Chapter 18: Test and Measurement Microphones

Dr. John Carey, Larson Davis, Inc.

A microphone provides an analog output signal which is proportional to the variation in acoustic pressure acting upon a flexible diaphragm. This electrical signal is then used to transmit, record or measure the characteristics of the acoustic signal. The most common applications are related to audio broadcasting, recording and reproduction, where the frequencies of importance are in the human hearing range, 20 Hz ?20 kHz. These microphones are often highly directional. This is a desirable feature when the intention is to reproduce the sound produced by a particular singer or instrument, particularly in the presence of background noise. Also, their ability to represent the measured sound level with precision is less important than their ability to reproduce the sound electrically in terms of parameters important to audio technicians, such as color, depth, warmth, etc.

Measurement microphones differ from those used for audio applications in that their primary role is to electrically reproduce the sound waveform without distortion and with a linear relationship between the voltage out and the pressure sensed by the microphone diaphragm. This precision must be maintained over a wide range of frequencies and amplitudes when measuring sound waves arriving from different angles. Furthermore, they are expected to maintain this degree of precision over a range of temperature and barometric pressure variations.