Signal-cancelling headphone project - any interest?

[Mark Hammer]

I picked up a second pair of inexpensive noise-cancelling headphones this past week ($20 in last week's Loblaw's flyer, for Canadian readers).  If you've never tried noise-cancellers, you owe it to yourself to.  The impact can vary, but like some kinds of effects, you notice their benefit the more you leave them on.  I sometimes wear mine just to have some solitude on the bus, since I always seem to end up sitting above the wheels, somehow.

Noise-cancelling headphones operate by a simple principle.  Small condenser-mic cartridges sit in the earpieces (or some similar location).  They hear what your ears would normally hear acoustically when the headphones have no signal fed to them through wires.  Unlike your ears, however, the sound detected by the mics is electronically inverted and fed to the headphone earpieces.  The combination of what your ears hear acoustically, and via the headphones, cancels out.  Voila!  Noise cancellation.

Although wonderful, there are a number of caveats and considerations for these beasts.  First, the mic element has to truly hear what YOU hear.  That implies not only directionality but identical bandwidth.  Of course, what you can hear with something over your ears IS a very different bandwidth than what you hear without such covering, and any filtering and bandwidth shaping of the mic signal going to the earphones has to take that into account.  There are also limits to how much cancellation can be achieved with any single fixed amount of anti-noise.

The two lower-priced pairs that I have are good at eliminating wheel-well noise and letting me hear the news on the radio coming home without having to blast my little radio and my ears.  It strikes me that a tunable version of such headphones could be very useful for some persons in gigging contexts.  If one could shift the passband of the mic-element signal, then some parts of the band sound/mix would recede into the background.  Maybe you want to hear less bass, ormaybe you need to hear voice more than anything else, etc.  I realize it IS possible to achieve something like this by having individual EQ'd headphone feeds to each musician, but that starts to get complicated and costly. You also can't tweak or defeat them when you're onstage and playing.  Most importantly, you still have to hear whatever is coming out the PA and stage monitors and bleeding through the physical headphone into your ears.  A sound-cancelling (rather than EQ'ing) arrangement implies that you could still hear more of what you wanted and less of what you didn't want, regardless of what the audience was hearing (which might even include ungodly resonances in the club).

So, any interest in pursuing something like this?  I don't have a project ready myself, but there IS an e-reprint of the omnipresent (really, he normally works on a submarine) Jules Ryckebusch's construction article from Electronics Now in 1997 available on-line: http://www.headwize.com/projects/noise_prj.htm   We can use that as a point of departure, and make recommendations about mic elements, filtering, features, chips, powering, etc as we go along.  I realize this is not an effect, per se, but it strikes me as being a VERY useful part of a stage rig for some people, and potentially as indispensable as A/B switching, mixers, or any of a host of other things people use to make life liveable as a gigging musician.

[cd]

I've experimented with those types of headphones before, including $$$ ones (Bose Quietcomforts).  My conclusion?  If you want isolation and noise reduction, don't waste your time.  Get some in ear sealing type headphones, like those from Etymotic.  10x better noise isolation and 10x better sound quality, though the price isn't quite as low as $20 (you do get what you pay for, though.)  The "in ear sealed" aspect takes some getting used to, and if the fit doesn't work for you they're useless, but they're way better (and simpler) than any noise cancelling gimmickry.

[troubledtom]

mark , i think it's a cool idea
  i play in a very loud metalfusion band and my drummer already has
hearinng loss and i told him of this idea and he said," thats a killer idea!".
           peace,
             - tom

[stm]

Mark,

I agree with cd's response. I tried some time ago some cheap noise cancelling headphones and indeed they were crap. They had a switch to turn the cancel effect on and off, but mostly it seemed to alter frequency response (like a mid notch).

I searched a lot on this technology in audiophile fora to see if it was worth to order an expensive set like Bose or if there were some mid-priced devices. Everything pointed in the sealed earphone direction.

I would consider using a pair of sealed earphones with a small mixer with dedicated equalization in the following fashion:

1) Let your own audio signal go through straight
2) Have an ambience mike and/or one or more line inputs from the musicians/instruments you want to have into your mix and equalize them independently. For instance, reducing bass content for guitars, letting pass only the 300-3kHz band for vocals, or whatever works for you.

Another issue to take into account is the SPL (sound pressure level) to be cancelled. For instance, in a normal room or inside a bus the active headphones would work fine, however, one guy reported that his active earphones worked fine during the cruise part of a commercial flight, but collapsed during takeoff and landing due to the inability to keep up with the high noise levels produced by the jet's engines under these situations. I'm pretty sure the same phenomenon would happen in a live band playing situation.

Also, any filtering added to the signals to be cancelled would vary their phase and make the cancelling action less efficient, if useful at all. In this respect maybe you would need to resort to filtering in the digital domain (with DSPs) in order to have phase variations under control.

