Car noise canselling

[hansibull]

Hi!
After watching Dave's video #600 about OP-amps, I started thinking about how you could invert a signal to "make it go zero".
If you have an inverting OP-amp connected to your AUX plug in your car, you could, theoretically cancel the noise.
It would be fun to test this out, so I guess I'm going to build one and test!
The problem is that if you speak, or listen to music, the OP-amp will also invert these signals.
So, how can you make the OP-amp invert just a specific signal (car noise), and not voices and music? Does is exist audio signal processors that could fix this?

[Marco]

You will just get an oscillator. For such a comparatively massive space with such huge and variable distances between the listener and the speakers it can only work for very low frequencies (ie. where wavelengths are multiple meters). Of course you'd need pretty big speakers as well at those frequencies.

[mjkuwp]

should clarify.... I think OP meant to cancel interior noise of the car on the inside.  This is done to help make phone calls possible and has been done in some car models to cancel noise that exists in the drivetrains.  Noise cancelling through the built-in audio system is cheaper than quieting the mechanical system.

[rob77]

using a microphone and an OPamp it won't work because of the delays (phase shift). you would have to do some digital signal processing to get some usable results.

[Mechatrommer]

dont cancel the noise you wont hear if somebody horn from behind or if you hit something...