US2937244A - Electrical-acoustic transducer - Google Patents

Description

y 1960 R. WEINGER 2,937,244

= ELECTRICAL-ACOUSTIC TRANSDUCER Filed Oct. 4, 1957 Z? N A INVENTOR 7 Mal 1% 71 217 6 BY a MQ M4114 ATTORNEY United States Patent ELECTRICAL-ACOUSTIC TRANSDUCER Ralph Weinger, Philadelphia, Pa., assiguor to Jetronic Industries, Inc.

Application October 4, 1957, Serial No. 688,295

Claims. (Cl. 179-188) The present invention relates to transducers of the type designed to interconvert electrical and acoustic energy, and more particularly to a transducer and housing therefor adapted to render the assembly operative and useful under conditions of varying ambient pressures. Specifically, the present invention relates to a transducer housing adapted to render the transducer operative in water under substantial hydrostatic pressures.

In US. Patent 2,798,902, issued July 9, 1957 to Daniel R. Kursman and Sigmund P. Rosen, there is disclosed an underwater wireless telephone system adapted particularly to provide for direct voice communication between divers, swimmers and the like. In the case of skin divers, i.e., divers operating without the benefit of conventional diving suits, a problem exists in providing a microphone for the swimmer affording good fidelity when operating at substantial depths in the water. First of all, it is apparent that the transducer unit must be completely sealed from the surrounding water. Secondly, when thus sealed by conventional techniques, the transducer diaphragm being exposed to the air pressure in the swimmers face mask, will become distorted and even inoperative at substantial depths underwater. This results from the fact that the pressure of the breathing gas supplied to the swimmers face mask is normally related to and higher than the ambient pressure. Thus, if the transducer unit is sealed, the pressures to either side of the transducer diaphragm become significantly unbalanced, and the transducer becomes distorted in operation and even inoperative.

In the art of underwater sound detection and transmission, numerous efforts have been made to solve similar problems. These efiorts in general have resulted in the development of sealed transducer elements, with which is associated a compressible gas containing bladder communicating with the interior side of the transducer diaphragm while the exterior side is exposed to the ambient hydrostatic pressure. For many purposes this approach to the problem has been found to alford an adequate solution, but for the present purposes it is not satisfactory. In the case of a skin diver, or any other type of diving operation, the pressure within the mask or helmet is normally higher than the ambient hydrostatic pressure. Accordingly, using the techniques of the prior art the pressures on either side of such a sealed transducer diaphragm would not be balanced, as is necessary for good fidelity, and the pressure loading of the diaphragm could even result in total inoperability. Additionally, such prior art transducer elements are specially designed and constructed to be gas and water tight, are not readily commercially available, and are expensive.

By the present invention the foregoing disadvantages of prior art devices are overcome, and an underwater transducer assembly is provided which is operative for use in diving masks, or for any other purpose, at any desired depth, is substantially unaffected by even large differences in pressure between the swimmers breathing gas inside the mask and the ambient pressure, and may employ any conice ventional transducer element which is not specially sealed to be gas tight. In general, the present invention comprises a transducer element of any conventional design or type, mounted within a gas and water impervious housing. A flexible gas filled bladder is associated with the housing in communication with transducer element. Since the transducer unit or element itself is not impervious to gas, regardless of the pressure exerted on the bladder, the transducer diaphragm is balanced with equal pressure on either side thereof. Immediately in front of the transducer diaphragm, but spaced somewhat therefrom, the housing is formed or provided with a flexible, elastic, gas and water impervious, sound transmitting membrane, so that acoustic energy impinging upon the membrane is transmitted to the interior of the housing and thus applied to the transducer diaphragm. When using this transducer assembly in conjunction with an underwater swimmers face mask, the housing is mounted on the mask with the membrane directed generally toward the mouth of the wearer. Although an unbalance between the ambient pressure acting on the bladder and that within the mask acting on the membrane does cause some distortion or loading of the membrane, this is inconsequential as compared with a corresponding distortion or loading of the transducer diaphragm, because the transducer diaphragm is mechanically loaded with transducer electrical parts or material whereas the membrane is free, the membrane can be made more elastic than the diaphragm, and distortion or loading of the membrane in no way affects the electrical parts of the transducer or their relationship.

It is therefore one object of the present invention to provide an acoustic electrical transducer assembly capable of operation with good fidelity under varying conditions of ambient pressure.

Another object of the present invention is to provide an acoustic-electrical transducer assembly for underwater use.

A still further object of the present invention is to provide an acoustic-electrical transducer assembly for use by underwater swimmers and divers.

