Ideally I would like to feed the mic to an amplifier system which connects to a set of speakers installed at different locations (same floor and other floors). If this is not possible, I would like to record the conversation for playing back at a later time. What kind of mic I could use? How should I organize the system? Dr. Rabin Raut, Videotron
Reply: A PZM would be ideal for this situation as long as its amplified audio is not sent to speakers that are near the microphone. I'd recommend a PZM-30D on the floor in the center of the circle of people. This microphone requires phantom power, which is supplied by the mixer that you plug it into. If your mixer does not have phantom power, connect the PZM to a phantom power supply such as the Crown PH-1A. The PH-1A is powered by the Crown PS-24 AC-DC adapter. Connect the output of the PH-1A to the mic input of your mixer. (See the figure below).
I'll call the group of people sitting on the floor the "local group". If there are loudspeakers near the local group, you need a way to send the PZM signal only to distant groups or participants. And you need a way to turn off the PZM when people in the local group are listening to questions fed to loudspeakers near them. In other words, you don't want the PZM to pick up the loudspeakers near the local group because this would cause echoes or feedback.
One way around this problem is to give each person in the local group an inexpensive earphone to listen to instead of loudspeakers. The earphone can be a low-cost "earbud" type of headphone which you can find in Target, K-Mart, Wall-Mart, Radio Shack, etc. You can use headphone extension cables where needed.
The figure above shows a suggested system. Connect the PZM and all distant microphones to the mixer, and connect the mixer to a stereo amplifier. (You might use a combined mixer/amplifier). Channel 1 of the amplifier drives an earphone box which has several headphone jacks all wired to the same cable from the amplifier. Ideally, this earphone box is driven off a headphone jack in the mixer, or is connected to amplifier channel 1 through a 100-ohm resistor. Channel 2 of the amplifier drives loudspeakers or earphones that are near the distant microphones. Each distant mic is placed very close each person speaking in order to avoid picking up the loudspeakers.
Another method: If you need broadcast-quality audio from the local group, give each person a clip-on lavalier microphone, such as a Crown GLM-100. Feed the mics into an automatic gated mixer, and from there to an amplifier and loudspeakers. With this system, you probably will not need to use earphones.