Electroacoustic transducer

Abstract

An electroacoustic transducer 1, particularly a flexural wave transducer, comprising at least one bend-resistant acoustic diaphragm 2 and a solid-state acoustic converter 3 for exciting this acoustic diaphragm 2 is described. In order to achieve an improved acoustic situation, it is proposed that this acoustic diaphragm 2 comprises a support material 4 coated with a synthetic resin, and that its acoustic output surface 5 is composed of at least two, particularly at least three, synthetic resin layers 6 which are joined to one another in a material-bonded form without joining means.

Description

Technical Field

[0001] The present invention relates to an electroacoustic transducer including at least one bend-resistant acoustic diaphragm and a solid-state acoustic transducer for exciting the acoustic diaphragm, and particularly to a flexural wave transducer.

Background Art

[0002] Electroacoustic transducers, or otherwise planar speakers or exciters, utilize solid-state acoustic transducers having a movable coil operating on the principle of electrodynamics, which are mechanically fixed to an acoustic diaphragm that can be constituted by any acoustic output object. The first part of this solid-state acoustic transducer is pivotally supported in a manner that vibrates at a right angle to the acoustic output surface of the acoustic diaphragm on a second part that is also usually mechanically fixed to the acoustic diaphragm. The solid-state acoustic transducer converts an electrical signal into kinetic energy and transmits it to any vibratable surface such as a bed, sofa, mirror, cabinet, storage, rack, or screen. Thereby, in particular, very low frequencies that are problematic in conventional subwoofers can be realized.

[0003] In particular, the mechanical characteristics of the acoustic radiation surface of the acoustic diaphragm are responsible for useful acoustic output. The acoustic diaphragm can transmit sound or acoustics only when it vibrates mechanically and thus has corresponding residual stress, i.e., residual stress that particularly increases the flexural rigidity. That is, the acoustic diaphragm must be at least bend-resistant for the acoustic diaphragm to be suitable for acoustic output.

[0004] Electroacoustic transducers that play a role in exciting a plate-shaped acoustic diaphragm or screen for the purpose of outputting sound are well-known, for example, from Patent Documents 1 to 3. Patent Document 4 discloses a correction member for adjusting the vibration behavior of a vibration system composed of an acoustic diaphragm and a solid-state acoustic transducer.

[0005] Patent Document 5 discloses another electroacoustic transducer, particularly a flexural wave transducer, comprising at least one acoustic diaphragm and at least one exciter for generating a lateral flexural wave in the acoustic diaphragm. The acoustic diaphragm is a rigid, substantially rectangular plate-like object pivotally supported within the regions of two mutually opposing peripheral edges, and at least one bearing is configured as a damping portion for accommodating one end region in a position-fixed form.

[0006] According to the teachings of Patent Document 6, an acoustic transducer is mounted on a panel member such that surface vibrations associated with the member act on the panel member, utilizing the resonance mode distribution of the member. Patent Document 7 of the same applicant presents a resonant multimode acoustic plate on which the transducer is mounted. The acoustic plate has a cavity for receiving and modulating acoustic radiation waves emitted from the panel surface. Patent Document 8 discloses an audio-visual device comprising a flat member configured to display image information and drivable to emit light, and a flat and bend-resistant acoustic diaphragm configured to output audio information and excitable to generate lateral flexural vibrations and thus acoustic radiation waves. According to its teachings, the acoustic output member is configured to have substantially the same spread as the member that emits light.

[0007] According to Patent Document 9, a planar speaker comprising at least two substantially flat acoustic diaphragms of different sizes is well-known. These diaphragms have their peripheral sides respectively accommodated within a frame and are each excited by an electrodynamic transducer, i.e., a solid-state acoustic transducer, to generate a flexural wave in each acoustic diaphragm. The diaphragms are each composed of a bend-resistant polystyrene panel coated on both sides, and the panel is joined to each frame via an elastic peripheral connection in the form of a conventional cone speaker.

[0008] In those known electroacoustic transducers, particularly, the acoustic pattern output therefrom provides only a moderately comfortable feeling to the ear, and the frequency response achievable within the audible band is far from that of a conventional HIFI speaker, which are specific drawbacks.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Summary of the Invention

Problems to be Solved by the Invention

[0010] From the above, the problem of the present invention is, advantageously, to present an electroacoustic conversion device of the type described at the beginning, characterized by improved acoustic reproduction, which is not necessarily related to the geometric shape of the acoustic diaphragm that does not have to be flat.

