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locating the bridge

Discussion in 'Luthier's Corner' started by Milothicus, Apr 29, 2002.

  1. where in the bridge's forward/backward saddle movement should the scale length be? do i put all the saddles at around their centre point and make that the scale length?
  2. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Owner: FBB Bass Works
    I generally place my bridges so that the saddle is under the scale length when just about adjusted closest to the front of the bridge.

    Rarely does a saddle need to be bumped to shorter than scale length to intonate a bass, at least in my experience. I'm sure there's a physics lesson in here somewhere.
  3. assuming that's true, here's the reason i came up with off the top of my head:

    the reason intonation goes bad is that as the string is being pushed down, the tension increases. if the frets moved up to the string (so that the tension of the string didn't change) it wouldn't be needed. To counteract that, we lengthen the string slightly to bring the pitch back down. you never need to shorten them, because fretting won't ever lessen the tension, dropping the expected pitch.

    it might make sense, because the thicker strings may not be as sensitive to changes in tension, so the change in pitch from fretting wouldn't have to be compensated for as much.

    no idea where this came from, just an idea.

    thanks for the help, by the way.
  4. neptoon

    neptoon Supporting Member

    Jul 25, 2000
    Melbourne, FL
    hey, that's one of the underlying principles of the buzz feiten tuning system...except, i believe the nut is pushed back a little.
  5. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
  6. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    Actually, I think the nut is pushed forward a little. (Or maybe we're meaning the same thing, but phrasing it differently.)

    The nut is a little closer to the 1st fret. This way, the fact that the tension goes up, increasing the pitch, is made up for by the fact that the speaking string length is shortened by less than a full fret length.

    This is the principle of a compensated nut, which has been used on guitars for years. There is a link to a site explaining it, I think in this forum
  7. michael tobias

    michael tobias MTD

    Mar 21, 2002
    intonation is an interesting thing....it changes as the strings wear out and the frets wear down. It also can change when the neck moves, changing the action height.

    The reason you compensate the bridge is this: when you press a string to a fret, you are actually stretching the string. The distance form the witness point for the fretted note is longer than the same piece of string that is not pressed. From geometry we know that the diagonal distance across a rectangle is greater than the horizontal distance.....a fretted note is the diagonal distance...in order for the note to be correct, you must move the saddle back from the theoritical point of intonation to compensate for the strecthing.

    When the mathematical placement for the notes was figured out it was done by moving a witness point along a string length. The point was just in contact enough to make the note without putting any real tension on the strings. Since there was no stretch or tension applied to the strings, adjustment for intonation was not necessary.

    There are lots of tuning methods that try to make instruments play in good tune. The traditional way of setting bridges on most stringed, fretted instruments is double the distance from the nut to the 12th fret and to allow about 1/16" added for the treble side and about 3/16-1/4 for the bass side depending on the string gauge. other variables include tapered core strings vs. full cores. On most instruments the closer you get to the center of the neck, the more in tune it sounds.

    When the note formula was concieved it did not allow for end tension. That is the fact that it takes more pressure to press a string down closer to its end point than it does in the middle....thus stretching the string more out of tune in the first positions...making it sharper than it should be.

    There have been several attempts to compensate for end tension. Excuse the plug but Buzz Feiten's system is my favorite. It is done by shortening the distance from the nut to the first fret and then you have to intonate the bass differently than tradition dictates...but it works.

    If you don't have BFTS, then using a 0 fret or having a tech very carefully cut the nut to a finer tolerance that factory settings will help the 1st position tuning, but it does not make it quite right. We have all learned over the years to accept certain anomolies in tuning and deal with them by shanging the tuning slightly for a different key or pulling the string slightly to make the intervals seem more in tune.

    Sorry for the long post, I seem to be rambling a bit...it is late and I am beat. I hope some of this helps.

    Peace, MT

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