Posted by
seestheday on
Mar 16, 2012; 12:37am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/QUIET-EXHAUSTS-tp3824396p3830534.html
Fiberglass might be more sound absorbent because it is more malleable (can be bent more easily).
This is because one other place for the force of the sound waves to go is into destructive kinetic force.
This would be my initial theory, I'd have to dust off some textbooks and break out a slide rule to make sure (kidding on that last point :-) ).
Sound waves are just kinetic pressure waves that move through the air (this is why sound isn't possible in outer space). The particles in the air that are being pushed make up the wave. When they hit something (like fiberglass or aluminum turnings) some force is imparted onto what they hit, and some bounces off (think pool table balls). If the thing that they hit is hard, then most of the energy is transferred through to the other side of the hard object (in this case, through the aluminum turnings, then the muffler, then the bike), and the remaining energy is absorbed destructively by the object or dumped as heat.
I imagine the aluminum would absorb more of the sound energy as destructive kinetic force (which is why the glass ends up flying out), but have a shorter lifespan than if you made the muffler with aluminum turnings (which would last damn near forever, but I wouldn't want to be behind you if it did start to fail).
Ah, newtonian physics logic problems. I haven't done these in a while.
Sent from my BlackBerry device on the Rogers Wireless Network
Date: Thu, 15 Mar 2012 16:24:56 -0700 (PDT)
Subject: Re: QUIET EXHAUSTS
seestheday wrote
Errr... I'm pretty sure that the reason the glass packing works is because it physically absorbs the sound waves and transfers it into kinetic energy. The kinetic waves would cancel each other out to some extent, and the rest would be transferred into the motorcycle, but it's so small you won't notice it because the engine alone generates much more kinetic movement (vibrations etc).
If it was only in-phase/out-of-phase cancellation then you'd have some coordinates in space that were quiet, but if you moved your head a little bit it would be extremely loud (think of dropping two pebbles into still water and watching the ripples interact with eachother, but mapped into 3-d space).
Now if you'll excuse me, I'm going to put on my pocket protector and go back to my game of dungeons and dragons.
What the ...?!?! You just blew my mind. I dont what you said,but it made sense. Sarge you are right about my steel wool rusting.It was a cheap shot at something that might not work.More of a test that actually panned out,so it stayed in.When it falls out 'glass will go back.I never knew about the bronze steel wool either. Very cool. I can get my hands on a lot of aluminum turnings from a machine shop a buddy works at. It'll be free so I'll may go that route. I just feel that the fiberglass should be quieter than any metal. I dont have any uber-scientific reason why that is,just a thought. Maybe I should consult Prof. Sees' on this one
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