Patent Publication Number: US-6219304-B1

Title: Device capable of being submerged and including an acoustic transducer

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device capable of being submerged in liquid such as water, like for example a device worn on the wrist such as watches. More particularly, the invention concerns a device of this type in which an acoustic transducer is mounted in the case. 
     BACKGROUND OF THE INVENTION 
     In order to guarantee water N resistance of watches worn on the wrist to a depth of immersion which may nominally reach thirty odd meters, mounting an acoustic transducer in the watch case without any communication path being provided between the transducer and the exterior capable of directly leading the sound waves is already known from the prior art. Such an assembly has the advantage of guaranteeing very good water tightness for the watch. However, since the acoustic energy has to reach the transducer or originate therefrom through the solid wall of the case, this solution is only possible if one is satisfied with mediocre acoustic quality. The band of frequencies which can be used is thus limited to the frequencies which succeed in passing through said wall. In practice, one has to work with the transducer resonance frequencies, these frequencies only being able to be transmitted effectively through a wall of the case if they correspond to a resonance frequency of such wall. This necessarily limits the range of frequencies able to be transmitted and is thus not suited to reproduction and/or reception of complex sounds such as speech or music. It will also be noted that such a wall inconveniently absorbs transmission of sounds transmitted or received by the transducer. 
     SUMMARY OF THE INVENTION 
     An aim of the invention is to provide a device of the type indicated hereinbefore fitted with an acoustic transducer mounted so as to be able to operate over a broad acoustic spectrum, in particular the acoustic spectrum corresponding to speech, while assuring a high degree of water resistance. 
     The invention thus concerns a portable water resistant device capable of undergoing submersion to a predetermined depth in a liquid such as water, in particular a water resistant watch, including a case in which is mounted an acoustic transducer so as to communicate, in a water tight manner, with the exterior of the case via acoustic energy, characterised in that 
     said acoustic transducer is mounted in said case facing a membrane which is able to be deformed, separating it in a water tight manner from an inlet cavity which is arranged in said case and in direct communication with the exterior, and in that between the membrane and said acoustic transducer an intermediate chamber is arranged, allowing deformation of said membrane by the action of external static pressure and delimited on the side of the transducer by a support element fixedly mounted in the case and capable of limiting the deformation of the membrane in the event of application of said external static pressure. 
     As a result of these features, when the device is not in liquid, the membrane is mounted so as to be able to vibrate freely by the action of the acoustic energy to be received and/or transmitted. Conversely, when the device is submerged, the membrane can be deformed by the action of the hydrostatic pressure, without, of course, being able to transmit the acoustic energy, but is protected from any deterioration because of the support assured by the support element. 
     Other features and advantages of the invention will appear during the following description, given solely by way of example and made with reference to the annexed drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partial cross-section of a timepiece made according to the invention and fitted by way of example with a microphonic transducer; and, 
     FIG. 2 is a sectional view taken along the line  2 — 2  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, the invention will be illustrated in its application to a timepiece such as a wristwatch. It is clear however that the invention can be applied to any other device having to include at least one acoustic transducer, the device being further capable of being submerged in a liquid such as water to a predetermined depth. Moreover, in the example described, the acoustic transducer is a microphone, however an acoustic reproductive transducer may also be advantageously used with the invention. 
     This being so, FIG. 1 shows a cross-section of a wristwatch  1  whose water resistance is guaranteed to a predetermined depth of water, a depth of 30 meters being a value often given in practice. 
     Watch  1  in FIG. 1 includes a case  2 , a crystal  3 , hands  4  and  5 , a dial  6  and certain parts of a time-setting mechanism  7 . All these elements, as well as those not visible in the drawing, such as the integrated circuit, the quartz, the miniature motor, the gear train etc. are conventional and thus do not need to be described here. Although this is not a limitative application of the invention, the device according to the invention fitted with the microphonic transducer could advantageously be a watch forming a portable telephone. 
     In the case shown, the device or watch  1  according to the invention, is mounted on a plate  8 , the latter resting on a back cover  9  of case  2 . Plate  8  has an opening defined by a circular wall  10 , of circular shape, wherein a microphone  11  is mounted. This latter may be of any suitable type, an electret microphone being preferred because of its small dimensions. By way of indication, a microphone of this type may have a diameter of approximately 6 mm and a height of approximately 2 mm. 
     In the example shown, the microphone itself is set in a housing  12  whose bottom  12   a  is pierced with holes  13  and acts as support element. However, it is also possible for microphone  12  to be a simple cylindrical body resting on a plate having through holes. 
     The opening in plate  8 , bounded by wall  10 , is provided above an inlet cavity  14 , of generally circular shape and opening out via a channel  15  at right angles to the exterior. 
