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adjustable bridge symmetry

Discussion in 'Setup & Repair [DB]' started by greitzer, Aug 23, 2003.


  1. Having read people's posts about the heights they set their strings at, it seems like a lot of bassists adjust the two legs, or posts, of their bridges to different heights. Say, the leg under the E and A strings is set at one height, while the leg under the D and G strings is set at a different height.

    I recently read on somebody's website that you shouldn't do this, because it creates uneven pressure on the table. It said both legs should be set with the same amount of threads showing. Currently I have the two legs on my adjustable bridge set at different heights. Is this really dangerous?
     
  2. Pacman

    Pacman Layin' Down Time Staff Member Gold Supporting Member

    Apr 1, 2000
    Omaha, Nebraska
    Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification
    I'm not going to claim to know the answer to this, but at least for the reasons you've heard, I'd think not. Raising the bridge will not create more tension or pressure, once the strings are tuned to pitch. If there were more pressure (tension) the bass would be out of tune.


    Or, I could be wrong.
     
  3. erik II

    erik II

    Jul 11, 2000
    Oslo, Norway
    I'm no expert...

    But if one leg is adjusted a lot higher than the other, the bridge will tilt and put more pressure on the lowest side. Also, inside pressure from the wheel rods may cause the feet or bridge to split.

    I don't think just a little height difference will do any harm though. But it's better to have the string grooves filed and bridge top curve adjusted to obtain preferred string heigths.
     
  4. Jeff Bollbach

    Jeff Bollbach Jeff Bollbach Luthier, Inc.

    Dec 12, 2001
    freeport, ny
    Erik is right, a little bit of diff is not dangerous. [but not recommended] How much is a little? Well, if you look at the legs and can see an obvious difference than it is probably too much. If close examination is needed or counting of threads then you're prolly OK.
     
  5. Thanks for the advice, folks. I will readjust my bridge so the two legs are equal, or at least nearly equal.
     
  6. Thor

    Thor Moderator Staff Member Gold Supporting Member

    I really don't believe that the height adjustment will affect the 'pressure' gradient that much.

    From a physics point of view, the downward force exerted by the string in the perpendicular plane
    i.e. 90 degrees to the string is only incrementally changed by the height adjustment. The corresponding change of de-tuning it relieves some, if not all, of this increased pressure in the perpendicular vector.

    You can measure this, I suppose, but I would suspect that the final pressure differential is marginal, and becomes ultimately a matter of personal preference.

    My violin players and scientists 2 cents worth.

    Thor
     
  7. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Consider the extreme cases: With the bridge at zero height, relative to a line drawn between the nut and tailpiece, the downward force is zero. As you raise the bridge the downforce increases, as as you apprioach an infintely tall bridge the downforce approaches the string tension.

    Of course not many of us use infinitely tall bridges, but there is a definite change in downforce as you change string angle, which is why luthiers sometimes raise the end of the tailpiece to reduce the downward force. Saying the change is "incremental" is of course true, but doesn't really quantify it.

    As for the matter of different heights on different sides of the bridge: At a minimum it'll make the adjusters bind as they are forced to accomodate the change in angle. Better to reshape the bridge.