I haven't measured the sound level because I don't have a meter, but they are much quiter than the small motor mounted mufflers. Plus they give it a lower key rumble instead of a popping sound. Any one who has used canisters can tell you they sound great. They sound similar to the exhaust on a snowmobile. In the air the plane is very quite until about 3/4 throttle when the prop rip becomes much louder than the exhaust. On a 23lb airplane I spend very little time over 3/4 throttle. If noise is a big concern I would recommend using a 3 blade prop instead, they are very quite.

xcellheli