Diaphragm with multiple thicknesses

Abstract

The invention relates to an acoustic diaphragm (16) intended to be coupled to a winding (20) that is movable via a coil support (22). The diaphragm (16) comprises a coupling portion (32) for the coil support that delimits a central portion and a peripheral portion. The diaphragm (16) has a central zone (38) extending in the central portion, having a first stiffness; and a reinforcing ring (40) comprising the coupling portion (32), having a second stiffness greater than the first stiffness, the first stiffness being between 5% and 65% of the second stiffness. The reinforcing ring (40) extends around the coupling portion (32), over 5 to 60% of the distance between the coupling portion (32) and the center (C) of the diaphragm, and over 50% to 100% of the distance between the coupling portion (32) and a peripheral edge of the diaphragm.

Description

Description Multi-layer membrane Technical Field

[0001] The present invention relates to the field of sound transducers, such as loudspeakers or microphones. More particularly, the invention relates to a diaphragm of an electrodynamic transducer. The invention also relates to an acoustic transducer comprising the diaphragm.

[0002] The invention finds multiple applications in fields where it is sought to obtain a transducer with sensitivity and / or bandwidth, that is to say a high ratio between the generated acoustic pressure and the voltage transmitted to the loudspeaker and / or a high frequency for the first mode of deformation of the diaphragm. Previous art

[0003] Acoustic transducers are devices that convert a physical signal, such as an electrical signal, into an acoustic wave, or vice versa. Examples of acoustic transducers include loudspeakers, earphones, headphones, and microphones.

[0004] We can distinguish four types of loudspeakers: bass loudspeakers called by the English terms "woofer" or "boomer"; midrange loudspeakers called "midrange"; treble loudspeakers also called by the English term "tweeter"; and wideband loudspeakers, reproducing a wide range of frequencies, often most of the audible spectrum (20 Hz-20000 Hz).

[0005] An electrodynamic loudspeaker typically consists of a voice coil mounted on a voice coil former. A diaphragm is mounted to the voice coil former, to which another voice coil is attached. The voice coil is usually located in the air gap of a magnetic motor comprising one or more permanent magnets and pole pieces that guide the generated magnetic field. The voice coil, placed in the magnetic field, is moved when an electric current passes through it, and this movement is transmitted to the diaphragm, thus converting the electrical signal into an acoustic wave.

[0006] The diaphragm is typically attached to the reel support at a central circular portion. The diaphragm is also connected to a fixed frame, such as a bowl, at its outer edge. This connection is achieved by a peripheral suspension which can be made of foam, rubber, or fabric, and can be hemispherical or flat in shape.

[0007] For the displacement force applied to the coil support to cause uniform movement of the diaphragm, the diaphragm must be sufficiently rigid. This is referred to as the pistonic movement of the diaphragm.

[0008] Conversely, if the membrane is not rigid enough, it deforms significantly, particularly at its resonant frequencies, impacting the induced harmonic distortion and the emitted sound wave. The frequency generating the membrane's first vibration mode is often referred to as the "breakup" in English-language literature.

[0009] In order to delay the "break-up" and ensure pistonic movement of the membrane up to very high frequencies (ideally > 20 kHz), we therefore seek to increase the rigidity of the membrane.

[0010] Furthermore, the heavier the diaphragm, the greater the electromagnetic force required to move it. At a constant acoustic electromagnetic force, a heavier diaphragm is said to have lower sensitivity. A diaphragm with good sensitivity is especially important for a headphone speaker, as the power handling is low.

[0011] In order to achieve the best acoustic performance, a loudspeaker, especially of the midrange, tweeter or full-range type, must have good sensitivity and pistonic movement over its entire frequency range.

[0012] Therefore, an acoustic membrane is sought that is rigid yet lightweight to limit distortions and ensure good sensitivity.

[0013] There are few materials that are both rigid and lightweight, with the exception of beryllium, which is very expensive and difficult to obtain. When other materials are used, manufacturers can adjust the frequency response, notably by changing the diaphragm thickness. In determining the thickness, the expert must then compromise between the diaphragm's rigidity, and therefore the speaker's bandwidth, and its sensitivity, which is related to its weight.

[0014] To lighten membranes while ensuring sufficient rigidity, it is known to use composites employing mixtures of thin, rigid and heavy materials on the surface and flexible and light materials on the inside, as illustrated in document US2006222201 A1. These solutions offer membranes with "sandwich" type structures with thicknesses on the order of a millimeter.

[0015] This is suitable for certain bass and midrange speakers. However, these solutions cannot be implemented in conventional headphone or tweeter speakers, for which the membrane thicknesses used are generally between 20 and 80 pm.

