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DIY active noise cancellation?

post #1 of 10
Thread Starter 
I was wondering if this is possible?

I open cans are great when you want to hear what's going on around you, but it would be nice if there was the option to flip a switch, and turn off the background noise.

With good mic placement, would it be possible to achieve something similar to the Bose (*spit* ) noise cancelling headphones?
post #2 of 10
Quote:
Originally Posted by MikeHunt79 View Post
I was wondering if this is possible?
Anything is possible! From what I understand the noise cancellation is done by taking the low external frequencies inverting the phase and mixing it with the input signal. The high frequencies are attenuated by the closed design of the headphone itself.

However, I believe it is there that lies the problem...I don't think it'll be that effective with open headphones. You can take the higher frequencies and try to invert and mix, but it won't work as well because of phase variations through different mediums...you'll never get it exact enough to sound good.
post #3 of 10
I don't see why not, but it'd probably take a lot of tuning. You could probably use a single opamp to sum the real signal with the inverted signal from the microphone for that channel. I imagine you'd need to do a lot of tuning with amplitude though.

Maybe tear a Bose pair apart?
post #4 of 10
rip the gear out a bose and put it in your amp is your best bet. Bose use to pretty sophisticated tequniques to make awfull speakers and headphones sound better... I think they have been using DSP's for over 20 years now. To use this is bad as the hardware sounds pretty nasty but to the consumer it's wonderfull as they get "big sound" out of a box the size of a match box (consumers care alot about size).
post #5 of 10
post #6 of 10
Thread Starter 
Quote:
Originally Posted by ericj View Post
Blimey, a little more complex than I thought... Still, it's good to see someone has done this already.
post #7 of 10
Quote:
Originally Posted by kipman725 View Post
rip the gear out a bose and put it in your amp is your best bet. Bose use to pretty sophisticated tequniques to make awfull speakers and headphones sound better...
The electronics in the Bose headphones will be optimised for those headphones, drivers, mic placement etc.
Just sticking them in another pair of headphones will not yield good results. The electronics have to be specifically tuned to the headset to achieve anything as good as the Bose system (the noise cancelling bit).

Quote:
Originally Posted by kipman725 View Post
I think they have been using DSP's for over 20 years now. To use this is bad as the hardware sounds pretty nasty but to the consumer it's wonderfull as they get "big sound" out of a box the size of a match box (consumers care alot about size).
I beg to differ. It has nothing to do with DSP technology. It's the way it is used that is the problem. A lot of high-end audio and video equipment use DSPs for signal processing with good results (provided the DSP is powerful enough).
The difference IMO is that Bose attempt to get a good sound out of crap systems by heavily processing the signal. Other manufacturers use DSP to optimise already decent systems.


Back to the question in hand, yes it probably is possible if you're willing to spend enough time playing around with equalisation and delay times. You will need to find the frequency response of the microphone(s) you are planning on using, and compensate for their placement and distance relative to the drive units of the headphone. You will therefore need some delay, since the background noise will hit the microphone before the headphone drivers, and you will need to apply some equalisation to compensate for the frequency response of the microphone and the headphones themselves.
post #8 of 10
Can't...provide...answer...keep...staring...at...M ike's...avatar...drooool...
post #9 of 10
Quote:
Originally Posted by MikeHunt79 View Post
I was wondering if this is possible?

I open cans are great when you want to hear what's going on around you, but it would be nice if there was the option to flip a switch, and turn off the background noise.

With good mic placement, would it be possible to achieve something similar to the Bose (*spit* ) noise cancelling headphones?
I tried building one on a bench back in university. Using a simple inverting opamp, PC mic for pickup, and two speakers (one for simulated noise from a signal generator, and one for the cancelling signal). It did not work well and I put a lot of effort into it! I think the tuning of various sensitivities is not easy.
post #10 of 10

There are some new IC:s out that can do this. I am looking for a DIY project for building a nice cancelling circuit that can be applied to any headphone. The project mentioned above, i.e http://headwize.com/projects/showfil...=noise_prj.htm

is about 10 years old. There has been some improvements to this idea since then. I am looking for an audiophile, mobile solution to pair with a Pimeta amp. 

 

Googling showed me this IC that might do the job:

http://www.electronicsweekly.com/products/2010/05/07/21488/noise-cancellation-ic-has-on-chip-calibration.htm

 

and this

http://www.gtronix.com/products/

 

and this:

http://www.rubidium.com/products.php?actions=show&id=16&CurrentPage=0

 

EDIT: Slight edit to let point get through


Edited by barsk - 9/3/10 at 4:59am
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