speaker grille 125a, 125b, 125c ‘matches’ or is visually compatible with a material that is used to manufacture the corresponding vehicle interior component 115a, 115b, 115c in which the electrostatic speaker 110a, 110b, 110c is installed. One specific example of how the vehicle audio system may be implemented in the vehicle 100 is illustrated in Figure 1B. As shown in Figure 1B, a first plurality of electrostaticspeakers 110a are installed in a front interior component (specifically a dashboard or dashboard trim) 115a of the vehicle 100. A second plurality of electrostatic speakers 110b are installed in different portions of a plurality of vehicle seat components 115b-for example, a few speakers are installed in each head restraint of the corresponding vehicle seat. A third plurality of electrostatic speakers 110c are installed in different portions of a plurality of vehicle side interior trim components 115c - for example, in the door panels of the vehicle 100. It should be appreciated howeverthat different vehicles will have different vehicle audio system arrangements; and therefore, the exact number of electrostatic speakers 110a, 110b, 110c that are installed (as well as their locations) are likely to differ from the illustrative example shown in Figure 1B. For example, although not shown, one or more electrostatic speakers may be installed within a vehicle seat base portion, or within an alternative vehicle trim component such as within a panel that is located in neither the door nor dashboard (e.g., within the boot of the vehicle). A vehicle audio system 200 (and more specifically, details of an electrostatic speaker which forms part of the vehicle audio system) will now be described with reference to Figure 2. As shown in this figure, the vehicle audio system 200 comprises a vehicle audio source 205 that is connected to an electrostatic speaker 210 via one or more signal processing and amplification components 215. The specific details of these signal processing and amplification components 215 are not the focus of this application and will not be described any further here. In summary though, these components 215 are arranged to amplify and process an incoming signal from the audio source 205 and output a suitable audio signal to the electrostatic speaker 210 for conversion into (and output as) sound waves. In other words, the electrostatic speaker 210 provides transducer functionality. Specifically, the electrostatic speaker 210 comprises an electrostatic transducer 220 that is configured to convert the incoming audio signal into sound waves. The electrostatic speaker 210 also comprises a speaker grille 230 that is configured to cover and protect the electrostatic transducer 220 from shocks, contact or physical impact as a result of its implementation location; whilst nevertheless ensuring that the outgoing sound waves pass through (relatively) unimpeded. Electrostatic transducers in their most general sense are designed to generate sound via a force exerted on a membrane (ordiaphragm) that is suspended in an electrostatic field. In orderto do so, electrostatic transducers typically comprise a membrane (e.g., a flexible sheet coated in an electrically conductive material) that is sandwiched between two electrically conductive stators (or grids), leaving a small airgap on either side of the membrane. The incoming audio signal is used to drive the stators resulting in an electrostatic field, proportional to the audio signal, being generated between the stators. The membrane is charged and held at a high voltage relative to the stators. A force is thus exerted upon the membrane causing it to move, driving the air on either side of the membrane to generate pressure waves (sound waves). In more detail with reference to Figure 2, the electrostatic transducer 220 comprises a pair of stators 235a, 235b and a membrane 240 that is located between the pair of stators 235a, 235b. These components are configured to operate in substantially the manner described above, namely, the stators 235a, 235b are configured to receive an incoming audio signal and generate an electrostatic field; and the membrane 240 is configured to move within the electrostatic field and create sound waves. As noted previously, for an electrostatic transducer to be operated correctly, the membrane that is located between the stators needs to be charged to a high potential (voltage). As such, the vehicle audio system 200 further comprises a high voltage module 245 that is configured to provide the necessary high voltage power to charge the membrane 240. An appropriate level of power provided by this high voltage module 245 would be derivable by the skilled person based on the operating conditions, but would typically be in the order of several thousand Volts (for example, between around 2 kV and 5 kV etc.). There are multiple advantages associated with the use of electrostatic transducers (e.g., improved audio response and sound quality obtained, improved versatility of implementation), and that it would be useful to implement electrostaticspeakers in vehicle audio systems in certain scenarios and under certain conditions in order to benefit from these advantages. In some instances, the audio signal that is output to the electrostatic transducer 220 may lie in a frequency range between 125 Hz to 50 kHz. Optionally, the audio signal includes the frequency range between 20 Hz and 20 kHz; between 500 Hz to 50 kHz, and more particularly between 1 kHz to 20 kHz, and still more particularly between 1 kHz to 2 kHz. The electrostatic transducer 220 provides particularly good performance and sound quality in these ranges of frequencies, and is therefore especially beneficial for replacing existing speakers in vehicle audio systems which operate at such frequencies. Turning now to specific details of the speaker grille 230, as noted above, the grille is configured to protect, and therefore serves as a cover for, the electrostatic transducer 220. As such, the material used to form the grille 230 typically needs to be substantially acoustically transparent (or be of a sufficient ‘acoustic grade’) to allow output of the sound waves that are generated by the electrostatic transducer. Examples of such typical ‘acoustic