Underwater loudspeaker

Aug. 6, 1963

F. R. ABBOTT

UNDERWATER LOUDSPEAKER

3,100,291

Filed Oct. 25, 1960

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United States Patent Office

3,100,291

Patented Aug. 6, 1963

3,100,291 UNDERWATER LOUDSPEAKER

Frank R. Abbott, 3953 Wildwood, San Diego, Calif. Filed Oct. 25, 1960, Ser. No. 64,971

Claims. (CI. 340—10) (Granted under Title 35, U.S. Code (1952), sec. 266)

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention pertains to electroacoustical transducers in general and in particular to an improved loudspeaker for projecting relatively high power sonic energy within an aqueous medium with a remarkably flat response throughout the five hundred to two thousand cycle per second frequency band.

The prior art includes many such loudspeakers, each of which may be sufficiently satisfactory for its own unique purpose, but none of which ostensively has the fidelity, the power per unit weight, or the overall compactness of the loudspeaker constituting the instant invention. For example, the smallest transducers known heretofore to be available with comparable power, fidelity, and range were, generally, at least a foot in diameter, a foot in height, and weighed one hundred pounds or more. Of course, smaller transducers have been made. However, since they usually incorporate flexing ceramic discs, the fidelity of frequency response leaves a great deal to be desired and, consequently, they are ordinarily limited to narrow band or perhaps resonant frequency type operations.

The present invention overcomes many of the aforementioned disadvantages of the prior art devices.

It is, therefore, an object of this invention to provide an improved underwater loudspeaker.

Another object of this invention is to provide an underwater speaker having a substantially flat response throughout the voice frequency band of five hundred to two thousand cycles per second.

A further object of this invention is to provide a high-power electroacoustical transducer that may be used for communication between submarine divers within one hundred yards range of each other.

A still further object of this invention is to provide an underwater loudspeaker that is compact in size and light in weight for the power and fidelity thereof.

Another object of this invention is to provide a reversible, broadband, waterproof, electroacoustical transducer that will broadcast and receive pressure energy through sea water while being submerged therein.

Another object of this invention is to provide a light weight means of voice communication that may be easily carried by submerged sea divers.

Still another object of this invention is to provide an underwater loudspeaker that is easily and economically manufactured and maintained.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a block diagram illustrating the cooperation of the transducer constituting this invention with an exemplary excitation and utilization means therefor.

FIG. 2 is an elevational view partially shown in crosssection and partially depicted pictorially of the underwater loudspeaker constituting this invention.

Referring now to the drawing and FIG. 1 in particular, there is shown a transducer 11 of the type constituting the subject invention connected by means of an electrical cable 12 to an excitation and utilization means 13. Said transducer is of the reversible type which generates and broadcasts acoustical energy upon appropriate excitation by proportional electrical energy and which produces 5 electrical energy upon excitation by proportional received acoustical energy. Electrical cable 12 may be of any appropriate type which may be submerged in water without leaking or shorting and may, for example, be of coaxial configuration if expedient or desired. Examples 10 of excitation and utilization means 13 are numerous—too numerous to define in detail—but it should be understood that any communications equipment may be employed that is adapted for generating and receiving appropriate signals and otherwise cooperatively interacting with trans15 ducer 11 is herein included.

FIG. 2 discloses a preferred embodiment of the instant invention as having an aluminum hemispherical shell 14 spatially disposed at substantially the diametrical section thereof from another aluminum hemispherical shell 15 20 in such manner as to form a hollow ball-like structure. Although shown as spherical, metallic shells in FIG. 2, said shells may be of any pertinent predetermined geometrical configuration and may be made of fiberglass, plastic, or any other suitable material having the proper 25 strength characteristics adapted for effecting mechanical impedance transformation between same and ambient sea water.

Shells 14 and 15 are held together to form a unitary overall structure but in such manner as to allow relative 30 movement therebetween along axis X—X by a resilient, flexible, rubber fabric tape ring 16 attached thereto by a cement 17 or other pertinent connecting means.

Inserted within the hollow portions of shells 14 and 15 is an electrostrictive energy converter 18 which extends 35 between the inner surfaces thereof along aforementioned axis X—X. The ends of said energy converter are attached to the inner surfaces of each of said shells, respectively, by means of cements 19 and 20 or other connecting means as desired.

_ Energy converter 18 includes a plurality of piezoele ctric discs 21 of ferroelectric, polarized barium titanate ceramic, lead zirconate, or other ferroelectric or electrostrictive ceramic, or the like. Although in this instance, the aforesaid piezoelectric discs are conventionally polarized dur45 ing the manufacturing process, it should be understood that externally applied polarizing potentials may be applied thereto by the utilization means if so desired, or in event the phenomenon of double frequency characteristics would not adversely affect overall operation, no pdlariza50 tion of the piezoelectric elements need be included. Abutting each face of each of said discs is a silver electrode 22 which, for example, may have been attached thereto by being painted thereon in the presence of a removable carrier vehicle and fired until the vehicle disappears, thus 55 leaving the silver securely adhering to the surface thereof.

Said discs are then stacked along operational axis X__X in such manner that adjacent silver electrodes electrically contact each other. In the herein disclosed preferred embodiment of the subject invention, insulated electrical 60 leads 23 and 24 are respectively connected to the aforesaid electrodes so that said piezoelectric discs 21 are electrically connected in parallel. However, it should be understood that it is within the teaching, scope, spirit, and purview of this invention to electrically connect piezoelec65 trie discs 21 in series if operational circumstances so· warrant, and that the subject discs and electrodes may be so insulated and so disposed to achieve such effect. Also, if so desired, said piezoelectric disc assemblies may be fixedly connected to each other as appropriate to provide the pre70 ferred structural configuration by means of an adhesive inserted therebetween.

