Absorption mufflers - fine tuning

[highboost]

Hi everybody,

I am working on an exhaust project to release for a popular turbocharged hatch platform.
I am trying to work around the constraints that have been placed (I took over this project from someone else who has since left)
Constraints - the system right now consists of 3" piping from the turbo back, with 3 absorptive mufflers.

I have been trying to do some research on muffler design, and there are a lot of resources out there, however in the interest of time I thought it best to reach out to the community on this one.

Given the 3 absorptive mufflers, what are some ways I can reduce the drone? I understand absorptive mufflers are not very efficient at attenuating the low frequencies.

What would be the effects of:
Reducing the perforated tube diameter ? (in other words, increasing the body to pipe ratio?)
How about decreasing the overall pipe diameter from 3" to 2.5"? How does volume/exhaust velocity relate to the different frequencies?

I appreciate any and all insight! I do apologize it my questions seem a little open ended or not detailed enough.

Thank you

 

[MikeHalloran]

Have you got any instrumentation?
Like a sound level meter, or a microphone and a spectrum analyzer?

You can probably make some progress with a laptop, a microphone, and a software spectrum analyzer. That will at least tell you what frequencies you are trying to tune out.

After collecting baseline data, I'd start removing mufflers one at a time and retesting, to see if any of them are actually doing anything.



Mike Halloran
Pembroke Pines, FL, USA

 

[highboost]

Thanks for the response Mike,

I do have that equipment (although new to me personally.
I suppose my main question was; given an absorptive muffler, what is a way I can increase the Transmission loss on that given muffler?

The resonance inside the cabin right now is acceptable for product release, but with my prior experience and how subjective exhaust systems can be (in the aftermarket) ; I do want to try and tone this down just a little bit.

Thank you!

 

[Lou Scannon]

Have a read through this.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[highboost]

Thank you very much for the information, I really appreciate it.

 

[Tmoose]

The depth of the absorptive layer determines how well it works on lower frequencies. 2 inch is way better tham 1 inch below 1000 Hx.

http://www.owenscorning.com/comminsul/documents/Insulation Specification Technical Data Guide.pdf

I believe if there is much length of pipe after the final muffler then wave action can build up to create new amplified noise.

Is this an inline 4 without balance shafts? It's pretty easy for those engines to get the exhaust system to dancing, and excite body panels. A nice long flexible bellows joint near engine can help decouple things. Or weights on the exhaust system to change pipe system lateral resonant frequencies.