HK1176692B - Removable acoustic radiating membrane, method of assembling the same, and musical or striking watch - Google Patents

Description

Removable acoustic radiating membrane, method of assembling the same, timepiece case and musical timepiece

Technical Field

The present invention relates to a removable acoustic radiating membrane for a musical watch or striking watch (striking watch).

The invention further relates to a striking watch case having a middle portion and a back cover, the removable sound radiating membrane being held between the middle portion and the back cover.

The invention also relates to a watch (watch) comprising a removable acoustic radiating membrane. The timepiece includes a timepiece case generally formed by a middle portion and a back cover removably secured to the middle portion in a sealing manner. A crystal is arranged on the side opposite to the back cover to close the casing in a sealed manner. A clock movement is held inside the watch case and is provided with a striking mechanism such as a music module. The music module can be actuated a determined number of times mainly for producing music. The removable acoustic radiating membrane is connected to the case so as to radiate sound generated by the striking mechanism toward the outside of the case.

Background

If the sound membrane is held fixed between the middle portion of the watch case and the back cover, a certain number of side openings may be provided on the peripheral portion of the back cover of the watch to transmit sound from the diaphragm toward the outside. The acoustic membrane must generally be made of a metal material of small thickness to ensure good acoustic transmission of the sound or music produced, for example, by the music module of a striking watch. However, in the case where a sound film having a small thickness is disposed between the back cover and the watch movement (watch movement), the film cannot withstand excessive pressure or vacuum pressure from environmental conditions. These environmental conditions relate to the physical conditions of the area where the striking watch containing the acoustic membrane is located. If the watch is used in a deep submergence environment, high pressures will therefore build up on the membrane. Under these conditions, such a thin acoustic membrane may deform and come into contact with the components of the chronograph travel unit. This makes it very likely to damage both the membrane and certain components of the watch movement, which are disadvantageous.

CH patent No 375664 discloses a solution to this problem. The patent discloses a waterproof wrist-type striking watch including an acoustic membrane and a device for limiting the flexing of the membrane towards the interior of the watch. The circular membrane is secured to the middle portion of the timepiece as a back cover via the peripheral edge of the timepiece. The second back cover of the case is fixed to the peripheral portion of the film and serves as an outer portion of the striking watch. The second rear cover includes a side opening through which sound passes. The stop means are arranged so as to limit the flexing of the membrane towards the inside of the watch. To achieve this, the support member is fixed at a central position on the membrane, and the center of the second back cover includes a stopper member for the membrane support member. The support member passes through an opening in the back cover at a position where the stopper member is to be fixed to the center of the membrane. In the case where the external pressure is high, the membrane supporting member abuts on the stopper member of the back cover so as to prevent the membrane from being excessively bent.

One drawback of the stop device disclosed in CH patent No 375664 for limiting the flexing of the membrane towards the inside of the watch is that: the support member is secured to the membrane by passing through an opening in a second back cover of the watch case. In these cases, dust may accumulate in the passages for the support members to pass through the rear cover of the case, which greatly slows down the acoustic transmission resonance from the membrane. This can also be disturbing to the person wearing the watch and can lead to itching or eczema, which is another disadvantage. This support member can also be handled from the outside and the membrane is not removable, which is a further disadvantage.

Disclosure of Invention

It is therefore an object of the present invention to overcome the drawbacks of the prior art mentioned above, and to this end, the present invention provides a removable acoustic radiating membrane for a musical striking watch or striking watch, which is of small thickness and has means which cooperate with the watch case to prevent any significant deformation once an excessive or vacuum pressure has occurred when the membrane is housed in the watch case.

The invention therefore relates to a removable acoustic radiating membrane for a musical striking watch or a striking watch, wherein the membrane can be removably fixed between a middle portion of a watch case and a back cover, characterized in that it comprises a retaining member intended to cooperate with a stop member of the back cover arranged entirely inside the watch case in order to limit the flexing of the membrane after being subjected to significant overpressure or vacuum pressure from ambient conditions.

The invention therefore relates to a striking watch case comprising at least a middle portion and a back cover mounted on the middle portion so as to close the case, characterized in that the back cover comprises a stop member having a housing arranged entirely inside the striking watch case and adapted to receive a retaining member of the removable acoustic radiating membrane of the invention, wherein the membrane can be removably fixed between the middle portion of the case and the back cover.

