I have a 9 hp subaru engine that operates a soil mixer. I find it obnoxiously loud. From other reading the 'mufflers' on many small engines are little more than spark arresters. The location of the engine (about 6 feet off the ground, and the exhaust (on top) make me think that it should be possible to direct most of the sound energy upward with an appropriate bell. Suggestions as to the actual structure appreciated. Do I want massive? light weight? exponential curve vs stepped?