EP2461219A1 - Acoustic membrane for a musical box or an alarm watch - Google Patents

Abstract

The membrane (1) has two elliptical shaped asymmetrical areas (2, 3), hollowed out of the membrane with different uniform thickness from each other and less than thickness of a bottom part (4) of the membrane to maximize natural vibration frequencies of the membrane within a specific frequency range, where the membrane is dome-shaped. One of the elliptical shaped areas is centered on the membrane and another elliptical shaped area is off center on the membrane, where the areas are partly superposed. An independent claim is also included for a striking or musical watch including a watch case.

Description

An acoustic radiation membrane for a music box, such as a musical watch, or a bell watch.

The invention also relates to a watch, which comprises an acoustic radiation membrane. The watch comprises a watch case consisting essentially of a middle and a bottom fixed and securely attached to the middle part. An ice is disposed on a side opposite the bottom to seal said box. A watch movement is maintained inside the watch case and provided with a striking mechanism that can be activated in specified periods of time to produce sound or music. The acoustic radiation membrane is connected to the box to radiate the sound produced by the striking mechanism to the outside of the box.

In the field of horology, a watch movement of a traditional architecture may also include a striking mechanism for generating a sound or a music. The timbre of the bell watch or the keyboard of the musical watch are arranged inside the watch case. Thus the vibrations of the timbre or the keyboard blades are transmitted to the trim parts. These pieces of clothing are for example the middle part, the bezel, the ice and the bottom of the watch case. These large pieces begin to radiate sound in the air under the effect of transmitted vibrations. When a sound is produced either by a stamp struck by a hammer, or by one or more blades of the vibrating keyboard, these parts of dressing are able to radiate the sound produced in the air.

In a traditional bell or musical watch, the acoustic output, based on the complex vibro-acoustic transduction of the trim pieces, is low. To improve and increase the acoustic level perceived by the user of the bell or musical watch, the material, geometry and boundary conditions of the trim pieces must be taken into account. The configurations of these pieces of clothing are also dependent on the aesthetics of the watch and operating constraints, which may limit the possibilities of adaptation.

It is known in the art of horology to use in a particular electronic watch, a membrane of the acoustic type, which is dedicated to vibro-acoustic transduction. To activate such a membrane in an electronic watch, it is placed a piezoelectric element for example on the membrane to make it vibrate as mentioned in the patent CH 581 860 . So that the sound radiation of the membrane is not lost in the watch, which must be sealed, it can be provided a double bottom of the watch case, which is open to the outside. In this case, the bottom of the watch case has one or more openings for transmitting the sound of the vibrating membrane.

Generally with the use of a traditional acoustic radiation membrane, there remains a problem of frequency bandwidth. In the case of a minute repeater watch, an alarm clock or a quartz alarm, excellent results can be obtained by amplifying a single dominant frequency, tuned with the exciter. On the other hand, in the case where the acoustic membrane must equip a music box, the frequencies to radiate efficiently must typically range between 1 kHz and 4 kHz. The acoustic response of the membrane must therefore be relatively uniform in this frequency range. However, standard uniform membranes never meet this condition, so the response level is generally very inhomogeneous in this frequency range.

In a standard bell watch, which is provided for example with an acoustic membrane, this membrane is sandwiched between a portion of the middle part and the bottom of the watch case. In the case of a luxury watch, the bottom can be made of a precious material, such as gold. It can occur in contact with the membrane usually made of steel with the gold bottom, an electrochemical potential difference especially in a humid environment. This is likely to promote the corrosion of said membrane at the contact with the gold background, which is a drawback. It must therefore also be found a stainless material with no potential difference with gold and whose internal damping is low.

The invention therefore aims to overcome the drawbacks of the state of the art mentioned above by providing an acoustic radiation membrane for a music box or a striking watch, made in such a way as to obtain the most uniform acoustic performance possible on the audible frequency band, essentially in the frequency range between 1 kHz and 4 kHz.

For this purpose, the invention relates to an acoustic radiation membrane comprising the characteristics defined in independent claim 1.

Particular forms of the acoustic radiation membrane are defined in dependent claims 2 to 12.

