Starting this thread so people can get an actual idea of how loud different exhaust systems are instead of always asking, "what is louder".
I just ordered a simple decibel meter off Amazon for around 30 bucks.
In order to have some consistency between parties here are some guidelines;
1. Have vehicle outside and warmed up.
2. Hold db meter approximately ONE meter away from exhaust at waist level.
3. Slowly rev the motor to 5000 rpm, read meter.
This is fairly close to the procedure used at German tracks and by German TUV (2/3 of motor max rpm for the M3 is 5478 rpm but hey 5000 will do). Its obviously not the loudest you can get it but it will be a consistent measure. Plus I don't want to wrap my motor out without it being under load.
Post your results as follows:
Misterschaft GT2 axle back
Stock X pipe
db @ 5000 rpm: 112.1
Yes it gets louder, for example I got 118.6 at 7000 rpm in my garage but then thats cheating. I understand that there are still a lot of variables left out there such as temp and humidity and some may question the quality of different meters. I can say for sure that an Iphone or other smart phone "decibel meter" ap will not do it for you. I downloaded a free one for android and it was telling me 80db under the same conditions.
Hope to see more readings soon! I will update this as other members post to build a data base.