There's an article titled "WHAT'S NEXT; To Quiet a Whirring Computer,
Fight Noise With Noise"
about researchers doing this to try to quiet a computer case fan he
http://query.nytimes.com/gst/fullpag...gewanted=print
So, it definitely seems doable, but not as easy as one would think.
However, I don't see any harm in actually trying to build the said
noise canceller,
even if it probably won't work. In the worst case, a few hundred
dollars
will be wasted on a good cause, and this question will be really
answered.
Building it should actually be quite trivial. All you have to do is
replace
the headphones with a pair of computer speakers that have an internal
amplifier (since they take what is essentially a headphone output
anyway).
This might take a bit of soldering, but shouldn't be a big deal.
Then, you could experiment with microphone and speaker placement
and see if it works. Most likely, if it will work, it will only work
with the
microphone and speaker close to the sound source (the fan), but it
might work if you put the speakers and microphone on your bed stand.
If you are interested, you could figure out what frequencies of noise
the
fan is putting out by recording the noise with a mic and then doing an
FFT/frequency analysis using some decent audio processing software
such as Cool Edit.
I do agree that the best remedy though would be to try to eliminate
the source of the noise. A better designed fan could have much lower
motor noise, and the noise due to air motion could be better too if
the fan blades have a better design. If you are using a separate speed
controller for the fan, that could also be causing noise if it is
creating
harmonics in the AC current going to the fan. A better speed
controller
could help in that case.
-Ilya