HK1173300A - Acoustic radiating membrane for a music box or striking watch - Google Patents

Description

Acoustic radiating membrane for music box or chronometer

Technical Field

The present invention relates to an acoustic radiating membrane (acoustic radiating membrane) for a music box such as a music watch or a time-telling watch.

The invention also relates to a watch comprising an acoustic radiating membrane. The watch comprises a case essentially formed by a middle part and a back cover detachably fixed in a sealed manner to the middle part. A crystal is provided on the opposite side of the back cover to close the watch case in a sealed manner. The timepiece movement is held inside the case and is provided with a striking mechanism that can be actuated at determined times to produce a sound or music. At least one sound radiating membrane is connected to the case so as to radiate sound generated by the striking mechanism toward the outside of the case.

Background

In the field of horology, a timepiece movement of conventional construction may also include a striking mechanism for producing sounds or music. The gong of a striking watch or the pin-barrel of a musical watch are arranged inside the watch case. Thus, the vibration of the gong or the pin barrel tongue is transmitted to the external part of the watch. These external parts are, for example, the middle part, the bezel, the crystal and the back cover of the watch case. These large components begin to radiate sound into the air under the influence of the transmitted vibrations. When sound is generated by a gong struck by a hammer or by one or more vibrating pin barrel tongues, these external parts are able to radiate the generated sound into the air.

In a conventional striking watch or musical watch, the acoustic efficiency of the complex vibration-sound conversion based on the external parts is low. In order to increase and augment the sound level perceived by a user of a striking or musical watch, the materials, geometry and boundary conditions of the external components must be considered. The construction of these external parts also depends on the aesthetic appearance of the watch and on the working stresses, which may limit the possibilities of adaptation modifications.

It is known in the art of watchmaking to use, in watches (in particular electronic watches), a membrane of the acoustic type, which is dedicated to the vibration-to-sound conversion. To trigger a membrane of this type in an electronic watch, for example, a piezoelectric element is placed on the membrane to cause the membrane to vibrate, as described in swiss patent No. 581860. In order to prevent the sound radiation from the membrane from disappearing in the watch that must be sealed, the case may be provided with a double back cover that must be open towards the outside. In this case, the back cover of the watch case has one or more holes for transmitting sound from the diaphragm.

In general, there is a problem of frequency bandwidth for using a conventional acoustic radiating membrane. In the case of a striking watch with minute questions, an alarm or even a quartz alarm, good results can be obtained by amplifying a single dominant frequency tuned using an exciter. However, if the acoustic membrane must be fitted into a music box, the frequency to be radiated effectively must typically be in the range of 1kHz and 4 kHz. Therefore, the acoustic response of the membrane must be relatively uniform over this frequency range. However, standard uniform films may not successfully meet this condition because the response levels in this frequency range are typically very non-uniform.

In a standard striking watch, for example fitted with an acoustic membrane, said membrane is sandwiched between a portion of the middle case and the back cover of the watch. In the case of a luxury watch, the rear cover may be made of a valuable material such as gold. The electrochemical potential difference between the membrane, usually made of steel, and the gold rear cover can occur upon contact, especially in a humid environment. This is liable to cause corrosion of the film where the film comes into contact with the gold rear cover, which is another drawback. Therefore, it is necessary to find a corrosion resistant material which has no potential difference from gold and has low internal decay.

Disclosure of Invention

It is therefore an object of the present invention to overcome the drawbacks of the prior art mentioned above by providing an acoustic radiating membrane for a music box or a watch, which is made to provide the most uniform possible efficiency over the audible frequency band, mainly in the frequency range of 1kHz to 4 kHz.

The invention therefore relates to an acoustic radiating membrane comprising the features defined in independent claim 1.

Particular embodiments of the acoustic radiating membrane are defined in the dependent claims 2 to 12.

One advantage of the sound radiating membrane according to the invention lies in the fact that it is made with at least one area of asymmetrical shape formed in the material of the membrane or with at least one area of asymmetrical shape having a different thickness from the overall thickness of the membrane. The membrane may include several asymmetrically shaped regions hollowed out in the material of the membrane. Preferably with two hollowed-out areas of different sizes. A first region is processed to obtain a first constant thickness, for example by etching or digging the film, and a second region is processed in the film to obtain a second constant thickness, which is smaller than the first thickness. Two asymmetrically shaped areas are machined to define, for example, first and second ellipses as the asymmetrical shapes. These ellipses are offset with respect to each other with respect to the center of the membrane and partially overlap.

