Acoustic device for a striking timepiece

Abstract

The present invention relates to an acoustic device (10) for a striking timepiece, including an acoustic membrane (20), at least one piezoelectric element (30; 30a, 30b; 30c; 32) arranged to cooperate with the acoustic membrane (20) and at least one electric circuit (40a, 40b) incorporating the piezoelectric element. The acoustic device (10) further includes at least one gong (12, 14) that can be struck by a hammer. The assembly comprising the piezoelectric element (30; 30a, 30b; 32) and the electric circuit (40a, 40b) is configured to adjust resonant frequencies of the acoustic membrane (20) according to the resonant frequencies of the at least one gong (12, 14). The invention also relates to a striking timepiece, in particular a clock or watch, comprising the acoustic device (10).

Description

Acoustic device for ringing room Technical field

[0001] The present invention relates to an acoustic device for a striking piece, comprising a membrane whose resonance frequencies are adjustable by piezoelectric effect. The invention also relates to a striking piece, in particular a timepiece, comprising such an acoustic device. State of the art

[0002] Striking pieces and in particular striking timepieces, for example of the grande sonnerie or minute repeater type, are well known. CH714635 and EP2942675 for example disclose a striking timepiece comprising a watch case housing an acoustic membrane and a watch movement equipped with a striking mechanism. This mechanism comprises at least one gong and a hammer for striking the gong. The sound produced by the impact of the hammer on the gong causes the gong and the membrane to vibrate, which contributes to the sound transmission between the inside and the outside of the watch case.

[0003] The disadvantage of the above-mentioned timepiece is that the acoustic membrane operates in a forced mode and does not resonate. The membrane is therefore not used to its full potential.

[0004] There are also watches comprising an acoustic membrane associated with a piezoelectric element in order to adjust the resonance frequency of the acoustic membrane. For example, FR2466903 discloses a mechanical watch equipped with an assembly consisting of a AUDEMA-29-PCT acoustic membrane and a piezoelectric element. The piezoelectric element is, according to one method of operation, controlled by an electronic circuit in order to vibrate the acoustic membrane to produce an audible sound. The watch also includes a mechanism for adjusting the resonant frequency of the acoustic membrane. This mechanism is mounted in the bottom of the case and comprises a rotating arm in contact with the membrane and movable to adjust its resonant frequency. This makes it possible to modify the frequency of the membrane-piezoelectric element assembly in order to amplify the sound.

[0005] The disadvantage of the above-mentioned mechanical watch lies in the quality of the sound emitted, which depends partly on the characteristics of the acoustic membrane.

[0006] An aim of the present invention is therefore to provide an acoustic device for a ringing coin so that it can emit a better quality sound.

[0007] Another object of the present invention is to provide an acoustic device for a ringing piece which allows the latter to attenuate the sound amplitude to obtain a mute mode. Brief summary of the invention

[0008] At least some of these aims are achieved in particular by an acoustic device for a striking piece, comprising an acoustic membrane, at least one piezoelectric element arranged to cooperate with the acoustic membrane and at least one electrical circuit integrating the piezoelectric element, in particular by its electrodes which, typically, can be constituted by its larger faces. The acoustic device further comprises at least one gong which can be struck by a hammer. The assembly comprising the piezoelectric element and the electrical circuit is AUDEMA-29-PCT configured to adjust resonance frequencies of said membrane as a function of the resonance frequencies of said at least one timbre.

[0009] According to one embodiment, each piezoelectric element is arranged directly in contact with the acoustic membrane and preferably has a shape at least partially complementary to that of the acoustic membrane.

[0010] According to one embodiment, the acoustic membrane is circular in shape. The piezoelectric element is circular or partially circular in shape.

[0011] According to one embodiment, at least one piezoelectric element has an at least partially annular shape. The piezoelectric element is arranged along at least a portion of the periphery of the acoustic membrane. This makes it possible to modulate the resonance frequencies of the membrane when the latter is radially stressed by the piezoelectric element.

