An electret microphone has air between the capacitive foils. To operate it in a pressurized 4 atmosphere air chamber, would have to be vented to prevent imploding.

Could perforating a tiny, tiny 0.1mm hole in the electret foil cause concernible degradation on its performance ?

Or, side venting the housing voids ? Or, ... ?

 

Figure 10 ----> http://www.openmusiclabs.com/learning/sensors/electret-microphones/

Figure 10 shows the outside case of the microphone is not hermetically sealed. I cannot tell from this diagram whether the space between the electret plate and pickup plate is sealed. In any case if you need a hole, it would be trough one of those plates because it seems rather difficult to go through the side into that cavity. Moreover, such a hole might short out the two plates, which means the hole would have to be made very clean with no burrs protruding into the cavity. You may have to disassemble a microphone to find out whether this cavity is sealed or not. I suspect it is not sealed, because barometric pressure variations might affect operation if it were sealed.

Edited March 27, 20169 yr by EdEarl

An electret microphone has air between the capacitive foils. To operate it in a pressurized 4 atmosphere air chamber, would have to be vented to prevent imploding.

Could perforating a tiny, tiny 0.1mm hole in the electret foil cause concernible degradation on its performance ?

Or, side venting the housing voids ? Or, ... ?

 

Figure 10 ----> http://www.openmusiclabs.com/learning/sensors/electret-microphones/

...Where is the noise?

The main noise sources in this microphone are pick-up noise and transistor noise. Since the entire capsule is sealed and grounded, the pick-up noise is very low and usually not noticeable. ...

Sounds like putting a hole in the capsule would increase the pickup noise.

It would be an odd design that wasn't already vented to deal with changes in air pressure due to the weather.

Wise assumption, John. For the slow and tiny atmospheric gradients. I wonder if rising 4 atmospheres in ~ten seconds will rupture the foil. The construction is gasketed and tightly crimped. Sometimes, the pcb-to-crimp is sealed with some adhesive for water tightness.

Will perforate one to compare before-and-after performance.

A bicycle pump achieves the 4bar, so try it.

Anything against a piezo microphone?

 

From fig 10, weather shouldn't be a big issue and wouldn't need a vent. If we're to believe the drawing, the compressed volume behind the "electret" membrane is only 1.5 mil for a 0.5 mil membrane. 1% pressure variation wouldn't make much. 4bar as opposed may deform permanently the membrane near the support.

 

Semiconductor technology could make a very smooth edge at the spacer, to climb the 1.5 mil height in 150 mil for instance, and then the membrane would survive a hig pressure.

Do you know the frequency response of the microphone?

Is there anything, apart from pressure equalisation, that limits the low frequency end of the range?