An advantage of the acoustic radiation membrane according to the present invention lies in the fact that it is made with at least one region of asymmetric shape formed in the material of the membrane or with at least one region of asymmetrical shape having a different thickness the general thickness of the membrane. It can include several asymmetrically shaped regions, which are excavated in the membrane material. Preferably, two excavated regions of dimension different are planned. A first region is machined for example by etching or digging in the membrane to have a first constant thickness, and a second region is machined in the membrane to have a second constant thickness less than the first thickness. The two asymmetrically shaped regions are machined to define, for example, first and second ellipses as an asymmetric shape. These ellipses are offset from each other with respect to the center of the membrane and overlap in part.

Thanks to the realization of the ellipses in the membrane, this makes it possible to have a double number of eigen modes of vibration for each ellipse with respect to a region of circular form. A maximization of the number of eigen modes in the audible frequency band is thus obtained, in particular between 1 kHz and 4 kHz. The overall response of the vibrating membrane is thus flattened by eliminating circular symmetry and using such an asymmetric region in the form of an ellipse in plan view.

Advantageously, the membrane may be made of amorphous metal or metal glass, or also of gold, or even brass or another material having a density, a Young's modulus and an elastic limit, which are similar. The arrangement of the asymmetric regions can thus make it possible to increase the number of eigenfrequencies in the useful acoustic frequency band, namely between 1 kHz and 4 kHz, in order also to increase the overall acoustic level. With such a membrane, the widening of the soundtrack can be combined with a very low internal damping, which makes it possible to obtain a very good sound output.

For this purpose, the invention also relates to a watch provided with an acoustic radiation membrane comprising the characteristics defined in the independent claim 13.

Particular shapes of the watch are defined in the dependent claims 14 to 16.

• la figure 1 représente de manière simplifiée une vue de dessus de la membrane de rayonnement acoustique selon l'invention,
• la figure 2 représente de manière simplifiée une coupe diamétrale selon A-A de la figure 1 de la membrane de rayonnement acoustique selon l'invention,
• la figure 3 représente un graphe de la force totale appliquée sur l'air par la membrane selon l'invention en comparaison d'une membrane circulaire, en fonction de la fréquence d'excitation de la membrane, et
• la figure 4 représente de manière simplifiée une coupe partielle d'une montre à sonnerie ou musicale, qui est munie d'une membrane acoustique selon l'invention.

The purposes, advantages and characteristics of the acoustic radiation membrane for a music box or a bell watch will appear better in the following description on the basis of at least one non-limiting embodiment illustrated by the drawings in which:

• the figure 1 is a simplified view of a top view of the acoustic radiation membrane according to the invention,
• the figure 2 represents in a simplified way a diametral section along AA of the figure 1 of the acoustic radiation membrane according to the invention,
• the figure 3 represents a graph of the total force applied to the air by the membrane according to the invention in comparison with a circular membrane, as a function of the excitation frequency of the membrane, and
• the figure 4 represents in a simplified manner a partial section of a bell or musical watch, which is provided with an acoustic membrane according to the invention.

In the following description, reference will be made mainly to the configuration of an acoustic radiation membrane, in particular to equip a music box, such as a musical watch, or a bell watch.

The figure 1 represents a top view of the acoustic radiation membrane 1 for a music box, such as a musical watch, or a striking watch. In this embodiment, the membrane 1 is made with a spatially inhomogeneous thickness, i.e. it includes regions, which have been machined in the total thickness of the membrane. The machined regions each have a different uniform thickness. Excavated regions of different thickness have circularly shaped shapes in plan view. The asymmetric shapes are preferably ellipses 2, 3 excavated in a bottom portion 4 of a circular membrane 1, which may be shaped like as explained below with reference to figures 2 and 4 . These ellipses 2, 3 are partly superimposed. The presence of several circular asymmetric regions makes it possible to considerably increase the number of eigen modes or eigenfrequencies of vibration. This therefore makes it possible to increase the bandwidth preferably between 1 kHz and 4 kHz and the uniformity of the amplification in this audible frequency band.

