US 3296582 A
Description (OCR text may contain errors)
UNDERWATER LISTENING AID FOR SUBMERGED PERSONNEL Filed July 23, 1946 JOHN M. IDE
. to. the difference in sound velocities in air and Water.
, 3,296,582 I UNDERWATER LIS IENING AID FOR SUBMERGED PERSONNEL John M. Ide,iAlexandria, Va. (2332 Massachusetts Ave., NW., Washington, D.C. 20008) Filed July 23,1946, Ser. No. 685,631 Claims. (Cl. 340.-5)
. coming from any direction except straight ahead reach the: two ears at slightly different times. i can estimate, bearingsto a few degrees, corresponding to time differencos of the order of one-one hundred thou- In air, the ears sandths of a second. With the ears submerged, the direction of underwater sound should be perceived in the same manner as in air, but the accuracy should be lower owing In water the situation is furthercomplicated by the masking effect of sound received by bone conduction through various parts of the head. Sound received through areas midway between the ears, particularly the top and back of the head, has no directional character but does contribute to the overall loudness.
Investigation has shown that submerged bone conduction hearing and submerged eardrum hearing are of the same. order. ,of sensitivity. It may be expected that effects of increasing depth will further attenuate the eardrum hearing. sensitivity, owing to the unbalance of static pressure on the drum. Since the bone conduction hearing is not so, affected, the directional indication usually arising from a binaural effectbecomes progressively lost, and tests have shown that, to a submerged person the soundsource appears more or less directly overhead at all times. Afirst object of the present invention is to remedy this, and to restore a binaural effect from which a direction indication may be gained by providing means for acousi which will be simple, and light in construction.
AprincipaLfeature of this invention is the use of a strip of material having acoustical impedance sharply different from that of the seawater, and in acoustic contact, with the central part of the bony structure of the head, in a helmet of light construction closely fitting the head. This and other features of the invention will become more apparent; from the following detailed description taken together with the accompanying drawing, wherein the single figure: is a perspective of a helmet constructed according to the principles of the present invention.
There is depicted in the figure a helmet of fabric or other light material having portions adapted to extend over and fit the sides of the head, and a centrally disposed portion 11. The portion 11 extends from front to back of the :helmet, and when worn willthus extend from the base of the skull to theforehead. The portion 11 forms an outer. covering for a sponge rubber strip 12 which provides a sharp acoustic mismatch with the seawater owing to the great number of air bubbles it contains. A
1 piece of fabric or light material 13 is sewed in to form a 1 pocket; containing the sponge rubber strip 12. The
stitches 14 indicate the line of the sewing. The portions 10 have holes 15 cut through so that the ears may be free.
United States Patent C) ice 3,296,582 Patented Jan. 3, 1967 18 suitably spaced, provided means for securing the helmet to the head of the wearer. The size of the rubber strip 12, while not critical, has been found to affect the effective hearing sensitivity considerably. A substantially uniform width of four inches, with a length which extends from the forehead to the base of the skull, has been found to be adequate.
Any suitable material having a sharp mismatch of acoustical impedance with that of the seawater can be substituted for the sponge rubber. For example, an inflated diaphragm or air cell fitted into the section 11 would have substantially the same effect. The sponge rubber has been found to withstand much use without appreciable deterioration.
An example of a direct application of these principles occurs in a system of underwater navigation for swimmers in underwater demolition teams or commando type operations. For beach reconnaissance which must be conducted with a large measure of secrecy, a small boat equipped with a suitable underwater sound source may be positioned in a known location offshore. Swimmers equipped with helmets as herein described are sent forth from the boat, and then are able to locate beach characteristics, obstacles in the approaches, etc., by orientating themselves with respect to the sound source, even though entirely submerged. In addition, this system provides a homing signal for expediting the return of the swimmers to the boa-t. Interruption or modulation of the sound source may be used as a danger signal or to impart information. Directional properties of an underwater sound source may be used to selectively guide an individual swimmer or group of swimmers down the beam in a special angular sector. In this way a special sector of beach may be investigated or obstacles avoided. This has the added advantage of even more security than the non-directional sound source affords. It is easy to see that multiplication of these systems will furnish a method of keeping formation, or of guiding a boat to or from a sound source. Such navigating procedures have been found to be effective despite ocean currents. The inherent simplicity and lightness of the equipment required to effect such operations allow their impromptu and extended performance under a great variety of circumstances.
No attempt has been made here to exhaustively point out or cover all the features or applications of the present invention. Many others than those described will be apparent to persons skilled in the art. The scope of the invention is to be defined in the following claims.
What is claimed is:
1. An underwater listening device for sub-merged personnel, comprising a strip of material having a substantially uniform width and an acoustic impedance lower than that of water arranged to extend fore and aft along the top of the head of a person substantially from the forehead to the base of the skull and limited in its lateral extent to omit coverage of the ears and sides of the head, and means for holding said stripin position.
2. A listening aid for underwater navigating personnel comprising a hood of relatively thin light material adapted to be worn on the head and carrying a relatively thick central portion in the form of a thickened strip of material having a sharp mismatch of acoustical impedance with that of water extending fore and aft from the forehead to the base of the skull and extending laterally approximately two inches from the center of the head toward each car over substantially the entire length of the strip.
3. A device for enhancing the underwater binaural hearing of a submerged human observer comprising, isolating means for acoustically damping underwater sound waves at the outer surface of the head of said observer, and positioning means maintaining contact between said isolating means and the head of the observer only over a 3 4 narrow continuous central portion of said outer surface 1,394,482 10/ 1921 Fessenden 1810.51 from the forehead to the base of the skull which is nearly 1,547,574 7/1925 Fay 1131-05 1 uniform in Width. 1,594,174 7/1926 Hart 2-3 4. The device according to claim 3 wherein said isolat- 1,810,655 6/ 1931 Haskillg 8 ing means comprises a water vresistant solid having at 5 1,836,551 11/1932 101165 least one pocket of gas trapped therein. 1, 1 11/1932 Shehter 1810.51 5. The device according to claim 3 wherein said posi- 2,140,716 12/1938 Pryale tioning means comprises a hood of lightweight fabric 2,296,335 9/ 1942 y t h h th l t' v W C a mg means 18 aflmhed 10 CHESTER L. JUSTUS, Primary Examiner.
References Cited by the Examiner CARL w. ROBINSON, DAVID GALVIN, Examiners. UNITED STATES PATENTS NORMAN H. EVANS, FREDERICK M. STRADER, 964,380 7/1910 Bowlker 18 1-0-51 P. H. BLAUSTEIN, T. D. JENNINGS, R. A.
1,080,690 12/ 1913 Hipkiss 23 1 FARLEY, Assistant Examiners.