[0012] According to one embodiment, at least one face of the acoustic membrane is covered by at least one piezoelectric element to occupy at least 70% of its surface, preferably at least 80%, or even at least 90% of its surface.

[0013] According to one embodiment, the acoustic device comprises at least one piezoelectric element configured to be powered by an electrical source integrated into the electrical circuit in order to operate in an active mode.

[0014] According to one embodiment, the electrical source consists of one or more other piezoelectric elements of the acoustic device. AUDEMA-29-PCT

[0015] According to one embodiment, the acoustic device further comprises a peripheral element in contact with the acoustic membrane by its periphery. The piezoelectric element is integrated into the peripheral element so that any expansion or retraction of the piezoelectric element exerts a voltage variation on the acoustic membrane to modulate its resonance frequencies.

[0016] According to one embodiment, the acoustic device comprises several timbres. An electrical circuit is assigned to each timbre and has specific characteristics allowing the resonance frequencies of the membrane to be adjusted according to the resonance frequencies of the timbre to which the electrical circuit is assigned.

[0017] According to one embodiment, the acoustic device comprises several timbres. A piezoelectric element is assigned to each timbre and has specific characteristics making it possible to adjust the resonance frequencies of the membrane as a function of the resonance frequencies of the timbre to which the piezoelectric element is assigned.

[0018] According to one embodiment, at least one electrical circuit comprises a switch making it possible to open or close the electrical circuit in order to respectively activate or disconnect said at least one piezoelectric element integrated therein.

[0019] According to one embodiment, the assembly comprising the piezoelectric element and the electrical circuit is configured to further distance the resonant frequencies of the membrane and the gong.

[0020] Another aspect of the invention relates to a striking timepiece comprising the acoustic device and a hammer arranged to strike the gong of the acoustic device. AUDEMA-29-PCT

[0021] Another aspect of the invention relates to a striking timepiece comprising the acoustic device provided with several gongs, and several hammers arranged to strike the respective gongs. The switch is actuated by a movement of a hammer or by a striking trigger member.

[0022] According to one embodiment, said at least one piezoelectric element is arranged on a face of the membrane located opposite a stamp. Brief description of the figures

[0023] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: - figure 1 illustrates, associated with gongs, a perspective view of an acoustic device intended to be mounted in a striking timepiece, according to one embodiment; - Figure 2 illustrates an equivalent circuit of a piezoelectric element and a control circuit comprising a switch; - figure 3 schematically illustrates a watch case of a timepiece comprising the acoustic device according to the embodiment illustrated by figure 1 or according to any one of the embodiments described below; - figures 4a and 4b illustrate two circuits integrating a piezoelectric element according to two embodiments; AUDEMA-29-PCT - Figure 5 illustrates a plan view of Figure 1 with an electrical diagram comprising an energy source according to an embodiment incorporating a variant; - figure 6 illustrates a plan view of the acoustic device for a timepiece, according to another embodiment incorporating a variant; - figure 7 illustrates a sectional view of the acoustic device of figure 6; - figure 8 illustrates, accompanied by stamps, a plan view of the acoustic device for a timepiece, according to another embodiment; - Figure 9 is a sectional view of Figure 8; - figure 10 illustrates a schematic view of the acoustic device for a timepiece, according to another embodiment, and - Figure 11 is a graph representing the resonance frequency of a gong of a timepiece and that of the acoustic membrane when the sound amplitude generated by the gong-membrane-electrical circuit assembly is in an attenuated, non-optimum and optimum mode. Examples of embodiments of the invention

[0024] According to one embodiment, and with reference to Figures 1 and 3, the acoustic device 10 is intended to be mounted in a striking part. By striking part is meant any striking or musical part, such as a striking timepiece, music box, automaton or other mechanical or semi-mechanical part configured to generate a striking sound. AUDEMA-29-PCT and / or music. The embodiments taken as examples in the present description refer in a non-limiting manner to a striking timepiece

[0025] This timepiece may in particular be a grand strike or minute repeater comprising one or more gongs 12, 14. Typically, the device 10 in particular fulfills the function of a partition which divides an internal chamber 6 of the timepiece to form a sealed housing 16 and an acoustic cavity 8. The housing 16 contains a watch movement equipped with a striking mechanism. The acoustic cavity 8 comprises through-holes 9 for diffusing the sound produced by the striking mechanism from the inside to the outside of the watch case 100.

