Crown Audio by Harman

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Clandestine listening room

I have a customer that is trying to mic a room for clandestine listening.
The room has a 10' ceiling, 20' x 20', and currently has 6 choir mics hidden in cable trays. The customer's customer is complainging about white noise and low signal-to-noise.
I am suggesting they replace the choir mics with PZM types. We have a high quality mic preamp, low Z, with 15VDC phantom power available. Which PZM unit would you suggest?
Bill Murphy
Protech Audio Corp.

Reply:  We recommend the PZM-10 or PZM-11. You can click on their data sheets here:

First, I’d try a mini omni lavalier mic (such as the Crown GLM-100) in one upper corner of the room. Tape the mic at the intersection of the ceiling and two walls. Listen to the audio signal of that single microphone, talk in the room from various locations, and see if the sound is clear enough. This corner mounting increases the mic’s sensitivity by 18 dB, and effectively removes the sound reflections from the ceiling and two walls. This results in less reverb in the audio pickup.

The next option is to put a lavalier mic in each upper corner of the room, and run the mics into a gated (automatic) mixer so that only one mic is on at a time. Here is Audio-Technica MX341a automatic mixer with 4 mic inputs:

Another option: Use four PZM-10 or PZM-11 mics in the ceiling, 10 feet apart, and run them into a gated mixer so that only one mic is on at a time. That way, you will pick up the talker with only one mic which is close to the talker (about 4 to 6 feet away), giving a clear sound.

Your noise problem with the choir mics might occur if all six mics are on at the same time so that their noise adds.