I like this muffler because it is fail safe.

--
Paul Lamar ...No rotor no motor.


Paul---what does this one do for actually modifying either the loudness or
resonance of the rotary?

Paul Vermillion
(partially completed BD-4)

All mufflers convert gas velocity to heat. The louvers are designed to
absorb this heat. Also I can't say what effect the breaking up of the
pressure wave front, if any, has on the noise. I suspect the frequency is modified.
I suspect high frequency waves don't propagate as far as low frequency
waves. However I am no acoustic  engineer.