Techy people - DIY Active Noise Cancellation for older cars?

[mr2j]

Would it not be great to have something for those early morning starts that was as simple as the flick of a switch to quieten down that bark and growl when you're Jurassic V8 stirs into life or that low droning, busy idle as your motor warms through on your gentle trundle out of the cul-de-sac?

How practicable is this for external application rather than just a solution for cabin noise? Presumably the basic principle is the same; a microphone --> something to process the signal and invert the phase --> a speaker to broadcast inverse phase 'anti-sound' to cancel out the sound.

I find currently that it's not the volume that is the problem but the resonance of the particular frequencies. A certain distance from the car, where the peaks and troughs of certain frequencies come into alignment is the zone most affected and can make ones teeth rattle.

I read an interview with a musician who was mixing an album in his flat dealing with some low frequencies and his immediate neighbours could hardly hear a thing but those a few doors/floors down were experiencing it as that's where the sound was amplified at the distance where peaks and troughs finally aligned.

Based on this basic grasp of the physics of it - would it be possible to have your signal processing computer linked up to your ECU so it could vary the frequency of the inverse phase based on engine RPMs rather than just relying on a microphone set up?

[Bibbs]

mr2j said:

Would it not be great to have something for those early morning starts that was as simple as the flick of a switch to quieten down that bark and growl when you're Jurassic V8 stirs into life or that low droning, busy idle as your motor warms through on your gentle trundle out of the cul-de-sac?

Like a bi-modal exhaust?

But no, I deliberately open the garage before starting mine, to make sure the neighbours can appreciate the noise. Then a few good blips before reversing out.

[mr2j]

Well, the point is that one might want to keep one's old exhaust that one loves the sound of so much.

I've noticed that anything with a bi-modal exhaust going past my house in the morning tends to cross over into BAAAAARRRRRPPP between the speed bumps anyway - not that it's necessary to stay in a lower gear for so long but I'm not complaining.

[mrnvh]

Are you sure its all in the exhaust too? There's a reason for those big plastic trays and bonnet insulators in the engine bay, it won't affect what you hear through the firewall but could be the first step.

You'd need more than one microphone too, and more than one speaker to have a complete anti-phase system. Barring modifying/replacing or covering the entire exhaust system (except the way out!) I'd be stuck for a solution.