The invention therefore also relates to a musical striking watch or striking watch, comprising: the striking watch case of the invention, wherein said case has a middle portion and a back cover provided with at least one side aperture, said back cover being fastened in a sealed and removable manner to said middle portion; a crystal enclosing the casing in a sealed manner; a watch travel device held inside the watch case and provided with a striking mechanism that can be actuated a determined number of times so as to produce a note or notes or music; and at least one removable acoustic radiating membrane of the invention, arranged in said watch case, characterized in that the retaining means of said membrane are arranged in a housing located in the stop means of said back cover, which is arranged entirely inside said watch case, so as to limit the flexing of the membrane after being subjected to significant overpressure or vacuum pressure from ambient conditions.

One advantage of the present invention comes from the fact that: the bottom portion of the membrane is held in a housing in an internal stop member of the back cover by a retaining member. This ensures that the membrane, which is both flexible and waterproof, is not excessively deformed by excessive pressure from ambient conditions and does not come into contact with parts of the ambulatory device. Mainly because the back cover comprises a side opening in order to enable sound radiation from the membrane towards the outside, the membrane is held at a distance from the traveller by the cooperation between the retaining means and the stop means, especially when the watch is used in a diving environment. During normal operation, the membrane can vibrate freely with the retaining member arranged with clearance in the stop member housing.

Since the stop member and the holding member are made of a metallic material, no significant sound attenuation is observed, since no joint is provided, but only a metallic-on-metal connection is provided between the two members. In the case of a stop element manufactured inside the watch case, no dust can accumulate in the stop element housing. Furthermore, once the back cover is fixed to the middle part of the watch case, the retaining member cannot be manipulated.

The invention therefore also relates to a method of assembling a removable acoustic radiating membrane according to the invention in a striking watch case according to the invention, characterized in that it comprises the following steps:

placing and positioning a removable membrane over the middle portion,

mounting the back cover of the case on the intermediate portion with the internal stop member oriented such that the tongue portion of the retaining member of the membrane is housed in the housing of the internal stop member,

rotating the back cover on the middle portion by about 90 ° to arrange the length of the retaining tongue between the two top detent portions of the stop member and the bottom of the housing of the back cover to effect assembly of the retaining member in the housing in the stop member in a bayonet-type assembly, and

securing the rear cover to the middle portion.

Drawings

The following detailed description more clearly describes objects, advantages and features of a removable acoustic radiating membrane for a musical striking watch or striking watch, and a watch incorporating said membrane, based on at least one non-limiting example, and with reference to the accompanying drawings, in which:

FIG. 1 shows a three-dimensional bottom view of a removable acoustic radiating membrane according to the present invention;

FIG. 2 shows a simplified transverse cross-sectional view of a striking watch or musical watch, the watch being provided with a removable acoustic membrane according to the present invention; and

figure 3 shows a three-dimensional bottom view of a musical watch or striking watch according to the invention before the back cover of the case is secured to the removable film and to the intermediate portion.

Detailed Description

In the following description, all those components of a striking watch or a musical watch, which are well known in the art, will be described only briefly. The description will now be made primarily in connection with the configuration of the sound radiating membrane and in particular the manner how the sound radiating membrane is held to cooperate with the back cover of the watch case.

Fig. 1 shows a three-dimensional bottom view of a removable acoustic radiating membrane 1 for a musical watch or a striking watch. In this embodiment, the removable film may be made in the form of a dome having a bottom portion 4 as the bottom of the dome and a peripheral edge 5 for assembly in the watch case, as described later in connection with fig. 2 and 3. The membrane 1 may be a circular membrane, for example with a diameter of 40mm at the edge and a diameter of 31mm at its bottom portion 4, as a non-limiting example. However, the membrane may also have other shapes than circular and may have different dimensions.

The peripheral edge 5 of removable membrane 1 can be fixed between the middle part of the watch case and the back cover. The peripheral edge further comprises a cavity 6 for receiving the hands of a striking watch case in order to position the membrane 1 in the striking watch case. The interior of the timepiece is sealed via this removable membrane, which is fixed between the middle portion and the rear cover of the case, but one or more side openings can be provided in the rear cover of the case in order to achieve acoustic radiation from the diaphragm towards the outside.

The removable membrane 1 comprises a holding means 7, preferably arranged in a central portion of the membrane, e.g. at the center of the bottom portion 4. Preferably, the retaining member is integral with the bottom portion 4, but a metal retaining member may also be screwed, driven or welded onto the bottom portion 4. The removable membrane 1 and the holding means 7 are made of a metallic material, such as titanium, or of a noble metal, such as gold, or of an amorphous metal.

