So I got a great deal on a used svrtech 2.5 td exhaust system from a local fellow just recently and have been enjoying it for some weeks now. For those that aren't familiar with the system it runs from header collecter all the way to tips using test pipes, xpipe, aero resonators, and aero mufflers.

Everything about it is great but due to the test pipes and the fact that aero mufflers don't do much in the way of sound deadening it's pretty beastly. So I have been planning to weld some resonators into the 16" straight portion to eliminate the bit of rasp and cabin drone I'm hearing but reasearch I've been doing into the use of resonators seems to say that it will only deal with the higher frequencies. Ie rasp. With 75% of my problem being drone should I be looking into a small straight thru muffler or would the longest I could fit resonator get me where I'm trying to go? Also another option is to get two magnaflow universal HFCs to weld in. I fear that would make it too quiet though.

I'm not looking for anything near stock quiet but I'd be bummed to go through buying and welding res.'s in and not be happy with the results.

If anyone who has done this could chime in it would be great.

Thanks much

 

Sure. You can add resonators or mufflers. Whatever will fit.

 

Indeed what I'm getting at is whether resonators will reduce both rasp and drone or just the former.

 

dont buy a exhaust if u dont like loud.....dam noobs....weld in more mufflers would quiet it down more then a resonator would....

 

Brilliant input thanks. Really looking for someone who's welded extra resonators in to advise the level at which it quieted what part of the exhaust note down. Afraid HFCs will quiet it down too
much. Plenty happy with loud but when I can't talk to my lady over the drone and I can spend 60 bucks to fix it why wouldn't I?

 

The best drone killer that I've encountered (that doesn't provide resistance to flow like a chambered muffler) is the hemholtz resonator on the MD shockwave 2 axle backs. You could consider that? Perhaps Tony will chime in regarding resonator vs muffler vs other to help kill the drone... He might be willing to sell you just the hemholtz resonator that you can add on to your own exhaust.

 

Smart idea! Hadn't considered it. Your right though. I wonder how precise the specs are on them? If it's just a basic idea and doesn't rely too heavily on exact bends/dimensions I don't think it would be too hard to fabricate one.

 

You can't just weld in a helmholtz resonator anywhere. Due to the nature of acoustic waves and phase cancellation, they work at a specific frequency based on its location along the exhaust pipe. Not to mention the physical dimensions and resonances characteristics of the resonator itself.

A muffler is just another type of resonator. Straight through mufflers are nearly identical to perforated core resonators, only difference being exterior dimensions and internal volume. OEM mufflers are unique in their design, usually utilizing specific volume chambers to get favorable acoustics, along with more pedestrian methods of sound deadening (perforated core tube, non-line of sight, muffler packing).

Proper volumed chambers and branch style helmholtz resonators are the best way to achieve what you want. However, it is not the cheapest, shortest, easiest or the simplest to approach. Generally, it takes a lot of measuring, testing, followed by calculations, building, experimenting, building again, etc... Typically the type of job an OEM would do for a prototype model.

Drone is cabin specific. The volume of the interior cabin resonates at certain exhaust frequencies. It's no coincidence that most droning exhaust cause it over a similar RPM range. The "boominess" associated with it is usually heard inside only, and is amplified to passengers. It's not nearly as offensive when heard from outside.

 

Right on TK. You nailed it.

OP, adding a resonator will reduce the high frequencies and some midrange frequencies, but be careful.... they can sometimes induce or increase low frequencies (IE drone).

Experimentation is the only way you can really know what the results will be.

It is possible however that the addition of LARGE mufflers near the back of the exhaust will reduce (but not eliminate) drone.

Experiment!

 

Thanks all for the advice. Precisely what I was looking for. Climbed
underneath last night and found a portion of a pipe was slightly touching the center cross brace. Can't beleive I didn't realize it before. Gonna strap that up today and weld in two resonators I picked up. If that doesn't do the trick I've heard good things about the application of heavy felt and certain dynamat type material to reduce in cabin drone. Think the lot of it should be plenty to remedy the problem. Thanks again.

 

Since the amount of drone is proportional to the sheer amplitude of the offending wave, drone can be reduced by means of an overall dB reduction. When measuring with a sound meter in the cabin, the frequency band of interest will still be amplified when compared to the rest of the spectrum, but its net volume will be lower.

The "big" muffler at the rear works well too. Aside from packaging, it's one of the contributing reasons as to why the OEMs place it there.

 

How did the two resonators help you out?

 

I was in the same boat, and decided to sell the exhaust rather than fix it.

The problem is, as TK & Hydrazine have mentioned, is that it's a guessing game when simply "adding a resonator". You're spending money w/o knowing if you're actually going to make it worse!

The best option is to buy an exhaust with a built-in resonator(s), as there is likely to be some science behind the size/placement, rather than simple guessing. Your best bet is to therefore hear the exhaust in person before buying. Youtube can give you a general idea of the tone of an exhaust, but is severely lacking in areas like drone & volume relative to the outside world.

 

Has anyone tried a moroso spiral flow resonator? How do these work in terms of reducing drone & unwanted rasp?

 

It does not have to be a guessing game. Take a recording of the drone/exhaust and then analyze it with a (free) spectrum analyzer on your PC. Identify the problem frequency. Many have had success with adjustable 1/4 wavelength resonators or side branch hemholtz resonators for killing drone. It does take some experimentation in choosing the correct dimensions but if you set up a clamp based system properly, you should only have to weld in some tee junctions once.

I believe this statement is incorrect. Placement of the helmholtz resonator is not as critical as you imply. The nature of the low frequencies targeted call for very long wavelengths. If you look at the mathematics involved you will see that the factors involved do not include placement along a duct. The Helmholtz frequency is proportional to the square-root of the quotient of aperture radius and cavity volume. The Helmholtz frequency of a bottle–shaped resonator is already well predictable taking into account only the kinetic energy of the air inside the duct.

 

There is a more scientific approach to this. Instead of estimating where to place the helmholtz pipe, the the drone frequency you want to cancel out and then it comes down to the length of the neck, size of the chamber, and the placement.