As it has been found during the acoustic radiation test of such a membrane, it is optimal to provide two asymmetric regions 2, 3 in the thickness of the membrane 1. These two regions in the form of ellipse different uniform thickness, are of different size or surface without being directly dependent on the size of the membrane. The membrane 1 may be a circular membrane with a diameter of about 40 mm at the edge and a diameter of about 31 mm at its bottom 4 by way of non-limiting example. These two elliptical regions occupy a large part of the surface of the membrane seen in plan so as to increase the number of eigen modes of vibration in the desired audible frequency band between 1 kHz and 4 kHz.

où E est le module d'Young, h est l'épaisseur de la membrane, a et b sont les demi-axes de l'ellipse, p est la masse volumique du matériau de la membrane, v est le coefficient de Poisson (à peu près de l'ordre de 0.3), n et m sont des nombres entiers, qui numérotent les modes de vibration et représentent le nombre de noeuds spatialement de la vibration correspondante de la membrane. Le nombre de noeuds dans la direction du demi-axe a et du demi-axe b est m-1, respectivement n-1. Dans le cas d'un mode indiqué par n=2 et m=3, cela correspond à une vibration, qui a deux noeuds dans la direction du demi-axe a, et un noeud dans la direction du demi-axe b. Dans le cas d'un mode indiqué par n=1 et m=1, il n'y a pas de noeuds dans l'une ou l'autre direction des demi-axes.The elliptical regions are normally determined taking into account the following simplified formula of the frequency ω of the vibration modes of an elliptical membrane: $${{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}}_{\mathrm{not}\mathrm{,}\mathrm{m}}\mathrm{\approx }\mathrm{E}\mathrm{\cdot }\mathrm{h}\mathrm{\cdot }\left(\mathrm{not}\mathrm{/}{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">b</figure-callout>}}^{\mathrm{2}}\mathrm{+}\mathrm{m}\mathrm{/}{\mathrm{at}}^{\mathrm{2}}\right)\mathrm{/}\left(\mathrm{\rho }\mathrm{\cdot }\left(\mathrm{1}\mathrm{-}{\mathrm{<figure-callout\; id="2"\; label="v"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">v</figure-callout>}}^{\mathrm{2}}\right)\right)$$

where E is the Young's modulus, h is the thickness of the membrane, a and b are the half-axes of the ellipse, p is the density of the membrane material, v is the Poisson's ratio (at about the order of 0.3), n and m are integers, which number the modes of vibration and represent the number of nodes spatially of the corresponding vibration of the membrane. The number of nodes in the direction of the half-axis a and the half-axis b is m-1, respectively n-1. In the case of a mode indicated by n = 2 and m = 3, this corresponds to a vibration, which has two nodes in the direction of the half-axis a, and a node in the direction of the half-axis b. In the case of a mode indicated by n = 1 and m = 1, there are no nodes in either direction of the half-axes.

According to the formula of the aforementioned vibration frequency, the frequency increases with the square root of the Young's modulus E and the thickness h, but on the other hand decreases by increasing the half-axes a and b, that is to say the surface of the ellipse. By way of comparison, for the same surface and the same thickness, and in the desired frequency range, an elliptical membrane has a double number of modes of vibration relative to a circular membrane. It is therefore possible to flatten the overall frequency response by eliminating the circular symmetry of the membrane. The asymmetric regions, preferably in the form of an ellipse 2, 3 of the acoustic membrane 1 according to the invention, are configured so that the first natural modes of vibration are in the audible frequency band between 1 kHz and 4 kHz. With such ellipses, this allows for better geometric optimization than for other asymmetric shapes.

ayant ce nombre de noeuds. Ces modes diffèrent entre eux par leur forme spatiale et/ou leur orientation dans le plan de la membrane. La différence d'énergie entre ces modes dépend de l'épaisseur et de la forme des régions S_j et peut donc être réduite à discrétion. Cette multiplication des modes dans chaque intervalle d'énergie permet d'élargir la bande de réponse de la membrane. Par simplicité de calcul et de réalisation pratique, il est considéré le cas spécifique où les régions d'épaisseur différente sont deux ellipses.It should be noted that a circular membrane of uniform thickness supports several eigen modes of vibration, which are defined by k _N. Each eigenmode is characterized by a defined number of nodes N. Thanks to the realization of regions of different thickness, which are called S _j with j ranging from 1 to n, and for each defined number of nodes N, it is counted several vibration modes $k_{\mathrm{NOT}}^l$

having this number of nodes. These modes differ from each other in their spatial shape and / or orientation in the plane of the membrane. The energy difference between these modes depends on the thickness and shape of the regions S _j and can therefore be reduced to discretion. This multiplication of modes in each energy range makes it possible to widen the response band of the membrane. For simplicity of calculation and practical realization, it is considered the specific case where the regions of different thickness are two ellipses.