Means for Solving the Problems

[0011] The present invention solves the set problem in that the acoustic diaphragm has a support material coated with a synthetic resin, and its acoustic output surface is composed of at least two, in particular at least three, synthetic resin layers joined to each other in a material joining form without joining means.

[0012] Depending on the type of the support material, an adhesion promoter can be arranged between the support material and the first synthetic resin layer. It is important that this acoustic diaphragm has a support material coated with a synthetic resin, and its acoustic output surface is composed of at least two, in particular at least three, synthetic resin layers joined in a material bonding form to each other without joining means, which means that no separate adhesion promoter is provided between these synthetic resin layers. These individual layers are preferably composed of the same synthetic resin. These synthetic resin layers are not simply adhered to each other, but rather, instead of these adhered layers overlapping to form a material bond, they are applied successively within a corresponding time period and finally joined to each other in a material bonding form. This means that the synthetic resin layers are bonded to each other by atomic or molecular forces without a separate adhesion promoter or a foreign adhesive and can no longer be separated from each other without breaking. For this purpose, the second layer and, optionally, subsequent layers must always be applied to the previous layer before the previous layer is mixed with a curing agent and cured to be fully cross-linked. At this point, on the one hand, the bonding of the layers in the required material bonding form is formed, and on the other hand, the shape of the partially cross-linked layer is already sufficiently stable or must already be partially cross-linked so that when applying the next layer, the previous layer does not form unwanted surface irregularities. Thereby, different from a single layer, a bending-resistant acoustic diaphragm is realized by the mutual tension of a plurality of individual layers, and this acoustic diaphragm is particularly suitable for acoustic output. When manufacturing two or more synthetic resin layers joined in a material bonding form without joining means, an acoustic diaphragm with stress formed between these layers is obtained, and this stress has the same effect as the stretched strings of a musical instrument. When the acoustic output surface has a plurality of synthetic resins, excellent audio output behavior has been observed. Currently, up to 10 layers have been tested. The determination of a significant number of the acoustic diaphragm and the solid-state acoustic transducer is the responsibility of those skilled in the art. If a special appearance is desired, the synthetic resin layers joined in a material bonding form can finally be coated with a conventional lacquer.

[0013] The synthetic resin of these synthetic resin layers is preferably based on a polymer system that can be crosslinked by polyaddition, preferably an epoxy-based or polyurethane-based system. In this context, "based on" means that the synthetic resin can generally contain, in addition to a polymer system having at least one curing agent and at least one prepolymer, additives such as fillers, colorants, and materials equivalent thereto.

[0014] The synthetic resin of these synthetic resin layers is preferably one or more of a two-component epoxy system having an amine-based curing agent and a three-component polyurethane system having a curing agent preferably based on blocked isocyanate. Both epoxy resin and polyurethane resin have been proven to be particularly suitable for the purposes of the present invention and have produced good results. This synthetic resin (thermosetting material) exhibits the appearance of liquid glass during and after processing.

[0015] In order to set the hardness, mechanical properties, and optical properties, the synthetic resin of these synthetic resin layers can have at least one other additive, such as an inorganic filler, for example, aluminum oxide. Furthermore, it has been clarified that by adding an inorganic filler, it is possible to reduce the generally undesirable shrinkage of the cured synthetic resin layer without impairing the optical or acoustic properties of the acoustic diaphragm in particular.

[0016] This support material can be substantially any material of any geometric shape suitable for covering with synthetic resin layers joined in a material-bonded form, in particular, a solid made of a sandwich-structured composite material, fabric, hollow body, glass fiber-reinforced plastic, and / or a wooden solid. It has been proven that a so-called dibond panel, which is a hard composite material with a sandwich structure, is particularly suitable as a support material. A dibond panel usually has two aluminum cover layers, between which a polyethylene core is embedded. This acoustic diaphragm or electroacoustic transducer can ultimately become, for example, a painting, sculpture, wall panel, ceiling panel, or the like.

