Electroacoustic transducer

Abstract

A description is given of an electroacoustic transducer (1), in particular bending wave transducer, having at least a bending-resistant acoustic diaphragm (2) and a structure-borne noise transducer (3) that excites the acoustic diaphragm (2) to vibrate. To achieve improved acoustics, it is proposed that the acoustic diaphragm (2) comprises a synthetic resin-coated support material (4), the sound emission surface (5) of which is formed of at least two, in particular at least three, layers of synthetic resin (6) that are bonded materially to one another without any bonding means.

Description

[0001] Electroacoustic transducer

[0002] Technical area

[0003] The invention relates to an electroacoustic transducer, in particular a bending wave transducer, with at least one rigid sound membrane and a structure-borne sound transducer that excites vibrations in the sound membrane.

[0004] State of the art

[0005] Electroacoustic transducers, also known as flat-panel loudspeakers or exciters, utilize a structure-borne sound transducer equipped with a voice coil operating according to the electrodynamic principle. This transducer is mechanically attached to the sound membrane, which can be formed by any sound-emitting body. The second part of the structure-borne sound transducer is typically mounted on a second part, which is also mechanically attached to the sound membrane, vibrating perpendicular to the sound-emitting surface of the sound membrane. The structure-borne sound transducer converts electrical signals into kinetic energy and transmits it to any vibrating surface, such as a bed, sofa, mirror, cupboard, shelf, or even screen. This allows for the realization of particularly very low frequencies, which conventional subwoofers struggle with.

[0006] The mechanical properties of the sound-emitting surface of the sound membrane are primarily responsible for usable sound emission. The sound membrane can only transmit tones or sounds if it vibrates mechanically and has a corresponding residual stress, in particular, residual stress that increases the flexural rigidity. The sound membrane must therefore be at least sufficiently rigid to be suitable for sound emission. An electroacoustic transducer used to excite a plate-shaped sound membrane or a screen to vibrate for the purpose of sound emission is known, for example, from WO 9709842 A2, WO 9709853 A2, and WO 9709698 A1. DE102007003165 A1 discloses a correction element for adapting the vibration behavior of the vibration system consisting of a sound membrane and a structure-borne sound transducer.

[0007] DE 102008059312 A1 discloses a further electroacoustic transducer, in particular a bending wave transducer, having at least one sound membrane and at least one vibration exciter generating transverse bending waves in the sound membrane, wherein the sound membrane is a rigid, approximately rectangular plate body which is mounted in the region of two opposite edges, wherein at least one bearing is designed as a damping part which stationary receives an edge region.

[0008] According to the teaching of WO 9937121 A1, acoustic transducers are mounted on panel elements in such a way that the associated surface vibrations act on the panel elements and their resonance mode distribution is utilized. WO 9952322 A1 by the same applicant shows a resonant multimode acoustic panel in which a transducer is mounted. The acoustic panel has a cavity that absorbs and modulates the sound radiation emitted by the panel surface. An audiovisual device with a flat element designed to display image information, which can be controlled to emit light, and with a flat, rigid element designed to emit sound information, the sound membrane, which can be excited to transverse bending vibrations and thus to emit sound, is disclosed in DE 102004032223 A1, according to the teaching of which the sound-emitting element is designed essentially coextensive with the light-emitting element.

[0009] From DE102015104478 A1 a flat loudspeaker is known with at least two essentially flat sound membranes of different sizes, which are each received at the edge in a border and which are each excited by an electrodynamic transducer, i.e. a structure-borne sound transducer, to generate bending waves on the respective sound membrane, wherein the membranes are each formed from a rigid polystyrene plate coated on both sides, which is connected to its respective border via an elastic edge connection in the manner of a conventional cone loudspeaker.

[0010] A particular disadvantage of the previously known electroacoustic transducers is that the sound they produce offers only moderate listening pleasure and that the achievable frequency response in the audible range is nowhere near that of conventional HIFI loudspeakers.

[0011] Description of the invention

[0012] The invention is therefore based on the object of providing an electroacoustic transducer of the type described at the outset, which is characterized by improved sound reproduction, preferably independent of the geometry of the sound membrane, which does not necessarily have to be that of a flat plate.