grade’ material that would be used in for grilles in existing vehicle audio systems would be a metallic and / or plastic mesh or grill material. However, such materials would not necessarily match or be visually compatible with the material of the vehicle interior component in which the speaker grille would be installed, since these components are typically made of panelling or softer fabric material. The present Applicant has appreciated that the use of an electrostatic transducer in the speaker means that non-typical ‘acoustic grade’ materials can be used for the speaker grilles. This allows for a wide range of materials to be used for the speaker grilles 230 of the present invention. For example, non-typical but sustainable materials that are intended to be used to make the vehicle interior components in which the speaker is installed could be considered. In such cases, the speaker grille materials used can be compatible (visually) with the materials of the corresponding vehicle interior component, and a seamless integration of speakers within vehicle interiors is thereby made much easier. These materials may include ‘breathable’ acoustically transparent fabric materials. In this context, the terms ‘breathable’ and ‘acoustically transparent’ are used substantially interchangeably to indicate that the material in question is a porous, perforated or loosely woven material, that has sufficient acoustic transparency to allow sound waves to be transmitted at a desirable level. Some examples of breathable fabric that could be used to make the speaker grille 230 include: (i) woven textile materials; (ii) a perforated or porous leather material; or (iii) perforated or porous leather-substitute material. More specifically, the perforated leather or leathersubstitute material could actually correspond to the typical leather material that has typically been (or will typically be) used to make the interior trim of a vehicle or in certain vehicle interior components, such as a head restraint or in the seat bases of the vehicle. The woven textile material may include a variety of materials, including existing materials used to make the vehicle interior components such as the vehicle seats. It may also include new textile materials that are being considered for use in the vehicle interior trim, as an alternative to the leather I leather substitute materials mentioned above, to achieve a more sustainable and environmentally friendly design. For example, the textile and woven materials manufactured by the company Kvadrat. Additionally or alternatively, the materials may be constituted from recycled materials. Figures 3 and 4 are FFT (Fast Fourier Transform) graphs 300, 400 illustrating the frequency response (‘acoustic performance’) of various different materials that have been tested by the present Applicant to ascertain their suitability for use in manufacturing the speaker grille 230 installed in the vehicle audio system 200 described above. More specifically, each graph plots the sound pressure (dB level) that is measured (after passing through the material) as a function of the frequency (Hz) of the sound that was generated by an electrostatic transducer. Figure 3 shows a comparison of seven different materials that were tested; Figure 4 shows a comparison of two of those materials only to highlight some additional benefits associated with one material in particular. First considering the graph 300 of Figure 3, at the lower frequencies (in this case, less than around 1 kHz), the majority of the seven materials appear to have very similar acoustic performance and frequency responses. However, at mid-range and high-range frequencies which are of particular interest in relation to use of electrostatic transducers (i.e., from around 1 to 1.5 kHz upto around 50 kHz), the responses of some materials diverge significantly from those of other materials. The frequency response curves plotted on the graph have been loosely grouped into three sets 305, 310,315, based on the relative acoustic performance of the materials which are associated with these curves. A first group of materials generates a first set 305 of frequency response curves exhibiting behaviour which corresponds to a relatively poor acoustic performance: a very low sound pressure level of between -45 dB and -20 dB is measured at the mid to high frequency range 320 between 3 kHz and 50 kHz, with the sound pressure level decreasing sharply with increasing frequency in that range 320. This indicates that the acoustic transmission for this set of materials in this frequency range is poor. This group of materials comprises two different designs of (plain) unperforated leather material, and a type of wood veneer that is typically used to manufacture certain interior components (e.g., door or panel trim components) in vehicles that are designed by the present Applicant. The set 305 of frequency response curves for this first group of materials are illustrated using dotted lines (of varying intervals). A second group of materials generates a second set 310 of frequency response curves exhibiting behaviour which corresponds to an acceptable I good acoustic performance: a relatively higher sound pressure level of between -20 dB and -5 dB is measured at the mid to high frequency range 320, and the decrease in sound pressure level with increasing frequency is much less steep than the curves 305 for the first group of materials. This indicates that the acoustic transmission for this set of materials in this frequency range is acceptable I good, and would be suitable for use to manufacture the speaker grille 230. This group of materials comprises two different designs of perforated leather material, and a woven fabric material that has typically been deemed to be non-acoustic grade - i.e., not necessarily sufficiently acoustically transparent to be suitable for use in previous vehicle speaker systems. One specific example of this material is that which has been manufactured by a particular textile company, Kvadrat. The set 310 of frequency response curves for this second group of materials are illustrated using dashed lines (of varying intervals). A third group of materials generates a third set 315 of frequency response curves exhibiting