Due to the fact that ellipses are made in the membrane, twice as many natural vibration modes are obtained for each ellipse compared to a circular area. The number of natural modes in the audible frequency range is thus maximized, especially between 1kHz and 4 kHz. Therefore, by removing the circular symmetry and using this type of asymmetric region in the form of an ellipse shown in a plan view, the overall response of the diaphragm can be flattened.

Advantageously, the membrane may be made of amorphous metal or metallic glass, or also of gold, or even of brass or other material having similar density, young's modulus and elastic limit. The arrangement of the asymmetric zones may also increase the number of natural frequencies (i.e. between 1kHz and 4 kHz) in the useful sound band in order to increase the overall sound level. With this type of membrane, an extension of the sound range can be combined with a very low internal attenuation, which provides a very good acoustic efficiency.

The invention therefore relates to a watch having an acoustic radiating membrane comprising the features defined in independent claim 13.

Dependent claims 14 to 16 define specific embodiments of the table.

Drawings

The objects, advantages and features of the acoustic radiating membrane for a music box or watch can be seen more clearly from the description given below on the basis of at least one non-limiting embodiment illustrated by the accompanying drawings, in which:

figure 1 shows a simplified top view of an acoustic radiating membrane according to the invention,

3 figure 3 2 3 shows 3 a 3 simplified 3 diametrical 3 section 3 view 3 along 3 a 3- 3 a 3 of 3 figure 31 3 of 3 an 3 acoustic 3 radiating 3 membrane 3 according 3 to 3 the 3 invention 3, 3

FIG. 3 shows a graph of the total force exerted by the membrane according to the invention on the air compared to a circular membrane, according to the excitation frequency of the membrane, an

FIG. 4 shows a simplified partial cross-sectional view of a striking or musical watch having an acoustic membrane according to the present invention.

Detailed Description

In the following description, reference will be made mainly to the construction of an acoustic radiating membrane to be fitted in particular to a music box such as a musical watch or a striking watch.

Fig. 1 shows a top view of an acoustic radiating membrane 1 for a music box or a striking watch, such as a music watch. In this embodiment, the membrane 1 is made with a non-uniform spatial thickness, i.e. it comprises a region machined in the total thickness of the membrane. The machined areas each have a different uniform thickness. In this top view, it can be seen that the dug out areas with different thicknesses have an asymmetrical circular shape. The asymmetric shape is preferably an ellipse 2, 3 hollowed out in the bottom part 4 of a circular membrane 1, which may be dome-shaped as described below with reference to fig. 2 and 4. These ellipses 2, 3 partially overlap. The presence of several asymmetric circular areas significantly increases the number of natural vibration modes or frequencies. This therefore increases the bandwidth, preferably between 1kHz and 4kHz, and the uniformity of the amplification within this audible band.

It can be observed during acoustic radiation testing of this type of membrane that preferably two asymmetric areas 2, 3 are made in the thickness of the membrane 1. The two regions, in the form of ellipses with different uniform thicknesses, have different dimensions or surfaces, but do not directly depend on the dimensions of the membrane. By way of non-limiting example, the membrane 1 may be a circular membrane having a diameter of about 40mm at the edge and a diameter of about 31mm at its bottom 4. As can be seen in plan view, these two elliptical areas occupy a large portion of the surface of the membrane in order to increase the number of natural vibration modes within the desired sound band between 1kHZ and 4 kHZ.

The elliptical area is generally determined taking into account the following simplified formula for the frequency ω of the vibration mode of the elliptical membrane:

ω² _n，m≈E·h·(n/b²+m/a²)/(ρ·(1-v²))

where E is the young's modulus, h is the thickness of the membrane, a and b are the half-axes of the ellipse, ρ is the density of the material of the membrane, v is the poisson's coefficient (on the order of 0.3 approximately), n and m are integers which are the number of modes of vibration and represent the number of spatial nodes 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, n-1, respectively. In the case of the mode represented by n-2 and m-3, this corresponds to a vibration having two nodes in the direction of the half axis a and one node in the direction of the half axis b. In the case of the pattern represented by n-1 and m-1, no node exists in either of the half-axis directions.

