Muffler shape/design, flow, and noise?
Muffler shape/design, flow, and noise?
(OP)
I am searching for information on mufflers and their designs. I've found a good bit of information scattered about, but still have a lot of questions.
Most of the muffler designs I am investigating are "straight through" designs, perforated cores with some sort of packing material around them. The first (and perhaps biggest) question I have is how does the length of the perf tube effect the attenuation rate. The next is how does the shape affect the attenuation as well. I *think* the can shape around the perf tube would effect the target frequency. (or would that be mostly the hole size in the tube??) So something like an oval shaped can would then theoretically have a broader spectrum it effects than a round can. am I on the right track here?
The next big catch is something like a borla XR-1, which is a straight through perf core in an oval tube, but also has a sheet perforated metal dividing the middle of the perf tube as well. This brings up the question of target frequencies again, as that effectively halfs the "pipe diameter" in that area. It also brings up a question of how much rotation is there in the flow of the exhaust gasses and would this kill that... and if it does/doesn't is that a bad/good thing?
TIA
-Michael McCoy
Most of the muffler designs I am investigating are "straight through" designs, perforated cores with some sort of packing material around them. The first (and perhaps biggest) question I have is how does the length of the perf tube effect the attenuation rate. The next is how does the shape affect the attenuation as well. I *think* the can shape around the perf tube would effect the target frequency. (or would that be mostly the hole size in the tube??) So something like an oval shaped can would then theoretically have a broader spectrum it effects than a round can. am I on the right track here?
The next big catch is something like a borla XR-1, which is a straight through perf core in an oval tube, but also has a sheet perforated metal dividing the middle of the perf tube as well. This brings up the question of target frequencies again, as that effectively halfs the "pipe diameter" in that area. It also brings up a question of how much rotation is there in the flow of the exhaust gasses and would this kill that... and if it does/doesn't is that a bad/good thing?
TIA
-Michael McCoy





RE: Muffler shape/design, flow, and noise?
Check out this Naca report on muffler design. It's pretty old but there is lots of information.
http://na
Shane
RE: Muffler shape/design, flow, and noise?
any more input?
Thanks
RE: Muffler shape/design, flow, and noise?
I did one for muffler 19; it came out about 95k, including a graph.
The second one will be much easier.
Mike Halloran
Pembroke Pines, FL, USA
RE: Muffler shape/design, flow, and noise?
I would say that the shape of the chamber (oval or round) has significantly less effect that the area and the length. There are some corrections,etc for shapes other than round tubes, but I don't have them in front of me. You can find LOTs of SAE papers on this stuff, but it sounds like you're on the right track for a basic analysis.
Shane
RE: Muffler shape/design, flow, and noise?
RE: Muffler shape/design, flow, and noise?
In the case of a pass tube that is perf'd its entire length, the silencer then behaves pretty much like an expansion volume, tuning primarily at a frequency corresponding to quarter-wave theory. That is, it will tune at odd integer multiples of the frequency determined by 4 x (four times) the silencer length; i.e., for length L, it will tune at nc/4L where n = 1, 3, 5...
Shorter lengths of perforation modify this behavior substantially.
There's an SAE paper detailing this, probably 15 or so years old.