A Stupid Question of Very Little Import

Discussion in 'General Harley Davidson Topic' started by gasbag, Jun 12, 2011.

  1. gasbag

    gasbag Active Member

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    I rarely ride with others, mainly because I have no friends and no one loves me.:bigsmiley15:
    However, I ride with my son every time he comes down to visit. He has a V-Rod, stage 1, V&H pipes, tuner and dyno tuned. Sounds very good.
    I have an Heritage, same package except SE II pipes. Also sounds very good.

    When we ride together and our rpms get close to each other we get an exhaust sound sort of like a "waaahwaaahwahwahwahwaah" vibrating between us. Kind of an echo sound. It's weird.

    Anyone know what that sound is called and what is causing it? I am curious.

    See? I told you it wasn't very important and yet you read all they way down to here.

    Well, thank you.:worthy
     
  2. av8rjim84

    av8rjim84 Member

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    This is a phenomena in physics called Harmonic interference. Some harmonic interference cancels each other out, like when you put on one of those fancy bose headsets and it cancels out the noise. In this case what you are hearing is an amplification of the sound caused by your two pipes resonating at the same time. Because they are still a little out of phase (not exactly the same and occuring at the same time) you hear that wah wah sound. Some of the time they amplify each other and others they cancel each other. If they were both exactly the same wave form and in phase, you would hear an extremely loud version of each of you, and if they were 180 degrees out of phase and the same wave form, you would hear a much quieter version of the two sounds, as they would cancel each other.

    Correction: Called Wave Interference, not harmonic interference. And it is either constructive or destructive.
     
  3. Rhys

    Rhys Active Member

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    I will take the bait. When I ride with my buddie the same thing happens, and we have actually talked about it. if we run side by side it does the wawawawawa your talking about, but if I change the rpms just a bit it goes away. I belive the two bikes together hides the exhaust pulse that you would hear from just one bike or riding at a further distance from each other. Its blending the two sounds together, thats just my two cents!!:newsmile011:

    Thats what I was trying to say!!!:laugh
     
    Last edited by a moderator: Jun 15, 2011
  4. av8rjim84

    av8rjim84 Member

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  5. opaka lips

    opaka lips Member

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    I'm not sure if this is the same phenomena but I think it is: My boat is powered by 2 outboard engines. I get the same (waaawaaaa) sound if both engines are not adjusted to the exact same RPM. By carefully adjusting the throttle on one of the engines I can eliminate the sound, which tells me that both engines are set to the exact RPM. The RPM guages confirm this. I've never experienced it when riding with a buddy, but will try and achieve the same effect next time I'm riding with a friend. Very Interesting!
     
  6. wilks3

    wilks3 Junior Member

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    Here I thought it was a Beatles song.
     
  7. Alamo

    Alamo Member

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    It is the harmonics of Harley Davidson. It is the harmonics of life. Do not try to understand it. It is mystic. Just enjoy it. Ride easy.
     
  8. gasbag

    gasbag Active Member

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    Thanks for the replies folks. Like I said, it is weird and I was curious.

    There are some smart people in here.
    And then there is me. Oh well, someone has to occupy the right end of the Bell Curve.:bigsmiley22:
     
  9. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    Great advice!

    Bodeen
     
  10. Billbo

    Billbo Junior Member

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    Just about the same as tuning a guitar. Two strings - same note - out of tune sounds like a "wahwahwah" going on when you strike both at the same time -- git ur in tune - the wah wah goes away. Note this wah wah gets faster the farther away from IN TUNE you are and slower the closer in tune you get. Therefore, the answer to you question is simple - get the two bikes 'in tune' with each other and no more 'wah wah' :):):)

    Bill