     At the periphery of the external face of bottom  12   a  of housing  12  a first mounting ring  16  is glued, which, with a second mounting ring  17 , is arranged for holding a circular membrane  18  gripped or fixed in another manner between the two rings. This membrane  18  thus separates in a water tight manner inlet cavity  14  from an intermediate chamber  19  communicating via holes  13  with microphone  11 , while transmitting the acoustic vibrations coming from outside the latter. Mounting ring  16  acts as a spacer means between membrane  18  and the support element and thus delimits the volume of intermediate chamber  19 . Mounting ring  17  also axially abuts a shoulder  20  surrounding inlet cavity  14 . According to an alternative embodiment, membrane  18  may be directly glued or fixed in another manner to ring  16  and ring  17  may be omitted. 
     In the example illustrated, first mounting ring  16  has a radial groove  21  arranged in its thickness. Back cover  9  has a groove  22  which follows groove  21  and which opens out into a pressure balancing membrane  23 . This latter may be mounted against a radial shoulder  24  provided on the inner side of a hole  25  made in plate  8  onto the outer side of which groove  21  opens out. Chamber  19  is thus in communication with membrane  23 . 
     This membrane  23  is sealed against liquids such as water, but it is permeable to gases such as air provided that the gas pressure varies slowly. Any abrupt variation in the gas pressure is thus blocked by this membrane. The latter may be made for example of sintered Teflon® or ceramics. 
     In the example described, case  2  of watch  1  also includes a device  26  placing the internal space thereof in communication with the exterior. In practice this comprises a passage  27  arranged in plate  8  and back cover  9  and sealed by a pressure balancing membrane  28  which, like membrane  23 , is sealed against liquids such as water, but permeable to gases whose pressure varies slowly. It may be made of the same material as membrane  23 . 
     Several alternatives can be envisaged for placing chamber  19  in communication with the exterior only for very slight variations in gas pressure. Thus: 
     groove  22  may be omitted, and the gas diffused by an escape path between the front surface of ring  16  and the surface of the bottom  12   a.    
     There may be only one communication with the exterior through a membrane such as membrane  28  mounted as shown in the figure, groove  22  communicating with the inside of the watch. 
     Housing  12  can be mounted in its recess arranged in case  2  so as to provide an escape path along its external wall to diffuse the low pressure variation gases towards the exterior along its external wall. 
     The device for placing intermediate chamber  19  in communication with the exterior solely for slow variations in the static pressure of the surrounding gases thus arranged, allows membrane  18  to be kept operational, even if the watch is brought by the wearer to different altitudes or is worn in climatic conditions inducing such slow variations. 
     It may be noted that in a certain way, membranes  23  and  28  constitute low-pass filters only allowing pressure variations of gases such as air, of very low frequency, typically of {fraction (1/10)} Hz and less, to pass. 
     It is to be noted that in the present embodiment example, chamber  19  is first of all in communication with the interior of case  2  and can only communicate with the exterior (still solely for slight variations in the static gas pressure) through communication device  26 . This arrangement is preferred here since the watch described may include other elements also requiring slow pressure compensation. It may concern for example an acoustic reproduction transducer. Communication device  26  may then be used for both transducers at the same time, which reduces to a minimum the places in the case where communication with the exterior exists for gases such as air. 
     Membrane  18  is made of a non-elastic material and it is not taut between mounting rings  16  and  17  in order to guarantee as much freedom of vibration as possible. A particularly suitable material for membrane  18  is Mylar®, its thickness being able to be comprised between 2 and 50 μm, a preferred value being 10 μm. It diameter is slightly greater than that of microphone  11 . It will be noted that such a membrane can transmit vibrations in a frequency range ranging from 200 Hz to 5 kHz. 
     The behaviour of membrane  18  is a follows. 
     When the watch is worn outside water, membrane  18  has a flat configuration in which it is distant from the grid formed by bottom  12   a  of housing  12 . It can thus transmit without interference the acoustic vibrations coming from the exterior to chamber  19  and hence to microphone  11  through holes  13  made in bottom  12   a.    
     Conversely, when the watch has just been submerged, membrane  18  will be deformed because of an abrupt variation in the differential pressure, to assume a curved shape in the direction of bottom  12   a , the pressure compensation path described hereinbefore not managing to balance the difference in pressures rapidly enough. From a certain hydrostatic value, the deformation of the membrane will be such that it is applied against bottom  12   a  of housing  12 , this latter forming an efficient support preventing any deterioration, and in particular irreversible deformation, of membrane  18 . 
     It will be noted that in the event that the transducer is a loud-speaker, the features of the membrane, in particular the thickness, the diameter and the material of which it is formed, will be adapted accordingly.