Thought exercise- Noise cancelling headphones + Stereo?

[Quagmire]

Was idly googling this morning for other stuff when I came across a pair of active noise cancellation headphones by phillips, for the price of £20 (Amazon)... I had previously thought that these were much more expensive normally.

http://www.amazon.co.uk/Philips-SHN2600-10-Cancelling-Headphones/dp/B003Z0CD0W/ref=sr_1_1?s=electronics&ie=UTF8&qid=1336902610&sr=1-1

So this got me to thinking - my stereo head unit has a stereo jack on the front as an input. Is there any reason why you couldn't somehow hook the output of the headphones into this and play the noise cancellation waveform out the stereo?

[CwazyWabbit]

How would you ensure it only cancelled the 'right' noises? I've never used noise cancelling headphones but I doubt they are selective about what they cancel out.

[Retroanaconda]

Some high-end cars are now using noise-cancelling to block out road/tyre/wind noise. The trick is to block out those noises, but not the passenger's talking!

A friend of mine was looking into doing it in his Land Rover, but I'm not sure how far he got with it.

[CwazyWabbit]

Hmmm, thinking about it maybe selecting the location for the microphones very carefully would help with that ..... you'd also need to worry about feedback when playing via your stereo speakers as I'd assume headphones are designed to avoid this by the relative positioning of the microphone to speaker.

Edit: It's an interesting idea and I'd be tempted to have a go if it wasn't for the number of projects I already seem to be part way through! lol

[western]

& what about wearing headphones while driving ? not a good idea as you would be totally isloated from the traffic.

[ejparrott]

Exactly what i keep telling the wife but she still insists on having her ipod in...

[CwazyWabbit]

.....

So this got me to thinking - my stereo head unit has a stereo jack on the front as an input. Is there any reason why you couldn't somehow hook the output of the headphones into this and play the noise cancellation waveform out the stereo?

& what about wearing headphones while driving ? not a good idea as you would be totally isloated from the traffic.

He's not talking about wearing headphones, the idea is to take the guts of the headphones (ie sound processing electronics and microphones) and use the output to feed into the car stereo so the stereo speakers output the noise cancelling sound.

Wearing headphones whilst driving is illegal isn't it?

EDIT: It appears there is no specific regulation prohibiting the use of headphones whilst driving, it is however not the most sensible idea.

Edited May 13, 2012 by CwazyWabbit

[David Sparkes]

Some wonderful posts in this thread, and as they all seem to be posted by people who have never worn 'noise cancelling headsets' , some wonderfully imaginative deductions have been made !!

Keep it up guys - I'm enjoying this :-))

Yes, I bought some many years ago.

I used them repeatedly in an open plan office environment, both to reduce the neighbour noise during normal hours, and especially when taking part in telephone audio conferences.

I've also used them, with positive benefits, while passenger in a Series 1 doing the John o'Groats to Lands End thing, over a couple of weeks.

I hardly drove that Series 1 at all, the owner driver was a little nervous.

I've never yet needed to drive while wearing them, but I did ensure they were packed, with both a fresh and a spare battery, when it looked as though I'd have to drive a Series 2 for 260+ miles. In the event, I didn't buy the vehicle.

The name is misleading, they don't actually 'cancel' noise, they reduce the peaks of sound. The pattern remains, but the volume high spots are cancelled. Note, this is different to the stupid advice often given, that vehicle noise can be cancelled by turning up the volume of the music.

The plug on the NC earphones is an input, not an output, so you cannot feed the 'cancelling' waveform through the plug into the input of a car stereo system.

I have never used this facility, as I've always understood tinnitus, or continuous noise, to be a bad thing.

The wearer of NC headphones will experience some reduction in noise level without switching the NC on, because the headphones themselves act as a slight barrier, but in no way can this be compared to the reduction experienced while wearing a hardshell protective headset, mandatory if anyone is working (employed) in noisy environments.