Thanks to the realization of two ellipses in the membrane, for each defined number of nodes, there are four modes of vibration, of which two modes of vibration by ellipse and not a single mode of vibration for a circular form of a traditional membrane. A maximization of the number of modes in the audible frequency band is thus obtained. The overall response of the vibrating membrane is thus flattened by eliminating circular symmetry and using such an asymmetric region in the form of an ellipse in plan view.

For the typical dimensions of a watch, with the two elliptical-shaped regions it is possible to obtain a better geometrical optimization than with any other asymmetrical shape. Depending on the sufficiently large size of each ellipse with respect to the size of the membrane, the first modes of vibration are with a uniform amplification in the desired frequency band, for example between 1 kHz and 4 kHz. The overall acoustic level is also increased for a user's perception of the notes radiated by the membrane of the music box or the ringing watch.

As described above, the circular membrane 1 may have a diameter equal to 40 mm at the edge and a diameter equal to 31 mm at its bottom 4. It may be made of a material, such as metal-based glass. zirconia, which has a density or density equal to 5'100 kg / m ³ . The material used for the membrane may have a Young's modulus, which may vary between 97 and 110 GPa, while its elastic limit may vary between 1.5 and 2.2 GPa. The maximum thickness of the membrane may be of the order of 0.3 mm, while the minimum thickness may vary between 0.1 mm and 0.2 mm, depending on the sound effects to be obtained. If the density is greater, while the Young's modulus is smaller, a membrane thickness greater than 0.3 mm may be allowed, but under these conditions, the membrane is less acoustically effective.

The size of the first ellipse 2, which is excavated in the bottom 4 of the membrane, is 12 mm for the half-major axis and 6 mm for the half-minor axis with a thickness of 0.15 mm. The size of the second ellipse 3, which is excavated in the bottom 4 of the membrane partially superimposed on the first ellipse and crossed, is 11 mm for the half-major axis and 7 mm for the semi-minor axis with a thickness of 0.2 mm. The centers c, c 'of the first and second ellipses 2, 3 can be shifted from each other for example by 13.5 mm, and the angle between the major axes of the two ellipses can be of the order of 60 ° . With a relatively similar size of the two ellipses, the density of vibration modes of the membrane is maximized in the desired audible frequency band. It can also be envisaged to adapt the thicknesses and the surface of the ellipses as a function of the desired sealing, the indeformability or the deformability of the desired membrane.

In general, the ratio between the half-axes of the ellipses excavated in the membrane and the radius of the circular membrane should in principle be in the range 2/3 to 1. The ratio between the two thicknesses of the ellipses must be in the interval 1/2 to 4/5. The minimum thickness must not be greater than 2/3 of the total thickness of the circular membrane.

The figure 2 represents a diametrical cut along AA of the figure 1 of the acoustic radiation membrane 1. This membrane can take the form of a bowl with a bottom 4 and a peripheral edge for mounting in particular in a watch case as explained below with reference to the figure 4 . The asymmetric regions in the form of ellipses 2 and 3 are formed in the bottom 4 of the membrane 1. Each region is excavated in the membrane with each a different uniform thickness. It should also be noted that the excavated regions may be indifferently on the movement side or on the outer side of the membrane not shown.

