Sensitive microphone

[brendonshaw1703]

I am working on a mini project for a school who want to detect sound levels in the classroom and been going around in circles for a few weeks. They want to measure sound levels but ranging from very low sound i.e. chair moving, door opening to levels of talking within the classroom.
I appreciate to get an accuracy levels a number of microphones located in different parts of the classroom would need to be used. But, just to be able to monitor sounds levels I would like to build a simple sound meter.
I have used many of the Arduino type microphones and built pre-amps using lm358, 386 and BC548 circuits but none of them provide the response I am looking for. Many of the circuits seem to be very noisy and not seeing the response which I am looking for.
Audio analogue electronics is not my area of expertise and looking for some ideas on suitable circuit and design.

 

[KrisBlueNZ]

Hi Brendon and welcome to Electronics Point

I think you need to start by choosing microphones. If you want low noise, well-defined frequency response, and well-defined directionality, you can't use those little electret microphones; you'll need some proper microphones.

Measuring sound levels in a room in a properly quantifiable way is not a simple matter, and I don't think there's anyone here with relevant experience. (I could be wrong though.) You might be better off trying a professional audio forum or searching Yahoo groups for people who work with sound level measurement. You should be able to get advice on microphone types, placement, and calibration.

As always you should start by doing your due Google diligence and searching for appropriate keywords like microphone types and placement for sound level measurement.

Professional microphones usually have low-impedance balanced outputs, which can drive long cables with minimal signal corruption. Balanced preamps are used at the other end of these cables, and these are often implemented with a couple of low-noise transistors followed by a good-quality op-amp; Google balanced microphone preamp for designs.

 

[Rick L]

Let me Google that for you.... http://bit.ly/1tTMudr

 

[(*steve*)]

If you follow that link you find a device based on an LM3914. Beware that an LM3915 would be the correct IC to use in this instance.

The LM3915 will light up an additional LED every time the sound gets twice as loud (approximately) Whilst that sounds like it would be really wrong, you'll find that it allows you to have a "natural" scale that ranges from barely audible at one end to screaming in your face at the other.

 

[davenn]

Measuring sound levels in a room in a properly quantifiable way is not a simple matter, and I don't think there's anyone here with relevant experience. (I could be wrong though.)

LOL Kris

I do build and sell calibrated sound monitors
They go into clubs, pubs and other organisations that have to comply to
various city council noise level ordinances

Dave