[0017] In simple cases, commercially available solid-state acoustic transducers can be attached to the acoustic diaphragm and firmly joined to the plate, for example, with an adhesive. However, since this method is not always possible, it can be considered advantageous for this solid-state acoustic transducer to be connected to the acoustic diaphragm via a connecting member fixed to or integrated with the acoustic diaphragm. In this case, the connecting member constitutes an adapter to which the solid-state acoustic transducer can be connected. This connecting member can, on the one hand, be connected to the acoustic diaphragm as well as possible, and on the other hand, be connected to the solid-state acoustic transducer as well as possible, and is configured in a geometric shape such that the sound waves generated by the solid-state acoustic transducer can be introduced into the acoustic diaphragm with as little unintended loss as possible.

[0018] Even in locations where there is no space to install the solid-state acoustic transducer, especially in exposed areas, in order to be able to introduce sound waves into the acoustic diaphragm, this solid-state acoustic transducer can be connected to the connecting member via a coupler, and this solid-state acoustic transducer can be arranged at an interval of 2 to 800 mm from the acoustic diaphragm, and this interval can be bridged by the coupler. In simple cases, this coupler is a rod with one end locked to the connecting member and the other end locked to the solid-state acoustic transducer. This coupler (rod) can also be connected to the solid-state acoustic transducer via a corresponding connecting member. That is, in order to ensure a clearer introduction of the solid-state sound from the solid-state acoustic transducer to the acoustic diaphragm, suitable connecting members (adapters) can be provided between the coupler and the support material and between the coupler and the solid-state acoustic transducer, respectively. It is also conceivable to connect these two connecting members directly, that is, without an intermediate connected coupler, using, for example, a threaded plug, a plug-in joint, or equivalents thereof.

[0019] In particular, when a coupler is provided (although not limited to this case), it is recommended that this solid-state acoustic transducer be suspended in the housing of the electroacoustic conversion device in a form that vibrates freely with respect to the acoustic diaphragm. For this purpose, a spring suspension for this solid-state acoustic transducer, a suspension in the form of a microphone spider, or equivalents thereof are recommended.

[0020] When this electroacoustic transducer has a support material with a sandwich structure including two metal layers, in particular aluminum layers, with an electrically insulated core disposed therebetween, the electrical conductors leading from the connection points to the solid-state acoustic transducer can be incorporated into at least one of the two metal layers in the form of a circuit board. That is, this support material, i.e., the metal layer itself, constitutes a circuit board for transmitting an electrical signal from a suitable connection point to the solid-state acoustic transducer. For this purpose, for example, the conductors through which electricity passes are incorporated into the metal layer by removing the material between those conductors. In some cases, the transmission of music, voice, or special sounds to an amplifier disposed within the electroacoustic transducer and connected to the connection points using suitable means is performed via Bluetooth, Wi-Fi, or a cable.

[0021] In order to further improve both the method of constructing and repairing the electrical contact portions between this solid-state acoustic transducer and the circuit board or between the circuit board and the electrical signal transmitter, it is proposed that each of the negative or positive contact electrodes at the connection points on the circuit board and / or the negative or positive contact electrodes at the contact points of the solid-state acoustic transducer be constituted by adhesive electrodes electrically connected to their respective negative or positive electrical conductors. Due to these features, in some cases, electrical soldering connections that can no longer be separated without being damaged can be omitted. Furthermore, by using the adhesive electrodes, in particular, the local arrangement configuration of the corresponding negative or positive connection points on the circuit board can be selected quite freely, and as a result, the advantage of achieving high flexibility in the arrangement configuration of each connection point can be obtained. The structure of the adhesive electrode that can be attached to this metal surface is, for example, similar to those well-known in TENS or EMS type therapeutic applications in relation to electrode pads. For example, the base material of the electrode can be composed of a silicone matrix embedded with a filler that requires electrical conductivity. As the filler, for example, various carbon-based fillers, in particular, particles of carbon black, graphite, or carbon nanotubes, or alternatively metal-based fillers or suitable inorganic fillers can be used. It goes without saying that this adhesive electrode is provided with corresponding cable terminals and the like.

[0022] In particular, when this electroacoustic transducer is exposed to large climate variations or thermal variations, it may be necessary to house the solid-state acoustic transducer in a hermetically sealed case filled with an inert gas such as helium. Thereby, even when various hairline cracks occur due to severe use, in particular, oxidation of the movable coil and iron core of the solid-state acoustic transducer is prevented, thereby extending the service life of the electroacoustic transducer.

