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I was recently wondering this, might be a stupid question but hey, here to learn :)...

Since the sound pressure level is defined as:

[tex]L_p = 20 log_{10} \left( \frac{p}{p_{ref}} \right)[/tex]

What would happen if you put a microphone in a perfect vaccuum? Obviously there can be no sound pressure [itex]p[/itex], so would the microphone measure a value of [itex]-\infty[/itex] dB? ([itex]lim_{x \rightarrow 0} log(x) = -\infty[/itex], right?)

Intuitively I would say no since with most microphones if you are in a completely silent room (except for thermal noise), they would measure 0 dB, right? And this would probably be the lowest spl the microphone can measure, any lower pressure will not move the vibrating coil?

Meh, just thought I'd ask.