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The cure for drone-- 1/4 resonance pipes aka J-pipes aka Helmholtz tubes

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The cure for drone-- 1/4 resonance pipes aka J-pipes aka Helmholtz tubes

 
Old 03-08-2013, 01:24 PM
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Default The cure for drone-- 1/4 resonance pipes aka J-pipes aka Helmholtz tubes

Here is it, boys. I don't know why it's taken me so long to get clued in. I don't recall ever seeing this mentioned around here, despite the endless bitching about Magnaflow drone.

The correct name is 1/4 resonance pipes, otherwise known at J-pipes, and incorrectly known as Helmholtz pipes (Helmholtz is correctly applied to chambers). They work by being open to the exhaust before the muffler, 1/4 of the legnth as long as one of the resonant soundwaves, and capped at the other end. The sound wave is then reflected back into the exhaust at 1/2 wavelength, perfectly out of sync with the wavelength that's coming after it, thereby canceling it out. This is essentially the same principle as noise-canceling headphones.

The G8 GT guys have been using them for a while. Here's a G8 GT setup. It's not the best executed, and he probably shouldn't have had the j-pipes resting on the muffler like that, but rather separated or welded on somehow. Anyway, this is just to give an idea of the setup.

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Here is a caddyforum thread by a V2 guy who had them added to his muffler delete. He links to another forum that goes into more theory.

http://www.cadillacforums.com/forums...ltz-pipes.html

His exhaust guy seems to be something of an artist, because this is hot. He welded the capped end back onto the muffler to give the setup extra rigidity:



Corsa mufflers work on the same theory. The contain tiny chambers that cancel resonance on a variety of fractional wavelengths, which is what leads to the very clear sound characteristic of Corsa.

Here's a cutaway of a corsa muffler:



I'm just putting this out there to spread the word and get some feedback from the better minds out there. I plan to get this done some time next week.

Last edited by DACTARI; 03-08-2013 at 01:32 PM.
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Old 03-09-2013, 06:14 AM
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I guess everybody likes their drone now. Definitely post up what you end up doing and how it works
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Old 03-09-2013, 08:38 AM
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Interesting. Has anyone tried the cone inserts as well? Even if its not as effective, they're much easier to install.
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Old 03-09-2013, 09:34 AM
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No one cares

Will keep you guys posted on what I do, but this is sure to work and will only cost on the order of $140 to get the pipes fabbed and installed.
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Old 03-09-2013, 10:14 AM
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Guess I didn't know about drone with Magnaflow. If I had B&B, I'd CERTAINLY do this.
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Old 03-09-2013, 11:12 AM
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Old but good tech.
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Old 03-09-2013, 12:09 PM
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Originally Posted by rand49er View Post
Guess I didn't know about drone with Magnaflow. If I had B&B, I'd CERTAINLY do this.
Is it really that bad with b&b? I guess i'll find out once I get everything on.
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Old 03-09-2013, 12:17 PM
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IIRC...B&B were the ones that sent out the cones to everyone to reduce the drone.
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Old 03-09-2013, 01:24 PM
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Most guys say they just "drive around" the drone. I wouldn't want drone dictate how I drive my car, though.
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Old 03-09-2013, 03:22 PM
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Originally Posted by rand49er View Post
Most guys say they just "drive around" the drone. I wouldn't want drone dictate how I drive my car, though.
Or they fix it with $60 worth of b-quiet ultimate or Dynamat. The spare tire tub resonates like a drum.
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Old 03-09-2013, 05:44 PM
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Magnaflow is not bad at all. A little drone in 6th gear between 55-59mph if there's a load on the engine.
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Old 03-09-2013, 07:21 PM
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I did this on my Fox Mustang, although I admittedly didn't put any real thought into it (as far as tuning the length of the resonator tubes). It definitely made a difference in some RPM ranges, but I could have made them more effective if I had bothered to do some math ahead of time. :p I bought a 180deg U-bend from Summit, cut it in half, and had them capped off and welded in running above the tailpipes (hidden by the rear bumper).

I know I took some pics, but they must be on my desktop.
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Old 03-11-2013, 01:32 PM
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At the exhaust shop getting these fabbed and installed.
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Old 03-11-2013, 02:49 PM
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Do I have this right, people install really free flowing cat back systems or perform a muffler delete then end up adding back in restrictions due to noise and expect these systems to perform better than stock or at least weigh less? This sounds like the type of mess I would stumble into. I did something similar with a vtwin sport bike.
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Old 03-11-2013, 02:53 PM
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No, the 1/4 wavelength pipe is capped at one es so no air flows through it. Air follows the path of least resistance, so it goes out the exhaust pipe. It's the sound that travels up and down the j-pipe, not the air. There is no harm to air flow or performance.
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Old 03-11-2013, 04:46 PM
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Math:

Length=(1100/Drone freq.)/4(*12)

What's the frequency kenneth?
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Old 03-11-2013, 04:57 PM
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No Math:

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Since SOLO has done their "Math" and the G* has a VERY similar engine (LSx) you can see in the picture the general size.
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Old 03-11-2013, 05:30 PM
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Done, and drone is gone!

Here's a link where some guys did the math already for a variety of RPMs: 1/4 wavelength resonance pipe l engths for drone at various RPMs

My drone peaked at 1600 RPM. Shout out to Greg at Mandrel Bending Solutions, who did the calculations and all the work. He calcualted 31.5 inches, and it happens to be the same as what the link above shows (though I found the link just now). He also made them adjustable so that I can shorten and lengthen them to try to zero in on exactly the right length.

Now that I've driven the car a bit, I would say the drone is 90% gone. There is some drone 1400 RPM under load, which is kind of an unrealistic rev range to be in. However, I will try lengthening the pipe a smidge to see if that gets it, while keeping the other drone at bay. All in all, success! I highly recommend this to anyone as a relatively cheap mod that works. If you can do your own welding, then i'ts basically free.

The exahaust note is not changed, however, now that it's not droning, I can actually hear the burble of the exhaust at low RPM, making it MUCH more enjoyable to drive. I forgot what it was like to hear wind noise and tire sounds, but not I hear them again. Great mod.



That's a pic from just before completing. He added some braces from the end of the j-pipe to the muffler to add some rigidity. The j-pipes are not visible from behind the car at all.
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Old 03-11-2013, 07:16 PM
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looking good and interesting read!
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Old 03-11-2013, 10:14 PM
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