I was at the Harley dealer today and they were in the process of testing all there stock and aftermarket exhaust systems. The specs are:
Tested .5 meters (20 inches) away from the back of the bike, 45 degrees up from the center of the rear wheel on the center line of the bike, spls less than
92 db at idle and 96db at 2000 rpm.
Apparently the Ontario Police are going to start enforcing this. Harley dealers are providing a printout of the tests to owners to show to police if they are stopped.
Unless the police have some kind of template it's going to be pretty hard to measure accurately.