MEASURED 1 F NOISE IN THE MEMBRANE MOTION OF CONDENSER MICROPHONES/

An acoustic isolation vessel described previously [K. C. T. Ngo and A. J. Zuckerwar, J. Acoust. Sec. Am. 93, 2974-2980 (1993)] has been empl oyed to investigate the background noise in condenser microphones over the frequency range from 2 Hz to 25.6 kHz. Measurements were conducte d on five B&K condenser microphones ranging from 1/8 in. to 1 in. diam eter and representing both pressure and free field types. The experime ntal evidence reveals the existence of a purely mechanical 1/f noise c omponent in the membrane motion of condenser microphones. The level of significance for the tested microphones, based on the t statistic, ra nges from 0.985 to 0.999. It is found that the membrane 1/f coefficien t correlates very well with the air layer resistance RA, which is resp onsible for the membrane damping. The theoretical implications of the existence of 1/f noise in the damped motion of vibrating systems are d iscussed.