http://www.iasca.comhttp://www.soundoff.org/usaci.htm
Those are the two main SQ competition formats.
MECA (
http://www.mecacaraudio.com/sqrules.php) has SQ competitions as well.
They are judged by ear for things like soundstaging, imaging, tonality and the like against a set of guidelines of how a vehicle
should sound. They are also judged for things like installation integrity, creativity, a portion of the judging is SPL, they are RTA'd, etc.
SQ comps aren't very popular and are quickly dying //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif