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The Parameters of Electret Microphones
- Dec 03, 2018 -

The parameters that characterize the performance of the electret microphone are as follows:

(1) Operating voltage. This is the minimum DC operating voltage that must be applied across the microphone when the electret microphone is operating normally. This parameter varies depending on the model. Even the same model has a large dispersion. Usually, the typical values given by the manufacturer are 1.5V, 3V and 4.5V.

(2) Operating current. This refers to the DC current that the electret microphone passes when it is static. It is actually the quiescent current of the internal FET. Similar to the operating voltage, the dispersion of the operating current is also large, usually between 0.1 and 1 mA.

(3) Maximum operating voltage. This refers to the maximum DC voltage that can be tolerated by the FET inside the electret microphone and at both ends of the source. When the limit voltage is exceeded, the FET will be damaged by breakdown.

(4) Sensitivity. This refers to the magnitude of the voltage of the audio signal that the microphone can produce under a certain external sound pressure. The unit is usually mV/Pa (millivolts/Pascal) or dB (0dB=1000mV/Pa). The sensitivity of a typical electret microphone is in the range of 0.5 to 10 mV/Pa or -66 to -40 dB. The higher the sensitivity of the microphone is, the greater the amplitude of the audio signal output under the same amount of sound is.

(5) Frequency response. Also called frequency characteristic, it refers to the characteristic that the sensitivity of the microphone changes with the change of the sound frequency, which is usually expressed by a curve. In general, when the sound frequency exceeds the upper and lower limits given by the manufacturer, the sensitivity of the microphone will drop significantly. The frequency response of the electret microphone is generally flat. The frequency response of the common product is better (ie, the sensitivity is more balanced) ranging from 100 Hz to 10 kHz, the better quality microphone is 40 Hz to 15 kHz, and the high quality microphone is up to 20 Hz to 20 kHz.

(6) Output impedance. This refers to the AC impedance of the output of the microphone at a certain frequency (1kHz). The electret microphone is impedance-transformed by an internal FET, and its output impedance is typically less than 3kΩ.

(7) Inherent noise. This refers to the noise signal voltage output by the microphone when there is no external sound. The greater the inherent noise of the microphone, the greater the noise mixed in the output signal during operation. The intrinsic noise of a typical electret microphone is very small and is a microvolt level voltage.

(8) Directivity. Also called directionality, it refers to the characteristic that the sensitivity of the microphone changes with the incident direction of the sound wave. The directivity of the microphone is divided into three types: unidirectionality, bidirectionality and omnidirectionality. The front side of the unidirectional microphone is significantly more sensitive to sound waves than other directions, and can be subdivided into three types: heart shape, super cardioid shape and super direction shape according to the shape of the directional characteristic curve; sensitivity of the bidirectional microphone in the front and rear directions Both are higher than the other directions; omnidirectional microphones have substantially the same sensitivity to sound waves from all directions. Most of the commonly used machine-mounted electret microphones are omnidirectional microphones.

 

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