sonic sounds were limited by the character- 

 istics of the waves and by their lethal effects 

 under certain conditions. 



The primary objective of this study was 

 to determine whether any quantity or quality 

 of underwater sound would attract or repel 

 young salmon. 



LABORATORY METHODS 

 AND EQUIPMENT 



The literature survey suggested that the 

 most promising field of study was in the low- 

 frequency range; therefore, frequencies from 

 5 to 20, 000 cycles per second (c .p. s .) were 

 chosen for use in the systematic testing pro- 

 gram . The United Control Corporation of 

 Seattle, Seattle, Washington, was awarded a 

 contract for the development and fabrication 

 of a transducer keyer and the necessary trans- 

 ducers to cover this range of sound. An 

 electromagnetic transducer was designed for 

 covering the range from 5 to 5, 000 c .p . s . 

 (fig. 1). For frequencies from 5, 000 to 

 20,000 c.p.s., a piezoelectric transducer, 

 using barium titanate crystals, was applied 

 (fig. 2). 



Each of the sound-producing units was 

 driven by an amplifier-oscillator -keyer unit 

 consisting of a 50 -watt amplifier, into which 

 an audio oscillator was fed. The transducer 

 keyer was included in the circuit to control 

 the signal from the oscillator to the amplifier 

 and to allow for the variation of both the 

 repetition rate and width of the pulse of any 

 frequency being tested. The transducers 

 and the keyer proved highly satisfactory in 

 the test. 



The research project was divided into a 

 laboratory phase and an open-water phase. 

 The laboratory work consisted of testing 

 fish in an experimental tank designed espec- 

 ially for this study. The tank, constructed 

 of 2 -inch cedar, was 11 feet long, 2 feet 

 wide, and 14 inches deep (fig. 3). The tank. 



with its five separate compartments, 

 was built to measure the distribution 

 of fish within the tank before and after 

 subjecting them to various sound situa- 

 tions . This method of measuring the 

 effects of sound on fish required com- 

 partment separators that could be raised 

 and lowered quickly and simultaneously. 

 The problem was solved with separators 

 of weighted sheet aluminum . 



The tank was designed with the 

 aid of underwater -sound engineers, who 

 were familiar with problems experienced 

 in underwater sound research. The most 

 difficult problem encountered in under- 

 water sound research within a confined 

 area is that of reverberation and standing 

 waves. Following the advice of the sound 

 engineers, the entire inner surface of the 

 tank was lined with 3 inches of rubberized 

 horsehair. This material, commonly 

 used in the manufacture of furniture, 

 proved satisfactory as soundproofing 

 down to a frequency level of about 50 c.p.s. 

 The later addition of a 1-inch layer of 

 waterproofed foam rubber under the horse- 

 hair added to the efficiency of sound ab- 

 sorption . 



During the first exploratory testing 

 in the laboratory, the low -frequency 

 electromagnetic transducer was mounted 

 directly on the end of the experimental 

 tank. This arrangement proved satis- 

 factory for frequencies above 500 c.p.s. 

 However, below this level vibrations were 

 carried through the walls of the tank . In 

 effect, the entire tank served as a trans- 

 ducer, and sound was introduced into the 

 water from all solid surfaces. It was 

 obvious from the pattern of surface wave 

 action that the sound within the tank was 

 nondirectional and that standing waves 

 were being created. 



The problem of standing waves 

 was eliminated by mounting the transducer 