[0023] To improve the behavior of extremely low frequencies, this solid-state acoustic transducer can be arranged between the acoustic diaphragm and the bass reflex bell to form a bass reflex. For this purpose, this bass reflex bell is arranged particularly within the housing of the electroacoustic transducer and is attached to the acoustic diaphragm so that the free end of this bell does not come into contact, and when sound is output, the free end of this bell does not come into contact with the acoustic diaphragm and a pressure chamber is formed between the acoustic diaphragm and the volume covered by the bell. This bass reflex bell can be fixed to the solid-state acoustic transducer via a holding device.

[0024] The method for manufacturing an acoustic diaphragm according to the present invention is that first, a first synthetic resin layer is applied to the acoustic output surface of the molding support material, and then, before the first synthetic resin layer is completely cured, a second synthetic resin layer is applied onto the first synthetic resin layer so that the first synthetic resin layer and the second synthetic resin layer are joined to each other in a material-bonded form without joining means. Thereafter, optionally, a third synthetic resin layer or, in succession, a plurality of synthetic resin layers are each similarly applied onto the previously applied synthetic resin layer.

[0025] The characteristics and properties of the synthetic resin layer of the above acoustic diaphragm apply similarly.

[0026] In one embodiment, first, a first synthetic resin layer is applied onto a support material for molding. As the synthetic resin, preferably, a two-component epoxy-based resin having an amine-based curing agent and / or a curing agent based on blocked isocyanate, for example, a three-component polyurethane-based resin having a flooring resin from Gobbetto (e.g., DEGA POLIEPO GC 505 EXTRA) is used. Preferably, "two-component" or "three-component" means that it can also have various additives such as inorganic additives. For this treatment, the resin is further diluted with a high percentage of alcohol. During this process, the support material is always vibrated using a vibrator. Regarding the first synthetic resin layer, 1.2 to 3.2 kg / m 2 , in particular, 2 to 2.4 kg / m 2 , particularly preferably, 2.2 kg / m 2 (kilograms of resin per 1 m 2 of the support material) is used.

[0027] Next, before the first synthetic resin layer is completely cured, the second synthetic resin layer is applied onto the first synthetic resin layer so that the first and the second synthetic resin layers are joined to each other in a material-bonded form without joining means. For this purpose, after the first or the previous synthetic resin layer is applied, it is necessary to apply the second or each separate synthetic resin layer within a time period of 6.5 to 8 hours, in particular, 7 to 7.5 hours. The exact time point is determined particularly by the processing temperature or the ambient temperature and relative humidity. Regarding the second and each separate synthetic resin layer, 0.6 to 1.2 kg / m 2 , in particular, 0.8 to 1 kg / m 2 , particularly preferably, 0.9 kg / m 2 (kilograms of resin per 1 m 2 of the support material) is used.

[0028] Preferably, a plurality of synthetic resin layers can be applied onto the support material up to a total thickness of 3.5 mm.

[0029] The present invention also relates to an acoustic diaphragm manufactured based on the method described herein.

[0030] Examples of the subject matter of the present invention are illustrated in the drawings.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0032] The present invention relates to an electroacoustic transducer 1, particularly a flexural wave converter, comprising at least one bend-resistant acoustic diaphragm 2 and a solid-state acoustic transducer 3 for exciting the acoustic diaphragm 2.

[0033] This acoustic diaphragm 2 comprises a support material 4 coated with a synthetic resin, and its acoustic output surface 5 is formed by at least two, particularly at least three, synthetic resin layers 6 that constitute the synthetic resin coating of the support material 4, and these layers are joined to each other in a material-bonded form without joining means.

[0034] The synthetic resin of these synthetic resin layers 6 is based on either an epoxy-based one with an amine-based curing agent or a polyurethane-based one with a curing agent based on blocked isocyanate. It is also possible to provide four or more synthetic resin layers 6. The synthetic resin of these synthetic resin layers 6 has at least one other additive such as a filler and / or a nucleating agent.

