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Old 5th January 2008, 02:29 AM   #1
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Default Max spl of electret capsule

Does anyone know what would be the typical maximum sound level capacity of an electret mic? I want to record the sound of a top fuel drag race engine and I have read that they can be as much as 153dB at 1 metre.
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Old 6th January 2008, 03:52 AM   #2
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Nothing will work for that. I think that at something like 163 dB the pressure varies from 2 atmospheres to a vacuum. That will destroy any microphone ever made, let alone a cheap $2 electret capsule.

There are two things to consider -- one is the diaphragm excursion, and the other is the maximum output level of the circuitry. I would be surprised if you could find an electret capsule that would handle more than 110 dB or so.

Good luck.
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Old 6th January 2008, 05:07 AM   #3
jcx is online now jcx  United States
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depends, a quick cruise of the Aco site shows up to 175 dB spl @ 3% thd spec

http://www.acopacific.com

pricey though

I'd look for a really small diaphram dimension in a cheap capsule for higher spl
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Old 6th January 2008, 09:02 AM   #4
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My next plan of attack was was to try a pressure sensor as a mic. Would need a bit of equalisation for sure, but there would definitely be one that would handle the SPL.
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Old 6th January 2008, 09:27 AM   #5
dnsey is offline dnsey  United Kingdom
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You could always make up a sort of 'ear defender' for your mic, to reduce the SPL at the element. Otherwise, a small speaker could perhaps be used.
There are idustrial mics available though with the max SPL capacity you need.
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Old 6th January 2008, 04:43 PM   #6
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Hi,

What a cheap electret mic can handle depends on the configuration of the fet buffer in it. Is it a 3 pin connection and wired correct as a source follower it can handle SPL up to 140 dB. Have used them that way in the mouth of a saxophone.

Is it a 2 pin connection wired as a drain follower then they start to compress and distort above 100 110 dB.

The pressure sensor can be a cheap option for very high levels, but they tend to be noisy for audio purposes. If you go for that, go for the small DIL ones with short stub or remove the stub.

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Old 6th January 2008, 05:13 PM   #7
djQUAN is offline djQUAN  Philippines
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I have tried the pressure sensor option but never got around to completing a prototype. as said earlier, it is noisy.

but I bet it can easily handle high SPL's although BW would be about DC to 200Hz or so.
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Old 6th January 2008, 05:56 PM   #8
EC8010 is offline EC8010  United Kingdom
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How about enclosing a largish diaphragm (18mm) microphone in a solid chunk of aluminium and drilling a 1mm diameter hole in the aluminium for pressure sensing? That ought to give 52dB of attenuation, bringing your expected level down to something manageable.
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Old 6th January 2008, 06:05 PM   #9
djQUAN is offline djQUAN  Philippines
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I think that would make a resonant chamber and mess up the freq response? or I may be wrong?
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Old 6th January 2008, 06:07 PM   #10
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by djQUAN
I think that would make a resonant chamber and mess up the freq response? or I may be wrong?
You might be right. Perhaps someone who knows more about acoustics than I do could comment.
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