Effective Radius of the PZM-20R?

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I was wondering if anyone had any information on the effective pattern radius of the PZM-20R. I am going to be using a group of them in a larger conference room and I want to know approxiamately how many I am going to need. The data sheet tells me they operate in a hemispheric fashion but tells nothing of the range. Any feedback would be much appreciated.



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brubart    0

Hi Dusty,

In a typical "live" or reverberant conference room, the maximum recommended radius is 3 feet. No person should be more than 3 feet from the nearest microphone. The PZM can pick up much farther than 3 feet, but the speech pickup starts to sound muddy at greater distances due to room acoustics.

The deader or more anechoic the room is, the bigger the radius of clear pickup. If possible, add acoustical absorbers and bass traps to the conference room to deaden the acoustics.

Outdoors, a PZM has a pickup radius of several miles -- if the sound source is a thunderclap!

To improve clarity, run the PZMs into an automatic (gated) mixer such as made by Shure and others. That mixer will turn off all mics except the one in use, which reduces muddiness.

For maximum clarity, use one Crown PCC or MB unidirectional boundary mic on every one or two people, and feed the mic signals to an automatic mixer.

Bruce Bartlett, Crown Microphone Engineering

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The FAQs say the maximum distance mouth-to-mic for the PZM-10 is 3 feet. I need better than that because I am unable to sway folks from ceiling mics

We would be using the be using Vortex 2280 or 2241s for DSP.

Room acoustic specifications are:

Ceiling Tile NRC Rating: 0.7+ & 0.9+

Ceiling Tile CAC Rating : 35+ & 25+

Background Noise Level: NC 40

Reverb time: .65


Under these conditions, what happens to the effective maximum distance for the PZM-10 and separation distance?


With the PZM-10 and Vortex, does the 3:1 still apply for phase cancellation?

I'm working on some corporate technical design specifications for conference room audio and need guidance.


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brubart    0

Any time a person sits between two mics that are on, the 3:1 rule is violated, so some comb filtering is inevitable. Sorry, I have no experience with how the Vortex affects the 3:1 rule.

The spacing between microphones should be 2X the distance from microphone to mouth. This results in even coverage of all the people (approximately equal loudness). So in a room with an 8' ceiling, if the mics are mounted in the ceiling, they are about 4 feet from the participants' mouths. So the mics should be 8 feet apart.

The Signal-to-Noise Ratio of the PZM-10 is 68 dB at 94 dB SPL, 48 dB at 74 dB SPL (conversation at 1 foot), and 36 dB at 62 dB SPL (conversation at 4 feet). The noise referred to is the mic's electronic noise in a room with no acoustic background noise. If 36 dB S/N is acceptable, then the 4-foot miking distance (of mics on an 8-foot high ceiling) should work.

That figure is for a mic directly above a person speaking. People between two mics will be a little farther away, so the S/N will be a little poorer.

If 30 dB S/N is acceptable, then an 8-foot miking distance should work. We're assuming that the Vortex is eliminating most of the audible room reverberation.

If the ceiling is very high, you could hang some 2 ft x 2 ft clear plexiglass panels 4 feet over the table and mount PZMs in them.

Hope this helps,

Bruce Bartlett

Crown Microphone Engineering

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