[0035] This support material 4 can be a composite material with a sandwich structure in which a polyethylene core is embedded between two round aluminum layers with a thickness of about 0.3 millimeters, a fabric, a solid made of glass fiber reinforced plastic, or a solid made of wood. In particular, FIG. 6 illustrates various structural variations of the electroacoustic transducer by means of various drawings, namely, the left pants, the upper right painting or wall panel, and the lower right sculpture, all of which illustrate a support material covered with at least two synthetic resin layers 6 joined to each other in a material bonding form without joining means.

[0036] This solid acoustic transducer 3 is connected to the acoustic diaphragm 2 via a connecting member 7 fixed to or integrated with the acoustic diaphragm 2. In the embodiments of FIGS. 3 and 4, the solid acoustic transducer 3 is directly fixed to the acoustic diaphragm 2, in particular, adhered thereto. In the embodiments of FIGS. 1 and 2, the solid acoustic transducer 3 is either directly inserted into a cutting groove on the rear side of the acoustic diaphragm (FIG. 1) or connected to the acoustic diaphragm 2 via a connecting member 7 integrated with the acoustic diaphragm 2 (FIG. 2). In particular, this connecting member 7 can be cast into a cavity of the acoustic diaphragm 2 for secure locking.

[0037] This solid-state acoustic transducer 3 is connected to the connecting member 7 via a coupler 8 (here a threaded rod), and at this time, this solid-state acoustic transducer 3 can be arranged at an interval of 2 to 800 mm with respect to the acoustic diaphragm 2. This solid-state acoustic transducer 3 can be suspended in the housing 10 of the electroacoustic conversion device in a form that vibrates freely with respect to the acoustic diaphragm 2 using a spring 9. In FIG. 2, the coupler 8 is a rod having one end locked to the connecting member 7 for the acoustic diaphragm and the other end locked to the solid-state acoustic transducer 3 via another connecting member 7. This coupler 8 is connected to the solid-state acoustic transducer via an appropriately adjusted connecting member 7 so as to ensure a clear introduction of the solid-state sound from the solid-state acoustic transducer 3 to the acoustic diaphragm 2.

[0038] Regarding this electroacoustic conversion device 1, the support material 4 can be configured in a sandwich structure composed of two metal layers 11, particularly aluminum layers, and an electrically insulating core 12 disposed therebetween, and an electrical conductor leading from the connection point 13 to the solid-state acoustic transducer 3 is incorporated in at least one of the two metal layers 11 in the form of a circuit board (FIG. 5).

[0039] In another embodiment shown in FIG. 6, the negative and positive contact electrodes of the connection point 13 and the negative and positive contact electrodes of the contact point 3a of the solid-state acoustic transducer 3 are each constituted by an adhesive electrode 13a electrically connected to the negative electrical conductor 11a or the positive electrical conductor 11b, respectively.

[0040] This solid-state acoustic transducer 3 can be housed in an airtight case 15 filled with an inert gas 14 (FIG. 3).

[0041] Furthermore, this solid-state acoustic transducer 3 can be arranged between the acoustic diaphragm 2 and the bass reflex bell 17 in order to form the bass reflex plate 16, and this bass reflex bell is suspended in the housing 10 via the holding means 18, or is suspended from the solid-state acoustic transducer 3 via corresponding holding means, here a combination of non-magnetic threaded bolts and nuts. As is common in conventional speakers, this housing can be provided with a sound-absorbing material in order to attenuate unwanted sound reflections within the housing 10.

[0042] Figs. 7 and 8 illustrate, by way of a cross-section in the peripheral region of a panel-shaped electroacoustic transducer, a panel which can be provided with a cut in the V-shaped groove 19 to form an edge region with the edge bent rearward from the acoustic output surface, in particular the production form of the edge of a painting, a mirror or the like. That is, these synthetic resin layers 6 also cover the edges of the finished panel, whereupon these edges are bent in the form of film hinges around the metal layer 11 on the side of the acoustic output surface which is not completely cut or around the support material 4 which is not completely cut.

Claims

1. An electroacoustic converter (1), particularly a bent wave converter, comprises at least one bend-resistant acoustic diaphragm (2) and a solid-state acoustic transducer (3) for exciting the acoustic diaphragm (2). The electroacoustic converter is characterized in that the acoustic diaphragm (2) has a support material (4) coated with synthetic resin, and its acoustic output surface (5) is composed of at least two, particularly at least three, synthetic resin layers (6) joined to each other in a material bonding manner without any bonding means.

