adis

I built a Helmholtz resonator to address some drone issues I was having with my current exhaust set up. My motivation was to practice on the Olds in preparation for doing it on my Vette when I swap to a straight 3" exhaust. I got the idea from several threads going on at other fora (here's the main one if you want to read my write-up: http://www.camaro5.com/forums/showth...102075&page=14 ) My thinking was that the Helmholtz resonator does not affect flow, only sound; so, in my free-flowing 3" straight exhaust for the Vette, I could have sound/tone control without affecting the flow (like what Corsa has perfected.) On the Olds, I just wanted to get rid of the annoying drone at 110-120 Hz. I don't have a tach, so I can't tell you at what RPM the drone was occurring, but my guess is that it was around 1500-2000. So I did the math as best I could (I'm a mathematical moron) and fabbed the resonating chambers up as best I could (my first welding project). The result was about 5dB drop at the target freq, and some collateral attenuation at what I assume are harmonic freqs. Subjective evaluation (the most important) confirms a noticeable tone change (5dB is a lot of energy). I would say that the resnators made the drone go from being "annoying" to being "present at a narrower RPM band." I think that if I was a better fabricator, and I would have seen greater attenuation, although not as much as to be able to modify the drone freq to the point where it fit in nicely with the rest of the exhaust orchestra. Any way: here are some pics for anybody whose interested. Welcome any criticism - adis

Initial Scope Reading:


Math?, We don't need no stinking math!


Resonators:








The Bottom Line:

nonhog

Nice write up. I love a good tough sounding exhaust but drone sucks.
Which mufflers are you running? Some seem worse than others.
I've yet to finish my 455 to go in my Cutlass at which time I will add my Pypes system w/ Xpipe.
I had a bunch of article on this saved on my computor that crashed the only one I can find now is this.... http://www.hotrodders.com/forum/i-di...ne-154608.html

Yours is far more detailed.
Have you done any Youtube videos?

adis

Sorry, the mufflers are Summit "Fully Welded" Turbos. I really don't like the sound of them from inside the car, but people outside the car have commented that it sounds OK. It's hard to get a recording of the drone since it is most pronounced when the engine is under load (ie. driving around.) For me it's in low gear doing about 20 mph, and in high gear doing about 45 mph (whatever that RPM is.)

Lady72nRob71

Excellent scientific writeup! Nice to be able to SEE how it will sound!