Noise cancelation

I've been kind of reading stuff in this forum.  I'm wondering about active sound cancellation.  I know I could possibly take the route of hacking up a good set of headphones with this and using the processor in my stereo.  Anyone have ideas on this?  I might look into how the passive cancellation works, I think it uses the speaker as the mic, to outphase the waves that are directly effecting it.  Which might seem best in a vehicle, because it would eliminate a sweet spot. 

Any thoughts would be nice.

It depends on what you're trying to accomplish.  I'm aware of several research activites that have been ongoing for several years by Toyota and Delphi and others using noise cancellation techniques in vehicles, especially for vibration dampning in vehicle structural components and engine, but nothing that has actually made it to market for consumers yet.  If you are talking about simply using a set of headphones as personal noise cancellation devices, there are several of those on the market.  The Bose set is supposedly good, although I've never used one.  I use a set from Sennheiser when I travel.  It does a great job on limiting rumble and the constant drone of airplanes, and the sound quality is great when used for music or movies.  If you're trying to create a silent cabin, that is a completely different animal.  I suppose you could use the custom chipset from a headphone as a guide and design your own circuitry.  The trick will be in deciding what sounds need cancellation and where you place your transducers/microphones, and in designing your speaker and amp system to match the decibel level of the loudest possible road noises.

Found what I'm looking for.  Use of a math program that will program a dsp.  I can have it pass the mic, along with the source sound.  The output is source sound with stuff from the mic on sound out phase.  Shouldnt be more than a hundred or so, vs a few hundred for a set of headphones that i'd just mutilate.