[0026] The acoustic device 10 generally has in this example a bowl shape with a rim forming a fixing flange 11. A central portion of the partition constitutes an acoustic membrane 20 on which are for example arranged a first and a second piezoelectric element 30a, 30b as illustrated in FIG. 1. The acoustic membrane 20 can for example be made of titanium, a material which has the advantage of having a relatively low modulus of elasticity and which is ideal for transmitting acoustic waves. A sapphire membrane can be used according to a variant for aesthetic reasons so that the user of the timepiece can contemplate, at least in part, the watch movement on the back of the watch case, in particular during operation of the striking mechanism.

[0027] In the example illustrated in Figure 1, the acoustic device 10 may further comprise a shoe 15 secured to the fixing flange 11 and on which are fixed a first and a second gong 12, 14 intended to be struck respectively by a first and a second hammer of the striking mechanism (not illustrated) of the timepiece. By this means, such a timepiece AUDEMA-29-PCT could typically produce two sounds of different tones, for example a low-pitched sound and a high-pitched sound. The acoustic device 10 can thus be adapted in particular for a minute repeater timepiece in order to indicate, on demand, the hours by a low-pitched sound, the quarters by a high-pitched-low-pitched sequence and the minutes by a high-pitched sound.

[0028] The shoe 15 or the assembly consisting of gongs 12, 14 and the shoe 15 is not necessarily part of the acoustic device 10. Preferably, the latter comprises only an acoustic membrane, at least one piezoelectric element arranged to cooperate with the membrane, at least one electrical circuit integrating the piezoelectric element and a frame for fixing the acoustic device in the watch case near a striking mechanism of the timepiece provided with at least one gong. The frame is adapted to support the various aforementioned elements of the acoustic device.

[0029] According to a non-illustrated variant embodiment, the timepiece comprising the acoustic device 10 may have only one gong. According to another non-illustrated variant embodiment, a timepiece comprising the acoustic device 10 may have more than two gongs, for example three, four, or even five gongs. This type of timepiece, called a carillon timepiece, may for example be composed of three, four, or five measures of three, four, and five notes respectively played on different frequencies. This device thus requires a greater number of gongs and hammers, i.e. three, four, or even five in the most melodic models.

[0030] According to the embodiment of FIG. 1, the acoustic device 10 further comprises a first and a second electrical circuit respectively integrating the first and second piezoelectric elements 30a, 30b. The device 10 is therefore suitable for a timepiece with two gongs 12, 14. AUDEMA-29-PCT

[0031] In order to be able to maximize the amplitude of the mechanical stress applied to the acoustic membrane 20 by the two piezoelectric elements 30a, 30b, at least one face of the acoustic membrane is covered by these two piezoelectric elements to occupy at least 70% of its surface, preferably at least 80%, or even at least 90% of its surface. According to a non-illustrated variant embodiment, a single piezoelectric element is arranged on one face of the acoustic membrane and covers it according to the aforementioned proportions.

[0032] The or each piezoelectric element 30a, 30b preferably has a shape at least partially complementary to that of the acoustic membrane. The acoustic membrane 20 may have a circular shape while the or each piezoelectric element 30a, 30b is circular or partially circular. For example, the two piezoelectric elements 30a, 30b may each have a semicircular shape comprising a rectilinear side facing each other as illustrated in FIG. 1.

