Audio microphones are designed for sound reception and recording applications that involve speech and music. Capacitance microphones include a thin surface and a rigid surface that are connected by wires to audio equipment. Sounds cause the air pressure to change, the surfaces to vibrate, and charges to move between the surfaces and the audio equipment. In electromagnetic microphones, changes in air pressure move a coil of wire. Since the wire is near a magnet, the electric charges in the coil move as a current.  

Audio microphones vary in terms of directional sensitivity. Omnidirectional microphones are sensitive in all directions. Bidirectional microphones are sensitive in two directions and directional microphones are sensitive in only one direction. Cardioid microphones are also unidirectional, with an effective sensitivity angle of approximately 130°. These microphones are called “cardioid” because their directivity graphs resemble a traditional depiction of a human heart. Supercardioid microphones have a narrow sensitivity angle, or pickup, of approximately 115° while hypercardioid microphones have a pickup of only 105°. Semicardioid microphones have a maximum direction of sensitivity at 180°.   

Audio microphones are designed for sound reception and recording applications that involve speech and music. Capacitance microphones include a thin surface and a rigid surface that are connected by wires to audio equipment. Sounds cause the air pressure to change, the surfaces to vibrate, and charges to move between the surfaces and the audio equipment. In electromagnetic microphones, changes in air pressure move a coil of wire. Since the wire is near a magnet, the electric charges in the coil move as a current.  

Audio microphones vary in terms of directional sensitivity. Omnidirectional microphones are sensitive in all directions. Bidirectional microphones are sensitive in two directions and directional microphones are sensitive in only one direction. Cardioid microphones are also unidirectional, with an effective sensitivity angle of approximately 130°. These microphones are called “cardioid” because their directivity graphs resemble a traditional depiction of a human heart. Supercardioid microphones have a narrow sensitivity angle, or pickup, of approximately 115° while hypercardioid microphones have a pickup of only 105°. Semicardioid microphones have a maximum direction of sensitivity at 180°.   

Differences in frequency response, dynamic range, and microphone sensitivity characterize audio microphones. Frequency response is the range of frequencies for which the microphone maintains a constant sensitivity. Variations from this linear, or flat, sensitivity are given in decibels (dBs). Dynamic range is the range of sound pressure levels (SPLs) for which the microphone meets its performance specifications. The inherent noise of the acoustic system establishes the low end limit. The maximum sound pressure level sets the high end limit. Microphone sensitivity, which measures a microphone’s responsiveness, needs to exceed the inherent noise of the system but not overload the preamplifier.

Audio microphones vary in terms of the signal-to-noise ratio, impedance, and polarization. The signal-to-noise ratio is a logarithmic ratio of the signal level produced by a standard pressure signal (e.g., 94 dB SPL) to the noise floor. Impedance is the resistance to flow of alternating current (AC). Typically, low impedance microphones are 100 to 500 ohms, and high impedance microphones are 10,000 ohms or more. In terms of polarization, some audio microphones have prepolarized electret backplates or utilize external capacitor polarization. External polarization requires a separate power supply. 

Audio microphones have nominal diameters that range, typically, from as small as 1/8” to as large as 1”. Different diameter microphones have different dynamic characteristics. In general, microphones with larger diaphragms are more sensitive and have narrower frequency response. Audio microphones also vary in terms of actual diameter and size, as well as thickness and height. 

Some audio microphones are equipped with special features. Digital microphones have integral analog-to-digital converters that render sound into computer-recognized formats. Integral pre-amplifiers boost microphone output from small to intermediate levels. Probe-style microphones have a long tip for measuring near-field levels or hard-to-reach places, while array type microphones measure 3-D sound fields around test objects. Designed for difficult conditions, some audio microphones are outdoor-rated or have a wind or turbulence screen.  

There are many applications for audio microphones. Some are designed for use in aircraft, cars, trucks, or other vehicles. Others are designed for use with computers or industrial workstations; consumer electronics or gaming; or telephones and voice communication products. Public facilities use audio microphones to provide information over loudspeakers. Recording studios or television or radio broadcast equipment requires professional-grade audio microphones.