Abstract:
In order to equalize the pressure between the interior of an unit accommodating chamber and the outside of a mike casing without reducing a waterproof performance and an acoustic characteristic, there is provided a waterproof type microphone, which includes a mike casing  11  provided with an unit accommodating chamber having a sound receiving opening portion  141 ; a mike unit accommodated in the unit accommodating chamber  14 ; and a waterproof membrane  19  airtightly mounted on the sound receiving opening portion  141 ; the waterproof microphone further including an venting hole  21  formed in the mike casing  11  to cause the unit accommodating chamber to be communicated with outside of the mike casing  11  and a pressure equalizing membrane  22  mounted on the venting hole  21.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a waterproof type microphone, and more specifically, to a waterproof type microphone which enables equivalent pressures between the interior of an unit accommodating chamber and the outside of a casing without impairment of the waterproof function. 
     BACKGROUND OF THE INVENTION 
     A headset type microphone is worn on the head of a user for a long period of time. For the reason, the headset microphone is different from a hand-held type microphone that it is often suffered from liquid such as sweat and spittle of the user. In addition, the headset microphone is often submerged in water of for example, swimming pool by sports instructors. As a result, such the liquid sometimes adversely affects the headset microphone. 
     Besides the headset microphone, for example, “Karaoke” (or orchestra) microphone is used in entertainment facilities where beverages such as beer and juice are served. For the reason, such the microphone is suffered from the beverage dashed thereon, and erroneous dropping thereof into the beverage. 
     Accordingly, as shown in FIG. 5, in a conventional accommodation of a mike unit  2  into an unit accommodating chamber  1   a  of a mike casing  1 , a sound receiving opening portion  1   b  of the mike casing  1  is covered with a waterproof membrane  3 , and an O-ring  5   a  is interposed between a support arm  4  of a headset and the mike casing  1  so that the unit accommodating chamber  1   a  is kept airtightly. 
     In this instance, the waterproof membrane  3  comprises a thinner plastic film made of materials such as polyethylene, and polyethylene terephtalate, which does not seriously affect vibration energy of sound wave passing therethrough so that excellent sensitivity, frequency characteristic and directivity are produced. 
     Furthermore, to provide an excellent acoustic characteristics, the waterproof membrane  3  is put on a support ring  3   a  in such a way not to be pulled by large tension applied thereto, and covers over a sound receiving opening portion  1   b  through the support ring  5   a . In addition, an O-ring  5   b  is also provided between the support ring  3   a  and the mike casing  1 . 
     However, the waterproof membrane  3  and the O-rings  5   a ,  5   b  seal the interior of the unit accommodating chamber  1   a  almost completely. So, the waterproof membrane  3  undergoes pressure differential between the interior of the unit accommodating chamber and the outside of the mike casing due to the changes in external atmospheric pressure and internal temperature and the like. consequently, the waterproof membrane  3  has a resonant point under tension. Theerefore, the acoustic characteristics become lessened. The possibility arises that the waterproof membrane  3  will be broken. 
     To prevent this, the internal volume of the unit accommodating chamber is increased. When the sound receiving portion cannot be formed in larger size, a bypass passage then brings the sound receiving portion into communication with a large volume portion which is separately formed within the mike casing, as proposed, for example, in Japanese Utility Model Publication No. 7-28793 Publication. 
     However, any of objectives of methods mentioned above is to maintain airtightness of the interior of the unit accommodating chamber. Therefore, basically, the problem of the pressure differential between the interior of the unit accommodating chamber and the outside of the mike casing is not solved. In order to solve the problem, it is contemplated to provide permeability for the waterproof membrane itself. However, an acoustically desirable material is even yet not found such the waterproof membrane. 
     Such the problem will be accomplished by the present invention. Accordingly, an object of the invention is to provide a waterproof type microphone which equalizes the pressures between the interior of an unit receiving chamber and the outside of a mike casing without degradation of the waterproof performance and acoustic characteristics. 
     SUMMARY OF THE INVENTION 
     For the achievement of the object described above, the present invention provides a waterproof type microphone including a mike casing disposed in an unit accommodating chamber having a sound receiving opening; the unit accommodating chamber having a mike unit accommodated therein, and a membrane mounted on said sound receiving opening, wherein said mike casing has a venting hole which brings said unit accommodating chamber into communication with the outside of the mike casing, and a water non-permeability membrane mounted on the venting hole thereof. 
