Ok that was fun... so heres the info I did all the testing with the most appropriate ECM, in the same location using the Niosh iPhone app 6' from the tip, in a 4000' bldg, warm engine. Idle, 5k and 7k.
Stock resonator 80dB, 94dB, 100dB (Quiet. Too quiet and rattly) Stock muffler with 2.5" tips on the OD of the muffler outlets 88dB, 97dB, 106dB (really nice deep tone and mellow volume) Open headers (LOUD) Probably maxed the 'meter' and the snow falling is insulation from the roof. 102db, 117dB, 124dB! (The dead are coming to complain about the noise) APH RACE Y-pipe only 100dB, 111dB, 118dB (Meaty) APH RACE y-pipe and muffler with single tip 90dB, 105dB, 110dB (Deep tone, and ok on the highway but your neighbors hate you. It's totally worth the performance increase though)