EP2881806B1 - Acoustic dispersion membrane for a musical watch - Google Patents

Description

The invention relates to an acoustic radiation membrane for a musical watch, or a striking watch.

In the field of horology, a striking mechanism can be provided in a watch movement so as to generate a sound or a music. The timbre of the bell watch or the keyboard of the musical watch are generally placed in the watch case. Thus the vibrations of the timbre or the keyboard blades are transmitted to the different parts of dressing. These pieces of clothing are for example the middle part, the bezel, the ice and the bottom of the watch case. These large pieces of clothing begin to radiate sound in the air under the effect of transmitted vibrations. When a sound is produced either by a stamp struck by a hammer or by one or more blades of the vibrating keyboard, these pieces of clothing are able to radiate the sound produced in the air.

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

To further improve the vibro-acoustic performance of the striking mechanism, it can be provided a membrane disposed inside the watch box. The membrane must be dimensioned so that all the notes generated by the vibration of one or more timbres, or the blades of a keyboard is radiated effectively. It is therefore important that the frequencies of the notes are close to those of the eigen modes of the membrane to enable it to come into resonance.

It can be seen in this respect that a high modal density over a restricted frequency band, for example between 500 Hz and 3.5 kHz, is difficult to obtain because this characteristic is only compatible with membranes of very low or very high stiffness. mass. These two characteristics are not advantageous, because by reducing the frequency of the first resonance mode around 1'000 Hz in this way, the frequency of the excited modes, which are not very acoustically efficient, is also reduced below 4'000. Hz. The mechanical energy is then dissipated in vibration modes of the acoustically inefficient membrane. The radiation efficiency, which is logically defined as the ratio between the energy of the radiated acoustic wave divided by the total energy transferred to the membrane, is then reduced over almost the entire frequency band of interest. It is therefore difficult to obtain a resonance on each generated note of the striking mechanism, which is a disadvantage of the membranes of the state of the art.

For example, the patent application EP 2 461 219 A1 , which describes an acoustic radiation membrane for a musical watch or bell. This acoustic membrane has a general shape of bowl with its peripheral edge sandwiched between a part of the middle part and the bottom of the watch case. This membrane is designed with one or two asymmetrically shaped regions formed in the membrane material. The two regions excavated in the general thickness of the membrane are of different size. These two regions form ellipses, which are offset from each other with respect to the center of the membrane and overlap in part. With these ellipses in the membrane, it is possible to have a double number of eigen modes of vibration for each ellipse with respect to a circular-shaped region. However, this does not make it possible to increase the bandwidth of a vibratory mode of the membrane to obtain an amplified vibratory response over a larger frequency band, which is a drawback.

The document FR1064970 discloses a domed watch window having the function of an acoustic radiation membrane.

The documents CH304446 and DE1080029 disclose membranes having a generally conical shape.

The object of the invention is therefore to overcome the drawbacks of the above-mentioned state of the art by providing an acoustic radiation membrane for a musical watch or a striking watch, made in such a way as to obtain an amplified vibratory response of the membrane on a greater bandwidth of frequencies.

For this purpose, the invention relates to an acoustic radiation membrane comprising the characteristics defined in independent claims 1 and 2.

Particular forms of the acoustic radiation membrane are defined in dependent claims 3 to 13.

An advantage of the acoustic radiation membrane lies in the fact that with a central portion of convex or conical shape, the vibration amplitude can be increased especially in the frequency band from 500 Hz to 3.5 kHz. With such a geometric complex shape of the acoustic membrane in a determined material and a defined overall thickness with plan dimensions, comparable to the plan dimensions of a box or watch ice, the acoustic response of the membrane is substantially improved compared to a traditional solution throughout the range of interest rates.

Advantageously, it is thus possible to guarantee an amplification of a set of notes generated in the musical watch or bell. The first mode of vibration of each generated note is therefore at least in the frequency range between 500 Hz and 3.5 kHz. In addition, peak width of the first mode of vibration is greater than for a flat-bottomed membrane of the state of the art.

