I passed at just under 100db with an Ashley system on my XR2. It was so loud people would crap their pants and move over if i touched the throttle on dual carriageways. Made me feel like a tool so i changed to a janspeed which came out at 96db. It's ususally tested at 2/3rds of full revs so give it a go and see how loud it is. If you search 100db on the internet you'll come up with plenty of examples to compare to. A human can scream at 110db and some people upto 120db so stick your face in your exhaust and have a screaming match if you easily win your fine! Please don't actually try that!! Sadly i know people that would.
A standard honda CRX came out at 90db with a fecked (blowing) rear silencer at 6000rpm so they are quite forgiving. Wouldn't have passed when the back box fell off on the way home there's a reason why vtecs need three large silencers to keep the noise down. The noise was out of this world though
Also i forgot to say does it give the test circumstances? eg. 45 degrees at 1 metre etc? that makes quite a difference.