[0013] The invention achieves the stated object in that the sound membrane comprises a synthetic resin-coated carrier material, the sound emission surface of which is formed by at least two, in particular by at least three, synthetic resin layers which are bonded to one another without the use of a connecting agent.

[0014] Depending on the type of carrier material, an adhesion promoter can be arranged between the carrier material and the first synthetic resin layer. It is important that the sound membrane comprises a synthetic resin-coated carrier material, the sound emission surface of which is formed by at least two, in particular at least three, synthetic resin layers that are bonded to one another without the use of a connecting agent. This means that no separate adhesion promoter is provided between these synthetic resin layers. The individual layers preferably consist of one and the same synthetic resin. The synthetic resin layers are not simply glued to one another; glued layers do not form a bond with one another, but are applied one after the other within a corresponding time window in such a way that they are ultimately bonded to one another. This means that the synthetic resin layers can be applied without the use of a separate adhesion promoter orare held together by atomic or molecular forces without foreign adhesive and can no longer be separated from one another without destruction. To achieve this, the second and any subsequent layers must always be applied before the resin mixed with a hardener of the previous layer has fully crosslinked. At this point, the previous layer must already be partially crosslinked to such an extent that, on the one hand, the required material-locking layer connection is formed and, on the other hand, the partially crosslinked layer is already dimensionally stable enough that no undesirable surface irregularities develop when the next layer is applied. This creates a sound membrane which, in contrast to a single layer, is so rigid due to the mutual tensioning of the multiple individual layers that the sound membrane is particularly well suited to sound emission.The production of two or more synthetic resin layers, which are bonded together without the use of fasteners, creates a sound membrane in which tensions develop between the layers, acting analogously to the taut string of a musical instrument. Excellent sound emission characteristics have been measured when the sound-emitting surface comprises multiple synthetic resin layers. Currently, up to ten layers have been tested. Determining a reasonable number of sound membranes and structure-borne sound transducers is the responsibility of the expert. The bonded synthetic resin layers can be finally coated with a conventional varnish if a special appearance is desired.

[0015] The synthetic resin of the synthetic resin layers is preferably based on a polymer system that can be crosslinked by polyaddition, preferably an epoxy system or a polyurethane system. In this context, "based" means that the synthetic resin can comprise, in addition to the polymer system, which generally comprises at least one hardener and at least one prepolymer, also additives such as fillers, dyes, etc. As the synthetic resin of the synthetic resin layers, a preferably 2-component epoxy system can comprise an amine-based hardener and / or a preferably 3-component polyurethane system can comprise a hardener based on blocked isocyanates. Both the epoxy resins and the polyurethane resins have proven particularly suitable for the intended application and deliver good results. The synthetic resin (thermoset) has the appearance of liquid glass during and after processing.

[0016] To adjust the hardness, mechanical, and optical properties, the synthetic resin of the synthetic resin layers can contain at least one further additive, such as an inorganic filler, for example, aluminum oxide. It has also been shown that the addition of an inorganic filler can reduce, in particular, the generally undesirable shrinkage of the cured synthetic resin layers without impairing the optical or acoustic properties of the sound membrane.

[0017] The carrier material can be virtually any material of any geometry suitable for being covered with the bonded synthetic resin layers, in particular a composite material in a sandwich construction, a textile, a hollow body, a body made of glass-fiber-reinforced plastic, and / or a wooden body. So-called Dibond panels, a rigid composite material in a sandwich construction, have proven particularly suitable as a carrier material. Dibond panels typically comprise two aluminum cover layers with a polyethylene core embedded between them. The sound membrane or electroacoustic transducer is ultimately, for example, a painting, a sculpture, wall or ceiling paneling, or the like.

