# Can Anyone tell me what is the default gain of Electret Microphone Amplifier 4466. I need the gain, to calculate the db SPL value.

I am using the MAX4466 microphone amplifier to calculate the db SPL level of sound. I have obtained the peak to peak amplitude in volts and I know that the microphone sensitivity is -44 db which translates to 0.0063096 V/Pa. 1 Pa is 94 db SPL.

so, say my voltage reading is 1.7 volts ; in db it = 20 log (1.7/0.0063096) = 48.6 db

Now acc. to a formula I found on this thread How to convert Volts in dB SPL

to calculate db SPL, I must add the mic sensitivity + 94 db SPL i.e 48.6 + 94 - 44 = 98.6 db SPL.

I don't completely understand why we do this?

Secondly, this formula is for unity gain. I don't know the gain of my device to subtract from the db SPL level and I can't seem to find this anywhere. Please help!

• Tried reading the data sheet? – PlasmaHH Feb 27 '16 at 9:17
• Hi, So from the data sheet I could gather that the gain margin is 20 dB. However, my db SPL calculations still seem off. I'm not sure if gain "margin" is in fact the gain of the op amp. – Shruti M. Feb 27 '16 at 10:15
• "Gain margin" is a measure of how close to unstable the amp is. "Gain" tells you its gain. And if it's an opamp the gain is determined by external components you can see and we can't. Try linking the datasheet and adding your circuit (use the circuit editor) if you need more help. – Brian Drummond Feb 27 '16 at 11:02
• If your microphone has a gain of 6.3 mV/Pa then an output level of 1.7 volts (RMS and not DC) is a massive sound pressure of 270 Pa or 143 dB SPL. I think you are erroneously measuring a DC level of 1.7 volts and believing that this indicates SPL. – Andy aka Feb 27 '16 at 11:43