[0033] According to one embodiment, the characteristics of the first electrical circuit 40a, preferably relating at least to its impedance z, have been chosen as a function of at least one resonance frequency of the first timbre 12. The choice of the impedance of the first circuit thus makes it possible to adjust the resonance frequencies of the membrane 20, by exciting the first piezoelectric element 30a, as a function of the resonance frequencies of the first timbre 12. Like the first circuit, the characteristics of the second electrical circuit 40b, preferably relating at least to its impedance, have been chosen as a function of at least one resonance frequency of the second timbre 14. The choice of the impedance of the second circuit, which is different from that of the first circuit, thus makes it possible to adjust the resonance frequencies of the membrane 20, by exciting the second piezoelectric element 30b, as a function of the resonance frequencies of the second timbre 14. AUDEMA-29-PCT

[0034] According to Figure 5, the first and second electrical circuits 40a, 40b each comprise a switch 70a, 70b mechanically linked so that when one opens, the other closes to form a switch. The first and second circuits 40a, 40b can thus excite, stimulate or activate, in turn, the first and second piezoelectric elements 30a, 30b in order to adjust the resonance frequencies of the acoustic membrane 20 according to those of the gong about to be struck by the corresponding hammer of the striking mechanism of the timepiece incorporating the acoustic device 10.

[0035] When the first and second circuits 40a, 40b are respectively open and closed, the excitation or activation of the first piezoelectric element 30a will modify the stiffness of the acoustic membrane 20 and thus modulate its resonance frequencies as a function of the resonance frequencies of the first timbre 12 while the second piezoelectric element is inactive. Conversely, when the first and second circuits 40a, 40b are respectively closed and open, the excitation or activation of the second piezoelectric element 30b will modify the stiffness of the acoustic membrane 20 and thus modulate its resonance frequencies as a function of those of the second timbre 12 while the first piezoelectric element 30a is inactive.

[0036] This results in a significant gain in acoustic intensity of the sound produced by the vibrations of the first and second gongs caused by the impact of the hammer associated with the gong of the striking mechanism of the timepiece. The switch 70a, 70b of each circuit 40a, 40b can be switched for example directly or indirectly by the movements respectively of the first and second hammers of the timepiece in order to modify the stiffness of the acoustic membrane according to the gong which is about to be struck by the associated hammer. A gain in clarity can also be obtained by modulating at least one of the resonance frequencies of the acoustic membrane on the fundamental frequencies of the two gongs. AUDEMA-29-PCT

[0037] Referring to Figure 11, the sound amplitude of the timbre-membrane system is optimum when the resonant frequencies of the membrane match those of the timbre. Although it is difficult to modify the stiffness of the acoustic membrane so that its resonant frequencies correspond exactly to those of the timbre, approaching it still allows a significant gain in sound intensity to be achieved.

[0038] According to an alternative embodiment, the properties of the first and second electrical circuits 40a, 40b are identical while the properties of the first and second piezoelectric elements 30a, 30b respectively differ so that their excitation by the first circuit 40a, respectively the second circuit 40b, makes it possible to adjust the resonance frequencies of the acoustic membrane 20 as a function of the resonance frequencies of the first and second timbres 12, 14 respectively. The properties of each piezoelectric element 30a, 30b can be chosen from one or a combination of properties including in particular the capacitance of the piezoelectric element, its contact surface with the acoustic membrane, its thickness and its mass.

[0039] According to another variant embodiment, both the properties of the first and second electrical circuits 40a, 40b and the properties of the first and second piezoelectric elements 30a, 30b are chosen so that the excitation of the piezoelectric element, by the electrical circuit specific to it, can modulate the resonance frequencies of the acoustic membrane so that these frequencies approach as closely as possible the resonance frequencies of the timbre with which the piezoelectric element is associated.