It should also be noted that instead of making asymmetrical regions 2, 3 by etching, milling or digging in the total thickness of the membrane 1, it can be envisaged to produce on a membrane of minimum thickness two regions. in the form of an ellipse in overthickness and which intersect. A first region has a first thickness greater than the minimum thickness of the membrane, and a second region has a second thickness greater than the first thickness of the first region. These elliptical regions thus form protruding portions on the membrane, but whose asymmetrical shape provides advantages equivalent to the advantages of the ellipses excavated in the membrane explained above. These regions can be obtained by selective deposition of the same material as the base material of the membrane. The material may be zirconia-based or platinum-based metal glass, or also gold.

It should also be noted that instead of producing asymmetrical regions 2, 3 by etching, milling or digging in the total thickness of the membrane 1, it can be envisaged to produce a circular asymmetric membrane, by modifying its properties. physico-chemical locally and in a deterministic manner during manufacture or after-treatment. This procedure makes it possible to produce uniform regions having circularly asymmetrical shapes and thus to multiply the vibration modes and to flatten the frequency response, according to the same physical principle explained above.

To the figure 3 a graph of the proposed frequency response of the proposed membrane compared with the response of an ordinary circular membrane made of the same material is shown. It is represented the total force Fz applied by the membrane on the air, as a function of the excitation frequency of the membrane. The circular membrane may be flat in this example and with a diameter of the order of 31 mm. The same excitation force was applied in all the cases considered.

The MA curve represents the response of an ordinary circular membrane (membrane strength on air) in the frequency range of 1 kHz to 4 kHz. It is noted that the force on the air of this ordinary membrane has only a peak of greater amplitude between 2.5 kHz and 3 kHz with a relatively low overall amplitude. Curve A represents the response of a circular membrane, in which is realized a centric ellipse of half-major axis equal to 15 mm and half-small axis equal to 9 mm with a thickness of 0.07 mm and a non ellipse centered half-major axis equal to 13.5 mm and half small axis equal to 10 mm with a thickness of 0.09 mm. Curve B represents the response of a circular membrane, in which is realized an ellipse centered half-major axis equal to 14 mm and half-small axis equal to 10 mm with a thickness of 0.08 mm and an ellipse non-centered half large axis equal to 12 mm and half small axis equal to 11 mm with a thickness of 0.1 mm. Finally curve C represents the response of a circular membrane, in which is realized a centric ellipse of half-major axis equal to 15 mm and half-small axis equal to 9 mm with a thickness of 0.09 mm and a centered ellipse of half large axis equal to 13.5 mm and half small axis equal to 10 mm with a thickness of 0.11 mm. The amplitude of the force applied to the air by the membrane, in which ellipses are produced, is maximized and relatively flattened for eigen frequencies of vibration between 1 kHz and 4 kHz, which is sought by the invention.

The figure 4 represents a partial section of a bell or musical watch 10. The watch 10 essentially comprises an acoustic radiation membrane 1 according to the invention for improving the acoustic performance of a note or notes produced by a striking mechanism. This acoustic membrane 1 may comprise two elliptical regions 2 and 3, excavated in the bottom 4 of the membrane. This acoustic membrane may be made for example in an amorphous metal or metal glass, which is a stainless material. The total thickness of this membrane 1 may be less than or equal to 1 mm, but preferably close to 0.3 mm.

The ring or musical watch 10 also comprises a watch movement 20, which is generally mounted on a plate 24. An edge piece 22 is fixed to the plate 24, which defines a watch cage. Usually both the plate 24 and the edge piece 22 are made of a metallic material.

The watch movement 20 comprises a striking mechanism, not shown. This striking mechanism may comprise at least one stamp mounted on a stamp holder integral with the plate 24, and at least one hammer rotatably mounted on the plate to strike said stamp in specified periods. The generally circular stamp surrounds the various parts of the watch movement of the ringing watch. Such a striking mechanism is provided to signal a programmed alarm or minute repetitions.

In a more elaborate embodiment of a musical watch, the striking mechanism may comprise a keyboard with a set of blades connected to a heel, which is attached to the deck 24. A note or a succession of musical notes are produced by keyboard blade vibrations. Each blade is normally configured to produce a particular note, but it can be expected to have certain groups of two blades for each group to produce the same particular note. To produce a music for example in programmed periods, the keyboard blades are lifted and released by pins integral with a cylinder or a disc rotating on the plate 24. Each activated blade oscillates mainly at its first natural frequency. The vibrations generated by the activated blades are transmitted to the watch's trim pieces, which must make it possible to radiate acoustically the sound produced by each vibrating blade.