Switching the NC on causes a slight reduction in 'noise', but the effect is mainly cumulative, as the brain adapts over time to the reduced noise level. This assumes the hearing hasn't already been permanently damaged due to excessive noise.

Due to the adaptive effect the difference is more noticeable when the NC headset is switched off and removed after a period of use, compared to when the NC is first switched on.

HTH, even if it does spoil the fun.

[CwazyWabbit]

Cheers David, that's my bubble burst

The idea of a noise cancelling environment created by your car stereo is still an intriguing idea though....

[nickwilliams]

I do quite a lot of long haul air travel and I've used several different makes and types of active noise cancelling headphones and ear plugs over the years. There is no doubt that the best of the bunch are the Bose ones I have at present but I've had (much!) cheaper Philips and Sony ones which did the business (except the last set of Sony earplug ones which did not work at all and went back for full credit against the Bose ones).

As David said above, they don't eliminate noise completely but they do reduce the overall levels, particularly for low frequency repetitive noise. They also reduce the high frequency noise, but I think that's mainly due to their effect as a simple barrier, like a pair of ear defenders. When flying they make the difference between being able to hear whatever you are listening to on your iPod properly (complete with all the base frequencies) and missing half the content (and most of the subtlety). They are particularly good when listening to classical music or low level speech.

I've also used them while driving my 300TDi 90 (which has no sound deadening or lagging at all) and they definitely make it a more pleasant drive, at least from a noise perspective. In fact, you can actually hear more of what's going on in the transmission and engine since they remove the continuous drone of the engine and less regular and lower level noises become audible. However, I found they contribute to a slight sense of being disconnected from your surroundings which I did not like. I suppose the most telling part of the story is that I wore them for a 2+ hour drive from the Peak District to the Yorkshire Dales in February, but I did not wear them on the way back.

With regard to the OP, active noise cancelling will certainly work in a car, and is used by some manufacturers. However, I suspect that it's not quite as simple as frigging the bits out of a pair of headphones since for the noise cancellation to work properly the reactive noise has to be superimposed 180 degrees out of phase with the background noise, which presumably means that the system has to be tuned to the dimensions of the vehicle. It would be an interesting experiment to try, though.

Nick.

[ProteuS]

I have a couple of sets of aviation headphones, both bose and Lightspeed.

As has been mentioned before, they really only work on continuous repetetive sounds. Which makes them great for reducing wind noise , engine hum , etc.

As nickwilliams says there is a vast difference between cheap and good noise cancelling circuitry, they do not silence everything though. I regularly use one of my sets in the 90 if I'm driving for any reasonable distance, I find it far more relaxing and although the stereo is quieter I can hear it comofortably. Both my sets have bluetooth and Aux ins on them so I can actually take a call in the 90 if necessary

Some vehicles do put noise cancelling out, but I think to do that they usually have a number of microphones around the car to register the waveforms and positions so that they can send out a cancelling signal from the speakers.

[Quagmire]

you'd also need to worry about feedback when playing via your stereo speakers

I think your probably right, the headphones would normally be listening to one environment (the bus, plane, train, car, whatever) and then playing the reverse waveform in another closed system (your ear). No idea what would happen when it began "hearing" it's own output.

The way 5th sounds on my vehicle I could just bolt the microphone to the gearcasing and that would be 99% of my noise gone

Funnily enough I was looking at them as the Mrs and I have to take a trip up to Nottingham soon which is a trip of around 180 miles from us. I thought I'd get her a pair so that she didn't complain about the lack of soundproofing in the 90.

[HoSS]

It wont work at all / very well in the way you are hoping.

Noise cancelling is done by subtracting the noise measure at a point by a microphone in the earpiece next to your ear, then the sound input to that ear has the noise subtracted by anti-phase addition.

Now the sound in a vehicle is not the same over that volume, you may hear some wind noise in your ear next to the window, and some gearbox noise from the other, thus you cant successfully blanket cancel it over a volume.

If there are vehicles doing it, as someone said it by a much more complicated system with multiple microphones and some more advanced electronics than those you could rip from a commercial NC headphone.