[0018] In a simple case, a commercially available structure-borne sound transducer can be attached to the sound membrane and rigidly connected to it, for example by gluing. However, since this option is not always available, it can be advantageous if the structure-borne sound transducer is connected to the sound membrane via a connection element that is attached to the sound membrane or integrated into the sound membrane. This connection element forms an adapter to which the structure-borne sound transducer can be connected. The connection element is geometrically designed in such a way that it can be optimally connected to the sound membrane on the one hand and to the structure-borne sound transducer on the other, and that the sound waves generated by the structure-borne sound transducer can be introduced into the sound membrane with as little unwanted loss as possible.

[0019] In order to be able to introduce the sound waves into the sound membrane even at particularly exposed points where there would be no space for mounting the structure-borne sound transducer, the structure-borne sound transducer can be connected to the connecting element via a coupler and the structure-borne sound transducer can be arranged at a distance of 2 to 800 mm from the sound membrane, which distance is bridged by the coupler. In a simple case, the coupler is a rod with one end attached to the connecting element and the other end to the structure-borne sound transducer. The coupling (rod) can in turn be connected to the structure-borne sound transducer via a corresponding connecting element. A suitable connecting element (adapter) can therefore be provided between the coupler and the carrier material and between the coupler and the structure-borne sound transducer in order to ensure a clean introduction of the structure-borne sound from the structure-borne sound transducer into the sound membrane.It is also conceivable to couple the two connection elements directly to one another, i.e. without an intermediate coupling, for example by means of a screw cap, bayonet lock or the like.

[0020] Particularly if a coupling is provided, but not exclusively for this case, it is recommended that the structure-borne sound transducer is suspended in a housing of the electroacoustic transducer so that it can vibrate freely with respect to the sound membrane. A spring suspension for the structure-borne sound transducer or a suspension in the manner of a microphone spider or similar is recommended for this. If the electroacoustic transducer comprises a carrier material in sandwich construction comprising two metal, in particular aluminum, layers, between which an electrically insulating core is arranged, the electrical lines leading from a connection point to the structure-borne sound transducer can be incorporated into at least one of the two metallic layers like a circuit board. The carrier material, i.e. the metallic layer itself, thus forms a circuit board with which electrical signals are conducted from a suitable connection point to the structure-borne sound transducer.For example, current-carrying lines are incorporated into the metallic layer by removing material between the conductors. The transmission of music, speech, or sound expertise to an amplifier, possibly located in the electroacoustic transducer and connected to the connection points by suitable means, takes place via Bluetooth, Wi-Fi, or cable.

[0021] In order to further improve the design and repair options for the electrical contact between the structure-borne sound transducer and the circuit board or between the circuit board and an electrical signal generator, it is proposed that the negative or positive contact pole of the connection point on the circuit board and / or the negative or positive contact pole of a contact point of the structure-borne sound transducer are each formed by an adhesive electrode electrically connected to a respective negative electrical line or positive electrical line. As a result of these features, any electrical solder connections that can no longer be removed non-destructively can be eliminated. Another advantage is that the adhesive electrodes allow the local arrangement of the corresponding negative or positive connection point on the circuit board to be largely freely selected, thus enabling a high degree of flexibility in the arrangement of those connection points.The adhesive electrode, which can be bonded to the metal surface, is constructed in a manner similar to that used, for example, in connection with electrode pads used in TENS or EMS therapy applications. For example, the electrode base can be formed from a silicone matrix or similar material, into which fillers required for electrical conductivity are embedded. Various carbon-based fillers, particularly carbon black, graphite, or carbon nanotube particles, or metal-based fillers or suitable inorganic fillers, can be used as fillers. It goes without saying that the adhesive electrode has a corresponding cable connection or similar.

[0022] Particularly in cases where the electroacoustic transducer is exposed to severe climatic or thermal fluctuations, it may be necessary to enclose the structure-borne sound transducer in a gas-tight enclosure filled with an inert gas such as helium. This prevents oxidation, particularly on the voice coil and iron core of the structure-borne sound transducer, even if it exhibits various hairline cracks after heavy use, thus increasing the service life of the electroacoustic transducer.

