# How to choose a microphone and make sure not to overcharge (clip) it?

I'm not sure that's the right forum to ask this question but I'll do it anyway.

In my project, I've to listen to different machines using a MEMS mic by fixing the microphone directly on to the machine. The problem that I get, is that all of the records that I need, are overcharged (clipped) so useless. My question is how should I choose the microphone for really loud measurements?

Thanks in advance for any hint.

• Question was crossposted to electronics.stackexchange.com/questions/129565/… – JRE Sep 17 '14 at 9:08
• @JRE is that a problem ? as I said I don't know which forum is that the right one for this question ? – Engine Sep 17 '14 at 9:11

1. Choose a commercial Sound Pressure Level meter to roughly measure the noise level close to the machine
2. Look at the data sheet of the MEMS and see if the specification matches the expected level with enough head room (at least 10 dB). IF not, chose a MEMS that meets this spec
3. Maker sure the MEMS is mechanically de-coupled from the machine, i.e. picks up only sound and NOT vibration.

A lot of microphone manufacturer don't indicate the maximum sound pressure which is measurable (the so called acoustic overload pressure (AOP)).

That is the only way of knowing if the mic will clipp in your case.

A rough indicator can be the sensitivity in combination with the operating voltage, as the microphone can not output more voltage than this (also this is not true for all). If you have the sensitivity in V/Pa, you can divide the operating voltage by it and get an estimation.

For example a B&K microphone: Operating Voltage: 10V Sensitivity: 53.6 mV/Pa = 0.0536V/Pa Output_Max = 10/0.0536 Pa = 186Pa ~ 139dB rel 20uPa

This estimation is usually to high the B&K is only rated up to 135dB, but gives a rough estimation.

Knowles and STM for example tell you the AOP of their MEMS mics.

• AOP - Acoustic Overload Point – jojek Jul 1 '16 at 7:36