Wrapping muffler to reduce resonance
 

I own the first Deluboz (Che) muffler from three or four years ago... sounds glorious with the top down or at the track... as long as you don't hang out in the 2-3k rpm range. I'd just avoid that range altogether, but it's quite a bit of extra work, requires staying in a lower gear most of the time around town, and it's really starting to annoy me.

Someone on the board suggested using header wrap to wrap my twin muffler chambers in an effort to reduce cabin resonance. Before I haul off and buy the stuff to do this mod, I'd like to know what other board members think or have tried.

What causes resonance? Will wrapping a muffler chamber with something fireproof and dense cut down on the resonance?

Resonance occurs when the exhaust pulses match the frequency of the return pulses within the muffler. It isn't a resonance of the muffler itself where changing it's mass will help. It's all internal to the muffler and external wrap won't help.

+1 The resonant frequency is determined by the length, diameter, volume, and internal design of the exhaust system. It's a lot like a musical instrument. You could attempt to mute a trumpet by wrapping but it wouldn't do any good either. Now put a mute in the bell and you change the resonant frequency. If you could interconnect the separate mufflers to get wave cancellation at 3k hz... sort of like a stock one. That would work.

So you guys are saying throw a pipe in the middle to connect the two cans together on Che's exhaust?

http://www.topspeedauto.com/ProductC...orsche-986.jpg

Looks like there is room to do it...

A cross over pipe might reduce the drone, but will likely not eliminate it completely without doing some R&D to determine location, diameter, etc.......

I have a simular exhaust set up ( stebro) that has a cross over pipe on the tail pipes right around where the bracket is on your system. Still has lots of drone. Didn't seem to solve anything

Just adding a cross pipe without tuning probably won't do much for you. The chances are the same that it'll get worse (low chance either way).

Dyna-Mat your interior, Randall. She'll be heavier, but she'll be quieter. :troll::dance::rolleyes:

Is resonance a noise or a vibration being transferred to the cabin where it turns into noise?

Not to get super technical and nerdy, but noise is essentially a vibration.

I'll take this off of me for a second. Let's all read a bit, shall we?

Resonance - Wikipedia, the free encyclopedia

I'd say it could be a combination of mechanical and acoustic resonance. Al you have to read is the initial set of paragraphs and the first set of examples after the break, unless you want to read the whole thing.

Basically, the car is a big speaker and if it's vibrated at the right frequency, you get booming. The pulses of air moving in and through the muffler are at the right frequency and amplitude to excite the entire car.

Yep, take a 1/2 full bottle of beer and blow across the top until it sounds a musical note (you know you have done this). You just found the resonant frequency. Drink some more beer and blow across again. Now you have a larger air volume and lower resonant frequency (deeper note). Finish the beer and shove cotton in the bottle until it no longer sounds/resonates. Now you have dampened the resonant frequency of the bottle.

Most aftermarket exhaust systems use larger diameter pipes and less dampening than stock so the car sounds bigger, deeper and louder. Few spend much time tuning the system to dampen out those resonant drone frequencies. Porsche and Fabspeed do a pretty good job at minimizing nasty 3k resonance through their exhaust system tuning and design. I don't know many other aftermarket systems who do it as well.

Could it be that they've changed something in that muffler? I installed mine maybe 2 weeks ago and I don't have any issue with resonance in the 2 to 3k range, whatever the gear.

It could be that the novelty hasn't worn off yet, but I had a 3 hour highway drive back from TWS over the weekend and I didn't find the noise intrusive.
Of course if I did, I would just crank up the stock Boxster stereo and cover that noise! LOL

Dynamat, or any of the knock-offs (JC Whiney actually has a good one), does a nice job. While I had my trans out last winter, I put a layer between the heat shielding and the floor of the trunk. If the engine comes out, I'm doing the inside of the engine compartment. Seems that if you get the dampener between the sound source and the car body, it works better then if it's applied on the inside of the car.
I've got headers/no cats/Borla and the carpet and factory sound deadener is gone. It's loud but liveable. And light. And fast.