[0023] To improve the low-frequency response, the structure-borne sound transducer can be arranged between the sound membrane and a bass reflex bell to form a bass reflector. The bass reflex bell is arranged, in particular, in a housing of the electroacoustic transducer, and the free edge of the bell is attached to the sound membrane without contact, so that the free edge of the bell does not touch the sound membrane during sound emission, and a pressure chamber is formed between the sound membrane and the volume spanned by the bell. The bass reflex bell can be attached to the structure-borne sound transducer via a holding device.

[0024] A method according to the invention for producing a sound membrane is characterized in that a first synthetic resin layer is first applied to a sound-emitting surface of a molding substrate. After that, before the first synthetic resin layer has completely cured, a second synthetic resin layer is applied to the first synthetic resin layer in such a way that the first and second synthetic resin layers are bonded together without the use of a bonding agent. After that, if necessary, a third or successive synthetic resin layer(s) are applied in the same way to the previously applied synthetic resin layer. The above-mentioned features and properties of the sound membrane and thus of the synthetic resin layers apply analogously.

[0025] According to one embodiment, a first synthetic resin layer is first applied to the molding substrate. The synthetic resin used is a 2-component epoxy system with an amine-based hardener and / or a preferably 3-component polyurethane system with a hardener based on blocked isocyanates, for example flooring resins from Gobbetto (e.g. DEGA POLIEPO GC 505 EXTRA). Preferably 2 or 3-component means that various additives can be present, such as an inorganic additive. For processing, the resin is further diluted with high-percentage alcohol. During processing, the substrate is continuously vibrated with a vibrator. For the first synthetic resin layer, a quantity of 1.2 to 3.2, in particular 2 to 2.4 and particularly preferably 2.2 kg / m 2 (kilograms of resin per m 2 carrier material).

[0026] Subsequently, before the first synthetic resin layer has completely cured, a second synthetic resin layer is applied to the first synthetic resin layer in such a way that the first and second synthetic resin layers are bonded together without the use of a bonding agent. For this purpose, the second or each subsequent synthetic resin layer must be applied within a time window of 6.5-8 hours, in particular 7-7.5 hours, after the application of the first or previous synthetic resin layer. The exact time is determined in particular by the process temperature or the ambient temperature and the relative humidity. For the second and each subsequent synthetic resin layer, a quantity of 0.6 to 1.2, in particular 0.8 to 1 and particularly preferably 0.9 kg / m 2 (kilograms of resin per m 2 carrier material).

[0027] Preferably, several synthetic resin layers up to a total thickness of 3.5 mm can be applied to the carrier material. The invention also relates to a sound membrane produced by the described method.

[0028] Brief description of the invention

[0029] The drawing shows an example of the subject matter of the invention.

[0030] Fig. 1 shows a section of an electroacoustic transducer with a rigid sound membrane and a structure-borne sound transducer in cross section,

[0031] Fig. 2 a design variant of an electroacoustic transducer in cross section,

[0032] Fig. 3 a design variant in which the structure-borne sound transducer is inserted into a gas-tight casing filled with an inert gas, in cross-section,

[0033] Fig. 4 a design variant in which the structure-borne sound transducer is arranged between the sound membrane and a bass reflex bell in cross section,

[0034] Fig. 5 a design variant in which electrical lines leading to the structure-borne sound transducer are incorporated into a metallic layer of the carrier material in rear view,

[0035] Fig. 6 several design variants of an electroacoustic transducer in various views,

[0036] Fig. 7 shows a corner region of a panel-shaped electroacoustic transducer in cross section and

[0037] Fig. 8 shows the corner area from Fig. 7 with flanks bent backwards from the sound emission surface.

[0038] Ways to implement the invention

[0039] The invention relates to an electroacoustic transducer 1, in particular a flexural wave transducer, having at least one rigid sound membrane 2 and a structure-borne sound transducer 3 which excites vibrations in the sound membrane 2. The sound membrane 2 comprises a synthetic resin-coated carrier material 4, the sound emission surface 5 of which is formed by at least two, in particular at least three, synthetic resin layers 6 forming the synthetic resin coating of the carrier material 4, which are bonded to one another without the use of a connecting agent.

