More on Electret Microphones

 Important specifications of an electret microphone are its directivity, sensitivity and signal to noise ratio. Directivity is the directionality or polar pattern and indicates how sensitive it is to sounds coming from different directions and angles. Omnidirectional microphones can pick up sound from any direction like an omnidirectional antenna. They are useful for picking up signals from a group of people. But this can also be a drawback as it can pick up ambient noise and unwanted sounds. Unidirectional microphones pick up sounds primarily from one direction and can eliminate background noises and unwanted sounds.


Sensitivity of a microphone measures how well it picks up sound. A sensitive microphone can pick up even weaker sound signals and sounds from a distance. There is also a related parameter known as sensitivity reduction, which is the decrease in gain when the voltage of the power source for the electret microphone decreases. Electret microphones with built-in battery for the JFET amplifier within could face this problem in the long run. Another very important parameter is the signal to noise ratio, which is a self explanatory term.

An important consideration while mounting an electret microphone in an enclosure is that it should be mechanically isolated from the enclosure so that vibrations of the enclosure are not transmitted to the microphone. Only sounds from the front holes of the enclosure should be received by the microphone. Holes should be at least 1.3 mm in diameter if it is a single hole or more than 0.8 mm in case of multiple holes. Some commercially available electret microphones have noise cancelling feature. They have two ports for sound to enter, one in the front oriented towards the desired sound and that in the back oriented towards more distant sound. Sound which is closer to the front port will make the diaphragm move more. Noise cancelling microphones are also called bidirectional microphones. They are useful in noisy environments like in helicopters and call centers.

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