Numerical Study on the Phase Sensitivity Variation in Low Frequency Primary Microphone Calibrations

Abstract

The low frequency phase characteristics of microphones in a monitoring system are crucial for characterizing large-scale natural and artificial activities—e.g., earthquakes, nuclear explosions, or rocket launchings. At present, microphones are simultaneously calibrated using in-situ or calibrator methods to get their phase consistency. However, the essential primary calibration, which traces their phase sensitivity to basic physical quantities, is grossly overlooked. Recently, we speculated that the microphone phase sensitivity is acoustically controlled by the pressure leakage and heat conduction effects in its back chamber, which will vary at low frequencies. Therefore, by means of the FEA (Finite Element Analysis) technique, simulations of laser pistonphone-based primary microphone calibrations are conducted both in the frequency and time domains. The frequency domain simulation quantifies the phase variation, while the time domain analysis helps us to understand the variation mechanism. It is found that the low frequency phase sensitivity is greatly influenced by its geometries and the venting state and should be pre-calibrated before serving.

Theoretical study on the phase sensitivity of condenser type acoustic transducers at low frequencies

“…The simulation verification corresponding to this section, in which complex factors as viscosity, heat conduction and wave motion effect can be seen in the reference of Figure 6. 28 The results are consistent with this section, so that the correctness of the theoretical model can be proved.…”

“…25,26 Secondly, these sound pressures couple with the diaphragm elasticity, and determine the diaphragm deformation. [27][28][29] Based on these, explicit sensitivity models characterizing the relationship between the diaphragm deformation and structures of acoustic transducer and pistonphone were derived. 27 The new models provide us with a means of studying the acoustic transducer phase response theoretically.…”