The retaining member 7 is arranged to cooperate with an internal stop member of the back cover of the watch case, as described below in connection with fig. 2 and 3. This limits the bending of the membrane after excessive pressure or vacuum pressure due to environmental conditions when the retaining means 7 is placed in the housing in the inner stop means of the cover back of the case. Typically, a membrane arranged in a sealed manner in a watch case is able to withstand high pressures when the watch is used in a deep diving environment.

The holding member 7 is preferably T-shaped, but may also be L-shaped. The holding means thus consist of a stem fixed to the bottom part 4 of the membrane and a tongue fixed to the stem parallel to the bottom part 4. The tongue is generally rectangular and is dimensioned so that its width allows the insertion of the retaining member into the housing in the internal stop member of the back cover of the sleeve. The tongue portion has a length dimension suitable for retaining the tongue portion in the case after a bayonet-type assembly in the back cover case of the watch case.

For a good sound quality of the diaphragm, the thickness of the diaphragm must usually be small, which makes the use of the holding means 7 necessary. The typical thickness of the film 1 is 0.3mm or less. In order to maximize the first natural (natural) vibration frequency of the membrane in the frequency band range between 1kHz and 4kHz, the membrane may have a non-uniform spatial thickness in its bottom portion. To achieve this, it may comprise at least a first region 2 having an elliptical shape, said first region being formed in the material of the membrane or being hollow. The first oval area 2 is formed by the side opposite to the side carrying the retaining means 7. In this first elliptical region 2, the thickness of the membrane may have a dimension of 0.15 mm.

The removable membrane 1 may also comprise a second area 3 having an elliptical shape formed in the material of the membrane. In this second region, the thickness of the film is of a size of 0.2 mm. The two elliptical areas 2 and 3 are partially superposed and are suitably dimensioned to maximise the number of natural vibration modes of the member lying predominantly in the frequency band range between 1kHz and 4 kHz. The shape recommended is an elliptical shape so as to have two natural vibration modes compared with a circular region.

It should also be noted that: instead of forming the oval regions 2, 3 in the total thickness of the membrane 1 by etching, grinding or hollow-forming, it is also possible to envisage producing a membrane with regions which have locally altered physicochemical properties in a deterministic manner during the production or after-treatment. This process allows uniform regions, such as elliptical regions, to be produced to multiply the mode of vibration and flatten (become monotonic) the frequency response.

FIG. 2 thus shows a transverse or diametric cross-section of a striking or musical watch 10. Timepiece 10 basically comprises a removable acoustic radiating membrane 1 provided with a retaining member 7 so as to cooperate with an internal stop member 27 of a metallic back cover 15 of the timepiece case. The membrane is also constructed so as to have two oval areas 2 and 3, which are formed in the material of the bottom portion 4 in a hollow manner, in order to improve the music or note or notes produced by the striking mechanism. The acoustic membrane may, for example, be made of an amorphous metal, which may be a corrosion resistant material.

Striking or musical watch 10 also includes a watch travel mechanism 20, which is typically mounted on a plate 24. Edge portion 22 is secured to a plate 24 that defines a striking watch frame. Typically, both the plate 24 and the edge portion 22 are made of a metallic material.

The chronograph walk device 20 includes a striking mechanism, which is not shown. The striking mechanism may include one or more bells mounted on the same bell carrier (gong-carrier) integral with the plate 24, and at least one or more hammers rotatably mounted on the plate for striking the bell at predetermined times. The striking mechanism is arranged to indicate a programmed alarm time or minute timer.

In a more elaborate musical watch embodiment, the striking mechanism may include a music module provided with a pin-barrel having a set of tongues connected to a heel that is fastened to the plate 24. A vibrating tongue with a pin cylinder produces a musical note or series of notes. Each tongue is typically configured to produce one particular note, but some groups of two or more tongues may be provided so that each group produces the same particular note. To produce music, for example at programmed times, the spiked cylinder tongue is raised and then released by a needle integral with a rotating disk or cylinder located on the plate 24. Each actuated tongue oscillates primarily at its first natural frequency. The vibrations generated by the actuated tongues are transmitted to the external part of the watch, which must allow the sound generated by each vibrating tongue to be radiated acoustically.

In this embodiment, the acoustic membrane 1 presents the shape of a dome, the top peripheral edge 5 of which is mounted in a sealed manner on the inner annular edge of the rear cover 15 of the casing via an annular gasket 18. The dome may have a diameter the same as the diameter of the striking glass 12, which may be between 20mm and 40 mm. The ring-shaped support 21 supports the plate 24 on one side by the edge portion 22 and rests on the top edge of the acoustic membrane 1. When metallic middle portion 14 is fastened to metallic back cover 15 of the watch case, support 21 and the peripheral edge of acoustic radiating membrane 1 are clamped between middle portion 14 and the edge of back cover 15.