And an additional object of the present invention is to provide an acoustic-electrical transducer assembly, wherein the transducer element is contained within a completely sealed housing. Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one specific example of the present invention had in conjunction with the accompanying drawings, wherein like numerals refer to like or corresponding parts, and in which:

Fig. 1 shows an underwater swimmers face mask incorporating a transducer assembly in accordance with the present invention; and

Fig. 2 is an enlarged cross-sectional view of a portion of Fig. 1, taken along line 22, particularly illustrating the transducer and housing assembly.

In the following specific example, the present invention is illustrated and described in the form of an underwater swimmers microphone. The invention, however, is not limited thereto, for it is also applicable to receiver transducer applications, and may find utility and advantage in other than underwater environments.

Referring to the drawings, the numeral 10 generally denotes an underwater swimmers face mask, having a glass sight plate 11 and inlet and exhaust tubes 12 and 13 for affording a flow of breathing atmosphere to the wearer. There are numerous types of breathing atmosphere supply systems for underwater swimmers, but forming no part of the present invention, a supply system is not illustrated or particularly described. However, whatever supply system may be employed, it normally provides an atmosphere in the interior of the mask 10 at pressures exceeding the ambient hydrostatic pressure. A transducer assembly in the form of a voice microphone, constructed in accordance with the teachings of the present invention, is mounted in the sight plate 11 and is generally denoted by the numeral 14.

The detailed construction of the microphone 14 is illustrated in Fig. 2. As there shown, a rigid housing 15 has mounted therein an acoustic-electrical transducer element 16. The transducer may be of any conventional form, such as a carbon button or induction type transducer, and has a conventional casing that is not sealed to the atmosphere. At one end the transducer has a conventional diaphragm 17, and an electrode contact assembly 18 at the other end to which the leads in conductor 19 are connected. Thus, acoustic energy impinging upon diaphragm '17 is converted to corresponding electrical signals by the transducer element 16, thus providing corresponding signalson conductor 19, as is well known in the art.

The housing 15 is generally cylindrical in shape and open at both ends. A compressible and gas and water impervious bladder 20, affording a gas reservoir 21, is applied over the back end of housing 15, sealing that end from the ambient surroundings. The mouth 22 of bladder 20 is cupped over the back end of housing 15, and an internal annular land 23 in mouth 22 of the bladder fits into an external annular groove 24 on the housing, to facilitate a water and air tight seal between these two elements. To secure this seal, a clamping ring 25, such as a conventional hose clamp, may be applied around the ex terior of the bladder mouth 22. Electrical connection to the transducer contact assembly 18 is had by conductor 19, which is an extension of waterproof cable 27 having a terminal connector 29. The cable 27 is fed into the microphone assembly through bladder extension 26, and the extension 26 is sealed about the inserted cable by means of a suitable packing gland 28.

Since water does seep into a diving mask during use, the inner end of housing 15 is also sealed by cementing a thin circular rubber membrane 30 to the inside surface of internal annular flange 31 on the housing. It is preferred that the membrane be supported by a coextensive, perforated, circular backing plate 32.

The microphone assembly above described may be mounted upon the sight plate 11 of mask 10. For this purpose, the housing 15 is formed with a reduced external diameter extension 33, designed to be received through an aperture in the sight plate, and to be fastened thereto by threaded annular nut 34, sandwiching the sight plate 11 between the nut 34 and an opposed annular shoulder 35 formed by the reduction in external diameter of the housing 15. An annular rubber grommet is placed about the periphery of the mounting aperture in the sight plate to atford a water tight seal between the housing 15 and sight plate 11.

Thus, when a swimmer applies face mask equipped with the above described microphone assembly, his speech is directed to the air and water tight, flexible, elastic membrane 30, which in turn transmits its resultant vibrations to the interior of the sealed housing 15. These speech vibrations are picked up by the diaphragm 17 of transducer 16, and thus converted to electrical energy and conveyed along conductor 19. Considering the pressure relationships when the swimmer descends under water, if the microphone assembly was formed at sea level, the interior of the housing and its associated bladder would be filled with air at normal atmospheric pressure. As the swimmer dives under water, the hydrostatic pressure increases and compresses bladder 20, causing the gas pressure within the housing 15 to equal at all times substantially that of the ambient hydrostatic pressure. Since the bladder is in communication with the front side of transducer diaphragm 17, and is similarly in communication with the back side thereof, because the transducer case 16 is not air tight, the transducer diaphragm 17 remains balanced at all times and is never loaded at any depth to which the swimmer descends. Inside the swimmers mask, a breathing atmosphere is being supplied by conventional skin diving breathing apparatus. The pressure of this breathing atmosphere is normally somewhat higher than that of the ambient pressure and impinges upon the membrane 30. The membrane is thus maintained in a substantially unloaded state by the opposing effects of the hydrostatic pressure developed on the inner side thereof by the bladder 20, and the breathing atmosphere pressure developed on the outer side thereof. When the breathing atmosphere pressure exceeds the hydrostatic pressure, some loading of the membrane does occur. However, because of the flexibility and elasticity of this membrane, the resultant loading of this membrane due to the unbalance of pressures on the front and back thereof has little effect upon the transmission of the swimmers speech waves to the interior of the housing 15, and hence to the transducer diaphragm 17. Also, as is apparent, loading of the membrane has absolutely no eifect on the static relationship of the parts of the transducer element.

