IASCA and EMMA both mandate that cars be judged at 90db set using a radio Shack type portable SPL meter, measured at head level using the Pink Noise Track prior to judging.
MECA judges between 85 and 95db, most end up right around 90db
for High Linearity Judging is done at 105db-110db.
when I judge, I write down the volume number I was judging on the score sheet and make an additional notation of the volume number used for high linearity as well.
this way there is no question about what volume level I was scoring a vehicle and the person can get in with the score sheet after and put it at the same volume level and listen for the areas they may have been deficient.
The reason that the organizations have standardized volume level and why I make the notation of the level is
1st to standardize judging for everyone
2nd-one of the biggest complaints from competitors is that this judge listens too loud or too soft
3rd--or they complain afterwards that they have no idea at what volume their car was judged so they dont know where to start to make adjustments.
when i was judged for EMMA, the rule was being able to hold a conversation over the music without raising your voice. I was quite surprised how low it was to be honest. I suggest getting hold of the relevant rulebook for what you want to enter.
I've been through the USACi online rules PDF twice and haven't seen anything specific about the db setting of the judging. Eitherway way I'm going to just measure t up to 90db for now since that seems to be a pretty common level mentioned
When mine was judged the once I competed recently.... LOL... the judge was pretty damn forgiving with the volume. I was TERRIFIED about the battery not holding out (not the best for sititing around and listening with) but I Was impressed, he let it fly a couple times but not much.
It's really no different than what I do here. In fact if I was the next car up after a judge was letting another rip I'd be pretty upset. Coming into my system with trashed ears and all.
I mean come on, everyone knows from tuning, that it's a rough gig, and you have to take frequent breaks or things get all askew.
C weighted SPL level using RS SPL meter or the Scosche Boomstick.
Neither devices are meant to be exact measurement devices but tools to keep each system and the judging level as consistent as possible.