It should be noted that: the acoustic membrane 1 can be fixed to the above-mentioned components in different ways via its edge 5. The membrane may be fixed via its edges at 2, 3, 4 or more points, or be fixed in an elastic manner or have a simple supporting state.

The rear cover 15 is removably mounted on the intermediate portion 14 by known means by means of a sealing gasket 19. The rear cover 15 may be secured to the intermediate portion by screws, as described below in connection with fig. 3. Watch crystal 12 is secured in an attractive manner to bezel 13 to close the watch case in a sealed manner. The dial 23 is held on the edge of the middle portion and is disposed below the striking face glass 12. For a mechanically struck striking watch 10, the time indicating hands 25 are provided on a dial plate, which usually carries time indicia on its periphery.

In the normal operating mode, the central portion 4 of the acoustic membrane is not in contact with the support 21 and the inner surface of the rear cover 15. Thus, sufficient space 17 is provided in the casing for the acoustic membrane to be able 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 apertures 16 are also provided transversely through the rear cover 15 to allow the acoustic membrane to radiate sound produced by the striking mechanism outwardly.

However, in the event of any significant excess pressure or vacuum pressure on the membrane, the retaining member 7 may be in metal-on-metal contact with the internal stop member 27 of the back cover, which retaining member is arranged with some clearance in a housing 37 in the internal stop member 27 of the back cover. The cooperation between the retaining means 7 and the internal stop means 27 prevents the membrane from undergoing significant deformation when the watch is used in a deep diving environment. The maximum estimate of the clearance on each side of the tongue and stem of the retaining member 7 may be, for example, 0.5mm for the clearance allowed to exist by the retaining member 7 in the housing 37 in the inner stop member 27.

During operation of the striking mechanism, one or more notes produced by the striking mechanism are transmitted directly to the removable acoustic radiating membrane to vibrate it. The connecting members 21, 22 and 24 also transmit vibrations to the acoustic membrane 1 at the edge of the acoustic membrane. Since the acoustic membrane comprises asymmetric areas in the form of ellipses 2, 3, formed in a hollow manner in the bottom portion 4 of the membrane, it is able to vibrate at a plurality of first natural frequencies, depending on the number of notes to be radiated. These first natural frequencies are preferably within a useful acoustic bandwidth of between 1kHz and 4 kHz. However, the second natural frequency of vibration of the note is higher than 4 kHz. This is advantageous since the second vibration frequency is typically acoustically lossy.

These desired natural vibrational acoustic frequencies of films that can be made from amorphous metals depend on physical properties such as density and young's modulus. The amorphous metal used may be, for example, a metal alloy based on titanium, zirconium, beryllium. Furthermore, for this type of acoustic radiating membrane 1, the level of attenuation observed is extremely low, which provides a very high level of acoustic efficiency for the acoustic membrane.

Due to the fact that this removable membrane 1 can be formed of a corrosion-resistant material, it can be mounted on a back cover 15, for example made of a noble metal such as gold. Even in a humid environment, there is no difference in the electrochemical potential observed, which means that no corrosion occurs upon contact between the membrane 1 and the rear cover 15.

Figure 3 shows a three-dimensional bottom view of musical watch or striking watch 10 according to the invention before the back cover of the case has been fixed to removable film 1 and intermediate portion 14. The steps of assembling removable acoustic membrane 1 in the watch cases 14, 15 are mainly shown.

The peripheral edge 5 of the removable acoustic membrane 1 is arranged on the periphery of the support of the watch movement (not shown). The membrane is positioned by an index pin (not shown) of the watch case. The membrane has a cavity on its periphery for receiving the index pin. The retaining means 7 of the membrane are positioned in this view so that the tongue is parallel to the bottom part 4 and its length is arranged in the direction of 3-9 points of the watch. It should also be noted the location of the oval areas 2 and 3, which are formed in a hollow manner within the material of the membrane on the side of the watch travel device. However, these oval areas 2 and 3 can also be made on the same side as the holding means 7.

