Mikey, I was just getting a number for my own reference and ten feet seemed reasonable. I did sound testing for 12 years and have a lab quality meter and I will be measuring all my planes and recording them for reference. I didn't try to match what IMAC or AMA requires for contests. I wasn't even aware there was a limit for there contests (what is their dBA limit and at what direction from the muffler)? I don't fly contests and my field doesn't have a sound limit currently. If things change I suppose I will do as others have done and pay the price to install a canister (I hope not for a while anyway). Thanks for the info.