speech signal. Such a system ordinarily consists of a microphone, power 

 supply, amplifier, modulator, and underwater transducer. Speech produced in 

 this manner can be understood only by a diver or a surface observer having an 

 appropriate receiver and demodulator. 



With the Aquasonics unit, a 42 kHz carrier signal is transduced into the water 

 after being modulated by the speech signal and the mixed signal is picked up 

 by a receiving coil, demodulated, and heard in the normal speech mode. The 

 PQC-2 (a military unit) uses an SSB suppressed carrier frequency signal of 

 8.0875 kHz. 



The purpose of this study was to provide information on how the units listed 

 above would perform over distance and, unlike our previous fresh water studies, 

 how they would perform in a salt water environment with its attendant sea 

 noises. Each diver/talker (N=4) was assigned a 50-word Griffith list (equated 

 for difficulty) to be read with each communicator at each distance. Each word 

 was preceded by the phrase, "You will say--." Figure 2 shows a diver/ talker 

 using a PQC-2. 



Figure 2. A diver/talker shown reading a word list via the PQC-2. 



In order to evaluate the communication systems, tape recordings of the lists 

 read by the divers were brought to the University of Florida and played to a 

 minimum of ten "semi -trained" listeners; i.e., students selected on the basis 

 of 1) being native speakers of English, 2) having normal hearing, and 3) being 

 capable of performing the required listening tasks. Before hearing the tapes, 

 listeners were required to score at least 927o on a screening test. 



SOUND LOCALIZATION IN SALT WATER 



In air, man depends on his directional sense of hearing to locate the source of 

 sounds, to warn him of approaching objects which emit acoustical signals, and 

 to differentiate among competing signals. Both theory and empirical evidence 



X-4 



