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Old 28th February 2008, 10:18 PM   #1
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Default Relating mic sensitivity to output voltage

I wanted to get an idea of the range of output voltages from microphones, so I did some searching, but I'm having trouble relating mic sensitivity figures to voltage. Can someone tell me what I'm missing in this calculation?

As a random reference, I looked at the specs for a Neumann U87ai, from their website.

-Using cardioid pattern, sensitivity is 28mV/Pa
-Max SPL is 117dB
-Max Vout is 390mV

Here was my logical thought process, which obviously is flawed somehow:

1 Pa is the pressure produced by 94 dBSPL

117dB = 94*1.244, so 117dBSPL should produce 1.244 Pa of pressure

With a sensitivity of 28mV/Pa, 28*1.244 = 34.8mV at 117dB

But they state the max output is 390mV.

So where did I go wrong? If I find a microphone spec that doesn't list max output voltage, how do I correctly convert the sensitivity to a maximum output based on the maximum SPL?
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Old 28th February 2008, 10:25 PM   #2
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decibels are logarithmic. 20dB is a factor of ten. 40dB is a factor of 100, etc.

.390v / .028v is a factor of 13.93. a factor of 13.93 is a shade under 23dB

117dB - 94dB = 23dB

It all matches up.
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Old 29th February 2008, 04:24 PM   #3
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