The relays would be powered from the power antenna output of the HU. When the HU is powered on, it would activate the relays (one for the front mic and one for the rear), which would switch them off, deactivating the ANC.
The pot would just decrease the gain of the mic in an attempt to make the ANC work with the external sub. My understanding of how the ANC works is that the mic picks up low frequency noise of the engine and outputs a signal (presumably from the sub) that is 180 degrees out of phase and of equal amplitude to the offending noise to cancel it. My theory is that when you add an external sub, that cancellation signal is too loud so rather than cancel it it actually recreates the noise it is trying to cancel but just 180 degrees out of phase. The noise I could hear coming out of the sub sounded like the vibration of the engine in eco mode but much, much louder. My thought was if I could decrease the gain of the mic, I might be able to bring the cancellation signal back to the level it should be. As I think it through though, I'd probably have to use the factory sub as it position relative to the car affects the phase. Either that or a sub amp with variable phase would be required. The more I think about it, the more I think it would be like herding cats as you said before. I'm sure a lot of engineering went into the ANC system and merely dropping the gain of the mic won't fix it but the relay to switch them off would work. I would just have to run a wire to the front and rear ANC mics to power the relays and I have to find 2 relays small enough to fit in the headliner.
I did some searching and found a post in another group instructing that you have to take apart the front mic assembly and cut the red wire going from the mic to the PCB inside the mic housing. Let me know if that sounds about right when you get back and thanks for the help.
-Joe
Hi Joe, I am not sure how the "relay or the pot" idea would work. I know most people have problems with the ANC & Sub, but I think the the ANC goes through all the speakers.
I am away from the house untill Weds. when I get back I could look up what mic is for the BT and what one is the darn ANC. :29: