output value of microphones

[alarassi]

hello everybody

i want to use an electret condenser micophone for my project to detect the heart sound of a person!
the signal has to be amplified but in order to amplify it i have to know the range of the required amplification!

i do have an output target for the amplified signal but the problem is that i'm confused how to determine or calculate the range of output value of the microphone!

i have been told i should convert the value of the frequency response of the mic to volts!
is it the correct way!? if the way is correct, the obtained MAX & MIN values shoud be in AC right ?
finally if it's AC, is it Vp-p or Vp ??

thank you

[t06afre]

A microphone convert the variating sound pressure to a electrical signal. Sensitivity indicates how well the microphone converts acoustic pressure to output voltage. A high sensitivity microphone creates more voltage and so will need less amplification at the mixer or recording device.
If you know the typical sound level of heart sounds, you could use the microphone sensitivity data to estimate the gain needed. What is your target for the amplified sound. Is it a AD converter or something else

[alarassi]

yes exactly my target is AD converter but i'll use clamping circuit befor the ADC!
i might use a microphone with frequency response -40±3db

i'm trying to find the typical sound level of heart sounds but it's hard to find! i'll keep searching on it but pls if you have any other way pls do help me

thank you

[retched]

Do you have or can you borrow a sound level meter? You can then hold it to your heart and get required readings. Using that for levels can be done.

I would use a DMM on the mic and hold the mic to your heart. The DMM will show you what the mic is putting out. Then using the datasheet for your DAC, you can find how you will need to adjust the signal via preamp if at all.

DMMs are slow however. You may want to use a signal generator to give you a constant to set your equiptment to.

[Audioguru]

In my electronic stethoscope project I used an electret mic mounted in the plastic lid from a jar. The lid became the "head" of the stethoscope. Then there was a small air space between the mic and the skin over the heart. The lid blocks most background sounds.

I first tried an LM386 power amplifier with a gain of 200 but my heartbeat in headphones was much too loud. With the project the gain from the opamps and LM386 amplifier is much less than 200.

[alarassi]

thank you guys for helping! it seems there's no direct way to calculate the output voltage and i don't have sound level meter to measure!
so i think i'll jst have some expirements and then adjust the gain based on the results!
thank you