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Message ID: 6565     Entry time: Wed Apr 25 00:20:01 2012
Author: Den 
Type: Update 
Category: PEM 
Subject: acoustic noise at 40m 

 Blue Bird Mic is suspended close to PMC now and outputs ~10 counts when pre-amp gain is 8 dB. This means that the mic outputs ~2.42 mV. Its sensitivity is 27 mV/Pa => acoustic noise is ~0.1 Pa or ~75 dB SPL.

If we buy Panasonic WM61A with their sensitivity -35 dB => they will output ~1.7 mV. We can amplify this signal without adding significant noise. For WM61A S/N ratio is given to be 62 dB. This is for some standard signal that is not specified. For Blue Bird mic it is specified according to IEC 651. So I assume SPL of the standard signal = 94 dB => noise level of WM61A is 32 dB (pretty bad compared to 7 dB-A of Blue Bird). But in our case for PSL S/N ratio is ~43 dB that is not too bad. PSL is noisy due to HEPA, acoustic noise level close to MC2 stack will be less. So we may want to consider Primo EM172/173 where the noise level is claimed to be 18 dB less. I think we should buy several WM61A and EM172.

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