     According to the above-mentioned arrangement, since the interior of the mike casing is connected with the outside thereof through the venting hole, no pressure differential between inside and outside occurs. Therefore, the waterproof membrane is not pulled by high tension to excess. Further, since the venting hole has a water non-permeability venting membrane mounted thereon, the mike casing is not susceptible to the entry of liquids from the outside thereof. 
     In the present invention, a support ring for supporting said waterproof membrane has an internal peripheral edge formed on the side of a waterproof membrane supporting face, and preferably the internal peripheral edge has a protective surface with a predetermined inclined angle or a predetermined curvature. Thereby, the waterproof membrane will be avoided from breakage thereof. 
     Furthermore, preferably, the waterproof membrane is supported on the support ring by an adhesive material which exhibits viscosity (elasticity) even after setting. Thereby, even though the waterproof membrane is pulled out by tension, the adhesive material with the viscosity will damp the tension. 
     The present invention also includes a waterproof membrane having a resonance preventing portion which is formed by fine rugged notches thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a waterproof type microphone according to one embodiment of the present invention. 
     FIG. 2 is an exploded assembly view of the above-mentioned embodiment. 
     FIG. 3 is a sectional view showing a support ring of a waterproof membrane according to the above-mentioned embodiment. 
     FIG. 4 is a sectional view showing a modified form of the waterproof membrane support ring. 
     FIG. 5 is a sectional view schematically showing a conventional waterproof type microphone. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described in detail hereinafter with reference to embodiments shown in the drawings. Referring to FIG. 1 (a sectional view) and FIG. 2 (an exploded assembly view), a waterproof type microphone  10  according to this embodiment is for a headset and comprises a mike casing  11  mounted on a support arm  4  of the headset. 
     In this embodiment, the mike casing  11  comprises a casing body  12  mounted on the end of the support arm  4 , and a casing cover  13  secured to the back side (the upper surface side in FIG. 2) of the casing body  12  by a fastening screw. The casing cover  13  is detachably secured to the back side of the casing body  12  so as to facilitate the wiring works in the casing body  12 , and the casing cover  13  has a seal member  131  such as rubber mounted on the inner surface thereof. 
     The casing cover  13  has an unit accommodating portion disposed at end thereof and formed in a cylindrical shape. The unit accommodating portion  4  has openings, of which one end forms a front sound receiving opening portion  141 , which is directed to the mouth of a speaker, and the front sound receiving opening portion  141  has a case ring  121  which fit therewith. The case ring  121  forms a portion of the case body  12 . 
     According to this embodiment, there is also a rear sound receiving opening portion  142  formed at the other end of the unit accommodating portion  14 . The front sound receiving opening portion  141  and the rear sound receiving opening portion  142  have a water repellent mesh, respectively, but not shown. 
     The unit accommodating portion  14  accommodates a mike unit  15  therein. In this case, the mike unit  15  is of a single directive unit. For this reason, the unit accommodating portion  14  is provided with the rear sound receiving opening portion  142  in addition to the front sound receiving opening portion  141  as described above. 
     The mike unit  15  is covered with a tubular spacer  16  made of synthetic resin, and held in a predetermined position in the unit accommodating portion  14  thorough the tubular spacer  16  Furthermore, the mike unit  15  has a circuit substrate  151  mounted therein for collecting electrical signals from the mike unit  15 . 
     There are an O-ring  171  and a waterproof membrane  18  disposed on the back surface side of the mike unit  15 , where is on the side of the rear sound receiving opening portion  142  of the unit accommodating portion  14 . There are also an O-ring  172  and a waterproof membrane  19  disposed on the front surface side of the mike unit  15 , where is on the side of the front sound receiving opening portion  141  of the unit accommodating portion  14 . Further, in this embodiment, an O-ring  173  is also interposed between the casing ring  121  and the case body  12  about the outer peripheral surface of the unit accommodating portion  14 . 
     A side wall of the unit accommodating portion  14  has a venting hole  21  bored therein, and the venting hole  21  brings the interior of the unit accommodating portion  14  into communication with the outside of the mike casing, and the venting hole  21  is provided with an pressure equalizing membrane  22 . The pressure equalizing membrane  22  may be mounted at either of the inside or outside of the unit accommodating portion  14 . 
     The pressure equalizing membrane  22  to be used comprises a water non-permeability membrane. At this time, this kind of the water non-permeability membranes are produced by various makers. In this embodiment, Microtex NTF1026-CO2 manufactured by NITTO DENKO-SHA or products with a performance similar to Microtecx is used. 
     In this embodiment, the tubular spacer  16  is also provided with a venting hole  161  corresponding to the venting hole  21 , since the mike unit  15  is covered with the tubular spacer  16 . 