Best regards,

stm

[cd]

Old review but guess which wins out:

http://www.enjoythemusic.com/magazine/equipment/1101/headphones.htm

[Mark Hammer]

The time-honoured rule of getting what you pay for knows no boundaries, and so I would expect costlier moulded-to-your-ear types to offer superior performance.

HOWEVER, my feeling is the disappointment some feel about noise-cancelling headphones stems not so much from the calibre of the headphones (though marrying good noise-cancelling electronics with crappy headphones is not exactly the best advertisement for the process), but from the fact that the overwhelming majority seem to have an on-off switch and nothing more in the way of controls - you can't tailor them to your individual, circumstantial needs. 

Personally, I find it impossible to conceive of a one-size-fits-all anti-noise signal.  That's the reason why I raised this thread.  Otherwise, I would have simply posted the link to the article and said "Neat circuit!".  I think what we see there is a start and nothing more.  I am certainly quite open to having to eat my words, but until we explore what kinds of improvements might be possible by tailoring the filtering (or anti-noise eq-ing, if you will), and sticking a few controls on the chassis beyond an on-off switch, I will remain hopeful that a better process can be achieved for modest dollars.

That is not to take anything away from the Bose, Etymotics, or any comparable high-end solution so well-planned that an on-off switch is all you need.  The Boss DC-2 is a much better chorus unit than any of the other stompboxes with 2, 3, or 4 controls, but it also has about 3 times the number of components inside, so one would expect it to be an elegant solution needing only an on-off button.  But, that being said, you can get sort of close in a lower cost context by providing a little tighter control over the processing, and I imagine the same thing can apply here.

Also, any filtering added to the signals to be cancelled would vary their phase and make the cancelling action less efficient, if useful at all. In this respect maybe you would need to resort to filtering in the digital domain (with DSPs) in order to have phase variations under control.

Wouldn't it be possible to stagger the phase of the two competing signals in a reasonably controllable way by simple allpass stages, or am I hopelessly naive?  remember, I'm not talking about *perfect* (insert a little tap-the-side-of-the-champagne-goblet "tingggggg" here) cancellation, merely more useful and adaptable than stock.

[cd]

Project here:

http://www.headwize.com/projects/noise_prj.htm

I will remain hopeful that a better process can be achieved for modest dollars.

you can get sort of close in a lower cost context by providing a little tighter control over the processing, and I imagine the same thing can apply here.

What is the ultimate goal though?  IMHO it's not so much the implemenation as the technology itself.  Unless you're talking about low end rumble from a jackhammer (which will always be felt through the face), the "brute force" method of noise isolation through sealed, in-ear headphones will beat any kind of noise cancellation technology every time.  It's certainly not as sexy from a technological (or marketing) standpoint, and there's no DIY electronics involved, but it works.

I'm not trying to be a killjoy here, but for anyone looking for excellent noise isolation and good sound quality in an elegant, easy to use package with zero maintenance (other than cleaning the earpieces), just buy a set of Shure E2c ($99) and be done with it.  This is a DIY forum and I realize the subjective "fun" of a DIY project eliminates the time cost of experimenting with, and putting together, different circuits, but you'd be hard pressed to come up with a better overall performing package with noise cancellation for less $$$.

[Mark Hammer]

Your comments are noted and appreciated, and I don't reject any of your arguments.

What is the ultimate goal though?

I'd have to say not the complete elimination of ALL noise, but rather the capacity to selectively eliminate specific sources/bands of distracting sound (hence "signal-cancelling" rather than "noise-cancelling").  In that regard, I'm aiming at something different than what the products you refer to aim for.  Hard to think of a better way to block extraneous noise sources than blocking access to the eardrum, but if you want to be picky about what you block, a different method is likely needed.

I'm not trying to re-invent the wheel.  I'm trying to make casters!

[bwanasonic]

I prefer the *in-ear* typre of noise cancelling phones:

http://www.minidisco.com/er-6.html

There is no decrease in audio quality, rather an increase. The trade off is some people just can't stand having them in their ears. But they sound great. Too bad the tapeop forum is offline, as there was a bunch of info there about noise-cancelling phones.

Kerry M

[bwanasonic]

I'd have to say not the complete elimination of ALL noise, but rather the capacity to selectively eliminate specific sources/bands of distracting sound

Mark, when you come up with noise-cancelling headphones with an *on/off drummer* switch…



Kerry M

[Mark Hammer]

when you come up with noise-cancelling headphones with an *on/off drummer* switch…

You read my mind!

[Penguin]

good idea mark i did something like this after reading the popular electronics article years ago for my stepfather and my mother who go on long motorcycle trips[well they did back then]  good idea man.  also helps to use more than one mic element per side.

ed