Acoustic Dynamics

On a generic completely open exhaust system: If one wanted to keep the loud clear overrun crackle from the exhaust but reduce the excessive booming low down bass sound around 500-2000 rpm, would it be adviseable to:


Place a small muffler on the central section of the exhaust, or place it at the end?

All other things being equal.

 

It's been my experience that the resonators at the end of the system smooth out the sound taking away highs, but not change the character of the sound. A second muffler/resonator or enlarging the primary can will change the character of the note. There is also the real effect of resonant harmonic dampning: two mufflers each of volume x in series will dampen more than one single muffler of 2x.

Good luck!

 

What kind of car? My 275 GTB had straight pipes with Snaps and was not excessivly loud.

 

Acoustics are a bit of a black art IMHO. What you want, from a tone perspective, is essentially a noise filter. That is, you want to dampen the low tones, and let the high notes pass? I might try a large baffeled chamber that hopefully will dampen the low notes but let the high notes pass?

Bill

 

Thanks guys.

The car is an Alfa Romeo 916 V6 24V. The current setup is straight through from the cats back.

Here are some sound clips:

http://www.youtube.com/watch?v=D9XYgecvbVY

http://www.youtube.com/watch?v=enZ6oBcqfIk

http://www.youtube.com/watch?v=1Ef2846SvYI

This is the setup: rear of car is top of image:

http://www.plaatjesupload.nl/bekijk/2008/07/19/1216434393-81.jpg

I tried the standard (large) muffler on the centre part (gold coloured pipe) It killed the sound completely.

Now I'm wondering how to use perhaps a smaller muffler (your advice is again on the centre?).

Wonder what the difference is between a short fat muffler:



and a long thin one:




PS: Whats a large baffled chamber?

 

There are basically two types of muffler commonly in use in modern sports cars. The absorptive type, which has a fiber absorptive material and the other is an hollow can ("acoustic box") with baffles to muffle the sound by internal reflection.

Personal opinion only here: the baffled mufflers all sound higher pitched and tinny to me.

I love the Alfa engine and it is traditionally held to be one of the best sounding. Depending on what you want, I think a absorptive muffler of about 14" length and then smoothed out with a tip resonator will give a very aggressive sound, but be quite toerable around town and on trips.

 

1. On the centre or on the rear of the car?

2. Whats a tip resonator?

3. I understand that absorptive will give a deep sound, I'm wary of it sounding like the souped up CRX crew around idle though. I love the way Unicorse sounds for example but they are far too expensive.

4. 14 inches. This is in accordance with advice I heard on other forums that longer cans will kill low down bass and leave high frequencies alone. (as opposed to short fat cans).

 

1. Center
2. Like an Ansa tip or others - one that has some fiberglass packing in it
3. Understand your concern exactly; it won't.

Here is a short video of a Mondial 3.2 with each side going through two 13" absorptive mufflers in series, no side to side mixing, followed by a resonated tip. The car had new carbs which had not been synch'd yet, so it pops just a little. It is much smoother now:

http://www.youtube.com/watch?v=j18BmXoP9kE

Here is a schematic and a photo of the system:
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Thanks alot.

I'm collecting info around the 'net. I'll try and keep you updated.

 

thanks - I am always up for learning more.

 

I have the factory Challenge exhaust on my 355CH which is an open exhaust. I inserted header baffles in the upper and lower pipes and it removed the low pitched resonance at the 2500-3500 range. Still quite loud but without the resonance.

 

What is a header baffle?