According to the aforementioned vibration frequency formula, the frequency increases with increasing young's modulus E and square root of thickness h, but conversely decreases with increasing half-axes a and b (i.e. elliptical surfaces). In comparison, an elliptical membrane has twice as many vibration modes as a circular membrane for the same surface area and the same thickness and in the desired frequency range. The overall frequency response can be flattened by removing the circular symmetry of the membrane. The asymmetrical region, preferably in the form of an ellipse 2, 3 of the acoustic membrane 1 according to the invention, is configured such that the first natural vibration mode is in the audible frequency range between 1kHZ and 4 kHZ. By using this type of ellipse, a better optimization of the geometry can be obtained than by using other asymmetric shapes.

It should be noted that a circular film with a uniform thickness can withstand the influence of k_NA defined number of natural vibration modes. Each natural mode is limitedThe number N of the fixed nodes is taken as a characteristic. Due to the fact that the S is called_j(where j ranges from 1 to N) regions of different thickness, and for each defined number of nodes N, counting a number of vibration modes having this number of nodesThe spatial shapes and/or orientations of these modes in the plane of the film are different from each other. The energy difference between these modes depends on the region S_jAnd thus can be reduced as desired. This increase in modes in each energy range allows the response band of the membrane to be expanded. For simplicity of calculation and for practical reasons, the particular case is considered here where the areas with different thicknesses are two ellipses.

Due to the fact that two ellipses are formed in the membrane, there are four vibration modes for each defined number of nodes, wherein each ellipse comprises two vibration modes, instead of only one vibration mode as in conventional circular membranes. The number of modes in the audible band is thus maximized. Therefore, by removing the circular symmetry and using this type of asymmetric region in the form of an ellipse seen in a plan view, the overall response of the diaphragm can be flattened.

For a typical watch size, better optimization of the geometry can be obtained by using two elliptical areas than by using any other asymmetric shape. If the size of each elliptical region is sufficiently large relative to the size of the membrane, the first vibration mode has a uniform amplification within the desired frequency band (e.g., between 1kHz and 4 kHz). The overall sound level is also increased so that the user can perceive the note (note) radiated by the membrane of the musical box or watch.

As mentioned before, the circular membrane 1 may have a diameter equal to 40mm at its edge and a diameter equal to 31mm at its bottom 4. The circular membrane 1 may be made of a material having a density equal to 5,100kg/m³Such as zirconia-based metallic glass. The material used for the membrane may have a Young's modulus between 97-110GPa, whileThe elastic limit may be between 1.5-2.2 GPa. The maximum thickness of the membrane may be of the order of 0.3mm, and the minimum thickness may be between 0.1mm and 0.2mm, depending on the acoustic effect to be obtained. If the density is greater and the Young's modulus is less, a film thickness of greater than 0.3mm may be tolerated, but under these conditions the acoustic efficiency of the film is reduced.

The dimensions of the first ellipse 2 dug out at the bottom 4 of the membrane are: the major semi-axis is 12mm, the minor semi-axis is 6mm, and the thickness is 0.15 mm. The dimensions of the second ellipse 3 dug out at the bottom 4 of the membrane and partially overlapping and intersecting the first ellipse are: the major semi-axis is 11mm, the minor semi-axis is 7mm, and the thickness is 0.2 mm. The centres c, c' of the first ellipse 2 and the second ellipse 3 may be offset with respect to each other, for example by 13.5mm, and the angle between the semi-major axes of the two ellipses may be of the order of 60 °. If the two ellipses have relatively similar dimensions, the density of the vibration modes of the membrane is maximized within the desired audible frequency band. It is also conceivable to adapt the thickness and surface of the ellipse according to the desired sealing, non-deformability or deformability of the desired film.

In general, the ratio between the half-axis of the ellipse dug out of the membrane and the radius of the circular membrane must in principle be in the range of 2/3 to 1. The ratio between the two thicknesses of the ellipse must be in the range of 1/2 to 4/5. The minimum thickness must be no more than 2/3 of the total thickness of the circular membrane.

3 fig. 3 2 3 shows 3 a 3 cross 3- 3 sectional 3 view 3 of 3 the 3 sound 3 radiating 3 membrane 31 3 in 3 the 3 diameter 3 direction 3 a 3- 3 a 3 of 3 fig. 31 3. 3 As described below with reference to fig. 4, this membrane may take the form of a dome having a bottom 4 and a peripheral edge for assembly in particular in a watch case. The elliptical asymmetric areas 2 and 3 are made in the bottom 4 of the membrane 1. Each region is excavated from the film at a different uniform thickness. It should also be noted that the excavated area may be located on the core side of the membrane or on the outer side of the membrane (not shown).

