Infrasonic pistonphone calibration of acoustic transducers

Abstract

A simple infrasonic pistonphone was developed for the low-frequency calibration of acoustic sensors. The pistonphone, which utilizes a variable speed dc motor and a crank-driven piston, has a frequency range of 20 mHz to 20 Hz. Digital techniques have been implemented to correct for the inherent distortion in the crank-driven piston design, enabling simpler mechanical construction without significant loss in calibration accuracy. As in similar design geometries [H. E. Dahlke and John J. Van Houten, J. Acoust. Soc. Am. 37, 1209 (1965)], the transition from an adiabatic to an isothermal pressure-volume relation is readily observed within the specified frequency range and results in a 0.5-dB reduction in calibration signal amplitude. A digital model for this transition is compared to data acquired using the pistonphone, and possibilities for increasing the calibration accuracy by use of this digital model are presented. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]