On the inner side of the striking watch, the metal back cover 15 has a stop member 27. The inner stop member 27 is formed by two hook-shaped catches, which are opposite to each other. Each catch has side walls perpendicular to the rear cover 15 and a top portion substantially parallel to the rear cover 15. The side walls and top portions of the two detents define a housing 37 for holding the retaining member 7 of the removable membrane by the bayonet-like assembly, as described herein. Of course, the housing 37 is dimensioned so as to allow clearance for the retaining means 7 of the membrane once positioned in said housing 37.

The metal back cover 15 is first placed on the intermediate part 14, as shown by the arrows in the figure, while ensuring that the two catches of the stop member 27 are oriented such that the width of the tongue of the retaining member 7 passes between the two catches just into the housing 37. Once this is done, the rear cover 15 is rotated through an angle of about 90 ° so that the length of the tongue is between the top portion of the catch of the stop member and the bottom of the housing 37. This defines a bayonet type assembly.

Once the assembly of the retaining member 7 in the housing 37 of the stop member 27 in a bayonet-type manner is completed, the back cover 15 can be screwed onto the intermediate portion via screws (not shown), each of which passes through a respective notched opening 11 in the back cover and is screwed onto a thread 31 in the intermediate portion 14. The peripheral edge 5 of the removable membrane 1 is thus held pressed in between the travelator support and the back cover 15 via a sealing gasket 18, as shown in fig. 2. The chronograph walk-time device is held in the sealed chamber since the membrane is fastened between the intermediate portion 14 and the back cover 15. Side apertures 16 in the rear cover are provided for acoustic radiation outwardly from the membrane. Through these apertures 16, the membrane can also withstand significant pressure depending on environmental conditions, especially when the musical watch is used for diving. However, the bending of the membrane is limited by the cooperation between the holding means 7 and the stop means 27, as described above.

From the above description, a person skilled in the art can design several variants of removable acoustic radiating membrane for a musical watch or a striking watch, without departing from the scope of the invention as defined in the appended claims. The holding means of the membrane may be arranged at an off-centre position with respect to the centre of the membrane. A plurality of holding means may be provided, which cooperate with specific stop means inside the watch case, respectively. The membrane may have a shape other than circular, for example rectangular, or it 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. The stop member may be a closure portion defining a housing for receiving a tongue of the L-shaped retaining member. The holding means may also have a helical shape.

Claims (22)

1. Removable acoustic radiating membrane (1) for a musical striking watch or striking watch (10), wherein said membrane can be removably fixed between a middle portion (14) and a back cover (15) of a watch case, characterized in that it comprises a retaining member (7) intended to cooperate with a stop member (27) of the back cover arranged entirely inside the watch case in order to limit the flexing of the membrane after being subjected to significant overpressure or vacuum pressure from ambient conditions, wherein, once the back cover is fixed to the middle portion, the retaining member cannot be manipulated and dust is not accumulated in the housing of the stop member.

2. Membrane (1) according to claim 1, characterized in that the retaining means (7) are arranged in the central portion (4) of the membrane.

3. Membrane (1) according to claim 1, characterized in that the retaining means (7) is T-shaped or L-shaped with a stem fixed to the bottom part (4) of the membrane and a tongue parallel to the bottom part (4) fixed to the stem.

4. Membrane (1) according to claim 3, characterized in that said tongue has the general shape of a rectangle, the width of which is dimensioned so that it can be inserted into a housing (37) located in an internal stop member (27) of the back cover of the timepiece case, while the length of which is dimensioned so as to retain the tongue in the housing after assembly in a bayonet-type assembly.

5. Membrane (1) according to claim 1, characterized in that the holding means (7) are integral with the bottom portion (4) of the membrane.

6. The film (1) according to claim 1, characterized in that its general thickness is 0.3mm or less.

7. The membrane (1) according to claim 6, characterized in that it comprises at least a first zone (2) with an oval shape formed in the material of the membrane, and in that the thickness dimension of the membrane in the first zone (2) is 0.15 mm.

8. The membrane (1) according to claim 7, characterized in that it comprises a second zone (3) of elliptical shape formed in the material of the membrane, and in that the thickness dimension of the membrane in the second zone (3) is 0.2mm, and in that the two zones are partially superposed in order to maximize the first natural vibration frequency of the membrane in the frequency band range between 1kHz and 4 kHz.

9. Membrane (1) according to claim 1, characterized in that it is made of noble metal or titanium or amorphous metal.

10. Membrane (1) according to claim 1, characterized in that it has a dome shape with a bottom portion (4) on which said retaining member (7) is fixed and has a peripheral edge (5) so as to be assembled between said middle portion of said watch case and said back cover.