[0040] Generally speaking, the selection of the properties of each electrical circuit and the selection of those of the piezoelectric element associated with the circuit of the acoustic device as described above are transposable AUDEMA-29-PCT for an acoustic device intended to be integrated into a timepiece whose striking mechanism comprises only one gong or three, four or even five gongs for the most melodic carillon timepiece models. In this case, the acoustic device may comprise three, four or five electrical circuits associated either with a common piezoelectric element or respectively with one piezoelectric element from among three, four or five separate piezoelectric elements.

[0041] More particularly, for the case of a timepiece whose striking mechanism comprises only one gong, the properties of the circuit, in particular its impedance z, and / or the priorities of the piezoelectric element (e.g. the capacitance of the piezoelectric element, its contact surface with the acoustic membrane, its thickness and / or its mass) are determined as a function of at least one resonance frequency of the gong. For the case of a timepiece whose striking mechanism comprises three, four or even five gongs, the properties of three, four or five electrical circuits and / or the priorities of a common piezoelectric element or of each piezoelectric element associated with each gong are chosen in a similar manner as a function of the resonance frequencies of the third, fourth and fifth gongs respectively.

[0042] Figures 4a and 4b illustrate two different electrical circuits, each incorporating a piezoelectric element. For example, varying the capacitance value of the circuit in Figure 4a makes it possible to modify the stiffness of the membrane. On the other hand, the circuit in Figure 4b is adapted to dampen the vibrations of the acoustic membrane 20 by dissipating, through the resistance of the circuit, the electrical energy created in the circuit. This makes it possible to configure the acoustic device 10 in a mute mode. In this case, the user can activate, using a switch, implemented by means of a push button for example, the element or each piezoelectric element in order to suppress, or at least attenuate, the sound emitted by the device. AUDEMA-29-PCT acoustic. According to this mode of operation, the stiffness of the acoustic membrane is modified in order to distance its resonance frequencies as much as possible from those of the timbre as schematically illustrated in figure 11.

[0043] In the situation where the or each piezoelectric element is used to amplify the vibrations of the membrane in order to obtain a gain in acoustic intensity, the circuit of the acoustic device 10 may also comprise a switch in the case where the user wishes to deactivate the piezoelectric effect on the membrane to obtain a lower intensity sound. In the deactivated mode, the sound transmission mode corresponds to that of conventional striking timepieces. Conversely, if the user wishes a greater gain, the circuit of the acoustic device may comprise an energy source 60 making it possible to operate the or each piezoelectric element in an active mode in order to exert a greater stress on the membrane.

[0044] The energy source 60 mounted in the watch case of the timepiece may typically be in the form of a battery, a micro generator, a capacitor, or any combination of such elements. For example, the micro generator may be mounted to transform part of the mechanical energy resulting from the user's action on a trigger intended to rewind the spring of a barrel of the striking mechanism.

[0045] According to another embodiment and with reference to figures 6 and 7, the acoustic device 10 comprises the acoustic membrane 20, a piezoelectric element 30 having an at least partially annular shape and arranged along at least part of the periphery of the membrane 20 and a frame secured to the membrane and provided with or consisting of a fixing flange 11 for assembling the acoustic device in the watch case. AUDEMA-29-PCT

[0046] This particular arrangement makes it possible to modulate, and in particular to reduce, the resonance frequencies of the membrane 20 when the latter is radially stressed by the deformation of the piezoelectric element 30. Preferably, the piezoelectric element 30 is in the form of a ring mounted against the circular edge of the acoustic membrane 20 in the plane thereof. The vibration of the membrane 20 electrically polarizes the piezoelectric ring 30 which exerts, by its deformation, a radial stress on the membrane. Preferably, the piezoelectric ring is powered by an energy source 60 so as to be able to operate in active mode.

[0047] According to another embodiment illustrated in Figures 8 and 9, the acoustic device 10 comprises the acoustic membrane 20 and a piezoelectric element 30c also having an at least partially annular shape and arranged along at least a portion of the periphery of the membrane 20. Preferably, the piezoelectric element has the shape of a ring arranged in an identical or similar manner to the aforementioned embodiment. The piezoelectric ring 30c may be intended to operate in a passive or active mode.

