SOOT: Electronic hearing protection

When I was active in Pistol shooting (in/outdoor 45 and 22LR) several of us used electronic earmuffs in the $75 price range. Really tamed the report of a 45...!

Paul in AJ AZ

The stuff prop pilots, etc. have uses electronic noise cancellation to cancel out low frequency noise, such as the prop buzz. Modern DSP hardware couls easily carry this technique to the top end of the hearing range, but there are problems with the wavelength of the noise that make it not work as well. At 20 KHz, the full cycle is 50 uS, multiply by 1100 Feet/Sec, and you get .055' = .66". So, a full wave is .66", a half wave is .33". If they put a microphone right outside your ear, it would be too far away to sense the proper signals that matter, namely what is happening right at your eardrum. So, the sounds would null out at that microphone's location, and not cut the high frequencies that you would hear. At low frequencies, it works fine.

High frequency noise is well attenuated by the foam in the ear muffs. as long as the rim makes a good seal.

The device you describe is basically a passive hearing protector, with a microphone, earphone and amplifier, designed to shut off when the sound exceeds the threshold. Instead of DSP processors, memories, A/D and D/A converters, etc. all this takes is about 3 transistors, and a dozen or less passive components. They could build this in China for about $1 (and probably do).

I seem to recall the good, pilot-grade stuff runs around $600 and up, way up, from David Clark, and I'm sure, others. But, it works best with constant drone, like a prop plane, and not at all with intermittent noise, like air blasts, gun shots, hammering, etc.

Jon

go to

and do a product search for "noise cancelling headphones" I think that is what you are after to remove the constant drone of machines but allow normal speech.

Brian

On Sun, 21 Sep 2003 20:06:44 -0500, Jon Elson wrote something ......and in reply I say!:

Thanks for that. I actually saw something about in-ear noise cancellation, presumably using a little "hearing aid" earpiece. That may be to try to get around the HF problems, which make sense as you describe them.

I suppose a really sophisticated DSP could actually know the distance, and allow for the phase problems even at HF! Of course if the whole thing was in an earpiece, then you can place the noise cancelling source right near the mic, and you are overcoming the problem.

As\S I said I suspected that what I read about was simply passive, with an amp and cutoff. I am not happy with that $600 price on the "real" stuff" Bummer!

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On Mon, 22 Sep 2003 20:11:00 -0400, keith bowers wrote something ......and in reply I say!:

Thanks Keith. I will check out the url.

I am finding this whole thing a bit snake oil. Hearing loss and tinnitus are terrble things, and I am abit annoyed about the dodgy claims being made.

Yes. I was surprised that some of them _did_ make claims about attenuation that were surprisingly poor. In other words they are crap earphones as well.

On Mon, 22 Sep 2003 21:42:41 -0400, keith bowers wrote something ......and in reply I say!:

Hehe. I just emailed some company asking about Peltor, saying that there seemed to be two standards, and whether, for instance, Pelrot were "real" active or passive with amps. Boy, did I get a reply.

"Dear Sir:

I believe you are unaware of the differences between hearing protection concepts. If one is to imply Peltor is not providing real hearing protection, they are mistaken. I believe what you are referring to is ANR.

A newer and more expensive approach to hearing protection is the active noise reduction (ANR) headset. These headsets not only provide an ..............."

There was a lot more, of a more useful nature, if rather comdescending.

On Sun, 21 Sep 2003 19:44:55 -0400, keith bowers wrote something ......and in reply I say!:

Keith

This is amazing!. There are phones out there for $250-300US, and they are _still_ only passive with amplifier. They certainly use some amazing fluff to describe them, with a strong implication that they are 'active". I checked that URL of yours, and that's certainly an ear-shutter

Everyone who considers paying for "electronic" ear muffs should check that URL, and think carefully about whaty they are getting. As somebody said, the electronics are worth very little to do what is described, and a good set of muffs (30dB plus) does NOT cost $150.

Thanks

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On Mon, 22 Sep 2003 08:44:49 +0100, "brian clode" wrote something ......and in reply I say!:

These ones are only good for about 12dB, _claimed_, at 1Khz. That is way off the 25-32dB that I need for real ear protection. They appear to use the principles that I am interested in, but are not really designed for protection.

It was posted here that the beasties I am after are still in the HI$ realms. This would appear true.

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On Tue, 23 Sep 2003 22:57:21 -0500, "D. Crockett" wrote something ......and in reply I say!:

Mine is definitely for industrial noise.

Do that already. The muffs I use are 32dB max, ranging up from about

23, as you say.

Haha! Yes. I do know and fear that sound!

I just have this feeling that these things should be described better, and that there is a confusion about "electronic hearing protection" and amplified passive protection, that is maybe being used a little freely by the vendors/manufacturers

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