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Acoustic Dynamics

Discussion in 'Technical Q&A' started by gold333, Jul 21, 2008.

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  1. gold333

    gold333 Rookie

    Jul 21, 2008
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    #1 gold333, Jul 21, 2008
    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.
     
  2. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Russ Turner
    #2 snj5, Jul 21, 2008
    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!
     
  3. BIGHORN

    BIGHORN In Memoriam

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    JOHN F KELLY
    #3 BIGHORN, Jul 22, 2008
    What kind of car? My 275 GTB had straight pipes with Snaps and was not excessivly loud.
     
  4. bill308

    bill308 Formula 3
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    #4 bill308, Jul 22, 2008
    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
     
  5. gold333

    gold333 Rookie

    Jul 21, 2008
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    #5 gold333, Jul 25, 2008
    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:

    [​IMG]

    and a long thin one:

    [​IMG]


    PS: Whats a large baffled chamber?
     
  6. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    #6 snj5, Jul 25, 2008
    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.
     
  7. gold333

    gold333 Rookie

    Jul 21, 2008
    5
    #7 gold333, Jul 25, 2008
    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).
     
  8. snj5

    snj5 F1 World Champ

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    #8 snj5, Jul 25, 2008
    Last edited by a moderator: Sep 7, 2017
    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:
    Image Unavailable, Please Login
    Image Unavailable, Please Login
     
  9. gold333

    gold333 Rookie

    Jul 21, 2008
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    #9 gold333, Jul 26, 2008
    Thanks alot.

    I'm collecting info around the 'net. I'll try and keep you updated.
     
  10. snj5

    snj5 F1 World Champ

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    #10 snj5, Jul 26, 2008
    thanks - I am always up for learning more.
     
  11. Llenroc

    Llenroc F1 Veteran
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    #11 Llenroc, Jul 27, 2008
    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.
     
  12. gold333

    gold333 Rookie

    Jul 21, 2008
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    #12 gold333, Aug 2, 2008
    What is a header baffle?
     

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