It should also be pointed out that, in addition to making the asymmetric areas 2, 3 by etching, milling or digging the total thickness of the membrane 1, it is also possible to envisage making two elliptical areas on the membrane with a very small thickness, located in the excess thickness and intersecting each other. The first region has a first thickness greater than the very small thickness of the membrane, and the second region has a second thickness greater than the first thickness of the first region. These elliptical areas thus form protrusions on the membrane, their asymmetric shape providing the same advantages as the previously described ellipses dug in the membrane. These regions may be obtained by selectively depositing the same material as the substrate of the film. The material may be a metallic glass based on zirconia or platinum, or may also be gold.

It should also be pointed out that, in addition to making the asymmetric areas 2, 3 by etching, milling or digging the total thickness of the membrane 1, it is also possible to envisage making a non-circularly symmetric membrane by locally modifying the physico-chemical characteristics of the membrane in a deterministic manner during manufacture or post-processing. This process enables the fabrication of uniform regions with non-circularly symmetric shapes, according to the same physical principles as described previously, thereby increasing the vibration modes and flattening the frequency response.

Fig. 3 shows a graph of the frequency response of the proposed membrane of the invention compared to the response of a normal circular membrane made of the same material. The total force Fz applied by the membrane to the air is shown in terms of the membrane's excitation frequency. The circular membrane may be flat in this example and have a diameter in the order of 31 mm. The same excitation force is applied in all considered cases.

Curve MA represents the response of a generally circular membrane (the force exerted by the membrane on the air) over a frequency range of 1kHz to 4 kHz. It should be noted that the force applied to the air by this conventional membrane has only a maximum amplitude peak between 2.5kHZ and 3kHZ, and has a relatively low overall amplitude. Curve a represents the response of a circular membrane in which a centered ellipse with a semi-major axis equal to 15mm and a semi-minor axis equal to 9mm and with a thickness of 0.07mm and a non-centered ellipse with a semi-major axis equal to 13.5mm and a semi-minor axis equal to 10mm and with a thickness of 0.09mm are made. Curve B represents the response of a circular membrane in which a centered ellipse with a semi-major axis equal to 14mm and a semi-minor axis equal to 10mm and with a thickness of 0.08mm and a non-centered ellipse with a semi-major axis equal to 12mm and a semi-minor axis equal to 11mm and with a thickness of 0.1mm are made. Finally, curve C represents the response of a circular membrane in which a centered ellipse with a semi-major axis equal to 15mm and a semi-minor axis equal to 9mm and with a thickness of 0.09mm and a centered ellipse with a semi-major axis equal to 13.5mm and a semi-minor axis equal to 10mm and with a thickness of 0.11mm are made. It is an object of the present invention that the amplitude of the force applied to the air by the membrane in which the ellipse is made is maximized and relatively flattened for natural vibration frequencies between 1kHz and 4 kHz.

FIG. 4 thus shows a partial cross-sectional view of a striking or musical watch 10. The watch 10 mainly comprises an acoustic radiating membrane 1 according to the invention for improving the acoustic efficiency of one or more notes produced by a striking mechanism. The acoustic membrane 1 may comprise two oval shaped areas 2 and 3 hollowed out from the bottom 4 of the membrane. This acoustic membrane may for example be made of amorphous metal or metallic glass, which are corrosion resistant materials. The total thickness of the membrane 1 may be less than or equal to 1mm, preferably close to 0.3 mm.

Striking or musical watch 10 also includes a timepiece movement 20, which movement 20 is typically mounted on a plate 24. The edge portion 22 is fastened to a bezel 24, which defines a bezel. Typically, both the deck 24 and the rim portion 22 are made of a metallic material.

Watch movement 20 includes a striking mechanism, not shown. This striking mechanism may comprise at least one gong mounted on a gong-carrier integral with plate 24, and at least one hammer rotatably mounted on the plate for striking said gong at a determined time. A substantially circular gong surrounds the various parts of the movement of the striking watch. The setting of this striking mechanism is used to indicate the programmed alarm time or three minutes.