Advantageously, the membrane may be made of amorphous metal or metal glass, or also of gold or platinum, or even brass, titanium, aluminum or another material having a density, a Young's modulus and an elastic limit , which are similar. With such a membrane, the widening of the soundtrack can be combined with a very low internal damping, which makes it possible to obtain a very good sound output.

• les figures 1a et 1b représentent de manière simplifiée une vue tridimensionnelle et une coupe diamétrale selon I-I de la figure 1a d'une première forme d'exécution de la membrane de rayonnement acoustique selon l'invention,
• les figures 2a et 2b représentent de manière simplifiée une vue tridimensionnelle et une coupe diamétrale selon II-II de la figure 2a d'une seconde forme d'exécution de la membrane de rayonnement acoustique selon l'invention,
• la figure 3 représente un graphe de la réponse en fréquence, intégrée sur tout le volume de la membrane, de l'amplitude de la vitesse selon la normale à la membrane pour une membrane standard en verre métallique, une membrane en verre métallique selon la première forme d'exécution et une membrane en verre métallique selon la seconde forme d'exécution selon l'invention, et
• la figure 4 représente un graphe du rapport entre les réponses en fréquence des membranes des première et seconde formes d'exécution selon l'invention et d'une membrane standard.

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

• the Figures 1a and 1b represent in a simplified way a three-dimensional view and a diametral section along II of the figure 1a of a first embodiment of the acoustic radiation membrane according to the invention,
• the Figures 2a and 2b represent in a simplified way a three-dimensional view and a diametral section along II-II of the figure 2a a second embodiment of the acoustic radiation membrane according to the invention,
• the figure 3 represents a graph of the frequency response, integrated over the entire volume of the membrane, the amplitude of the speed according to the normal to the membrane for a standard metal glass membrane, a metal glass membrane according to the first form of embodiment and a metal glass membrane according to the second embodiment of the invention, and
• the figure 4 represents a graph of the ratio between the frequency responses of the membranes of the first and second embodiments of the invention and a standard membrane.

In the following description, reference will be made mainly to the configuration of an acoustic radiation membrane, to equip including a musical watch, or a bell watch. The acoustic radiation membrane is made with a complex shape to amplify the vibration amplitude of different notes generated in a watch case. The membrane is dimensioned in such a way as to amplify in particular the first mode of vibration in a frequency band of 500 Hz to 3.5 kHz.

The Figures 1a and 1b represent a first embodiment of the acoustic radiation membrane 1, which can equip a musical watch or a bell watch. Depending on the shape of the watch case, the acoustic radiation membrane 1 may be in plan view of a generally rectangular, or polygonal or preferably circular shape as shown in FIG. figure 1a .

The membrane 1 is configured for example in the form of a bowl with an active central portion 2, which is generally convex, and a cylindrical side wall 3, which is terminated by a peripheral edge 4. The active central portion 2 is preferably curved towards the outside of the bowl, but could also be curved on the inside of said bowl. The active central part 2 represents in this case a bottom of the membrane. The active central portion 2, the side wall 3 with the peripheral edge 4 generally form a single piece of the same material, which may be metallic.

It should be noted that instead of a peripheral edge, it can be provided a border in the form of several peripheral portions distributed around the perimeter of the side wall 3 for fixing the membrane in a watch case.

The acoustic radiation membrane 1 may be formed in one piece in a material, which may be amorphous metal or metallic glass in the example described and with reference to figures 3 and 4 explained below. However this membrane can be made of another material, such as gold or platinum, or even brass, titanium, aluminum for example with a density, a Young's modulus and an elastic limit, which are similar.

Preferably, the domed central portion 2 further comprises a mass 2 'added to the center of the domed central portion. This mass 2 'may be an additional piece fixed on the active central part 2 or preferably of material with the active central portion 2 and only define an extra thickness of the material near the center of the membrane 1. This mass 2' added to the central portion 2 reduces the first natural frequency of the radiated note, but without reducing the stiffness of said membrane.