[0048] For this purpose, the acoustic device 10 further comprises at least one or more piezoelectric elements 30a, 30b arranged, like the embodiment illustrated in particular in FIG. 1, on one face of the acoustic membrane 20 to cover at least 70% of its surface, preferably at least 80%, or even at least 90% of its surface. In the active mode, the or each piezoelectric element 30a, 30b is electrically connected to the piezoelectric ring 30c.

[0049] Thus, when the striking mechanism of the timepiece is actuated, the acoustic membrane 20 vibrates under the action of the vibrations produced when the hammers strike the gongs, which allows the or each piezoelectric element 30a, 30b to produce AUDEMA-29-PCT electricity to power the piezoelectric ring 30c. The active mode allows greater stresses to be applied to the acoustic membrane 20 from its periphery. It is thus possible to vary the stiffness of the acoustic membrane 20 over a wider range. The amplitude of the lowering of the resonant frequency of the acoustic membrane 20 can therefore be greater compared to an embodiment operating in passive mode.

[0050] According to any of the aforementioned embodiments, the or each piezoelectric element 30a, 30b may be in the form of thin layers, for example with a thickness of the order of a few tens or hundreds of micrometers, typically of the order of 0.2 mm, or even more. These layers are fixed on at least one face of the acoustic membrane 20, preferably on the face on the timbre side. The piezoelectric layers 30a, 30b may be fixed for example by gluing. According to an alternative, the piezoelectric layers 30a, 30b may be deposited with a CVD or PVD process. The piezoelectric layers 30a, 30b may be made of different materials, in particular quartz, ferroelectric oxides or group III-V semiconductors.

[0051] The or each piezoelectric element 30a, 30b may typically comprise two electrodes of opposite polarities. These electrodes may be in the form, for example, of plates arranged on two opposite faces of the piezoelectric element when the latter is in the form of a thin layer.

[0052] According to another embodiment illustrated by Figure 10, the acoustic device 10 comprises an acoustic membrane 20 and a peripheral element 50 connected to the acoustic membrane 20 by its periphery. The peripheral element can for example be in the form of a ring 50 surrounding the acoustic membrane 20 and connected thereto by fixing means 34. The acoustic device 10 comprises in AUDEMA-29-PCT in addition to a piezoelectric element 32 integrated in the ring so that any expansion of the piezoelectric element 32 exerts an increase in the tension of the acoustic membrane 20 causing an increase in its resonance frequencies. Conversely, a retraction of the piezoelectric element will compress the membrane and cause a reduction in its resonance frequencies. In general, it can be mentioned that any expansion or retraction of the piezoelectric element exerts a variation in tension on the acoustic membrane making it possible to modulate its resonance frequencies.

[0053] The piezoelectric element 32 may be intended to operate in a passive or active mode. It may for example be powered by an energy source 60, such as that already mentioned previously, or at least one other piezoelectric element of the acoustic device 10.

[0054] Although in the illustrated embodiments the outline of the membrane is circular, it may have other shapes. In this case, the shape and arrangement of at least one piezoelectric element on the membrane will be adapted accordingly in order to maximize the contact surface between the piezoelectric element and the membrane.

[0055] Various modifications may be made to the above-mentioned embodiments without departing from the scope of the invention defined by the appended claims. For example, the partition, fulfilling the function of a frame intended to be fixed in a watch case, may take different forms. Furthermore, as mentioned above, the or each gong may be integral with a striking mechanism present in the watch case of the timepiece and not with the acoustic device as illustrated by the figures. AUDEMA-29-PCT

Claims

Claims 1. Acoustic device (10) for a striking piece, comprising an acoustic membrane (20), at least one piezoelectric element (30; 30a, 30b; 30c; 32) arranged to cooperate with the acoustic membrane (20) and at least one electrical circuit (40a, 40b) integrating the piezoelectric element, characterized in that the acoustic device (10) further comprises at least one gong (12, 14) which can be struck by a hammer and in that the assembly comprising the piezoelectric element (30; 30a, 30b; 32) and the electrical circuit (40a, 40b) is configured to adjust resonance frequencies of said membrane (20) as a function of the resonance frequencies of said at least one gong (12, 14).