In a more elaborate musical watch embodiment, the striking mechanism may include a pin barrel having a set of tongues attached to a heel that is fastened to the plate 24. The vibrating tongue of the pin barrel produces a note or a series of notes. Each tongue is typically configured to produce a particular note, but there may be some set of two tongues so that each set produces the same particular note. To produce music, for example, at a programmed time, the pin barrel tabs are raised by pins integral with a rotating disk or cylinder on the plate 24 and then released. Each actuated tongue oscillates predominantly at its first natural frequency. The vibrations generated by the actuated tongues are transmitted to the external parts of the watch, which must allow the sound generated by each vibrating tongue to radiate in an acoustic sense.

In this embodiment, the acoustic membrane 1 takes the shape of a dome, the top edge of which is mounted in a sealed manner via an annular gasket 18 on the inner annular edge of the back cover 15 of the watch case. The diameter of this dome may be the same as the diameter of the crystal 12 and may be between 20-40 mm. An annular support 21 supports the backplate 24 on the side having the edge portion 22 and rests on the top edge of the acoustic membrane 1. When the middle part 14 is fastened to the back cover 15 of the watch case, the support 21 and the peripheral edge of the sound-radiating membrane 1 are clamped between the middle part 14 and the edge of the back cover 15.

It is noted that the acoustic membrane 1 may be fixed via its edges in a different way than described hereinbefore. It is conceivable to fix the membrane via its edge at odd points in 2, 3, 4 or more positions, or to fix the membrane elastically or with a simple bearing condition.

The rear cover 15 is removably mounted on the intermediate member 14 by known means with a sealing gasket 19. The crystal 12 is in particular fixed to the bezel 13 so as to close the case in a sealed manner. The dial 23 is held on the edge of the intermediate member and is disposed below the crystal 12. For a mechanical striking watch 10, the time indicating hands (not shown) are provided on a dial which also typically carries hour symbols around its periphery.

The center portion of the acoustic membrane is not in contact with the support portion 21 and the inner surface of the rear cover 15. Thus, sufficient space 17 is provided in the case to enable the acoustic membrane to vibrate freely or radiate acoustically. The acoustic membrane 1 and the back cover 15 thus together form a double back cover. One or more holes 16 are also provided laterally through the rear cover 15 to allow the acoustic membrane to radiate sound generated by the striking mechanism towards the outside.

During operation of the striking mechanism, one or more notes produced by the striking mechanism are transmitted directly to the acoustic membrane to vibrate it. The connecting portions 21, 22 and 24 also transmit vibrations to the acoustic membrane 1 at the edge of the acoustic membrane 1. Since the membrane comprises oval shaped areas 2, 3 hollowed out at the bottom 4 of the membrane, the membrane is able to vibrate at several natural frequencies depending on the number of notes to be radiated. These first natural frequencies are preferably within the useful acoustic band between 1kHz and 4 kHz. However, the second natural frequency of vibration of the note is above 4 kHz. This is advantageous since the second vibration frequency is usually acoustically harmful.

These desired natural acoustic vibration frequencies of the membrane, which may be made of amorphous metals, depend on physical properties such as density and young's modulus. Furthermore, for this type of acoustic radiating membrane 1, a very low level of attenuation can be observed, which provides a very high level of acoustic efficiency for the acoustic membrane. Furthermore, assuming that the second natural frequency mode is substantially close in frequency to the first natural frequency mode having an orthogonal orientation, the destructive interference effect of the second natural frequency is mitigated. In other words, the membrane never vibrates in a pure second natural frequency mode.

Due to the fact that the membrane is made of a corrosion resistant material, the membrane can be mounted on a back cover, for example made of a noble metal such as gold. No electrochemical potential difference was observed even in a humid environment, which means that no corrosion occurred at the contact between the membrane 1 and the back cover 15.

For example, the metallic glass or amorphous metal used to make the film may also be a metal alloy based on titanium, zirconium and beryllium. Thus, as a more specific example, the amorphous metal alloy may include 41% zirconium, 14% titanium, 12% copper, 10% nickel, and 23% beryllium. The Young's modulus of the alloy was 105GPa, and the elastic limit was 1.5 GPa. The amorphous metal alloy may also be formed from 57.5% platinum, 14.7% copper, 5.3% nickel, and 22.5% phosphorus. In this case the Young's modulus of the alloy was 98GPa, and the elastic limit was 1.4 GPa.