In an alternative embodiment, the membrane may be made of two materials M1 and M2, which have different mechanical properties. The added mass may in particular be made in the material M2, while the rest of the membrane may be made of a material M1. It can also be envisaged that the domed or conical central part can be made by depositing a material M2 on a membrane made of a different material M1.

The acoustic membrane 1 can be mounted in a not shown watch case with its peripheral edge 4, which is traditionally clamped between the bottom and the middle of the watch case with a seal. After mounting the membrane in the watch case, the domed central portion is non-contact with other parts of the watch so as to freely vibrate according to its fundamental mode of vibration. It is of mono-polar spatial form and therefore very acoustically effective. The central portion 2 is disposed close to and without contact with the bottom of the watch case. According to Figures 1a and 1b , which represent the membrane according to views from below, the central portion 2 is generally domed on the bottom side of the watch case.

The convex central portion 2 from its connection to the side wall 3 may have a diameter greater than 15 mm and preferably between 20 and 40 mm. This diameter may be substantially equivalent to that of an ice cream shows not shown, since the peripheral edge 4 can be pinched between a peripheral support of the bottom of the watch case and a circular inner rim of the middle part. The thickness of the central portion 2 may be identical at any point except at the location of the added mass 2 '. This thickness may be greater than 50 microns and preferably less than 1 mm, while the thickness of the extra thickness 2 'of the central portion may be for example twice the thickness of the surrounding central portion. The extra thickness 2 'may be circular in plan view of diameter greater than 1.5 mm and preferably between 2 and 4 mm, and extending towards the center of the bowl.

The domed central portion 2 is thus dimensioned according to the material constituting it so as to amplify the vibration in the frequency band from 500 Hz to 3.5 kHz. The acoustic response of the membrane is thus substantially improved in this frequency band. As the membrane is mounted in a bell or musical watch, the first mode of vibration of each note generated is therefore at least in the frequency range between 500 Hz and 3.5 kHz.

It should be noted that the thickness of the central portion 2 of the membrane 1 may be variable. The thickness may for example be greater in the center of the central portion independently of the added mass 2 'and gradually decrease, for example in a linear manner, to the periphery of the central portion 2. It may also be expected that this thickness varies in crenellations from the center to the periphery of the central portion 2. Other variations in thickness of this central portion may be envisaged so as to ensure an amplification of the first vibration mode of the notes generated in the frequency range between 500 Hz and 3.5 kHz.

où r représente la moitié du diamètre de la partie centrale, h représente la hauteur depuis la liaison de la paroi latérale et de la partie centrale et jusqu'au centre de la partie centrale, et α représente l'angle depuis le centre de la sphère de la calotte sphérique entre le centre de la partie centrale à la liaison entre la paroi latérale et la partie centrale.As shown on Figures 1a and 1b , the convex central portion 2 may be a spherical cap. This spherical cap can be defined according to the following formula: $$\mathrm{r}/\mathrm{h}=\sin \left(\mathrm{\alpha }\right)/\left(1-\cos \left(\mathrm{\alpha }\right)\right)$$

where r represents half of the diameter of the central portion, h represents the height from the bond of the side wall and the central portion to the center of the central portion, and α represents the angle from the center of the sphere spherical cap between the center of the central part to the connection between the side wall and the central part.

For the first embodiment of the membrane 1 shown in Figures 1a and 1b the angle α may be between 3 ° and 8 °, preferably between 4 ° and 5 °. For a diameter of 15 mm, the height h of the spherical cap may be of the order of 0.3 mm, whereas for a diameter of 40 mm, the height h of the spherical cap may be of the order of 0.8 mm. The radius of the spherical cap can be defined N times higher, especially between 6 and 8 times greater than the diameter of the central portion.

It should also be noted that the domed central portion 2 may be of ovoidal shape or be composed of several convex portions intersecting or spaced apart from one another.

