Sensors: Sound

Sound

Microphones

Sound Sensor

A sensor for detecting sound is, in general, called a microphone. The microphone can be classified into several basic types including dynamic, electrostatic, and piezoelectric according to their conversion system.

The dynamic microphone still has big demands primarily in the music world, while the piezoelectric microphone is extensively used primarily for a microphone for low-frequency sound-level meters.

For measurement, electrostatic type (condenser) microphones are most popular because they can be downsized, have flat frequency responses over a wide frequency range, and provide markedly high stability as compared to other types of microphones.

The condenser microphones are available in two types: bias type and back electret type. The difference is whether the DC voltage is applied from the outside or permanently electrically polarized polymer film is used in place of applying voltage. In general, the bias type provides higher sensitivity and stability.

Sound Intensity Microphones

Sound intensity is a measure of the "flow of energy passing through a unit area per unit time" and its measurement unit is W/m2. The sound intensity microphone probe is designed to capture sound intensity together with the unit direction of flow as a vector quantity. This is achieved by incorporating more than one microphone in a probe to measure the sound energy flow. Conventional microphones can measure sound pressure (unit: Pa), which represents sound intensity at a specific place (one point), but can measure the direction of flow. The sound intensity microphone is therefore used for sound source probing and for measuring sound power.