measuring sound is a serious science...get this, my modified Milltek passed sound the other day (as it always does) but a stock cayman S did not! The guy got black flagged due to sound. It was an overcast and humid day and that seems to keep the sound "in". What I find weird is that the cars with the higher pitched exhausts get black flagged more often then lower pitched cars.
A CS at full throttle makes a high pitched whoosh sound and got nailed, F360's and F430's get nailed more than a GT3RS or 944 Turbo (open 3" exhaust). A radical with full muffler gets nailed more easily than a race prepped C6 Z06 Vette with turn downs...

I always thought that bass traveled further and with more power than treble...but what do i know?
The Ferrari SP33 (like $6 million race car...) sounded sick and was right around the limit but the McLaren F1LM was WAYYYY over and horribly annoying andf I could hear it way into town (but wow, what a car!)

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'06 Cayman S -JIC Cross, Quaife, CCW C14 wheels,MPSC's, Milltek cat back, GT3 seats Schroth harnesses, TC design bar, Pagid yellows, GT3 cup brake ducts,de-snorked, vanilla air freshener