The Figures 2a and 2b represent a second embodiment of the acoustic radiation membrane 1, which can equip a musical watch or a bell watch. Depending on the shape of the watch case, the acoustic radiation membrane 1 may be in plan view of a generally rectangular, or polygonal or preferably circular shape as shown in FIG. figure 2a as defined for the first embodiment. The dimensions and the material used for producing the membrane 1 of the second embodiment are similar to those defined for the first embodiment. For simplicity, it will not be repeated the description of these dimensions or material.

The essential difference of this second embodiment is that the central portion 12 of the acoustic radiation membrane 1 is generally conical. This conical shape preferably extends outwardly of the bowl-shaped membrane, which further comprises the side wall 3 and the peripheral edge 4 for holding the membrane in the watch case.

The central portion may preferably be composed of two conical portions 12, 12 ', which are concentric and connected to each other. The first conical portion 12 starts from the center of the membrane 1 and is configured with a first opening angle with respect to the central axis of the membrane. The second conical portion 12 'starts from the periphery of the first portion 12 and ends at the side wall 3 with a second opening angle different from the first opening angle. Preferably the second opening angle is smaller than the first opening angle. By way of non-limiting example, the first opening angle may be of the order of 86 °, while the second opening angle may be of the order of 79 °.

The border 4 with the side wall 3 are made of material with the two conical portions 12, 12 'to form a single piece. The thickness of each conical portion 12, 12 'may be identical at any point. However, it can be expected that this thickness decreases linearly from the center to the periphery of the membrane. This thickness may be greater than 50 μm and preferably less than 1 mm. The diameter of the first conical portion 12 may be between 80% and 90%, preferably close to 85% of the diameter of the complete central portion. For a diameter of the central portion of 15 mm, the diameter of the first conical portion 12 may be of the order of 12.5 mm, while for a diameter of the central portion of 40 mm, the diameter of the first conical portion 12 can be of the order of 33 mm. However, the dimensions of the first and second conical portions 12, 12 'may be different from those mentioned above and with a second opening angle, which may also be greater than the first opening angle.

The production of an acoustic radiation membrane having a central portion in curved or conical form, allows substantially more than a factor of 2 to be removed, the fundamental mono-polar vibration mode acoustically effective of all the other modes of excited vibration. These other modes of vibration have a multipolar distortion and are acoustically ineffective. The advantage is that, according to this construction, the membrane vibrates in a mono-polar deformation even in the presence of a significant frequency disagreement between the activation frequency and the resonance frequency of the fundamental mode.

To properly represent this advantage, we can refer to the graphs of figures 3 and 4 . The figure 3 represents a graph of the frequency response, integrated over the entire volume of the membrane, the amplitude of the speed according to the normal to the membrane. This quantity is mathematically defined by R (f) = ∫ _Vol | v _z (x, y, z, f) | dx dy dz for a standard metal glass membrane, a metal glass membrane according to the first embodiment and a metal glass membrane according to the second embodiment of the invention. The figure 4 represents a graph of the ratio between the frequency responses of the membranes of the first and second embodiments of the invention and the standard membrane.

Next to the graphs represented in figures 3 and 4 it is found that the peak width of the first vibration mode between 1.5 kHz and 2 kHz, for example at 1.75 kHz, is larger and with a greater amplitude than for a peak of the first vibration mode of a standard membrane. In addition, the vibrational response is increased below and above the resonance frequency. On the one hand, the first excited mode of vibration of the membrane according to the invention is at a frequency substantially greater than the frequency of the first excited mode of the standard membrane. This antiresonance phenomenon, which occurs for activation frequencies between the fundamental mode and the first excited mode of the membrane, is greatly reduced. On the other hand, thanks to its almost uniform modal deformation, the fundamental mode is more easily activated, even in an inertial activation regime, at low frequency. This improves the response below the resonant frequency. In this way, the membrane is vibrated according to the spatial distortion of its fundamental mode even in the presence of a relatively important frequency disagreement.

Such an acoustic radiation membrane made with an active central part of complex shape, in particular of curved shape or of conical shape, therefore makes it possible to increase the amplitude of vibration in the frequency range from 500 Hz to 3.5 kHz. This differs advantageously compared to a standard membrane, whose central portion is flat.

