I've been thinking about how to reduce the "packyness" of my exhaust system. It has too much high pitched snap -"Cherry bomb" sound, and not enough bassy rumble. I have an idea about cutting a 2.5" hole in exhaust before the muffler, and welding in a 2.5 inch pipe that goes to another muffler, which is capped and a dead end. The function of the auxilary muffler would be to absorb the energy that makes this annoying sound. KIND of like a x-over pipe does, but this would basically do this by providing "space" or volume in the exhaust system to absorb energy.

SO I was telling a friend about this idea, and he said, "Oh, I've heard of that before. Except you don't use an extra muffler, you just weld on a section of pipe that dead ends. It's called a '1/4 wave pipe'."

Anyone heard of this? If so are there any formulas to figure the length and diameter of this pipe? Please comment...

-Tom

 

Anyone?

I'm thinking that another muffler that is capped will work better than just a piece if dead-end pipe.

-Tom

 

The main "problem" is, you're talking about "¼ wave"; but any given piece of pipe is ¼ wavelength long at ONLY ONE RPM.

Meaning, tuning an exhaust system that way, only works AT ONE RPM.

Kind of like TPI runners, that only reinforce at their one ("tuned") RPM, and are more or less transparent at all RPMs lower and an "anti-forcement" at all RPMs higher than that ONE (3600 RPM in the case of TPI).

¼-wave stubs are very common in RF systems. Look around at any broadcast or other high-power radio transmitter, and that's what you'll see used as a 2nd-harmonic filter in almost every one. But that's because transmitters usually operate at, or only within a very narrow band of, one frequency (the electronic analog of RPM in this case).

A shorter stub might get rid of that obnoxious glass-pack type of sound that some exhausts make. If you use some sort of a real-time audio spectrum analyzer to determine the primary frequency components of the sound you want to get rid of, and then tune the stub to that freq, you might be able to do some good.

Calculation is super easy; once you know the frequency, you calculate the wavelength by the formula

velocity = wavelength x frequency

Where velocity is the speed of sound, which is about 332 meters per second; and divide that by 4.

 

Thanks for the good reply.

I THOUGHT it was a "tuned" concept when I heard the term "1/4 wave", but since I was explaining a chamber that absorbs sound to my friend, I thought that maybe he was on the same page as I, but he wasn't I guess.

SO...this brings me to my next question. Forgetting about "tunning", can I just put on a junction, and another muffler that's dead-ended, in an effort to absorb sound? Will that work? I imagine that it will be SORT of like a H-pipe; It will allow the exhaust system to "see" space that can abosrb sound waves somewhat.

-Tom

 

Well...I think I'm just going to go ahead and try this, and see what happens. I'll report back.

-Tom