A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Most microphones use the change of capacitance caused by the diagrapham mechanical vibration to produce an electrical voltage signal. In a condenser microphone, the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. There are two types of microphones of this kind: Pre-polarized Microphones and 200V Polarized Microphones.

Measurement microphones can be divided into three groups: Free-field, Pressure-field, and Random-incidence. The difference of the testing results by three types of measurement microphones would be smaller than 0.3 dB when the frequency to be measured is lower than 5000Hz; while the difference could be larger than 10 dB if the frequency to be measured is higher than 16000 Hz. So it is crucial to choose the right microphone to get an accurate measurement result.