From the description that has just been given, several variants of the acoustic radiation membrane for a musical watch or a striking watch can be designed by those skilled in the art without departing from the scope of the invention defined by the revendications. The mass added to the central portion of the membrane may be placed at a location other than the center of the membrane and a plurality of added masses may also be provided. It can also be envisaged that the mass added to the central portion can be made of a material M2 different from a material M1, in which the other parts of the membrane are made.

Claims (13)

1. Acoustic radiating membrane (1) for a musical watch or a striking watch (10), the membrane including an active central portion (2) and an edge portion (4) for holding the membrane in a watch case, the central portion (2) being configured in a convex shape between the edge portion and the centre of the membrane and having dimensions devised to promote the vibration of the membrane according to a first unipolar deformation mode, following the activation of the membrane by one or more frequencies within the range between 500 Hz and 3.5 kHz, the membrane being of a generally circular shape, its central portion being a spherical cap,
   characterized in that said spherical cap is a part of a sphere of a radius between 6 and 8 times greater than the diameter of said central portion (2).
2. Acoustic radiating membrane (1) for a musical watch or a striking watch (10), the membrane including an active central portion (12, 12') and an edge portion (4) for holding the membrane in a watch case, the central portion (12, 12') being configured in a conical shape between the edge portion and the centre of the membrane and having dimensions devised to promote the vibration of the membrane according to a first unipolar deformation mode, following the activation of the membrane by one or more frequencies within the range between 500 Hz and 3.5 kHz, the central portion including two concentric conical portions (12, 12'), a first conical portion (12), which starts from the centre of the membrane and is configured with a first opening angle in relation to the central axis of the membrane, and a second conical portion (12'), which starts from the periphery of the first portion (12) with a second opening angle that is different from the first opening angle,
   characterized in that the first opening angle of the first conical portion (12) is larger than the second opening angle of the second conical portion (12').
3. Membrane (1) according to claim 1, the membrane having a general dome shape with the central portion (2) defining a base and attached to a lateral wall (3), and a peripheral edge portion (4) from the lateral wall, characterized in that the lateral portion is convex towards the exterior of the dome.
4. Membrane (1) according to claim 1, characterized in that the central portion (2) comprises an added mass (2'), which is a part fixed to the central portion or thickened portion of the central portion.
5. Membrane (1) according to claim 1, the membrane having a general dome shape with the central portion (2) defining a base and connected to a lateral wall (3), and a peripheral edge portion (4) from the lateral wall, characterized in that the central portion (2) with the added mass (2'), the lateral wall (3) and the peripheral edge portion (4) form a single piece created in the same metallic material.
6. Membrane (1) according to claim 1, characterized in that the thickness of the central portion (2) is identical from the centre to the periphery of the central portion.
7. Membrane (1) according to claim 1, characterized in that the thickness of the central portion (2) decreases substantially linearly from the centre to the periphery of the central portion.
8. Membrane (1) according to claim 2, the membrane having a general dome shape with the central portion (2) defining a base and connected to a lateral wall (3), and a peripheral edge portion (4) from the lateral wall, characterized in that the second conical portion (12') is connected to the first conical portion (12) and the lateral wall (3).
9. Membrane (1) according to claim 8, characterized in that the first and second conical portions (12, 12') extend towards the exterior of the membrane in a dome shape.
10. Membrane (1) according to claim 2, characterized in that the diameter of the first conical portion (12) is between 80% and 90%, preferably around 85% of the diameter of the whole central portion.
11. Membrane (1) according to claim 2, characterized in that the thickness of the conical portion (12) is uniform.
12. Membrane (1) according to claim 2, characterized in that the thickness of the first and second conical portions (12, 12') decreases linearly from the centre to the periphery of the membrane.
13. Membrane (1) according to claim 1, characterized in that the central portion (2) includes an added mass (2'), which is a part fixed to the central portion or a thickened portion of the central portion, and in that the added mass is manufactured in a material M2 different from a material M1, in which the other parts of the membrane (1) are manufactured.

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