packing will reduce noise but you can only put in so much, the baffels is what really cancels out the sound, check this out.
How Can You Cancel Out Sound?
The key thing about sound waves is that the result at your ear is the sum of all the sound waves hitting your ear at that time. If you are listening to a band, even though you may hear several distinct sources of sound, the pressure waves hitting your ear drum all add together, so your ear drum only feels one pressure at any given moment.
Now comes the cool part: It is possible to produce a sound wave that is exactly the opposite of another wave. This is the basis for those noise-canceling headphones you may have seen. Take a look at the figure below. The wave on top and the second wave are both pure tones. If the two waves are in phase, they add up to a wave with the same frequency but twice the amplitude. This is called constructive interference. But, if they are exactly out of phase, they add up to zero. This is called destructive interference. At the time when the first wave is at its maximum pressure, the second wave is at its minimum. If both of these waves hit your ear drum at the same time, you would not hear anything because the two waves always add up to zero
Inside a Muffler
Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. these baffels may be positioned so the gases and sound go thru at different areas by bouncing of walls within the pipe. In the end an appropriate muffler will have cancelled out most waves in phase and you only have left out of phase waves which cancel out noise. I'll look for a webite tomorrow that had a really good example of how it all works, I modified a set of pipes even building my own baffles from this site, sounded ok and didn't have any problems
