Noise Cancelation

[Dundain]

Correct me if Im wrong, but you can cancel one frequency out by using another frequency? I dont remember exactly how it was explained in our physics class, but this would seem to be a relatively simple thing to lower the noise of a Delta fan...just cancel it out with another noise source...

 

[littleprince]

it it would take is a mic, signal processors and a speaker...
u have to cancel the frequencies exactly so you get standing waves...

in other words you can't just turn on 2 delta fans and let them cancel each other out....

 

[cnhoff]

You have to cancel those waves by sending out the same signal, but 180° phase shifted.

Then you don't get standing waves, you don't get any waves at all any more!

 

[littleprince]

i thought you got standing waves?

like if you create waves from two sides in a fish tank, the waves pass through each other?

 

[cnhoff]

You have standing waves in most musical instruments, like flutes or anything like that.

The interesting thing is that adding up the original wave and the 180° phase shifted one makes zero, so there is no noise any more at this place!

 

[littleprince]

time to go read up on some physics....

 

[gogeeta13]

so should i get another delta?

 

[littleprince]

can't find info on the net....
other than theres a bunch of pilot headsets that do it...

 

[Dundain]

So hwo complex of a project would this actually be to accomplish? And how expensive for that matter? Because I know most noise-cancelation headphones are pretty damn expensive...but if it would be possible to cancel the noise of a Delta fan out for cheap...well, overclocking will become even more fun

 

[zogg]

If you build your encloser with uneven unparralell sides, you will have mechanical cancelation and kill most the standing waves. Just make sure you are going to generate Uneven Harmonics


Zogg

 

[mindiris]

You can "cancel" the sound only at the location where it would be heard. The waves still exist, and pass right through each other unaltered assuming there are no other interference.

 

[WarCon]

I just had a crazy idea. You could get a mic splitter or an amplified mic (stick it in your box) and use your other input on your sound card and write a tune-able phase cancellation routine that was timed for approximate distance from unit and speaker arrangement (would have to run all the time in the background) and use your system speakers. Suppose it could be done with an add in board and a speaker loop from your sound card to it and the board could have the mic right on it. Wouldn't be that hard to program a self contained microprocessor to run a modifiable routine.

Ok I am a nut, I admit it.......

For those of you that sleep in the same room with your computer you could even have two separate settings. One for in front of the comp and the other for in the bed.

Ok I know I should stop but, if you used a battery power mic or one on a very long cable you could have the routine tune itself for various locations or if you were rich you could wear one all the time and it would tune you in anywhere in the room. Your guests might suffer with twice the sound at points, but it would be quiet to you.

 

[hovenas]

WarCon:
Invent it, patent it and sell me one!

 

[MrWhiteUK]

You could also end up with the waves combining doublig the noise output!:disgust:

 

[Beethoven]

Here...have some fun...

Take one of your MP3's an convert it to a WAV file. Open in up in a sound editor (SoundForge...if that still exists). Go from Stereo to Mono, back to Stereo so you know have a left & right channel with the same waveforms. Next, phase shift(or flip) one of the channels 180 degrees.

Now put your L & R speakers close together and hit play. You will notice that the sound "feels" muted. Of course, this will come no where near 100% cancellation, and it depends on your speakers and where you are in position to them.

BTW, it would be nearly impossible to record the sound of your fan with a mic, shift the signal and replay it to cancel the noice becuase of the delay in processing the signal. You would probably end up making 2x as much noise as before.

 

[goshdarnindie]

I actually started looking into this project last week, and I have come to the conclusion that it would not be financially possible for the reasons mentioned here but also because of the point source nature associated with a fan. Sound waves are emitted from the fan in all directions whereas any speaker you use will create a conical output that will only link up with the original source in an insignificant spacial volume. Plus, getting the two in sync would be next to impossible.

So, it sounds good in freshmen physics, but if it could easily be done, industry would have already done it a manufacturing setting.

 

[speedtriple]

In fact you must create "anti sound" with the same amplitude and 180 deg fase shift.
The problem is it works good with known frequencies and known spaces like an airphone, but noise of a fan is random. To solve this you need an other PC to calculate the right anti-sound so at the same time there is a new source of noise born