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Noise cancelling headphones

Post Date: 2008-04-16
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Mortok View Drop Down
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Posts: 30 		  Quote Mortok Quote  Post ReplyReply bullet Topic: Noise cancelling headphones
    Posted: 16 Apr 2008 at 10:07pm
The other day i was in a Frys store looking at different noise cancelling headphones. There was a display of Creatives new Aurvana X-Fi headphones.  As soon as i turned on the noise cancelling feature it was like i entered a vacuum.  Voices and footsteps and the like could still be heard quite clearly but the drone of background noise disappeared.  Not only that but they also feature the crystalizer enhancment like offered on their XFI Fatal1ty sound card. If your around a pair on display you should check them out. Beware though  the price is 300 dollars.   Im still debating but since i work in a high noise environment i just might have to have these.  Just thought id pass it on.
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Tyler Lowe View Drop Down
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Posts: 0 		  Quote Tyler Lowe Quote  Post ReplyReply bullet Posted: 16 Apr 2008 at 11:04pm
That does sound nice. I work in a high noise environment too, but man, that $300 is a steep price to pay over the *free* disposable plugs my company provides me. If they are as nice as you say, I will avoid that display like the plague when I see it, before I get sucked into buying a set. Tongue
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widdlecat View Drop Down
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Posts: 840 		  Quote widdlecat Quote  Post ReplyReply bullet Posted: 16 Apr 2008 at 11:54pm
I always feel a bit leery about noise cancellation products for long term usage. This is why. The concept is to amplify and transmit an out-of-phase signal of similar characteristics and level to provide cancellation. The problem arises when the out-of-phase signal isn't accurate. Then it's adding more noise that you may or may not notice depending upon the frequency of the artifact. I used to work with audio components so I understand this really. What I am getting at is that while it may settle the nerves and allow for rest or better concentration, in the long run, it may have the same affect as wearing headphones with music blaring all the time. That is to say, tinnitus can occur. I would confer with an ear doctor before considering extended usage. The fidelity of even a $700 plus set of headphones are sometimes less than accurate as far as the ears are concerned, so $300 is no mean feat for a quality attempt at such a product. Of course price doesn't always guarantee quality as I own a $1200 pair of headphones that aren't as good as a $650 set that I prefer the most.

Sorry for droning on, but audio consulting, manufacturing and reviewing was my profession for many years hehe.
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Mythius101 View Drop Down
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Posts: 134 		  Quote Mythius101 Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 12:32am
Woo a fellow audio buddy.  I'm an audio engineer!

But everything you said is true.  It may *sound* silent to you, but the headphones are actually making sound constantly to cancel out background noise.
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Tyler Lowe View Drop Down
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Posts: 0 		  Quote Tyler Lowe Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 2:05am
Oh good!

Maybe one of you two audio tweaks can explain this one to me. The way noise cancellation was illustrated to me was as two sine waves set at a 180* shift in phase. I know that has to be about the most simplistic explanation one could make, but... (and this part has been sort of rattling around in my brain for years now)

How do you get something to recognize both frequency and amplitude of an incoming signal, in real time, and produce something exactly 180* out of phase, also in real time in order to result in true sound cancellation?
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widdlecat View Drop Down
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Posts: 840 		  Quote widdlecat Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 6:50am
With recorded audio it is actually pretty easy to set the signal 180* out of phase. Just record it out of phase. Wire the input of the microphone backward. The degree of efficacy is dependent primarily upon the fidelity of the mic and the headphones involved. Naturally, the rest of the recording and playback must be high quality for best results. Still, it's fairly easy to trick the ear and mind. The result will always be that of a delay as well as slightly inaccurate representation of the sound around you. That's why intermittent and immediate sounds will come thru. Under theoretically ideal conditions, there would be a resultant sound pressure of zero. However, since there must be a delay to reproduction, it's only theoretical. With studio mics and best quality headphones, true high fidelity reproduction equipment, analog sampling... (several thousands of dollars and quite a few lbs) true noise abatement can be achieved. I worked with a professor on a highway noise abatement program utilising enormous transducers and amplification to great results. They would be awesome subwoofers for the home! LOL!
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MrNanite View Drop Down
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Posts: 507 		  Quote MrNanite Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 8:32am
Well, in the end, you won't have something that is *EXACTLY* 180 degrees out of phase.  Maybe more like 170-175 or so.  The catch is that if you can process an incoming signal fast enough, you can send out the cancelation wave on the other side *JUST ABOUT* in time for it to cancel the incoming noise.  At least, that is the hope of it all.
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Tyler Lowe View Drop Down
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Posts: 0 		  Quote Tyler Lowe Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 11:09am
The recorded portion I understood. Thanks for the explanation and story about the highway noise reduction though Widdlecat, that will give me something to look up and read about on a rainy day. Big%20smile

It was more of a "how the heck do you get this to work instantaneously at all, let alone in a cheap set of electronics designed for the consumer?" type question. It looks like the reality is, you don't. I've worked with phase shifting of extremely high power signals over large distances before, and looking at these devices, the product claims just seemed too good to be true.
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MrNanite View Drop Down
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Posts: 507 		  Quote MrNanite Quote  Post ReplyReply bullet Posted: 17 Apr 2008 at 12:48pm
Yes, you don't.  Especially in a cheap set.   Basically there is a mic on the outside and electronics in the middle.  It will read from the outside mic (ignore whatever the speakers inside are sending) and process that signal and add the two.  But, it's *not* instantaneous nor is it 100%.  But in a good set, it's close enough to trick you out.
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widdlecat View Drop Down
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Posts: 840 		  Quote widdlecat Quote  Post ReplyReply bullet Posted: 18 Apr 2008 at 2:42pm
The end result of noise cancellation is that it fools the mind enough that if you have trouble concentrating in a noisy environment otherwise, it will alleviate the stress. I personally think it has it's uses, but wouldn't recommend anyone to use for extended periods. Just those times when you think the noise is gonna drive you nuts or if you're under pressure to finish your term paper and your roomie wants to watch tv. Tongue

I wonder how well it can stop nagging or crying babies... hmmm...
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