2. Acoustic device (10) according to claim 1, in which each piezoelectric element (30; 30a, 30b) is arranged directly in contact with the acoustic membrane (20) and preferably has a shape at least partially complementary to that of the acoustic membrane (20).

3. Acoustic device (10) according to claim 2, wherein the acoustic membrane (20) is circular in shape, said at least one piezoelectric element (30a, 30b, 30c) being circular or partially circular in shape.

4. An acoustic device (10) according to claim 3, wherein said at least one piezoelectric element (30c) has an at least partially annular shape and is arranged along at least a portion of the periphery of the acoustic membrane (20) to modulate its resonance frequencies when said membrane (20) is radially stressed by said at least one piezoelectric element (30c). AUDEMA-29-PCT 5. Acoustic device (10) according to one of claims 1 to 3, in which at least one face of the acoustic membrane (20) is covered by at least one piezoelectric element to occupy at least 70% of its surface, preferably at least 80%, or even at least 90% of its surface.

6. Acoustic device (10) according to one of the preceding claims, comprising at least one piezoelectric element (30; 30a, 30b; 30c; 32) configured to be powered by an electrical source (60) integrated into the electrical circuit (40a, 40b) in order to operate in an active mode.

7. Acoustic device (10) according to the preceding claim, in which the electrical source (60) is one or more other piezoelectric elements of the device (10).

8. Acoustic device (10) according to claim 1 or 2, further comprising a peripheral element (50) in contact with the acoustic membrane (20) by its periphery, the piezoelectric element (32) being integrated into the peripheral element (50) so that any expansion or retraction of the piezoelectric element (32) exerts a variation of tension on the acoustic membrane (20) to modulate its resonance frequencies.

9. Acoustic device (10) according to one of the preceding claims, comprising several timbres (12, 14), in which an electrical circuit is assigned to each timbre and has specific characteristics making it possible to adjust the resonance frequencies of said membrane (20) as a function of the resonance frequencies of the timbre to which the electrical circuit is assigned.

10. Acoustic device (10) according to one of the preceding claims, comprising several timbres (12, 14), in which a piezoelectric element (30a, 30b) is assigned to each timbre and has specific characteristics making it possible to adjust the resonance frequencies of said membrane (20) as a function of the resonance frequencies of the AUDEMA-29-PCT timbre to which the piezoelectric element (10a, 30b) is assigned.

11. Acoustic device (10) according to one of the preceding claims, in which at least one electrical circuit (40a, 40b) comprises a switch (70) making it possible to open or close the electrical circuit in order to respectively activate or disconnect said at least one piezoelectric element integrated therein.

12. Acoustic device (10) according to one of the preceding claims, in which the assembly comprising the piezoelectric element and the electrical circuit is configured to further distance the resonance frequencies of the membrane and the timbre.

13. A striking timepiece comprising the acoustic device (10) according to one of claims 1 to 8 and a hammer arranged to strike the gong (12, 14) of the acoustic device (10).

14. A striking timepiece comprising the acoustic device (10) according to claim 9 or 10 and according to claim 11, and several hammers arranged to strike the respective gongs and in which the switch (70) is actuated by a movement of a hammer or by a striking trigger member.

15. A striking timepiece according to claim 13 or 14, wherein said at least one piezoelectric element (30; 30a, 30b; 30c; 32) is arranged on one face of the acoustic membrane (20) located opposite a gong (12, 14). AUDEMA-29-PCT

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