In this embodiment, the acoustic membrane 1 is cup-shaped, the upper edge of which is sealingly mounted by an annular liner 18 on an inner annular flange of the bottom 15 of the box. The diameter of this bowl, which may be equivalent to the diameter of the watch crystal 12, may be between 20 and 40 mm. An annular support 21 supports on one side the plate 24 with the edge piece 22 and rests on the upper edge of the acoustic membrane 1. At the time of attachment of the caseband 14 to the bottom 15 of the watch case, the support 21 and the peripheral edge of the acoustic radiation membrane 1 are clamped between the caseband 14 and the base rim 15.

It should be noted that it may be provided to fix the acoustic membrane 1 by its border in a different way than that presented above. It can be envisaged that the membrane is fixed pointwise at 2, 3, 4 or more points by its border, or that it is fixed elastically or with a single support condition.

The bottom 15 is mounted by known means and removably on the middle part 14 with a seal 19. A watch crystal 12 is fixed in particular to the bezel 13 to seal the watch case. A dial 23 is held at the edge on the middle part and arranged below the watch crystal 12. For a mechanical bell watch 10, hour indication hands, not shown, are provided on the dial, which also carries hourly indices on the periphery.

The central portion of the acoustic membrane is not in contact with the support 21 and the inner surface of the bottom 15. As a result, sufficient space 17 in the box is provided so that the acoustic membrane can freely vibrate or radiate acoustically. The entire acoustic membrane 1 and the bottom 15 thus constitutes a double bottom. One or more openings 16 are also provided laterally through the bottom 15 to allow the acoustic membrane to radiate the sound produced by the striking mechanism to the outside.

During operation of the striking mechanism, the note or notes generated by said striking mechanism are transmitted directly to the acoustic radiation membrane 1 to vibrate. A vibration transmission to the acoustic membrane 1 is also provided at the edge of the acoustic membrane by the connecting pieces 21, 22 and 24. As the acoustic membrane comprises regions in the form of an ellipse 2, 3 excavated in the bottom 4 of the membrane, it is likely to vibrate at several first eigenfrequencies according to the number of notes planned to radiate. These first natural frequencies are preferably located in the useful acoustic band between 1 kHz and 4 kHz. The second natural frequencies of vibration notes are however located above 4 kHz. This is advantageous because the second vibration frequencies are often destructive of sound.

These desired natural frequencies of sound vibration of the membrane, which may be of amorphous metal, are dependent on physical properties, such as density and Young's modulus. In addition with such an acoustic radiation membrane 1, there is a very low damping, which provides a very good sound performance of this acoustic membrane. In addition, the destructive interference effect of the second eigenfrequencies is mitigated, since a second eigenfrequency mode is generally close in frequency of a first eigenfrequency mode having an orthogonal orientation. In other words, the membrane never vibrates in a pure mode of second natural frequency.

Due to the fact that this membrane is composed of stainless materials, it can be mounted on a background for example of precious metal, such as gold. No difference in electrochemical potential is thus observed even in a humid environment, so that no corrosion occurs in contact with the membrane 1 and the bottom 15.

The metallic glass or amorphous metal used, for example, for producing the membrane may also be a metal alloy based on titanium, zirconium and beryllium. Thus, by way of a more specific example, the amorphous metal alloy may comprise 41% of zirconium, 14% of titanium, 12% of copper, 10% of nickel and 23% of beryllium. The Young's modulus of this alloy is 105 GPa and the elastic limit is 1.5 GPa. The amorphous metal alloy may also consist of 57.5% platinum, 14.7% copper, 5.3% nickel and 22.5% phosphorus. The Young's modulus of this alloy is in this case 98 GPa and the elastic limit is 1.4 GPa.