[0016] In document CN118018918A, another solution proposes sandwich-type structures adapted for tweeters that use a substrate such as magnesium, aluminum, or titanium, stiffened by a layer of amorphous carbon. These composites allow for high breakup, but when the density of the substrate material and / or the thickness of the substrate are increased, the diaphragms lose sensitivity.

[0017] US patent 4471028A discloses a membrane comprising a layer forming a reinforcing structure with hexagonal honeycomb-type openings to stiffen the membrane. The honeycomb structure reduces the layer's weight, but it is not optimal for stiffening the membrane in a purely radial direction, which is desirable to ensure pistonic motion up to a high breakup.

[0018] In US7315628B2, a membrane is described comprising at least three thick parts formed radially from a central part towards an outer periphery, and a semi-thick part formed between the thick parts which gradually thins from the outer periphery towards the central part of the membrane.

[0019] This solution offers good rigidity in the radial direction. However, it is poorly suited to loudspeakers, particularly full-range drivers and tweeters, which have a dome, inverted dome, M-shaped, or inverted M-shaped design. Adding material to the center increases the amplitude of the diaphragm's first vibration mode and therefore potentially increases distortion.

[0020] Finally, US patent 11323817B2 discloses a diaphragm comprising a skin formed from a low-density material and a frame integrated into the skin. The frame has a higher density than the skin and thus acts as a reinforcing structure, providing additional rigidity to the skin and increasing the rigidity of the diaphragm. The frame may include a plurality of openings formed between an outer and an inner edge of the frame. This solution is interesting but is not suitable for loudspeakers with a dome, inverted dome, M, or inverted M shape. Description of the invention

[0021] The invention aims to address at least one of the problems or drawbacks encountered in the prior art. In particular, the invention aims to provide an acoustic diaphragm with high breakup and good sensitivity, suitable for all types of loudspeakers, including tweeters, midrange drivers, full-range drivers, and headphone drivers. In other words, the invention aims to provide an acoustic diaphragm that is lightweight and sufficiently rigid for high-fidelity sound reproduction applications and suitable for full-range drivers and tweeters with a dome, inverted dome, M, or inverted M shape.

[0022] Accordingly to a first aspect, the invention relates to an acoustic membrane having an upper surface and an opposite lower surface, said membrane being intended to be coupled at its lower surface to a moving coil via a coil support; the membrane includes a coupling portion for the coil support which delimits a central portion and a peripheral portion of the membrane.

[0023] The membrane is remarkable in that it comprises a central zone extending into the central portion, having a first stiffness; and a reinforcing ring comprising the coupling portion, having a second stiffness greater than the first stiffness; and in that the reinforcing ring extends around the coupling portion, over 5 to 60% of the distance between the coupling portion and the center of the membrane, and over 50% to 100% of the distance between the coupling portion and a peripheral edge of the membrane.

[0024] Stiffness is the characteristic that indicates a body's resistance to elastic deformation. The stiffer a part is, the greater the force required to achieve a given deflection. Stiffness depends on the mechanical properties of a material and the dimensions of the body formed from that material.

[0025] It is generally known that an increase in membrane stiffness causes a proportional increase in the frequency of the membrane's first vibration mode. Research has shown that by increasing the membrane stiffness only in the reinforcement ring extending on either side of the coupling portion, the increase in the frequency of the membrane's first vibration mode is no longer proportional to the increase in stiffness but is significantly greater.

[0026] In other words, the reinforcing ring thus created causes an increase in the frequency of the membrane's first vibration mode, which is surprisingly greater than the increase in stiffness. It is therefore possible to obtain a membrane with a high breakup and good sensitivity compared to known membranes.

[0027] The resulting membranes can have a thickness of less than 100 µm. The solution proposed by the invention can therefore be adapted to membranes of all sizes, including membranes intended for midrange, tweeter, full-range speakers, or for headphones.

[0028] Advantageously, the first stiffness is between 5% and 65% of the second stiffness. Preferably, the first stiffness is between 5% and 10% of the second stiffness in the case of a multilayer membrane and between 10% and 40% in the case of a membrane composed of a single material with several layers.

[0029] Calculating the membrane's stiffness at any point depends on its dimensions. To define the stiffness, we assume a "section" normal to the membrane and consider its stiffness to be that of a beam to disregard its geometry.