[0040] The synthetic resin of the synthetic resin layers 6 is based either on an epoxy system with an amine hardener or on a polyurethane system with a hardener based on blocked isocyanates. More than three synthetic resin layers 6 can also be provided. The synthetic resin of the synthetic resin layers 6 comprises at least one further additive, such as a filler and / or nucleating agent.

[0041] The carrier material 4 can be a composite material in a sandwich construction with two approximately 0.3 millimeter-thick aluminum layers between which a polyethylene core is embedded, a textile, a body made of glass fiber-reinforced plastic, or a wooden body. In particular, Fig. 6 shows several design variants of an electroacoustic transducer in various views, namely a pair of trousers (left), a picture or wall panel (top right), or a sculpture (bottom right), all of which form the carrier material coated with at least two synthetic resin layers 6 that are bonded together without the use of fasteners.

[0042] The structure-borne sound transducer 3 is connected to the sound membrane 2 via a connection element 7 that is fastened to the sound membrane 2 or integrated into the sound membrane 2. According to the exemplary embodiments according to Fig. 3 and 4, the structure-borne sound transducers 3 are fastened directly to the sound membrane 2, in particular glued thereto. According to the exemplary embodiments according to Fig. 1 and 2, the structure-borne sound transducers 3 are either inserted directly into a milled recess in the back of the sound membrane (Fig. 1) or connected to the sound membrane 2 via a connection element 7 integrated into the sound membrane 2 (Fig. 2). In particular, the connection element 7 can be cast into a recess in the sound membrane 2 for secure anchoring. The structure-borne sound transducer 3 is connected to the connection element 7 via a coupling 8, here a threaded rod, wherein the structure-borne sound transducer 3 can be arranged at a distance of 2 to 800 mm from the sound membrane 2.The structure-borne sound transducer 3 can be suspended in a housing 10 of the electroacoustic transducer by means of springs 9, allowing it to vibrate freely relative to the sound membrane 2. According to Fig. 2, the coupling 8 is a rod that engages at one end with the connection element 7 to the sound membrane and at the other end with the structure-borne sound transducer 3 via a further connection element 7. The coupling 8 is in turn connected to the structure-borne sound transducer via a correspondingly adapted connection element 7 in order to ensure a clean introduction of the structure-borne sound from the structure-borne sound transducer 3 into the sound membrane 2.

[0043] For the electroacoustic transducer 1, a carrier material 4 in sandwich construction comprising two metal layers 11, in particular aluminum layers, between which an electrically insulating core 12 is arranged, wherein the electrical lines leading from a connection point 13 to the structure-borne sound transducer 3 are incorporated in the manner of a circuit board in at least one of the two metallic layers 11 (Fig. 5).

[0044] According to a further embodiment shown in Fig. 6, both the negative and positive contact poles of the connection point (13) and the negative and positive contact poles of a contact point (3a) of the structure-borne sound transducer (3) are each formed by an adhesive electrode (13a) electrically connected to a respective negative electrical line (11a) or positive electrical line (11b).

[0045] The structure-borne sound transducer 3 can be inserted into a gas-tight casing 15 filled with an inert gas 14 (Fig. 3).

[0046] In addition, the structure-borne sound transducer 3 can be used to form a

[0047] The bass reflector 16 can be arranged between the sound membrane 2 and a bass reflex bell 17, which is either suspended in the housing 10 via a holding means 18 or suspended from the structure-borne sound transducer 3 via a corresponding holding means, here a non-magnetic screw-nut combination. As is usual with conventional loudspeakers, the housing can be equipped with a sound-absorbing material to dampen unwanted sound reflections in the housing 10.

[0048] Figs. 7 and 8 show the production of the flanks of a panel, in particular a picture, mirror, or the like, which has a cross-sectional view of an edge region of a panel-shaped electroacoustic transducer and a cut V-groove 19, allowing the formation of a corner region with flanks bent backwards from the sound-emitting surface. The synthetic resin layers 6 thus also cover the flanks of the finished panel, with the flanks being bent like a film hinge around the metal layer 11 on the sound-emitting surface side, which is not completely cut through, or the carrier material 4, which is not completely cut through.

