544 



SCHEVILL, BACKUS, AND HERSEY 



[chap. 14 



specifically for studying animal sounds ; many research programs continue to 

 depend on the AX-58, its successor the Brush AX- 120, or similar audio- 

 frequency transducers. Within their limited frequency range (see Fig. 1 ; this 

 and Fig. 2 are calibrations by the U.S. Navy Underwater Sound Reference 



BRUSH AX-58 HYDROPHONE 

 (OPEN-CIRCUIT VOLTAGE) 



FREQUENCY (kc/s) 



Fig. 1. Response of a representative Brush Development Co. AX-58 hydrophone. (After 

 Hersey, 1957, Fig. 8b. By courtesy of the Journal.) 



MASSA AX- 40 HYDROPHONE 

 (OPEN - CIRCUIT VOLTAGE) 



< o 

 o < 



FREQUENCY, (kc/sl 



Fig. 2. Response of a Massa AX-40 hydrophone. 



Laboratory) they have excellent signal-to-self-noise characteristics, but they 

 do not respond uniformly to frequencies higher than 9 kc/s. The Massa AX-40 

 designed by Massa for Schevill in 1952 has a broad high-frequency range 

 (Fig. 2), but unfortunately it is rather insensitive and has a bothersome response 

 peak which limits its usefulness. More recently designed hydrophones respond 

 uniformly over a much broader range of frequencies, but they are so insensitive 



