Answer:
Flow Master muffler?
Depending on the series, it uses baffles and chambers that muffle the sound.
Baffles are small holes in piece of metal. Works kind of like a sound proofing room.
The chambers are kind of like walls, that the exhaust sound hit and bounce off of.
The mufflers make the tone deep because in all cases, "the deepest bass is the one the has to find you". So by hitting all those walls its diminishing the high pitch sounds, and by the time it gets to you its just the deep tone.
Hard to explain