The best I could do on my own is to use my Umik-1 mic, that I am sure hears better than me.:D With HVAC off, here's what I have managed:\n\nI highly doubt anyone in my room can hear any sort of harmonics at levels below -70 dB from 11 feet regardless of the frequency range, but I think it is a good idea to stick to gear that can do -75 or even -80 dB THD+N. Unfortunately that would rule out a lot of AVR, integrated amps and many separates, based on measurements I have seen.\n\nThat's just me, being a crazy audioholics. Practically speaking, I firmly believe for videos and even many music genres, -65 dB would probably be enough to guarantee most people will fail in DBT sessions for amp A vs amp B. Now, obviously I can hear distortions from my speakers as those are above the noise floor for sure.\n\nThis is only in terms of THD+N and noise floor, obviously there are many other factors.\n\nBy the way, I am sure you have read it, but for those interested, AH seems to have never failed to have a good article on just about everything we need. Here's one on human hearing sensitivity:\n\nhttps:\/\/www.audioholics.com\/room-acoustics\/human-hearing-amplitude-sensitivity-part-1\n\nand below are the noise floor, 1\/48 smoothing and no smoothing, for my HT room:\n\n\n\n\n\nI can get it that quiet in my room too, when the hvac isn't running, but that's not very often this time of the year. Even just the fridge kicking on adds noise. With the hvac on I'm at about 40 - 45 dB.