behaviour which corresponds to a consistently good acoustic performance: a relatively high sound pressure level of around OdB is measured at the mid to high frequency range 320, and the curve 315 is general flat across this frequency range. This group of materials only includes a single material type - a perforated grille material - that has typically been used to manufacture the speaker grilles which are currently used in existing vehicle audio systems. The frequency response curve 315 for this third set of materials is illustrated using a dash-dot line. To summarise, Figure 3 shows that the second group of materials - the different designs of perforated leather materials and the woven textile material - having the second set 310 of frequency response curves demonstrate a sufficiently good acoustic performance across the mid to high frequency range 320 that they can be considered suitable for use with an electrostatic transducer for implementation in a vehicle audio system. It is noted that this second group of materials comprises material types that would also be suitable to manufacture parts of certain vehicle interior components in which portions of the vehicle audio system 200 would be installed. For example, as discussed previously with reference to Figure 1E3, electrostatic speakers may be installed within portions of the seats (e.g., in the head restraint). Some or all of the seats may therefore also be manufactured using a selection of the materials in this second group, since the acoustic performance of these materials has now been determined to be suitable for use as a speaker grille. Additionally, portions of some vehicle interior trim components (e.g., portions of the dashboard and / or door panels) may be made of textile materials that are the same as or similar to the ones in this second group of materials. As a result, electrostatic speakers comprising speaker grilles that are made of such materials can be incorporated into those vehicle seat and interiortrim components as part of the overall vehicle audio system, but without resulting in a loss of audio performance. Moreover, the ability to use the same (or matching) materials to manufacture both the vehicle interior component, and the speaker grille installed therein, maintains consistency in the visual appearance of the vehicle component as a whole. Figure 4 shows a pair of frequency response curves 405, 410 for two of the materials that were considered in Figure 3, to allow the detailed responses of each curve to be more easily appreciated. The first curve 405 illustrates the acoustic performance of the type of wood veneer material that is typically used in components of vehicles designed by the present Applicant; this material was previously discussed as forming part of the group of curves 305 associated with the first set of materials. The second curve 410 illustrates the acoustic performance of the non-acoustic grade woven textile material (e.g., that manufactured by Kvadrat); this material was previously discussed as forming part of the second group of curves 310 associated with the second set of materials. The first curve 405 is illustrated using a dotted line and the second curve is illustrated using a dashed line. As was noted above, the wood veneer material which generates the first curve 405 is not particularly suitable for use as a speaker grille for electrostatic speakers operating in the mid to high frequency range, since its performance in that range is poor. By contrast, the non-acoustic grade woven textile (Kvadrat) material with the second curve 410 has a much shallower and slower drop-off in frequency response at that mid to high frequency range. It is therefore considered potentially suitable for use in speaker grilles for electrostatic speakers operating in that range. Figure 4 highlights a further (unexpected) advantage associated with the use of the non-acoustic grade woven textile (Kvadrat) material, in relation to its good acoustic performance in a specific mid-range of frequencies 415 between 1 and 2 kHz. Specifically, in that frequency range 415, the sound transmission of the non-acoustic grade woven textile material is actually naturally suppressed (‘naturally damped’) - this is evidenced by the fact that the sound pressure levels for the second curve 410 in this frequency range 415 are significantly lower than the sound pressure levels for the first curve 405. The natural damping that is achieved by this These were just a generic selection of materials that were no acoustic grade, there is a constant list of materials and surfaced design are interested in implementing they are generally constrained by acoustic transparency requirements but this widens to pool of materials that may be suitable woven textile material is advantageous as it means that no (or at least significantly less) artificial damping, suppression or attenuation needs to be applied to the audio signal in that frequency range 415, as compared with other types of material. By contrast, conventional audio speaker systems would require equalisation in this frequency range. This effect can also be seen in relation to the curves of the other materials shown in Figure 3. This (unexpected) advantage, achieved by the electrostatic speaker system and in relation to the non-acoustic grade woven textile material in particular, reduces the signal processing burden on the vehicle audio system, which is beneficial in terms of improving the simplicity and ease of implementation of the electrostaticspeaker. As such, it is possible to expand the range of materials that can be used in electrostatic speaker grilles, provides multiple benefits in relation to flexibility of design and installation, all whilst maintaining high audio quality from the speakers. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. An electrostatic speaker for a vehicle configured to be disposed within a vehicle interior component, the electrostatic speaker comprising:an electrostatic transducer configured to convert an audio signal into sound waves for output; anda grille configured to protect the electrostatic transducer, wherein the grille is made of a material that matches or is visually compatible with a material of the vehicle interior component.

