Interesting. Looks kinda lilke a cutaway of a Bose speaker. Exhaust 'tuning' is a bit of a black art, and the math is beyond me.
I do know that for each spark of the plug, there are two pressure waves exiting. One is the expanding gas, and the other is pure sound pressure, both of which move at two distinct speeds. Both of which utilize the available 'space' in different manners.