Resonance tuning
 

Started installing a Magnaflow catback on the MS3 and in spite of reading here that this is one of the least loud exhausts, the drone was absolute eye socket rattling at anything lower than about 3500 rpm. This with catless DP and TP.

Proceeded to install one of the short Vibrant resonators to try to get rid of the drone. Installed it just after the TP. It helped a tad at rpms lower than 2800 but not much. At anything higher than that however, the drone starts fading away and it also lowers the exhaust note at WOT. Cruising at 3k rpm is actually tolerable now. Just about the same as stock.

Researched a little about resonators and drone and it appears there are lots of factors at play. A long, straight, section in the exhaust will apparently increase the likeness of drone. The location of the muffles in the system also has an effect. The magnaflow set up has the muffler a little front of the rear axle. Then, there are other options such as terminator boxes that some use on dual exit systems.

Has anyone successfully shifted unwanted resonances from the lower rpms to the higher ones?

What I am looking for is an increasingly louder tone after about 3.5K rpms and as little drone as possible in the lower rpm range. What can I do to shift it that way?

Just have a Helmholtz resonator welded in.

put a cat in. removes the raspiness and adds more growl.

Where?
Already have a resonator after the test pipe.
Don't think resonators cure the low rpm drone. A dump, or side chamber, or exhaust dump pipe might.

By raspiness do you mean low rpm drone?

Helmholtz is a completely different resonator type that's welded in perpendicular to the exhaust piping that cancels out the drone frequency. When you blow across the top of a beer bottle it gives you a different sound depending on how much volume of air is in the bottle. Once you know what the drone frequency is you can do a math calculation to figure out how long the resonator piping needs to be and have it welded in. Then as the exhaust gases flow over the Helmholtz piping the drone frequency will be canceled.

Here is an example of it being used in an aftermarket application.

http://i79.photobucket.com/albums/j1...W_Hemholtz.jpg

They are also used in OEM applications such as the OEM S2000 exhaust.

I have just CS downpipe and midpipe with a magnaflow cat in the midpipe with the stock catback. so I can't comment much on messing with different catbacks, but I have no drone, or atleast none that bothers me at cruising speeds.

Pipe diameter and length play a role in resonant frequency (e.g. a pipe organ). Generally speaking, the larger the diameter, the lower the resonant frequency. Plus, lower frequencies tend to be "felt" more than higher frequencies, so the perceived effect is drone.

That said, I ran the UR resonated test pipe for a little while with a UR DP and CBE. It REALLY tamed things down, to the point where I thought it was *too* quiet, lol. I believe @specvspeedfreak had it installed for a bit and experienced the same thing. It might be worth checking out.

since you have been hacking away already with your exhaust, call up racing beat and order just he muffler from the cbe system (it's like $130) and replace your magnaflow muffler with it (placement of the muffler sounds like its the same).... My gen1 setup was catless dp, stock piping (all resonators removed) and the RB muffler...It's a really nice drone free exhaust..Before that I had stock mufflers and front resonator removed (too much drone but great sound..

If the RB muffler becomes too quiet for you I guess you can remove the vibrant resonantor lol...

UR resonated TP cuts down the noise alot as well.. It takes away the gurgle, I really dont recommend it unless you intend running running muffler-less.

From my experience the issue with adding cats, whether in TP or DP location, is that they will overall dampen the note of the exhaust. What I am trying to accomplish is a low noise level / drone free note up to about 3.5K rpm and then progressively louder.

The inline resonator after the TP actually didn't shift / elimnate the drone, It dampened the note in the higher rpms. At least that seems to be the case on this platform with 3" piping and the magnaflow set up.

The Helmholz resonators look very similar to what other call "exhaust dump pipes" or side chambers. Now, in the pic from Tripplejumber they are located just before the muffler. On the system below for a G37 it's right by the DP.

Before I lower my self esteem even further trying to attempt to calculate where the ideal place is to locate the side resonators, is there a generic rule of thump as to where the note will shift depending on where you install the side pipes?