Thus in accordance with the present invention, there is provided a sonic-electrical transducer assembly, wherein a conventional unsealed transducer unit is contained within a completely sealed housing. The transducer is thereby completely protected from the ambient medium, such as water, yet is capable of faithful reproduction to the maximum fidelity inherent in its construction at any pressure to which the assembly may be subjected. At the same time, the transducer is equally effective even when the housing is subjected to substantially different pressures at the two flexible and pressure responsive areas thereof.

The foregoing specific description of one embodiment of the present invention is presented merely by way of example, and it is not intended to limit the scope of the invention either to its use in a microphone embodiment, to underwater transducers, or to the specific details of the disclosed embodiment. Other uses, environments, and embodiments of the invention will be apparent to those skilled in the art, and such as are within the spirit and scope of the appended claims are considered to be within the purview of the present invention.

What is claimed is:

1. An acoustic-electrical transducer assembly comprising, an acoustic-electrical transducer element having a transducing diaphragm, and a housing completely enclosing said element and sealing the same from the ambient medium, said housing including as a wall portion a flexible bladder for maintaining the interior of the housing at a pressure substantially equal to the ambient pressure, and said housing further including as a second wall portion a thin, flexible, elastic, sound transmitting membrane, said diaphragm being positioned adjacent to but spaced from said membrane, whereby acoustic energy can be transmitted between said diaphragm and the exterior of said housing through said membrane.

2. An acoustic-electrical underwater transducer assembly comprising, an unsealed acoustic-electrical transducer element having a transducing diaphragm, and a housing completely enclosing said element and sealing the same against ingress of water, said housing including as a wall portion a flexible rubber bladder for maintaining the interior of the housing at a pressure substantially equal to the ambient hydrostatic pressure, and said housing further including as a second wall portion a thin rubber sound transmitting membrane, said diaphragm being positioned adjacent to but spaced from said membrane, whereby acoustic energy can be transmitted between said diaphragm and the exterior of said housing through said membrane.

3. In combination, an underwater divers face mask, and an acoustic-electrical transducer assembly mounted thereon, said assembly comprising, an unsealed acousticelectrical transducer element having a tranducing diaphragm, and a housing completely enclosing said element and sealing the same against ingress of water, said housing including as a wall portion a flexible bladder located exteriorly of the mask for maintaining the interior of the housing at a pressure substantially equal to the ambient hydrostatic pressure, and said housing further including as a second wall portion a thin rubber sound transmitting membrane located interiorly of the mask, said diaphragm being positioned adjacent to but spaced from said membrane, whereby acoustic energy can be transmitted between said diaphragm and the interior of said mask through said membrane.

4. An acoustic-electrical transducer assembly comprising, an acoustic-electrical transducer element having a transducing diaphragm, and a housing completely enclosing said element and sealing the same from the ambient medium, said housing including a rigid body portion seating said element therein, said portion having two openings, a flexible bladder affixed over one said opening for maintaining the interior of said housing at a pressure substantially equal to the external ambient pressure, a thin, flexible, elastic, sound transmitting membrane aflixed over the other said opening, and a perforated rigid backing plate supporting the inside surface of said membrane, said diaphragm being positioned adjacent to but spaced from said membrane, whereby acoustic energy can be transmitted between said diaphragm and the exterior of said housing through said membrane.

5. In combination, an underwater divers face mask, and an acoustic-electrical transducer assembly mounted thereon, said assembly comprising, an unsealed acousticelectrical transducer element having a transducing diaphragm, and a housing completely enclosing said element and sealing the same against the ingress of water, said housing including a rigid body portion seating said element therein, said portion having two openings, a flexible rubber bladder aflixed over one said opening and located exteriorly of the mask for maintaining the interior of said housing at a pressure substantially equal to the external hydrostatic pressure, a thin rubber sound transmitting membrane affixed over the other said opening and located interiorly of the mask, and a perforated rigid backing plate supporting the surface of said membrane interiorly of said housing, said diaphragm being positioned adjacent to but spaced from said membrane, whereby acoustic energy can be transmitted between said diaphragm and the interior of said mask through said membrane.

References Cited in the file of this patent UNITED STATES PATENTS

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