Below are some sound measurements taken within the SAE guidelines.
Stock Exhaust
idle - 74dB
SAE - 81dB
Stock DP & Cat with COBB Cat Back
idle - 80dB
SAE J1169 - 88dB
COBB DP, Stock Cat, COBB Cat Back
idle - 79dB
SAE - 93dB
COBB DP, COBB Catless Test Pipe, COBB Cat Back
idle - 83dB
SAE - 98dB
COBB DP, COBB high flow Catted Test Pipe, COBB Cat back
idle 80dB
SAE 94dB