3
\$\begingroup\$

I'm using Electret Microphone Amplifier - MAX4466 with Adjustable Gain and I'm getting the output voltage ranging from 1.5V to 3V (which, to my knowledge, is already amplified by MAX4466). I know that the sensitivity of the microphone is -44dB @ 1kHz. It is also stated on the mentioned product page that the gain can be adjusted from 25x to 125x by adjusting the trimmer pot on the back of the breakout as needed.

Max4466 Mic Amp Breakout with Trimmer Pot to Adjust the Gain

I'd like to know a way to figure out the op-amp gain and ultimately, calculate SPL dB (Sound Pressure Level) from the measured voltage. Any help is appreciated. Thanks. Typical Application Circuit

\$\endgroup\$
4
\$\begingroup\$

Microphone sensitivity is quoted at

-44 ±2 dB, f = 1KHz, 1Pa 0dB = 1V/Pa

This means that for 1 Pa RMS sound pressure on the microphone you get -44 dBV RMS at 1kHz. Still confused?

Well, -44 dBV translates to \$10^{-44/20}\$ volts = 6.31 mV RMS and 1 Pa translates to a decibel sound pressure level of 94 dB SPL.

So your microphone produces a 1kHz sinewave of amplitude 6.31 mV RMS when subjected to a SPL sinewave of 94 dB.

As for the gain of the Maxim circuit, without a circuit diagram I can't help you any further.

\$\endgroup\$
14
  • \$\begingroup\$ Thanks. I've added a circuit diagram that I hope what you asked for. \$\endgroup\$
    – J.Jay
    Jan 18 '16 at 3:56
  • 1
    \$\begingroup\$ Mid-band gain (1 kHz) is about 11. The upper -3dB point is about 16 kHz (high frequency) and the lower one about 16 Hz. \$\endgroup\$
    – Andy aka
    Jan 18 '16 at 8:47
  • \$\begingroup\$ Firstly, thank you so much for your time. Those are the ideal/calculated values, aren't they? Is there a way to measure the actual gain? And also, I'd like to know where you got those values from. \$\endgroup\$
    – J.Jay
    Jan 19 '16 at 14:37
  • 1
    \$\begingroup\$ @J.Jay the mid-band gain will be as accurate as the resistor tolerances. If you want to measure it, use a signal generator and an oscilloscope but if the resistors are 1% or better then there is no point because the visual accuracy of the scope screen is probably worse than 2%. \$\endgroup\$
    – Andy aka
    Jan 19 '16 at 14:42
  • 1
    \$\begingroup\$ Gain of a non-inverting op-amp amplifier = 1 + R2/R1. R2 is 100k and R1 is 10k hence mid-band gain = 1 + 10 = 11. At the higher frequencies the upper 3 dB point is when the 100pF has 100k impedance = \$\dfrac{1}{2\pi F C}\$ or F = \$\dfrac{1}{2\pi RC}\$ \$\endgroup\$
    – Andy aka
    Jan 20 '16 at 15:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.