Audio Microphones Information
Audio microphones are designed for sound reception, sound reinforcement and recording applications that involve speech and music. They are responsive to voice frequencies and designed to reduce background noise. Products for industrial environments such as factories and warehouses may be sealed against dirt, dust and corrosive vapors.
Types of Microphones
The IHS Engineering360 SpecSearch database provides information about these and other types of audio microphones.
- 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. I
- 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.
- Wireless microphones use RF frequencies to communicate with audio equipment. As their name suggests, they do not have a cord or cable.
- Digital microphones have integral analog-to-digital converters that render sound into computer-recognized formats.
- Probe-style microphones have a long tip for measuring near-field levels or hard-to-reach places.
- Array type microphones measure 3-D sound fields around test objects.
Suppliers may also offer stereo and USB microphones.
When selecting products, buyers can search for audio microphones by directional sensitivity.
- Omnidirectional microphones are sensitive in all directions.
Image Credit: Digi-Key Corporation
- Bidirectional microphones are sensitive in two directions and directional microphones are sensitive in only one direction.
Image Credit: Star Micronics
- 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°.
Image Credit: Star Micronics
Other Performance Specifications
Audio microphones are characterized by differences in frequency response, dynamic range, and microphone sensitivity.
- Frequency response is the range of frequencies for which the device 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 product 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 the device responsiveness, needs to exceed the inherent noise of the system but not overload the preamplifier.
Audio microphones also vary in terms of the signal-to-noise ratio (SNR), impedance, and polarization. Some have prepolarized electret backplates or use external capacitor polarization, which requires a separate power supply.
Features and Applications
Products that are designed for extreme conditions may be outdoor-rated or have a wind or turbulence screen. Integral pre-amplifiers boost the output from small to intermediate levels. With regard to applications, audio microphones are used in aircraft, cars, and trucks; with computers or industrial workstations; and to provide information to listeners over loudspeakers. Recording studios, professional sound reinforcement, television or radio broadcast equipment require professional-grade audio products.