Is input SPL in direct proportion to output in volts?

FAQ #1328 Updated September 30, 2008

Question:

Let's say we have a mic with sensitivity of -74dB open circuit for 94dB SPL,

For 94dB we have -74dB = 200uV

Then for an output of 200uV/2 = 100uV input SPL is 94/2 = 47dB
is that correct?

or do we have to convert SPL dB to linear?


---- 07/12/2001 08:34 AM ----------------------------------------------
OK, If I have an output of 100uV, that would equal to -80dBV, but my question was, what would be the INPUT SPL for an output of -80dBV (100uV)?

In other words, if I want to plot input SPL vs output (V or dBV), what are the values for:

100 uV -> ? dB SPL
200 uV -> 94 dB SPL (Given by specs)
300 uV -> ? dB SPL
and so on

Thanks

Answer:

At 07/11/2001 04:38 PM we wrote - No, that is not correct. The dB is a logarithmic scale.

If you have an output of 100 uV, that would equal -80 dBV. Every time you halve the voltage, the signal drops by 6 dB.

Also see:

How do I compare the sensitivity of two microphones?

At 07/12/2001 10:00 AM we wrote - As you can see from the following table, the dB increase/decrease in the input (expressed in dB SPL) directly corresponds to the dB increase/decrease in the output voltage (expressed in dBV). So, if the input decreases by 4 dB, then the output of the microphone will also decrease by 4 dB. So, take the given specification, subtract 4 dB from it, and then use the equation to calculate the voltage.

BTW, in audio, we hardly ever talk about raw voltage. Instead we discuss things in terms of dBV. That is why you will see that term used all the time.

Equation: (value in dBV) = 20 log (voltage)



INPUT OUTPUT
dB SPL uV dBV
88 100 -80
94 200 -74
98 300 -70
100 400 -68

 

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