Hey guys,

I know this is a noob questions...but can someone please explain to me the purpose of a resonator on test pipes or on a cat-back exhaust?

Thanks!

 

fine tunes the exhaust note and pitch, helps prevent rasp, etc.

 

Think about it, where is the sound coming from? It comes from the engine. The resonator cancels out nasty frequencies of sound using destructive interference - wave canceling wave in specific range of frequencies, i.e. the ones that tend to produce the most "bad" sounds.

http://auto.howstuffworks.com/muffler4.htm

"...the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust."

That's why a resonator is always larger than the pipe going into it - the size of the openings and overall diameter determine which part of the sound (wave form) is cancelled out. It literally removes undesireable sounds, which is why when you hear a car w/o one, it usually sounds like a chainsaw.

If the high pressure wave is allow to hit the tailpipe unimpeded, the "muffler" (often not much more than a nearly empty resonator itself, w/maybe a perf pipe) actually will amplify all the sounds across all frequencies if the exhaust exit tip is larger than the pipe - megaphone effect. Just listen to a fart can with a 4" diameter tip on a Honda, that's what's happening.

Note how my resonator sits relative to the size of this 2.5" pipe on an Altima, it is about 4" in diameter and the sound quality is night/day without one.

Obviously if you want max flow a resonator isn't helping that, but most good ones are pretty non-restrictive, and the payback in nice resonance in the exhaust sound is more than worth any flow constriction, unless your running a race car. Even then, most tracks today have noise limits.

 

Great explaination! Thanks for your help guys!

 

The stock exhaust has a nice sounds to it....does the OEM system come with a resonator?

 

Poke your head under there and take a peek.

 

Yes, although they (Nissan) calls it a Center Muffler. After the cats, at the base of the 2:1 "Y" pipe there is a resonator/muffler, then the pipe goes back to the main muffler you see at the back of the car.

I agree it does have a good sound, and I hear quite a few compliments on the stock exhaust (ok, it's a little different with an intake) mostly from my BMW/Porsche friends who kind of stare with this "does not compute" look on their face ("Japanese car -> Sounds Good?")

 

So is there a difference between a resonator and/or of a silencer?

I'm thinking about gettin a JIC Ti exhaust with resonator. Since it comes with a resonator, it should reduce the loudness relatively to non-resonatored Jic, right? But can it come with a silencer as well? And will this reduce alot of flow or hp?