Looking for a microphone which goes to 50kHz or so

John-Smith · 2015-01-04T20:20:58+00:00

There is an allegation that a particular aviation headset causes tinnitus. It is one of a number of active noise reduction (ANR) headsets on the market. An ANR headset uses basically a mike, a tiny speaker and some op-amps inside each earcup, and the speaker is driven so as to generate a zero SPL inside the earcup. That would just give you noise reduction, and the audio would get cancelled too, so they feed the audio into the summing node of the op-amp, so you hear it OK. So... all the components required for oscillation are in place! And it's true that some of the cheaper ones do "whistle", or give out an audible hiss. The headset in question (I have two - $1000 each) certainly doesn't whistle, to my hearing, so if it does it will be high up, and because some pilots are teenagers, it would have to be well above 20kHz otherwise there would be loads of complaints. I can't see any possible route to ear damage other than a very high pitch oscillation, possibly confined to when there is an incoming audio. So I would like to test for this. I have a TEK digital scope which can do FFT, and have a Marconi 2024 spectrum analyser which goes from 10kHz to 2.4GHz :) Can anyone suggest what sort of microphone would work well? I don't want to spend loads of money on it, say $100 max, and it needs to be easy to interface. I was also going to get a ribbon tweeter (loads on Amazon for about $40) to test the frequency response of the mike with, using my HP3314A signal generator. But of course the tweeter won't be flat-output anyway. But then I am only testing for *any* component above what the headset is supposed to be emitting... Any suggestions would be much appreciated.

J

Jeff Liebermann 11 years ago

NavCom radios are all analog audio. It has to be that way in order for intercoms, recorders, common headsets, common mics, etc to all work together. They might be digitized at some point insider the radio, but not at the connector interface.

Incidentally, these radios use 100 ohm, high level, carbon microphone equivalent xmitter inputs. Carbon microphones may have gone out of fashion about 40 years ago, but their legacy is still with us today. The good news is that the DC bias needed to make the carbon mics work is quite useful for running electret preamplifiers.

Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Vote

J

Jan Panteltje 11 years ago

On a sunny day (Mon, 05 Jan 2015 13:13:03 -0800) it happened Jeff Liebermann wrote in :

I was under the impression the guy was taking about noise reduction headphones with build in electronics. The interface can be made to match anything.

Vote

C

ChesterW 11 years ago

There may be other failure modes. For example, since the headphones use acoustic phase cancellation inside the ear cups, it's easy to visualize operation where the sound level actually increases above ambient under some set of conditions.

Another possible pathology is if the system is efficient at reducing low frequency noise, but not high frequency noise. In this case the user may subjectively feel that the noise is at a low level, while actually being exposed to a damaging level of noise at higher frequencies.

It's an interesting project. Let us know how it turns out.

ChesterW

Vote

R

Ralph Barone 11 years ago

200 kHz from an SM58? Wow! Are you sure that you're not actually seeing magnetic coupling between the headphone voice coil and the mic?

Vote

P

Phil Allison 11 years ago

** Errr - yeah !!

Funny thing is, the measured response was almost flat from 8kHz upwards.

As the acoustic output fell, magnetic coupling neatly took over.

.... Phil

Vote

R

Ralph Barone 11 years ago

Oops, hadn't read your original post carefully enough and didn't realize that you'd already figured out the deception mode of your setup. But a hell of a party trick...

Vote

M

makolber 11 years ago

The water faucet in my kitchen running at full speed makes pretty flat white noise out to beyond 20 kHz.

Mark

Vote

P

pedro 11 years ago

Many of the early Cessnas relied on a cabin speaker and hand-held (carbon) mic. Wasn't a fun time because you needed the speaker drive wound up quite high.

Vote

J

John-Smith 11 years ago

pedro wrote

A lot of more recent planes have that too but it's totally unusable, due to the ambient noise level.

Vote

A

Alexander Y. Sure 11 years ago

I have tested ultrasonic transducers with this MEMS mike:

It is specified up to 80kHz. *All* the dots for ground must actually be connected.

Regards Werner Dahn

Vote

A

Alexander Y. Sure 11 years ago

Correction: It's this one:

Sorry for the mistake.

Werner

Vote

J

John-Smith 11 years ago

"Alexander Y. Sure" wrote

Many thanks - by coincidence I have just emailed them earlier!

Vote

J

John-Smith 11 years ago

Noted - thanks :)

"Alexander Y. Sure" wrote

Vote

J

John-Smith 11 years ago

I finally did the experiment with that Knowles mike, on Bose X and Bose A20 headsets

formatting link

both showed NO obvious inaudible emissions.

There an elevated noise floor which all ANR headsets seem to exhibit but it is almost certainly irrelevant in the application: a piston engine aircraft with a massive ambient noise level.

John-Smith wrote

Vote

A

amdx 11 years ago

Thanks for the follow up with your finding., too often the original poster never makes a second post even though many are trying to help but need more info. Mikek

This email has been checked for viruses by Avast antivirus software. http://www.avast.com

Vote

Looking for a microphone which goes to 50kHz or so

Join the Discussion

Didn't find your answer?