Most underwater communication systems between divers rely on ultrasonic carriers which necessitate a demodulator carried by each diver. Since most underwater tasks require a diver's full attention to operate bulky, awkward implements under unfavorable conditions, a demodulator package could get in the way and, in some instances, create a hazard or otherwise compromise a diver's effectiveness.
A "Sonic Communication System" disclosed in U.S. Pat. No. 3,150,345 by J. E. Freeman, selectively transmits and receives audio information in a body of water. His system provides for underwater and above surface use and has a capability for selectively connecting an audio frequency input source to a loudspeaker, transducer or combination of the two. While the system represents a meritorious advance in the state-of-the art, it appears to be limited in that it is not adaptable for use by several divers and a surface station and may add unneeded equipment when arduous undersea tasks are performed.
An electroacoustic transducer developed by Ralph Weinger and disclosed in U.S. Pat. No. 2,937,244 attempts to give a diver a communication capability without duly burdening him. The Weinger pressure compensating technique employs a bladder interconnected transducer to reduce the problems associated with distortion or loading of the transducer diaphragm. The purpose of the pressure compensation system of Weinger is to improve the operation of the "System And Method For Underwater Communication" disclosed by D. R. Kursman et al., in U.S. Pat. No. 2,798,902. In the Kursman et al., communication system, electrical energy patterns are modified into different electrical signal patterns in accordance with a selected function to render it most effective for underwater transmission. Kursman et al., recognized that distortion problems may be prevalent with signal modification techniques, for example, heterodyning, and they sought to improve the transducer's operational characteristics. However, signal modification techniques necessarily calls for electronics to be carried by a diver which might interfere with the job at hand.
Thus, there is a continuing need in the state-of-the art for an underwater communication system which reliably permits acoustic communications between divers and their surface support vessel while not overly burdening the divers with unnecessary instrumentation packages.