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Discussion Starter #1 (Edited)
Thought I'd share my drone solution with everyone here. I have a JBA 3" competition exhaust that sounds GREAT, however the drone in the 1800-2000 RPM range would make your ears bleed. :eek:

After doing some research it turns out there's a noise cancellation technique that works beautifully at resolving it. The concept was developed by a fellow named Helmholtz and if you're interested in the science behind it go here: http://www.phys.unsw.edu.au/jw/Helmholtz.html

Basically the idea is that sound waves are directed into a specifically sized "container" where they reflect back and cancel subsequent sound waves of the same frequency. The size of the container dictates the wave frequency that is canceled.

It turns out that for exhaust sound waves at the 1800-2000 RPM range, the size of this container should be a 2.25" x 28" pipe capped at one end. This pipe is to be connected to your exhaust at any point before the mufflers and can be bent in any shape, it's the length and diameter that are important.

I can attest 100% that this works, below are pictures of the Helmholtz resonator pipes I had added to my exhaust. So, if you love the sound of your exhaust, don't want to buy a new one that may still drone, this is your solution. It cost $140 to have the pipes made and welded onto my exhaust.
 

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Interesting. No pics btw.

Do you have an L99 with or without a tune.

You need a sig son!
 

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Discussion Starter #3
Interesting. No pics btw.

Do you have an L99 with or without a tune.

You need a sig son!
Hmmm, the pics should be there now
 

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That's what GM did on the intake. Sound theory. It looks like you made sure they were angled a little so moisture wouldn't collect. Nice job. That's stainless, right?
 

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Discussion Starter #5
That's what GM did on the intake. Sound theory. It looks like you made sure they were angled a little so moisture wouldn't collect. Nice job. That's stainless, right?
Good point....make sure your muffler shop installs them such that moisture will not collect in the resonator.

Yes, the exhaust and the resonator are stainless.
 

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The resonators would be good places to hide cutouts too, if you can't see the ends.:devil:
 

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Very nice!
 

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Discussion Starter #9
Yes, a convertible is another solution for drone. LOL!
 

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Discussion Starter #10
The resonators would be good places to hide cutouts too, if you can't see the ends.:devil:
That's actually not a bad idea, although I suspect most people with cutouts would want them placed closer to the engine.
 

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Is there a formula to use to get that exact dimension of tubing. The G8 guys have been doing this for a while and some of there aftermarket catback systems have a "j-pipe" option, which is basically the same concept. The Borla Stinger on my car have crazy amount of drone and I love to try the j-pipe idea. I've never seen it done on a mustang; probably because most mustang guys like obnoxious sounding exhaust.
 

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Wish I had read this earlier. Just picked up my 2SS/LS3 with new JBA 3" system with LTs. The drone btween 1750 and 1900 is just nuts. I will get the J pipes but since my range is outside of the 1800 -2000 should they be longer or shorter. Cam and charger come next but i need to fix this.

So where does the drone come from anyway? We are curious.
 
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