Killing Drone With 1/4-wave Tubes

[David Pepiton]

You've never heard of it?

David Pepiton

hahaha thats funny. in all honestly kias quality has greatly improved over the last few years.

anyways it was a custom exhaust I actually learned a lot of info from that car.

heres a few pics of the pig:

http://i164.photobucket.com/albums/u12/31bravo_1988/CIMG2316.jpg
http://i164.photobucket.com/albums/u12/31bravo_1988/CIMG1530.jpg


anyways id like to see some math equations for this there drone issues

 

[MFE92]

The threads I linked to are full of the math, but in my case, it worked like this:

1900 rev per minute * 4 pulses per rev / 60 seconds per minute = 125 pulses per second

The speed of sound in air depends upon the temperature. I assumed 1075 feet per second, which according to my research is appropiate for 113 degrees temperature. Seems fair for a pipe that's connected to the exhaust system, but which doesn't actually see any flow, because it's capped.

To find the wavelength of each sound pulse:

1075 feet per second / 125 pulses per second = 8.5 feet or 102 inches. You want the quarter-wave tube to be 1/4 of the wavelength, or 25.5 inches, in my case.

 

[Boosted92LX]

The threads I linked to are full of the math, but in my case, it worked like this:

1900 rev per minute * 4 pulses per rev / 60 seconds per minute = 125 pulses per second

The speed of sound in air depends upon the temperature. I assumed 1075 feet per second, which according to my research is appropiate for 113 degrees temperature. Seems fair for a pipe that's connected to the exhaust system, but which doesn't actually see any flow, because it's capped.

To find the wavelength of each sound pulse:

1075 feet per second / 125 pulses per second = 8.5 feet or 102 inches. You want the quarter-wave tube to be 1/4 of the wavelength, or 25.5 inches, in my case.

From the photos the length of pipe after the bend in the "J" appears to be roughly 1/2 the length of the longer leg. Would this length be critical to the intersection point of the waves, or is overall length the only factor here? Also how about the size of the radius of the bend? I'm guessing the radius wouldn't be critical and if not it would sure help with fitment..

 

[MFE92]

You can make these things spaghetti-shaped if you want, the critical factor is overall length.

 

[FastDriver]

That's good stuff, and something I may look into. My car drones like an SOB, but I've got particularly loud straight through muffs. Thinking about doing an electric cut out since back pressure reduction is so significant on a turbo car, but I still want it quiet.

 

[Gearbanger 101]

Get on it MFE. I've got some nice 2 1/2" mandrel bent J-bends here just waiting for me to do something with. I need a guinea pig to iron out the details first before I go splicing them into my exhaust system.