Abstract
In a previous paper [T. M. Marston and T. B. Gabrielson, J. Acoust. Soc. Am. 119, 3378 (2006)], a simple total-immersion calibrator for infrasonic microphones was described. This calibrator has been improved and so has the correspondence with theory. The Rott equations for thermoviscous acoustics have been incorporated in a stepwise solution for the acoustic field. These equations account for the transition between boundary-layer flow in which the main field is almost isentropic, and the very-low-frequency approach to isothermal pressure oscillations. The entire microphone body is placed in the calibrator so that the pressure-equalization leak functions normally. The calibrator operates from 0.02 Hz to 20 Hz and includes a DC-coupled piezoresistive differential pressure sensor for comparison calibration; however, the model, which incorporates the geometry of the calibrator pipe, the temperature, and the piston stroke, permits response estimation without dependence on the reference sensor. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]
Published Version
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