Microphone Overload

Distortions in a sound system are all too often blamed on the microphone. In fact, it is rarely the microphones fault, but the preamp it is connected to. A quality microphone should be able to handle sound pressure levels of 140dB or more without failing. NOTE: 140dB is 10dB higher than the human pain threshold.

However, the overload point of any microphone should be taken into account. The levels produced by a vocalist “eating” the microphone may be close to 130dB, when close micing a drum set, the sound pressure levels may exceed 140dB. Different applications require different peak sound pressure level tolerances (most of the time). Condensers are more susceptible to overload when under powered, even if the sound pressure levels are within the tolerances of the microphone. If the condenser is battery, change the battery, if the microphone is externally powered, increase voltage to the microphone (if recommended by the manufacturer).
It is important to take into consideration the sensitivity of the microphone as well. Take a microphone with a rating of -47dBV at 94dB SPL. If this microphone is used to close mic a drum and the peak level is 140 dB SPL, the output level would them be:

-47 + (140 – 94) = -1dB

This is very close to one volt, and will most likely overload the mixer’s preamp unless the signal is reduced with a pad.

-By John Redick

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