Simultaneous Primary Calibration on the Infrasonic Amplitude and Phase Sensitivities of Condenser Microphones and Comparison With Theoretical Results

Investigation of sound pressure leakage effect for primary calibration down to 10−2 Hz using a laser pistonphone system

“…Alternative calibration methods have been developed by NMIs and various universities [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Among them, the laser pistonphone method originally proposed by the National Physical Laboratory in the United Kingdom has gained prominence [6].…”

“…Although the direct determination of gap impedance is enabled by geometrically measuring the gap dimension [13], precise measurement is more difficult for narrower gaps. Alternatively, NMIs and some research groups conventionally measure the decay time until the chamber pressure reaches 1/e of the initial pressure after a step pressure input [6,7,11,[17][18][19]. Assuming that the chamber interior is adiabatic, the decay time is equivalent to the product of the gap impedance and chamber impedance, i.e.…”

“…This discrepancy was pointed out by He et al [23], and it remains a large uncertainty source. Recently, gapless pressure-generating ports, such as a membrane-sealing structure between the piston and chamber and a sealed loudspeaker have been proposed [17][18][19]21]. Because such pressure-generating ports are not rigid, this type of laser pistonphone requires additional care when calculating sound pressure.…”