Reciprocity calibration in a compliant cylindrical tube

Abstract

A new method for absolute calibration of electroacoustic transducers is described which permits low frequency reciprocity calibration in a test apparatus of small dimensions. The method takes advantage of the reduced wave speed in a cylindrical water column bounded by a compliant PVC tube to reduce the length of the standing wave to dimensions which can be easily handled in the laboratory. Results of a limited series of experiments show a mean reproducibility of :0.8 decibels in a one-meter long tube at frequencies between 750 and 1100 Hz and sound speeds from 330 to 365 meters/second. The hydrophone voltage sensitivities obtained by the method, however, systematically differ by 1.5 decibels from those measured by comparison with a standard hydrophone; additional research will be required to resolve this discrepancy.