11. The film (1) according to claim 1, wherein the peripheral edge (5) of the film comprises a cavity (6) for receiving a watch case index needle for positioning the film in the watch case.

12. Striking watch case comprising at least a middle portion (14) and a back cover (15) mounted on the middle portion so as to close the case, characterized in that the back cover comprises a stop member (27) having a housing (37) arranged entirely inside the striking watch case and adapted to receive a retaining member (7) of the removable acoustic radiating membrane according to claim 1, wherein the membrane can be removably fixed between the middle portion of the case and the back cover, and wherein, once the back cover is fixed to the middle portion, the retaining member cannot be manipulated and no dust is accumulated in the housing.

13. Watch case according to claim 12, characterized in that the internal stop member (27) comprises two hook-shaped catches opposite each other, each catch having a side wall and a top portion so as to define a housing (37) between the two catches such that the retaining member of the removable film can be held via a bayonet-type assembly.

14. Timepiece case according to claim 13, wherein the housing (37) between the two detents is dimensioned so as to leave clearance for the movement of the retaining means of the removable membrane.

15. The striking watch case according to claim 12, wherein said back cover comprises one or more side apertures (16) to radiate outwardly at least one sound generated in said striking watch case.

16. A musical striking watch or striking watch (10), said watch comprising: watch case according to claim 12, wherein the case has a middle portion (14) and a rear cover (15) provided with at least one side aperture (16), said rear cover being fastened in a sealed and removable manner to the middle portion; -a crystal (12) closing the casing in a sealed manner; watch travel device (20) held inside the watch case and provided with a striking mechanism that can be actuated a determined number of times so as to produce a note or notes or music; and at least one removable acoustic radiating membrane (1) according to claim 1, arranged in the watch case, characterized in that the retaining member (7) of the membrane is arranged in a housing (37) located in a stop member (27) of the back cover, arranged entirely inside the watch case, so as to limit the flexing of the membrane after being subjected to significant overpressure or vacuum pressure from ambient conditions, wherein, once the back cover is fixed to the intermediate portion, the retaining member cannot be manipulated and no dust accumulates in the housing.

17. Striking watch (10) according to claim 16, characterized in that the retaining member (7) is T-shaped with a stem fixed to the bottom part (4) of the membrane and a substantially rectangular tongue fixed to the stem parallel to the bottom part (4), and in that the internal stop member (27) comprises two hook-shaped catches opposite each other, each catch having a side wall and a top part so as to define a housing (37) between the two catches so that the retaining member of the removable membrane can be retained after a bayonet-type assembly.

18. Chronograph watch (10) according to claim 16, characterized in that the membrane (1) is held on the inner edge of the back cover (15) of the case and on a portion of the middle part (14), and the periphery of the membrane (1) and of the annular support (21) of the travel device are clamped between the middle part (14) of the case and the inner edge of the back cover (15).

19. Striking watch (10) according to claim 18, characterised in that said membrane (1) has the shape of a dome, the top edge of which is clamped, together with said annular support, between the middle portion (14) of the casing and the inner annular edge of the back cover (15), an annular sealing gasket (18) being placed between said edge of the back cover (15) and the annular edge of the membrane, and the central portion of the membrane not being in contact with the support (21) and the inner surface of the back cover (15) of the casing, so as to define a space (17) allowing the membrane to oscillate freely.

20. Method of assembling a removable acoustic radiating membrane according to claim 1 in a striking watch case according to claim 12, characterized in that it comprises the following steps:

placing and positioning a removable membrane (1) on the middle portion,

-mounting the rear cover (15) of the case on the intermediate portion, with the internal stop member (27) oriented so that the tongue of the retaining member (7) of the membrane is housed in the housing (37) of the internal stop member (27),

rotating the rear cover (15) on the intermediate portion by 90 ° so as to arrange the length of the retaining member (7) between the two top detent portions of the stop member (27) and the bottom of the housing (37) of the rear cover, in order to achieve the process of assembling the retaining member (7) in the housing in the stop member (27) in a bayonet-type assembly, and

-fixing the back cover (15) to the intermediate part, wherein the retaining member cannot be manipulated and no dust is accumulated in the stop member once the back cover is fixed to the intermediate part.

21. The method of claim 20, wherein the back cover is secured to the middle portion by a number of screws, each screw entering a corresponding notched aperture in the back cover and each screw being threaded into a corresponding thread in the middle portion.

22. The method according to claim 20, characterized in that the orientation of the film on the middle part is provided by peripheral cavities (6) able to receive index pins of the striking watch case.