How would you prevent implosion of electret microphone ?

[Externet]

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/

[EdEarl]

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, 2016 by EdEarl

[Acme]

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.

[John Cuthber]

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

[Externet]

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.

[Enthalpy]

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.

[John Cuthber]

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?