Passive audio surveillance microphone are not really passive, because of used the electret microphone. Its power supply is usually powered by a 2200 ohm resistor. Passive CCTV microphone have very low sensitivity and are typically only -30~-40dB. When the speaker is 1 meter away from the passive audio surveillance microphone, its output signal level is even less than 1mVpp. High output impedance and weak output signal are very susceptible to interference. Therefore, passive CCTV microphone are generally not suitable for security surveillance and long-distance sound pickup, but can only appear in the form of computers and mobile phones. At this time, the distance from the mouth of the speaker is very close, and the signal intensity can reach 20mVpp or more, which is not easily interfered.
The biggest advantage of electret microphones is their low cost. A key component in the electret microphone is the silver-white nickel-plated diaphragm. The low price of a high-quality nickel-plated electret microphone has led to a large number of customers using the MIC level interface at a time, but due to its poor performance, it has gradually been phased out and switched to the LINE level interface. Security monitoring users should be careful when they have audio requirements. LINE level interface network cameras and active audio surveillance microphone should be used as much as possible. If you have purchased a MIC level interface network camera, you should consult a professional CCTV microphone manufacturer for assistance. Active cctv mic designed specifically for MIC level interface network cameras are better than passive audio surveillance microphone. The reason is that the active CCTV microphone can perform noise reduction filtering on the voice signal, and the active audio surveillance microphone output impedance can be as low as 50 ohms or less, which can be more effective against noise interference. But in terms of overall performance, it is still not as good as the LINE level interface.
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