2. The electrostatic speaker of claim 1, wherein the material of the grille is the same as the material of the vehicle interior component.

3. The electrostatic speaker of claim 1 or claim 2, wherein the grille cover material corresponds to a breathable fabric.

4. The electrostatic speaker of claim 3, wherein the breathable fabric corresponds to any one or more of the following: a woven textile material; a perforated or porous leather; or perforated or porous leathersubstitute material.

5. The electrostatic speaker of any preceding claim, wherein the audio signal lies in a frequency range between 125 Hz to 50 kHz.

6. The electrostatic speaker of claim 5, wherein the audio signal includes the frequency range between 1 to 2 kHz.

7. The electrostatic speaker of any of claims 1 to 6, wherein the vehicle interior component corresponds to any one of the following: a head restraint of a vehicle seat; an interior trim component of the vehicle; and a base portion of a vehicle seat.

8. A vehicle audio system comprising a plurality of electrostatic speakers according to any of claims 1 to 7.

9. The vehicle audio system of claim 8, wherein the plurality of electrostatic speakers are of different sizes and / or are disposed in different locations within the vehicle.

10. A vehicle comprising the electrostatic speaker of any of claims 1 to 7, or the vehicle audio system of claim 8 or claim 9.Application No: GB2416144.0 Examiner: Peter EasterfieldClaims searched: 1 to 10 Date of search: 14 March 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance Y 1-10 EP 2161948 Al (IVECO) whole document Y 1-10 US 11611818 Bl (MILLER et al) see col 1, lines 14-37 Y 1-10 US 2024 / 351531 Al SCHLEMMER et al) see paras [0011], [0012], [0042], [0043] Y 1-10 US 2023 / 232140 Al (MILLER et al) see paras [0003]-[0005] Y 1-10 US 2022 / 348147 Al (PREISLER et al) whole document Y 1-10 US 2007 / 187173 Al (PRICE) see paras [0001]-[0007] Y 1-10 WO 2020 / 225573 Al (WARWICK ACOUSTICS) whole documentCategories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKCX :Worldwide search of patent documents classified in the following areas of the IPC_____________B60N; B60R; H04R____________________________________________The following online and other databases have been used in the preparation of this search reportSEARCH-PATENTInternational Classification:Subclass Subgroup Valid From H04R 0019 / 02 01 / 01 / 2006 B60N 0002 / 879 01 / 01 / 2018 B60R 0011 / 02 01 / 01 / 2006

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