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[DavidTurner]

Here is a copy/paste from the current version of Sound System Engineering:
If we raise two microphones to the same level in a reinforcement system, we will have to reduce the overall gain 3 dB to avoid the system going into feedback (remember how decibels combine). Since each microphone is sampling the sound field, every time you double the number of open microphones (NOM), we will have to lower the gain 3 dB, Fig. 14-3. Therefore the loss in gain caused by more than one open microphone is: NOM (in dB) = 10logNOM .

I suspect you mean it's proportional to 1/NOM, otherwise that equation fails a basic check of dimensional analysis.

Chris

[David Morison]

Edit - post withdrawn due to actually being awake & paying more attention now.

[DavidTurner]

The crucial difference between this and what you posted previously is that you've now included the qualifier "loss in" before the word gain - previously you said the gain itsself was equal to 1/NOM.

Not the same thing at all

I don’t get your point. What I read in this is that for each doubling of open microphones there is a 3dB loss in potential acoustic gain - in other words, 1/2 the available acoustic power.



Nonetheless, read it how you like. I was just quoting something I read years ago.


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[David Morison]

I don’t get your point. What I read in this is that for each doubling of open microphones there is a 3dB loss in potential acoustic gain - in other words, 1/2 the available acoustic power.

Nonetheless, read it how you like. I was just quoting something I read years ago.

Ya know, looking back I think I must have thought you were saying something different, must've been a bit tired at the time.
Sorry about that,
David.

[DavidTurner]

Ya know, looking back I think I must have thought you were saying something different, must've been a bit tired at the time.
Sorry about that,
David.

No worries sir.


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