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Microphone sensitivity is usually measured in mV/Pa. If one mic is say 25 mV/Pa and another is 13 mV/Pa how much more sensitive is it in application? How can I figure out how much more gain the mic is actually outputting in dB? I feel like I should know this but I don't.

bpert
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Sensitivity measures the voltage at the output pins of the mic for a given sound pressure level. 13 mV/Pa means that an air pressure oscillation with an amplitude of 1 pascal (94 dB SPL) at the mic capsule would produce a voltage oscillation with an amplitude of 13 mV at the XLR pins.

Gain is basically the ratio of output level to input level.

In this case we're not talking about an input and output, but you can still talk about the relative gain difference, which would be (25 mV)/(13 mV). The sound pressure level (1 pascal) is the same for both, so it cancels out. The relative gain difference is then 25/13 = 1.9, or about 2x as much voltage for the same pressure.

In decibels, the difference would be 20·log10(V1/V2), so +5.6 dB for your example. A doubling in voltage is about 6 dB, so you could guess this just by recognizing that 25 is almost twice 13.

endolith
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  • @endolith I think your html code got jumbled - I don't understand your answer :( – Utopia Sep 02 '10 at 20:53
  • @Ryan I've added to it. Which part don't you understand? – endolith Sep 02 '10 at 21:09
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    @endolith Excellent explanation. I do know this stuff but usually it takes some effort to get my head around the concepts of loudness, sound pressure level and dB scales and how they translate into each other. To me, your answer is very clear, thus required no such effort, thanks :) (@Ryan I don't see any html in there?) – EMV Sep 02 '10 at 21:24
  • 20*log10(V1/V2) Log? – Utopia Sep 02 '10 at 21:39
  • 20 times the base 10 logarithm of the ratio of the two voltages. :) – endolith Sep 03 '10 at 01:02
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    Thanks for the great explanation with math to show what you mean too! I wanted to assume that it would be about twice the output since it is twice the voltage, but I was unsure if their were other aspects that I hadn't considered. For some reason I thought that different SPL's might react differently for each microphone, sort of how different frequencies react differently with each microphone. But when you said it "would produce a voltage oscillation with an amplitude of 13 mV at the XLR pins" it makes more sense to me. – bpert Sep 03 '10 at 01:25
  • "Twice the output" does not mean twice as loud, though. It means 6 dB louder. Loudness is proportional to dB, not voltage. – endolith Sep 03 '10 at 01:33
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    @endolith loudness is proportional to frequency varying from person to person. generally 10dB SPL is twice as loud, but for mid-range frequencies only.

    6dB difference in SPL or Voltage is equivalent to moving twice as far away from a sound source or halving the distance between source and mic. (in free-field conditions, exact figure variable indoors)

     – jb1t Sep 04 '10 at 14:00
  • The perception of loudness is proportional to dB, and frequency-dependent. It has a logarithmic relationship to voltage, not a linear relationship. http://en.wikipedia.org/wiki/Loudness – endolith Sep 05 '10 at 00:37