[0030] The stiffness El of a beam comprising several layers is obtained by the following calculation:

[0031] [Math 1]

[0035] With :

[0036] Ai = Bti is the cross-sectional area of ​​the i-th layer and ti is its thickness;

[0037] And is the Young's modulus of the i-th layer in the longitudinal direction;

[0038] [Math 3] Sri ydA K = — is the vertical center of mass of the i-th layer; and

[0039] [Math 4] is the moment of inertia of the i-th section around its centroid.

[0040] To simplify, we consider that the width of each section of membrane that we wish to compare is equal and therefore that the term B is the same in the areas Ai of different stiffness and thickness.

[0041] It is thus understood that the thicker the membrane, the lower its elastic deformation, and consequently the higher its stiffness.

[0042] Thus, the difference in stiffness between the central zone and the reinforcing ring can be easily obtained by varying the thickness of the membrane between the central zone and the reinforcing ring.

[0043] Advantageously, the central zone comprises a thickness of between 35% and 90% of the thickness of the reinforcing ring. Preferably, the thickness of the central zone is between 60% and 70% of the thickness of the reinforcing ring.

[0044] Advantageously, the central zone has a thickness between 20 µm and 40 µm, and the reinforcing ring has a thickness between 30 µm and 80 µm respectively. These membranes are therefore suitable for small, wideband, headphone-type tweeters.

[0045] In embodiments of the invention, the membrane includes a fixing ring extending from the peripheral edge of the membrane to the reinforcing ring; and the fixing ring has a stiffness lower than the second stiffness.

[0046] The fixing ring helps to limit the weight at the end of the membrane. During the first vibration mode, the presence of the fixing ring allows control of the amplitude of membrane displacement at the peripheral edge.

[0047] Preferably, the stiffness of the fixing ring is equal to the first stiffness. The fixing ring can simply be made of the same material as the central area.

[0048] Advantageously, the fixing ring extends over a distance of less than 10% of the distance between the peripheral edge and the center of the membrane. The fixing ring is therefore sufficiently small to allow for significant stiffening of the membrane around the coupling portion.

[0049] In some embodiments, the membrane comprises a core including at least one layer of at least one first material, and the reinforcing ring includes at least one layer of at least one second material fixed to the core, the second material having a stiffness equal to or greater than the first material.

[0050] The reinforcing ring can then be formed simply by bonding an additional layer of material to the membrane core. The material of the additional layer can be chosen based on its mechanical properties to achieve optimal membrane performance.

[0051] Preferably, the core forms the central zone, and the core also forms the fixing ring. A single addition of material at the reinforcing ring thus allows all zones of the membrane to be formed.

[0052] Advantageously, the second material layer is fixed to the core on the lower surface of the membrane. The second material layer then has no visual impact on the membrane and does not degrade its perceived quality.

[0053] Advantageously, the second material layer is fixed to the core on the upper surface of the membrane.

[0054] According to a second aspect, the invention relates to an acoustic transducer comprising a chassis on which are mounted a magnetic motor and an acoustic membrane according to the first aspect. Brief description of the drawings

[0055] The invention will be well understood and other aspects and advantages will become clear upon reading the following description, given by way of example with reference to the attached drawings on which:

[0056] [Fig. 1] is a perspective and cross-sectional view of a loudspeaker comprising an acoustic membrane according to an embodiment of the invention;

[0057] [Fig. 2] is a lateral cross-sectional view along a radial plane of a membrane according to an embodiment of the invention;

[0058] [Fig. 3] is a lateral cross-sectional view along a radial plane of a membrane according to another embodiment of the invention;

[0059] [Fig. 4] is a lateral cross-sectional view along a radial plane of a membrane according to another embodiment of the invention;

[0060] [Fig. 5] is a bottom view of a membrane according to one embodiment of the invention. Detailed description of the invention

[0061] In the following description, the term "include" is synonymous with "include" and is not restrictive in that it allows for the presence of other elements in the desktop or module to which it refers. It is understood that the term "include" includes the terms "consist of".

[0062] An embodiment of an acoustic transducer 10, for example a loudspeaker, illustrated in [Fig. 1], comprises a chassis 12 on which a magnetic motor 14 and an acoustic diaphragm 16 are mounted. The loudspeaker 10 can be a bass, midrange, tweeter, or full-range loudspeaker. Preferably, the loudspeaker is a midrange, tweeter, or full-range loudspeaker.

[0063] The magnetic motor 14 includes an air gap 18 in which is housed a movable coil 20 wound around a coil support 22. In some cases of loudspeakers, for example of the wideband type, or for headphones, the coil 20 can be directly attached to the diaphragm 16 without using the coil support 22.

