The only reference to a sound rule in the AMA is in the criteria for a Leader Club application, where one of the optional criteria is that the club has a sound rule, and then adds an example of "such as 90 db at 9 feet.

IMAC is changing their sound rule this year to eliminate any reference to a ground level sound check (formerly 96db at 25 feet). Nobody was doing the checks anyway. They are keeping the subjective inflight sound score, but giving the judges more latitude by allowing the judges to assign a 0-10 score, rather than just 0, 5, or 10. They are also increasing the K value of the sound score.

Brad