Starting from the description just given, a person skilled in the art can envisage several variants of acoustic radiating membrane for musical boxes or timepieces, without departing from the scope of the invention defined by the claims. The acoustic membrane may be located in a middle part of the watch case through which a hole is formed for sound radiation of the vibrating acoustic membrane. The acoustic membrane may be located on an external part of the watch case but is provided over at least one aperture in the watch case so that one or more notes produced by the striking mechanism can cause the membrane to vibrate. Several acoustic membranes may be provided, which are arranged in several positions within the watch case or overlap each other. The membrane may have a shape other than circular, for example rectangular, and may be flat. The membrane may include an elliptical region on a first side and another elliptical region on a second, opposite side of the membrane.

Claims (16)

1. An acoustic radiating membrane (1) for a music box or a striking watch (10), characterized in that the acoustic radiating membrane (1) is made with at least one non-circularly symmetrical shaped area formed in the material of the membrane or with at least one non-circularly symmetrical shaped area hollowed out in or protruding from a portion of the membrane.

2. Membrane (1) according to claim 1, characterized in that the membrane (1) comprises a plurality of areas (2, 3) of asymmetrical shape.

3. Membrane (1) according to claim 1, characterized in that the membrane (1) comprises at least two asymmetric areas, each area being hollowed out in the membrane with a different uniform thickness, so as to maximize the first natural vibration frequency of the membrane in the frequency range between 1kHz and 4 kHz.

4. Membrane (1) according to claim 1, characterized in that one or more asymmetric areas (2, 3) have an elliptical shape.

5. Membrane (1) according to claim 4, characterised in that the oval shaped areas are dug out of the membrane with a uniform thickness different from each other and smaller than the thickness of one bottom part of the membrane.

6. Membrane (1) according to claim 4, characterised in that the oval shaped areas are tabs made on the minimum thickness of the membrane, each oval shaped area having a different thickness from the other area.

7. Film (1) according to claim 5 or 6, characterized in that it has the general shape of a dome with a bottom (4), in which bottom (4) regions (2, 3) are made which are oval in shape.

8. Membrane (1) according to claim 5 or 6, characterised in that the first region (2) of elliptical shape is centred on a circular membrane, the second region (3) of elliptical shape is off-centred on said membrane and these two regions are partially overlapping.

9. Membrane (1) according to claim 8, characterised in that the ratio between the half-axes of the two ellipses (2, 3) hollowed out of the membrane and the radius of the circular membrane must be in the range 2/3 to 1, the ratio between the two thicknesses of the ellipses must be in the range 1/2 to 4/5 and the minimum thickness of each ellipse must not be greater than 2/3 of the total thickness of the circular membrane.

10. A membrane (1) according to claim 2, characterized in that the uniform thickness of the membrane is 0.3mm or less, the thickness of the first region (2) of elliptical shape being of the order of 0.15mm and the thickness of the second region (3) of elliptical shape being of the order of 0.2 mm.

11. Film (1) according to claim 1, characterized in that it is made of gold or titanium or amorphous metal or metallic glass.

12. Membrane (1) according to claim 1, characterized in that the asymmetrically shaped areas are formed in the substrate of the membrane by locally altering the physico-chemical properties of the material in a deterministic manner.

13. A striking or musical watch (10) comprising: a watch case having a middle part (14) and a back cover (15) provided with at least one lateral hole (16), wherein the back cover is fastened to the middle part in a sealed and removable manner; a crystal (12) for closing the case in a sealed manner; a watch movement (20) held inside the watch case and having a striking mechanism that can be actuated at a determined time to produce one or more notes; and at least one sound-radiating membrane (1) according to claim 1 arranged in the watch case.

14. Watch (10) according to claim 13, characterised in that the sound radiating membrane (1) is held on the inner edge of the back cover (15) of the watch case and on one part of the middle part (14) and in that the periphery of the sound radiating membrane (1) is clamped, together with the periphery of the support (21) of the movement, between the middle part (14) and the inner edge of the back cover (15) of the watch case.

15. Watch (10) according to claim 14, characterised in that said sound-radiating membrane (1) has the shape of a dome, the top edge of which is clamped, together with the ring support, between the middle part (14) and the annular inner edge of the back cover (15) of the case, an annular sealing gasket (18) being provided between the edge of the back cover (15) and the annular edge of said membrane, and the central part of said sound-radiating membrane is not in contact with the support (21) and the inner surface of the back cover (15) of the case, so as to define a space (17) allowing the free oscillation of said membrane.

16. Watch (10) according to claim 13, characterised in that a plurality of sound-radiating membranes (1) are connected to the watch case and are arranged independently of each other or one above the other.