I am going to experiment a little with this. If the results are bad I'll just add a CAT somewhere. Changing the muffler would be the last thing I do if all else fails.

http://image.modified.com/f/30056741...7+close_up.jpg

RB muffler is exactly as you described you want. Why go through putting in side pipes?You will just be experimenting at that point.. I have never seen it done on a 4 banger....The problem is the muffler. Get a known quieter muffler and you will be happy. Hence the reason why I recommended RB. ...and it's easy too, 2 cut 2 welds (as long as the muffler length is same)

subbed for info on resonator/muffler options since when I did test pipe I discovered both my stock resonators were gutted before I bought it lol.

I have a feeling that had a big effect on volume versus removing second cat and still having 2 resonators in the way...

The Helmholtz resonator will eliminate the drone frequency. I will be doing it to my car hopefully this summer.

What's the range of cost to do this?

Not that much but I'm not sure of the exact price.

tell them you'll send business there way if you give them a discount, i'll probably be interested in doing this. I feel self concious when I start my car in the line to pick up the kids when the doors open haha.

MILFs not impressed by loud, sexy exhaust???

Ah, they're going to a catholic school.

They only impressed by jesus fish.

And Volvo's.

I have plans for enhancing my mommy mobile though, so maybe that will help.

Never dated an older woman before...

I heard the Jesus mod lets you drive your car on water.

header wrap the entire exhaust

mmmm header wrap... ill do that when I put gold reflective tape everywhere so engine bay looks like Apollo command service module. exhaust tip too? (:

http://upload.wikimedia.org/wikipedi...Apollo16LM.jpg

my exhaust is wrapped, it indeed quiets the drone

Did you stop at the muffler? I'll probably give it a try pretty soon if I find enticing prices for that amount of wrap if it is effecitve hehe

just jacked the car up

Whats the ID of the RB muffler pipes?
3"?

Where are you going to put it? And where are you getting it from?
Ebay haz none. lol

Subbed... Studied this a bit in college, and had a real nifty experiment in anti-noise I did a while back. I could make your car black helicopter quiet... It's be expensive though...

Yes, RB is 3 inch

Making it quite overall is not the mission. That wouldn't be too hard.
It's making it quite at low rpms and loud with a nice tone at higher rpms that takes more to it.

I put the 3 inch Vibrant Ultra Quiet reso into the racepipe section, itself, of my TurboXS catless dp/rp to tame the drone. It worked fantastically. But I do have the stock 2.5 inch CBE behind it.

I see no reason OP might not try to add another big straight through open reso either in the racepipe or anywhere else it would fit. You can see right through them - like an open stove pipe with sound absorbing shell around the pipe. Extremely effective for me, while still keeping the growl at higher rpm when WOT.

Tomas, did you ever try this? I'm trolling your threads this morning, lol. Mainly watching videos, but this one looks cool.

There will be standing waves in the exhaust, so you're smart to question "where" the best place is for the chamber. In a perfect world, you'd place it right at the standing wave peak, for the most offending rpm. But this position will change as rpm changes, so you'll never get it exactly right.

You might be able to just listen under the car as someone walks up the rpm, and see if you can find "roughly" the right spot.

After that, it's important to make the chambers "tuneable", so you can vary their length and dial in that perfect null to help dampen the desired note. There have to be some equations on the web somewhere, i've never really looked into it much. But it's an interesting idea.

Wouldn't putting Helmholz resonators (or exhaust dump pipes or side chambers) right after DP will have negative effect performance wise? More exhaust turbulence etc...

If yes, I think it should be added somewhere in the end. Like in this pic:

http://www.planet-9.com/attachments/...n-hks_350z.jpg

BTW this thread some what deals with similar issues. May be useful for you:

Exhaust drone resonator fix - design and construction - Page 6 -

Lol, yeah. I feel like you are stalking me which is both scary and sexually arousing.
I'll do this one (easy) and the LSD one later (harder)

There are shit loads of equations for calculating chamber sizes for helmholz resonances with factors such as air temperature, velocity, chamber lengths and diameters, pipe lengths, yadayada. I looked at them in wikipeadia and promptly decided that I wasn't nearly smart enough to figure out where, in what dimensions, and in what direction I should put the chambers in. Too many variables for mongo.

