[ucsbwsr]

Greetings Gentlemen,

My goal is to start a thread where we can collect data and results from people who have experimented with either Branch or Helmholtz resonators. There inevitably will be some variation as people will start with different exhaust systems and run resonators in different locations but since we are all of the N54 family hopefully we can notice some commonalities which will make this endeavor easier for fellow members.

I personally am suffering from some drone with my custom exhaust system and am looking into solutions. Branch and Helmholtz resonators are very effective at eliminating drone if installed correctly but the data collection, calculation, and fabrication can be challenging and may vary results. These types or resonators are seen on aftermarket systems in the JDM world and are also integrated into many factory and aftermarket exhaust systems (Helmholtz resonators can be included as part of the muffler's internals).

For those who are unfamiliar with the function: these resonators are typically closed at one end, allowing the sound waves from the exhaust to enter, rebound off the far end, and cancel out incoming sound waves (assuming the dimensions of the resonator are correct). In addition, since most are closed-ended resonators exhaust flow is not negatively effected and they can be built for a fair price which makes them a great value. A cool feature of branch resonators is they can be placed in different locations and since they are only collecting sound waves they do not need to flow "down stream" with the exhaust; they can point forward, be bent, be spiral, as long as they are the correct length and diameter they should work. This flexibility makes them very appealing for vehicles like ours where space is limited.

Branch resonators are typically a capped tube where Helmholtz resonators are a canister or a larger chamber; branch resonators are easier to calculate but Helmholtzs are capable of cancelling a wider range of frequencies (this is my amateur understanding). For a greater explanation please check out the links below and ask our good friend Google.


Here is the data that would be useful to collect (the more the better):
- What was your exhaust system pre-resonator?
--- Pipe Diameter?
--- Cats, Resonators, Mufflers?
- What RPM range did you experience drone? *
- Where did you locate your resonator(s)?
- What was your measured exhaust temp at that location?
- What was your end equation?
- What was the design/specs of your resonator?
- What were the results? *
- Please share any pictures or video footage

* If you have any analyzer graphs of before and after please not the program used and the results.


Below are some useful links on the topic and some photos showing the difference in the resonators.

Evan


http://mkiv.supras.org.nz/articles/exhaust_drone.htm

http://www.e90post.com/forums/showthread.php?t=844032

http://www.e90post.com/forums/showthread.php?t=838213


BRANCH RESONATOR


HELMOLTZ RESONATOR

['___']

Resonator location with respect to distance from the engine is also important in calculating what size chamber is needed.

[CannonFodder]

Glad to see people are still working on this. I have contributed to he maths in the other threads. If anyone has any questions let me know.

[C.Pop]

Rather than compile data, which is useful but maybe not as much of a step towards resolving your problem, why don't you get this mic:

http://www.parts-express.com/dayton-...droid--390-810

And purchase something like "audio tools", which has both an RTA (yawn) and a FFT (yahoo!).

It is extremely easy to identify that frequency(ies?) that are the issue. Then go into the math world and start fooling around to reduce/eliminate the resonances.