It is all covered in the AMA Competition rules:
http://www.modelaircraft.org/events/...aerobatics.pdf See section 5 starting on page 2.
And another piece of enlightenment: Re: "how does the AMA Enforce Sound limitations at all of their registered sites?"
There is only one AMA site, and that is at Muncie. Sound limitations apply only to certain rulebook events. Except for specific AMA rulebook events, sound limitations that may be in place at club flying sites are enforced in any manner deemed to meet the requirements as set by the club. The AMA has nothing to do with this on the local level.
Is there some reason people will argue a point to death rather than going to the AMA web site to find out the information?