[0064] The acoustic membrane 16 has an upper surface 24 and an opposing lower surface 26. For the purposes of this description, the upper surface 24 of the membrane 16 is considered to be the surface oriented towards the sound emission space; while the lower surface 26 is opposite the magnetic motor 14 of the loudspeaker.

[0065] Membrane 22 can be a circular membrane or of any shape. Preferably, membrane 22 is a circular membrane with an "M" shaped profile as illustrated in [Fig. 2], or an inverted "M" as illustrated in [Fig. 3]. 3], or dome, or inverted dome. Generally speaking, the membrane has a center C, and a peripheral edge 28 shown in [Fig. 4],

[0066] The membrane 16 is coupled at its lower surface 26 to the moving winding 20 via the coil support 22, and it is coupled at its peripheral edge 28 to the chassis 12 via a suspension 30.

[0067] The membrane includes a coupling portion 32 for the reel support, which delimits a central portion 34 and a peripheral portion 36 of the membrane. The coupling portion may form a ring. In the embodiments illustrated in the figures, the membrane 16 includes an annular fold at which it is fixed to the reel support 22. For simplification, and for a better understanding of the invention, the coupling portion 32 is considered here to coincide with the fold.

[0068] Thus, the central zone 34 of the membrane 16 extends between the center C and the coupling portion 32, and the peripheral portion 36 extends between the coupling portion 32 and the peripheral edge 28.

[0069] The membrane 16 comprises a central zone 38 extending into the central portion 34, having a first stiffness; and a reinforcing ring 40 comprising the coupling portion 32, having a second stiffness greater than the first stiffness.

[0070] The first stiffness is therefore less than the second stiffness. For example, the first stiffness has a value between 5% and 65% of the second stiffness. Preferably, the first stiffness is between 5% and 10% of the second stiffness in the case of a multilayer membrane and between 25% and 40% in the case of a membrane made of a single material with several layers.

[0071] The reinforcing ring 40 extends around the coupling portion, over 5 to 60% of the distance between the coupling portion 32 and the center C of the diaphragm, and over 50% to 100% of the distance between the coupling portion 32 and the peripheral edge 28 of the diaphragm. Preferably, in the case of a midrange, tweeter, or full-range loudspeaker diaphragm, the reinforcing ring extends around the coupling portion, over 5 to 60% of the distance between the coupling portion and the center C of the diaphragm.

[0072] In order to obtain different stiffnesses, the central zone 38 and the reinforcing ring 40 can be formed with the same materials but different thicknesses, with different materials, or with a combination of these two solutions.

[0073] For example, in the embodiments shown in figures 2 to 4 the central zone 38 is formed by a zone thinner than the reinforcing ring 40.

[0074] Regardless of the materials chosen for the core and reinforcement ring, the core can have a thickness ranging from 35% to 90% of the thickness of the reinforcement ring. Preferably, the core thickness is between 60% and 70% of the thickness of the reinforcement ring.

[0075] For example, the central zone has a thickness between 20 pm and 40 pm, and the reinforcing ring has a thickness between 30 pm and 80 pm respectively.

[0076] For another example, for a central zone with a thickness of 20 pm, the reinforcing ring can have a thickness between 30 pm and 37 pm.

[0077] Membrane 16 can be produced by machining, thermoforming, injection molding, or in single-layer or multi-layer configurations, such as bonding. Membrane 16 can also be produced by 3D printing.

[0078] In the case of a multilayer membrane, the layers can be formed from the same material or from different materials. For example, membrane 16 may have a core comprising at least one layer of a first material, and the reinforcing crown may comprise at least one layer of a second material fixed to the core, the second material having a greater stiffness than the first material.

[0079] The core of the membrane 16 may include at least one layer of a composite or "sandwich" type material.

[0080] For example, membrane 16 may include at least one layer of a material selected from Plexiglas foam, PVC (polyvinyl chloride) foam, or polystyrene foam. And, membrane 16 may include at least one additional layer of a material selected from glass fiber, carbon fiber, polyethylene fibers, aramids, and paraaramids (Dyneema™, Spectra™, Kevlar™, Vectran™).

[0081] A person skilled in the art will understand that it can combine layers of materials having different dimensions and mechanical properties, and arranged in such a way as to form the central zone 38 and the reinforcing ring 40.

[0082] The reinforcing ring 40 can be formed by a visible overthickness at the lower surface 26 or the upper surface 24 of the membrane 16. The overthickness can be obtained, for example, by adding material at the level of the reinforcing ring 40.