From the description that has just been given, several embodiments of the acoustic radiation membrane for a music box or a striking watch can be designed by the man of the without departing from the scope of the invention defined by the claims. The acoustic membrane may be located in the watch case at the middle of the case with an opening through the caseband for the sound radiation of the acoustic membrane in vibration. The acoustic membrane may be located on an outer portion of the watch case, but disposed at least on an opening of the housing so that the note or notes generated by the striking mechanism can vibrate the membrane. Several acoustic membranes can be arranged in several places inside the watch case or superimposed. The membrane may have a shape other than circular, for example rectangular and be flat. The membrane may include an elliptical region on a first face and another elliptical region on a second opposite face of the membrane.

Claims (16)

Acoustic radiation membrane (1) for a music box or striking watch (10), characterized in that it is made with at least one region of asymmetric shape formed in the material of the membrane or with at least one region of asymmetric shape having a thickness different from the general thickness of the membrane. Membrane (1) according to claim 1, characterized in that it comprises several regions (2, 3) of asymmetrical shape. Membrane (1) according to one of the preceding claims, characterized in that it comprises at least two asymmetric regions, each region being excavated in the membrane with a different uniform thickness, to maximize the first natural frequencies of vibration of the membrane in the frequency band between 1 kHz and 4 kHz. Membrane (1) according to one of the preceding claims, characterized in that the asymmetrical region or regions (2, 3) have an ellipse shape. Membrane (1) according to claim 4, characterized in that the elliptical regions are excavated in the membrane with a thickness different from each other and less than the overall thickness of the membrane. Membrane (1) according to claim 4, characterized in that the elliptical regions are protruding portions made over a minimum thickness of the membrane, each protruding region having a thickness different from each other. Membrane (1) according to one of claims 5 and 6, characterized in that the membrane has a general shape of bowl with a bottom (4) in which are formed the regions (2, 3) elliptical. Membrane (1) according to one of claims 5 to 7, characterized in that a first region (2) in the shape of an ellipse is centered on the circular membrane, in that a second region (3) in elliptical shape is off-center on the membrane, and in that the two regions overlap in part. Membrane (1) according to claim 8, characterized in that the ratio between the half-axes of the two excavated ellipses (2, 3) in the membrane and the radius of the circular membrane must be in the range of 2/3 at 1, in that the ratio between the two thicknesses of the ellipses must be in the range of 1/2 to 4/5, and in that the minimum thickness of each ellipse must not be greater than 2/3 of the total thickness of the circular membrane. Membrane (1) according to one of claims 2 to 5, characterized in that the overall thickness of the membrane is 0.3 mm or less, in that the thickness of a first region (2) in the form of ellipse is of the order of 0.15 mm, and in that the thickness of the second region (3) in the form of an ellipse is of the order of 0.2 mm. Membrane (1) according to claim 1, characterized in that it is made of gold or titanium or amorphous metal or metal glass. Membrane (1) according to claim 1, characterized in that the region of asymmetric shape is formed in the base material of the membrane by modifying the physico-chemical properties locally of the membrane material and in a deterministic manner. A bell or musical watch (10), comprising a watch case, which comprises a middle part (14) and a bottom (15) with at least one lateral opening (16), the bottom being fastened securely and removably to the middle part , an ice (12) sealing the box, a watch movement (20) maintained inside the watch case and provided with a striking mechanism that can be activated in periods determined to produce a note or several notes, and at least one acoustic radiation membrane (1) according to one of the preceding claims, which is arranged in the watch case. Watch (10) according to claim 13, characterized in that the acoustic membrane (1) is held on an inner rim of the bottom (15) of the box and a part of the middle part (14), and in that the periphery of the acoustic membrane (1) is clamped with the periphery of a support (21) of movement between the middle (14) and the inner rim of the bottom (15) of the box. Watch (10) according to claim 14, characterized in that the acoustic membrane (1) has a bowl-like shape, an upper edge of which is clamped with the annular support between the middle part (14) and an inner annular flange of the bottom (15). ) of the box, an annular seal (18) being placed between the bottom flange (15) and the annular edge of the membrane, and in that a central portion of the acoustic membrane is not in contact with the support (21) and an inner surface of the bottom (15) of the box to define a space (17) in order to be able to oscillate freely. Watch (10) according to claim 13, characterized in that several acoustic radiation membranes (1) are connected to the watch case and spaced from one another or superimposed.

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