In response to the chat room question about active ambient noise cancellation for use with a speaker system as opposed to headphones, I don't think such a device currently exists. There are certainly white noise devices that can be used to drown out ambient noise, but those would negatively impact your listening experience moreso than simply turning up to the volume on the sound system to hopefully accomplish the same goal. I did see a couple articles about a device called Sono (not Sonos), that attaches to a window and uses a microphone to detect ambient noise so that it can actively cancel it out (using the window pane as a speaker) and that you can even selectively filter some noises out while allowing others to pass, but this device is currently only in the concept and initial prototype phase. Even if it did exist, I doubt that it would be able to completely cancel out the noise of your window AC unit while not impacting the audio from your sound system. The filters would have to be extremely precise with controls that allow you to easily distinguish between what is noise and what is not.
This is a good question though, and I would be surprised if AVR manufacturers are not putting research into this problem. It seems that if it was possible to do what you want, the sound system would be the best device to do it since it more directly connected to the audio that you want versus the noise that you don't want and already has the speakers available to perhaps cancel out the noise.
Last edited by HockeyoAJB; 07-08-2014 at 03:38 PM.