In order to alleviate the possibility of shorting and in

3,100,291 capacitation due to the presence of moisture or water on the piezoelectric converter assembly, it is encapsulated within an epoxy resin chamber which may, for instance, take the form of a plastic tube 25 having sealed plastic plugs 26 and 27 at the ends thereof. Moreover, if desired, any suitable potting material may be used to fill any of the volume of tube 25 not occupied by the aforesaid piezoelectric disc and electrical lead assemblies. Although optional, in many instances, use of such potting material would ostensively improve the strength and insulation characteristics of the entire electrostrictive energy converter. Furthermore, electrical leads 23 and 24 are brought out of said plastic tube through a waterproof electrical coupling 28 ^affixed to the external surface thereof by means of cement 29 or any other pertinent adhesive or connecting means.

As previously mentioned, the entire piezoelectric converter unit is mounted within the ball-like structure formed by shells 14 and 15 and is attached thereto at each end respectively by cement 19 and 20 so that movement of the ends thereof will likewise move said shells and vise versa. Of course, any appropriate connecting means may be employed between these elements, but it has been found to be economical to manufacture and maintain the subject transducer when cement is used.

Mounted on the outside of the tubular portion of electrostrictive energy converter 18 is a toroidal transformer 30 having approximately fifty or one hundred to one turns ratio having a low impedance, tapped, primary winding 31 adapted for matching four, eight, sixteen, or fifty ohm inputs and a 'high impedance secondary winding 32 adapted for connection to electrical coupling 28 through leads 33. Said windings are electrically insulated from each other by insulation 34 and are toroidally wound about a cylindrical laminated silicon iron magnetic core 35. For support purposes, a sponge rubber mounting means 40 is inserted between the inside diameter of the toroidal transformer and the outside diameter of the energy converter. Although, for many practical purposes, a snug fit has been found sufficient to hold said transformer and converter in their predetermined relative positions during normal operations, a cement 36 may be used to insure against adverse slippage.

Electrical leads 37 connect the primary winding of the toroidal transformer to a waterproof electrical coupling 38 which, in turn, is connected through cable 12 to excitation and utilization means 13.

A mounting bracket 39 adapted for connection to a support means extending from a carrier vessel is attached to any preferred location on the outer surface of either shell 14 or 15. Or, if so desired, said mounting bracket may be replaced by a handle which would facilitate the subject transducer’s being held by the hand of a submerged diver.

Briefly, the operation of the present invention is as follows:

While being hand carried by a submarine diver or supported by a. carrier vessel, the subject loudspeaker is completely submerged in water, where it projects or receives pressure wave energy in the sonic or acoustical range of frequencies. Because it is especially efficient in the five hundred to two thousand cycle per second frequency band, it is particularly useful in human voice communication under water.

When broadcasting, it, of course, must be excited by an appropriate transmitter, and when receiving, it must be coupled to an appropriate receiving set. In either case, the transmitter or receiver may be disposed in close proximity with the loudspeaker or it may be located at some place remote therefrom, depending on the length of the interconnecting cable therebetween.

Broadcast of acoustical energy occurs as a result of the compression and decompression of the ambient water in contact with the exterior surface of the relatively moving hemispheres. Depending on the design choice of physical size of said hemispheres in relation to the wavelengths of the acoustical energy projected thereby, the subject loudspeaker may have omnidirectional, substantially bi-directional, or other radiation patterns.

Projection of acoustical energy is effected by supplying electrical intelligence signals to the toroidal transformer which increases the voltage thereof and feeds them to each of the parallel connected! electrodes and, thus, to the piezoelectric discs. Obviously, the toroidal transformer becomes superfluous and may be deleted from the transducer in event the intelligence signals supplied thereto are already of sufficient voltage to be useful. However, even the large capacitance afforded by parallel connection of the piezoelectric discs is ordinarily insufficient for semiconductor or transistor amplifier drive. Incorporation of the disclosed toroidal transformer facilitates the use of such amplifier drives for actuating the transducer. When polarized, either externally or inherently, to provide a fixed electrostrictive bias, the piezoelectric discs expand and contract in accordance with the intelligence characteristics of the applied alternating excitation current. Because said discs are stacked along a common operational axis, the relative movement between ends of converter unit becomes the sum of the expansions and contractions of all of the discs combined. Due to the fact that the Young’s Modulus of Elasticity of epoxy and plastic resins are less than that of barium titanate, tube 25 offers only a negligible restraint on the expansion and contraction of the converter unit, and, accordingly may be disregarded for all practical purposes.

Relative movement between the hemispherical shells is permitted as a result of the cut at the diametrical plane therebetween and the inter-connection thereof by the resilient molded tape ring. Waterproofing of the internal volume of said shells is also conveniently effected by use of said ring and the adhesive cement used therewith.

Although the above operational expansion has been primarily directed at using the invention as a projector, it should be obvious that the reverse process would cause it to function as a hydrophone, as well.

In addition, although many of the structural elements of the preferred embodiment have been exaggerated in size in order to facilitate disclosure thereof in the drawing, it should be understood that the proper design choices regarding size is incorporated as part of the teaching herein. Thus, for example, the thickness of the silver electrodes, the thickness of the piezoelectric discs, and the thickness of the cement therebetween, if any, etc., should be such as to provide optimum operation during any given operational circumstances.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.