2. In the electroacoustic converter according to claim 1, An electroacoustic converter characterized in that the synthetic resin of the aforementioned synthetic resin layer (6) is based on a polymer system that can be crosslinked by polyaddition, preferably an epoxy system or a polyurethane system.

3. In the electroacoustic converter according to claim 2, An electroacoustic converter characterized by one or more of the following: the epoxy system is preferably a two-component epoxy system having an amine-based curing agent; and the polyurethane system is preferably a three-component polyurethane system having a blocked isocyanate-based curing agent.

4. In the electroacoustic converter according to any one of claims 1 to 3, An electroacoustic converter characterized in that the support material (4) is a solid made of a sandwich-structured composite material, a woven fabric, a hollow body, or a glass fiber reinforced plastic, or a solid made of wood.

5. In the electroacoustic converter according to any one of claims 1 to 3, An electroacoustic converter characterized in that the solid-state acoustic transducer (3) is connected to the acoustic diaphragm (2) via a connecting member (7) that is fixed to the acoustic diaphragm (2) or integrated into the acoustic diaphragm (2).

6. In the electroacoustic converter according to claim 5, An electroacoustic converter characterized in that the solid-state acoustic transducer (3) is joined to a connecting member (7) via a coupler (8), and the solid-state acoustic transducer (3) is positioned at a distance of 2 to 800 mm from the acoustic diaphragm (2).

7. In the electroacoustic converter according to claim 5, An electroacoustic converter characterized in that the solid-state acoustic transducer (3) is suspended within the housing (10) of the electroacoustic converter (1) in such a manner that it vibrates freely relative to the acoustic diaphragm (2).

8. In the electroacoustic converter according to any one of claims 1 to 3, An electroacoustic converter comprising a support material (4) having a sandwich structure in which an electrical insulating core (12) is placed between two metal layers (11), particularly an aluminum layer, and an electrical conductor leading from a connection point (13) to a solid-state acoustic converter (3) is incorporated in the form of a circuit board into at least one of these two metal layers (11).

9. In the electroacoustic converter according to claim 8, An electroacoustic converter characterized in that each of the negative or positive contact electrodes of the connection point (13) and / or the negative or positive contact electrodes of the contact point (3a) of the solid-state acoustic converter (3) is composed of an adhesive electrode (13a) electrically connected to the respective negative electrical conductor (11a) or positive electrical conductor (11b).

10. In the electroacoustic converter according to any one of claims 1 to 3, An electroacoustic converter characterized in that the solid-state acoustic converter (3) is housed in an airtight case (15) filled with an inert gas (14).

11. In the electroacoustic converter according to any one of claims 1 to 3, An electroacoustic converter characterized in that the solid-state acoustic transducer (3) is positioned between the acoustic diaphragm (2) and the bass-reflecting bell-shaped body (17) to constitute a bass reflector (16).

12. A method for manufacturing an acoustic diaphragm for an electroacoustic converter according to any one of claims 1 to 3, A method characterized by first applying a first synthetic resin layer onto the acoustic output surface of a moldable support material, then, before the first synthetic resin layer is completely cured, applying a second synthetic resin layer on top of the first synthetic resin layer so that the first synthetic resin layer and the second synthetic resin layer are joined to each other in a material bonding manner without the need for bonding means, and then, optionally, applying a third synthetic resin layer or, in succession, a plurality of synthetic resin layers on top of the previously applied synthetic resin layer using the same method.

13. In the method according to claim 12, Regarding the first synthetic resin layer mentioned above, 1.2 to 3.2 kg / m ２ , especially 2-2.4 kg / m ２ 2.2 kg / m² is particularly advantageous. ２ The amount used is 0.6 to 1.2 kg / m² for each of the second synthetic resin layer and the other synthetic resin layer. ２ , especially 0.8-1 kg / m ２ The method is characterized in that, particularly advantageously, an amount of 0.9 kg / m2 is used, and in this case, the support material is preferably vibrated using a vibrator during the processing of the synthetic resin layer.

14. In the method according to claim 12, A method characterized by coating multiple synthetic resin layers onto a support material to a total thickness of 3.5 mm.

15. An acoustic diaphragm obtained by the method of claim 11.

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