[0083] In the case of a multilayer membrane 16, the reinforcing crown 40 can be formed by at least one additional layer of material compared to the central zone 38, for example a layer of glass fiber, a carbon fiber, polyethylene fibers, aramids and paraaramids (DyneemaTM, SpectraTM, KevIarTM, VectranTM).

[0084] The upper surface 24 of the membrane 16 is preferably flat, and the additional layer(s) of the reinforcing ring 40 are preferably fixed to the lower surface 26 of the membrane 16 so as not to be visible to a user. An additional layer of material is then in contact with the reel support 22.

[0085] According to variants illustrated in [Fig. 4], the reinforcing crown can also be formed by at least one additional layer of material arranged at the top surface of the membrane so as to indicate to the customer the presence of this innovation and improve the perceived quality visually.

[0086] According to variants illustrated in [Fig. 3], the reinforcing ring can also be formed by at least one layer of additional material arranged on the upper surface of the membrane, and another layer of additional material arranged on the lower surface of the membrane. Naturally, the two layers of additional material can have different thicknesses.

[0087] As illustrated in [Fig. 5], the membrane includes a fixing ring 42 extending from the peripheral edge 28 to the reinforcing ring 40. The fixing ring allows the membrane 16 to be fixed, for example by gluing, to the suspension 30 which is fixed to the frame 12. The fixing ring 42 advantageously has a stiffness lower than the second stiffness of the reinforcing ring 40 in order to limit the weight at the peripheral edge.

[0088] The stiffness of the fixing ring 42 can be equal to the first stiffness of the central zone 38. The fixing ring 42 can have the same composition as the central zone 38. For example, the membrane 16 can have a core comprising at least one layer of a first material, the core forming both the central zone 38 and the fixing ring 42. The reinforcing ring 40 can then be formed by at least one layer of a second material fixed, for example glued, to the core.

[0089] The fixing crown 42 can extend over a distance of less than 10% of the distance between the peripheral edge 28 and the center C of the membrane 16.

[0090] In conclusion, the invention thus makes it possible to obtain an acoustic membrane with a high and controlled breakup and good sensitivity, for all types of loudspeakers, including tweeters, midrange drivers, full-range drivers, and headphone drivers.

Claims

Demands 1. Acoustic membrane (16) having an upper surface (24) and an opposing lower surface (26), said membrane (16) being intended to be coupled at its lower surface (26) to a movable winding (20) via a coil support (22); the membrane (16) includes a coupling portion (32) for the coil support which delimits a central portion (34) and a peripheral portion (36) of the membrane; characterized in that the membrane (16) comprises a central zone (38) extending into the central portion (34), having a first stiffness; and a reinforcing ring (40) comprising the coupling portion (32), having a second stiffness greater than the first stiffness; the first stiffness is between 5% and 65% of the second stiffness; and in that the reinforcing ring (40) extends around the coupling portion (32), over 5 to 60% of the distance between the coupling portion (32) and the center of the membrane (C), and over 50% to 100% of the distance between the coupling portion (32) and a peripheral edge (28) of the membrane.

2. Acoustic membrane (16) according to claim 1, wherein the central zone (38) comprises a thickness between 35% and 95% of the thickness of the reinforcing ring (40).

3. Acoustic membrane (16) according to claim 2, wherein the central zone (38) has a thickness of between 20 µm and 40 µm, and the reinforcing ring (40) has a thickness of between 30 µm and 80 µm 4. Acoustic membrane (16) according to any one of the preceding claims, wherein the membrane comprises a fixing ring (42) extending from the peripheral edge (28) of the membrane to the reinforcing ring (40); and the fixing ring (42) has a stiffness less than the second stiffness.

5. Acoustic membrane (16) according to claim 4, wherein the fixing ring extends over a distance of less than 10% of the distance between the peripheral edge (28) and the center (C) of the membrane (16).

6. Acoustic membrane (16) according to any one of the preceding claims, wherein the membrane comprises a core including at least one layer of at least one first material, and the reinforcing ring (40) includes at least one layer of at least one second material fixed to the core, the second material having a rigidity equal to or greater than the first material.

7. Acoustic membrane (16) according to claim 6, wherein the layer of second material is fixed to the core on the lower surface (26) of the membrane.

8. Acoustic membrane (16) according to claim 7, wherein the layer of second material is fixed to the core on the upper surface (24) of the membrane.

9. Acoustic membrane (16) according to claim 7, wherein the reinforcement layer (40) comprises a layer of a second additional material fixed to the core on the lower surface (26) of the membrane.

10. Acoustic transducer (10) comprising a chassis (12) on which are mounted a magnetic motor (14) and an acoustic diaphragm (16) according to any one of the preceding claims 1 to 9

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