Voltage From A Microphone?

The modern international standard for microphone specification is that sensitivity is given for a sound pressure level (SPL) of 1Pa. That where the '/Pa' comes from.

Your question asks for the voltage when the SPL is 3Pa.

The voltage output of a microphone at a given SPL can be expressed in volts. Or the voltage can be expressed in terms of a reference voltage. The reference voltage is, by convention, 1 volt.

'dBV' means decibels with respect to 1volt..

For example, say V = 20mV = 0.02V. Then the ratio of V to the reference voltage (1volt) is 0.02/1. This ratio, expressed in dB, is 20log(0.02/1) = -34dB. Note the use of '20' in front of the log.

(Also note the negative sign comes from the fact that we are taking the logarithm of a number less than 1.)

-60dB refers to a ratio of a voltage V to the reference voltage (1volt)

-60 = 20log(V/1)

-3 = log V

V = 1x10⁻³ volts = 1mV

So 60dBV/Pa. is telling us that the output is:

- a voltage of 3mV per Pa or

- a voltage 60dB below 1 volt, per Pa.

Both of the above are equivalent.

For a linear microphone, voltage output is proportional to SPL. So at SPL=3Pa, the output voltage is 3 x 1mV = 3mV.

Note that as the dBV/Pa value gets bigger, the microphone gets LESS sensitive.

A microphone of sensitivity -30dBV/Pa is MORE sensitive than one with sensitivity -40dBV/Pa.