Claims

Patent claims 1. Electroacoustic transducer (1), in particular a bending wave transducer, with at least one rigid sound membrane (2) and a structure-borne sound transducer (3) that excites vibration in the sound membrane (2), characterized in that the sound membrane (2) comprises a resin-coated substrate material (4) whose sound emission surface (5) is formed by at least two, in particular at least three, resin layers (6) which are bonded together without fasteners.

2. Electroacoustic transducer according to claim 1, characterized in that the synthetic resin of the synthetic resin layers (6) is based on a polymer system crosslinkable by polyaddition, preferably an epoxy system or a polyurethane system.

3. Electroacoustic transducer according to claim 2, characterized in that the preferably 2-component epoxy system comprises an amine-based hardener and / or the preferably 3-component polyurethane system comprises a hardener based on blocked isocyanates.

4. Electroacoustic transducer according to one of claims 1 to 3, characterized in that the carrier material (4) is a composite material in sandwich construction, a textile, a hollow body, a body made of glass fiber reinforced plastic or a wooden body.

5. Electroacoustic transducer according to one of claims 1 to 4, characterized in that the structure-borne sound transducer (3) is connected to the sound membrane (2) via a connecting element (7) attached to or integrated into the sound membrane (2).

6. Electroacoustic transducer according to claim 5, characterized in that the structure-borne sound transducer (3) is connected to the connecting element (7) via a coupling (8) and that the structure-borne sound transducer (3) is arranged at a distance of 2 to 800 mm from the sound membrane (2).

7. Electroacoustic transducer according to claim 5 or 6, characterized in that the structure-borne sound transducer (3) is suspended freely oscillating in a housing (10) of the electroacoustic transducer (1) with respect to the sound membrane (2).

8. Electroacoustic transducer according to one of claims 1 to 7 with a carrier material (4) in sandwich construction comprising two metal layers (11), in particular aluminium layers, between which an electrically insulating core (12) is arranged, characterized in that the connection point (13) electrical conductors leading to the structure-borne sound transducer (3) are incorporated into at least one of the two metal layers (11) in the manner of a circuit board.

9. Electroacoustic transducer according to claim 8, characterized in that the negative or positive contact pole of the connection point (13) and / or the negative or positive contact pole of a contact point (3a) of the structure-borne sound transducer (3) are each formed by an adhesive electrode (13a) electrically connected to a respective negative electrical line (11a) or positive electrical line (11b).

10. Electroacoustic transducer according to one of claims 1 to 9, characterized in that the structure-borne sound transducer (3) is inserted into a gas-tight shell (15) filled with an inert gas (14).

11. Electroacoustic transducer according to one of claims 1 to 10, characterized in that the structure-borne sound transducer (3) is arranged between the sound membrane (2) and a bass reflex bell (17) to form a bass reflector (16).

12. Method for producing a sound membrane for an electroacoustic transducer according to one of claims 1 to 11, characterized in that a first layer of synthetic resin is first applied to a sound-emitting surface of a shaping support material, after which, before the first layer of synthetic resin has completely hardened, a second layer of synthetic resin is applied to the first layer of synthetic resin in such a way that the first and the second layers of synthetic resin are bonded together without the use of any connecting agent, after which, if necessary, a third or successive layer(s) of synthetic resin are applied to each of the previously applied layers of synthetic resin in the same manner.

13. Method according to claim 12 characterized in that for the first synthetic resin layer an amount of 1, 2 to 3.2, in particular of 2 to 2.4 and particularly preferably of 2.2 kg / m² is used. 2 and for the second and each subsequent layer of synthetic resin, an amount of 0.6 to 1.2, in particular 0.8 to 1 and particularly preferably 0.9 kg / m² 2 is used, wherein the carrier material is preferably vibrated with a vibrator during the processing of the synthetic resin layer.

14. Method according to claim 12 or 13 characterized in that several layers of synthetic resin up to a total thickness of 3.5 mm are applied to the substrate material.

15. Sound membrane obtainable by a method according to claim 11 or 12.

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