     As described above, according to the present invention, even though pressure variation is caused by outside air, the pressure differential between the outside of the mike casing and inside of the unit accommodating portion  14  is almost reduced, since the venting hole  21  is bored in the side wall of the unit accommodating portion  14  to allow the interior of the unit accommodating portion  14  to be communicated with outside of the unit accommodating portion  14 . 
     Moreover, the waterproof performance is not reduced, since the pressure equalizing membrane  22  of the water non-permeability membrane is mounted on the venting hole  21 . Therefore, the waterproof membranes  18  and  19  are allowed to be mounted by the stable tension applied thereto so that excellent waterproof performance and excellent acoustic characteristics are maintained. 
     Furthermore, though not shown in detail, the outer surface of the tubular spacer  16  is plated by metal, and a part of the metal plate is connected with an earth line of a circuit substrate  151 . In this manner, the tubular spacer  16  can be used also as an electromagnetic seal for the mike unit  15 . 
     The waterproof membranes  18  and  19  are formed out of an extremely thin (for example, 4 μm thickness) plastic film, for example, such as polyethylene, polyethylene terephtalate, etc., both of which are supported by the support rings  20 ,  20 . 
     Since the both support rings  20 ,  20  have same construction, one of the support rings  20  will be described with reference to FIG.  3 . The support ring  20  is made of, for example, phosphorbronze or metal such as stainless, of which one surface is provided with waterproof membranes  18  and  19  mounted thereon through an adhesive not shown. A water proof supporting surface  201  has an inner peripheral edge provided with a convex curved surface  202  to the side of a waterproof membrane support surface thereof. 
     The convex curved surface  202  comprises a surface for protecting the waterproof membranes  18  and  19 . Therefore, for example, even if the waterproof membranes  18 ,  19  are, as indicated by the chain line, pulled inwardly of the support ring  20  by the tension caused by the outer pressure, the waterproof membranes  18 ,  19  are cut from the edge portion. The protective surface may be formed by a tapered surface  203  having a predetermined inclination angle as shown in FIG.  4 . 
     While the waterproof membranes  18  and  19  are loosely mounted on the support ring by almost no tension through an adhesive. In this embodiment, an adhesive with adequate viscosity (elasticity) after setting, such as a silicon rubber adhesive or a 2-liquid epoxy adhesive is used, which has low hardness after setting. 
     According to the arrangement described above, when the waterproof membranes  18 ,  19  are pulled by the tension of external pressure or the like, the waterproof membranes  18 ,  19  are effectively prevented from the excessive tension because of the damping tension caused by the viscosity of the adhesive. 
     Furthermore, though not shown in detail, the waterproof membranes  18 ,  19  has a fine rugged portions formed by the grain transfer processing, for example so that the resonance of the waterproof membranes  18 ,  19  can be reduced. 
     In the embodiment described above, the rear sound receiving opening portion  142  is also disposed on the back side of the unit accommodating portion  14  because of the unidirectional mike unit. However, if the mike unit  15  has a non-directional performance, there is no need for providing the rear sound receiving opening portion  142 , and accordingly, the O-ring  171  and the waterproof membrane  18  are also may not be mounted on the back side of the unit accommodating portion  14 . 
     Furthermore, in the above-mentioned embodiment, although the descriptions were given with respect to only the waterproof type microphone for headset, it should be observed that the present invention is not limited to the water proof type microphone for headset, and, other waterproof type microphones are off course can be applied. 
     As described above, according to the present invention, the mike casing is provided with the venting hole which brings the unit accommodating chamber into communication without side of the casing, the venting hole is provided with the water non-permeability membrane as the pressure equalizing membrane, and thereby equal pressure is provided between the interior of the unit accommodating chamber and the outside of the mike casing. 
     Furthermore, the waterproof membrane is effectively prevented from the breakage caused by the tension applied thereon, since the support ring has a protective surface formed at the inner peripheral edge to the side of the waterproof membrane, the protective surface having a predetermined inclination angle or a predetermined curvature. 
     Moreover, when the waterproof membrane is mounted on the support ring, the adhesive with viscosity after setting is used. Even though the waterproof membrane is pulled by tension applied thereto, the viscosity of the adhesive damps the tension. Thereby, the waterproof membrane is prevented from the breakage thereof caused by the tension applied thereto. 
     Moreover, the resonance of a single membrane is suppressed, since the waterproof membrane has the fine rugged notches. 
     Therefore, excellent acoustic characteristics can be maintained.