ACOUSTIC FILTERS PART Ⅱ: THE FOUR-MICROPHONE METHOD OF EXPERIMENTAL VERIFICTION OF ACOUSTIC CHARACTERISTICS OF MUFFLERS

摘要

An experimental method that complements computer modeling of transmission characteristics of mufflers is devised. It is an extension of well-established two-microphone method of experimental investigation of acoustic characteristics of materials. The four-microphone method is actually the two-microphone method that is applied two times at two different locations of an acoustic system. The method does not require use of dedicated dual-channel Digital Frequency Analyzer. If the excitation signal is random, stationary and ergodic, microphones do not have to be accurately calibrated and they do not need to be phase-matched either. Under these conditions, even in-situ measurement can be done with ordinary microphones and both measurements have not to be simultaneous.