If one could identify the correct spot in the pipe system where the drone happens I guess you could install a chamber there and then adjust / tune it's volume till you are happy with frequencies that were eliminated at a certain rpm. The problem is that the drone does not really present itself while revving the car at say 2800 rpm. They usually presents themselves while decelerating or accelerating. So when the engine is either in high vacuum engine brake or under load and passes a specific rpm range.

I can not exactly tell you what works - but I can tell you what did not work. Or at least not very well.

1. Magnaflow 3" muffler system with catless DP and catless TP --> the most noise. Drone and vibrations at multiple RPM ranges. Only subjectively nice frequencies at 4500 rpm and above. Anything below sounded like cow poop.

2. Same as above but with bullet 3" Vibrant resonator --> less noise overall. Less drone at cruising rpms but still some drone between 2600 and 3100 rpm (cruising RPM for me in 6th gear) Very nice high rpm / wot frequencies.

3. Same as above but now with metal core catted Ultimate racing V2 DP --> less noise overall (not what I wanted). WOT frequencies not as nice (subjective I guess) as in #2 . Still some drone at 2600 to 3100 rpm but less than in #2 .

4. Same as above but now with flex coupling and V band where the 2 3/4" pipe used to be. Yeah - there is a section in the magnaflow system right after the test pipe that was 2 3/4" which is bullshit --> No difference at all. I though it might function as a resonating chamber but it did not.

5. Instead of resonator after test pipe / before muffler I installed the resonator past the muffler where the exhaust tip goes ---> No difference at all. I had read in the always true and reliable interwebz resonator after muffler works but IMO it does not. At least on the MS3.

If I had to do it over again I would NOT get the catted DP. Instead, I'd get the ultra quite Vibrant resonator. I haven't personally heard it in action compared to the standard resonator but I spoke to Vibrant and they said the ultra quite one will achieve exactly what I want, which is low noise levels at low rpm's and nice crispy notes at WOT. Might still do it someday when other projects are behind me. I think I have enough space where the current resonator is to switch them out.

http://i1211.photobucket.com/albums/...photo-21-1.jpg

http://i1211.photobucket.com/albums/...photo-23-1.jpg

I don't think there is much of a performance detriment with the helmholz chamber. They do not really divert air flow, just cancel out sound waves. It might not be inherently obvious that air does not travel in the same direction as sound. Air has density and travels with a certain degree of inertia in a given direction. Sound does not. It bounces all over the place on all kinds of surfaces and can reverse direction any time.

As to location of the resonator, it'd be interesting to hear what the difference would be installing one in the location of the TP vs. right before the muffler. Past the muffler in my limited experience so far was shown as useless.

I've been tossing around the idea of fabbing an aluminum exhaust for my 6, 4" if possible. I've heard aluminum sounds like shit... so it would be cool to play around with the helmholtz stuff at that time. I've been intrigued with them ever since greg (triple jumper) sent me a link a while back. I do lots of RF at my job, and the concepts are pretty much the same.

I can haz 5" cat back exhaust made?

18" cat back.

Small update on this.
Hated the catted down pipe from UR. Even the V2 with the 600 HP metal core. It just slowed engine response and made the turbo too laggy for my taste. So back to catless DP now. In addition, I changed the vibrant bullet resonator for an ultraquite one. It is overall quiter than the bullet one but still keeps a nice high RPM sound. Not as growly as the bullet resonator but still has a lil meanness to it. Only problem is that the fucker is HEAVY and barely fits over the mid chassis brace.

http://i1211.photobucket.com/albums/...t/photo-59.jpg

http://i1211.photobucket.com/albums/...t/photo-57.jpg

http://i1211.photobucket.com/albums/...t/photo-58.jpg

Just to add to this thread, have you seen CPE's exhaust design for the focus st?

Products | Custom Performance Engineering

Is that an 18" ?

And what made you choose this location? I have been doing a lot of reading myself lately..only to find a lot of inconsistencies..Definitely one of those subjects that is ultimately hindered by the reviewer's ears/intelligence.

No. It's the shorter one.
Chose the location because it was the longest straight piece of pipe in the system.

Ha! Looks like helmholz resonators on the side there.

Dynomax® Performance Exhaust | Mufflers | Dynomax VT? Muffler

It's 9.75" wide, not sure if it'll fit. But, looks and sounds promising.