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Bridge adjustment question

Discussion in 'Setup & Repair [DB]' started by Chris Fitzgerald, Nov 11, 2002.


  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Now that the weather has been changing down here in KY, my strings keep getting lower and I have to adjust my bridge more often to keep the string height where I like it. I've heard various stories (myths?) about bridge adjusters, and would love to hear the Lex Luthier types chime in on several topics:

    1) "You should always adjust both adjusters by the same amount because x+y= z to the 43rd coefficient" (paraphrase) But what if your E string is at the right height, but your G string is low?

    2) "When you raise the bass adjuster, it actually raises the treble strings instead" Huh?

    3) "The idea of height adjustable bridges is ridiculous because x+y= z to the 43rd coefficient, which will kill your sound" This one makes more sense intuitively, but I'd still love to hear more.


    Basically, what it comes down to is that sometimes my G string seems to be speaking in the correct proportion to the other strings, and other times (usually when it's too low), it sounds too quiet. What is the best way to adjust for this setupwise (besides the obvious, "the sound is in your fingers, man....").

    I'm sure I'll think of more annoying questions, but these will do nicely for starters. :)
     
  2. Aroneng

    Aroneng Supporting Member

    Sep 7, 2001
    Ft. Lauderdale, FL
    1. Raising both adjusters the same amount: If you adjust only one side you are applying a side force to the foot/adjuster. Ex. raise only the treble adjuster. The bass foot is acting like a pivot (but it is not made to be a pivot). Result is side force on the adjuster which acts upon the foot. Too much side force and you will crack/break the foot.

    2. Raising the bass adjuster raises the treble strings: Take a piece of string and hold it between your thumb and pointer finger of each hand (this becomes your bridge without any curvature). Holding the string in a flat plane, now raise your right hand (bass adjuster). The vertical motion of the string increases across the entire lenth of the string with the exception at you left hand (treble adjuster/foot). So raising the height of the bass adjuster will affect the height of the treble strings but to a lesser degree.

    3. No comment. But if you don't have adjusters and the strings are buzzing due to strings height, maybe bridge adjusters are in order.

    Try changing the curvature of your bridge to change individual string height.
     
  3. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I understand that part, but what I don't get is how I can set the curvature of the bridge in one season to get the balance I want and have it be fine, and then when the weather changes, the balance can get all whacked between the strings. It would seem like the strings would all change heights at once and in relation to each other, but it doesn't seem to work out that way. As I said, the main problem seems to be with the G string....it sounds best when it's at about 6mm (or 1/4", whichever you prefer). What should I do during a weather change where the E string stays put, but the G string lowers. Is it safe/advisable to raise only the treble side? It's what I've been doing during cold/arid periods, but i want to make sure I'm not damaging my bass by doing so.

    Thanks for the detailed reply. :)
     
  4. sean p

    sean p

    Mar 7, 2002
    eugene, oregon
    my thought regarding 'raising the bass adjuster actually raises the treble strings' is that, as aroneng pointed out, there's a pivoting effect that occurs when one foot is raised. if we raise the bass-side adjuster and it causes a 'pivot' - a movement of the strings not only up but left (looking from above, i.e. the fingerboard), then the treble side strings are now sitting further to the left, i.e. over a lower section of the (curved) fingerboard. this could increase their height off the fingerboard just by moving them to the left.

    conversely (since algebra i never know if it's conversely or inversely) this will cause the bass-side strings to be incrementally lower due to their moving (left) toward a higher portion of the (curved) fingerboard.

    i mean, if we really wanted to know we'd just get out the damn ruler and putz around with the things for a little while. :)
     
  5. I have heard of people having a bridge for summer and another for winter. However we have a pretty drastic change in temp and humidity here in Minnesota.
     
  6. anonymous0726

    anonymous0726 Guest

    Nov 4, 2001
    The 'string theory' works with a flat bridge. You have a situation where you have to matched curves. When you raise the bass adjuster, the E string moves up and toward the middle of the fingerboard. The G string hieght stays pretty much put, but moves away from the center of the fingerboard. Being that the middle of the fingerboard is higher than the sides, the net result is that the E string gets lower and the G string gets higher.

    The easiest way to study this (make sure no one is around :)) is the place your hands in such a way to represent the two curves. And study the movement. Remember, that since you are only moving one adjuster, the side that you're adjusting doesn't go straight up and down, but makes a bit of an arc.

    Getting the bridge too out of whack will put funny stress on axles of the adjuster, which will be trying to split the bridges parts open. The adjusters aren't fit with extremely tight tolerences, plus wood will distort, so there is some room for play.

    The 43'rd bit is beyond me. No help on that from me.
     
  7. Aroneng

    Aroneng Supporting Member

    Sep 7, 2001
    Ft. Lauderdale, FL
    I would disagree that as you raise the bass adjuster that the net effect is lowering the E string (closer to the fingerboard) and moving the E string closer to center. Yes I agree the E string is moving closer to center of the fingerboard. But most of the movement is going to be in the vertical direction so the E string should be raised further away from the fingerboard. The side movement caused by the arc is little until you raise the adjuster large amounts.

    Bridge adjusters will vary depending on who made them. I mean the diameter of the threads and their pitch (how many threads/mm or threads/inch). So if you have fine threads, one turn of the adjuster will give you less vertical motion as compared to a coarser thread. How far can you go? Depending too as Ray said on the fit of the adjuster in the foot. You have some room to play with. Rather not experiment to the extremes.
     
  8. Jeff Bollbach

    Jeff Bollbach Jeff Bollbach Luthier, Inc.

    Dec 12, 2001
    freeport, ny
    I'm feeling obsolete-some good responses here.

    How much diff between the adjusters in terms of uneven heights? As Aroneg said it depends on the style of adjuster. Basically there are only two. Woods, which all have a large shaft diameter relative to the leg, and metal, which are much thinner. Wood adj. must have a large diameter shaft due to some threading issues. The threads will always be coarse and one turn will raise the bridge quite a bit. The shafts occupy a large % of the leg cross section and any disparity is likely to result in leg cracks. I've seen many. This is ONE reason I do not use them. A quarter turn difference is all I would recommend. As far as metal goes-one full turn diff is safe. Of course, it would always be better to address this issue by changing the bridge curvature.

    Tonal diff twixt solid vs wood adj. vs metal adj.?
    Studies[scientific ones] have been done on this. The results were quite varied. Anecdotically speaking, I've been asking this question for quite along time[20 yrs]. I don't ask it any more. I've been lucky enough to ask this of many accomplished players. Many great players claim they hear a difference-just as many claim not. Bottom line- adjusters are necessary. Wood adjusters have a lot of structural issues. Metal has less.
     
  9. anonymous0726

    anonymous0726 Guest

    Nov 4, 2001
    I use this technique a lot when my bridge get out of whack from many adjustments. If one side or the other seems low, or, differently put, when the strings aren't centered properly (but the bridge feet are where they're supposed to be), E side up to raise the G, G side up to raise the E.

    With the EbolaGatos on, since I have my bass set up for Spiros, I had to raise the G side a bit so that the E and A don't rattle excessively at the height where I like 'em.

    Remember, as the curves clash, it takes very little side-to-side movement to change the relative height of the string to the board.

    Just my experience.
     
  10. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    You mentioned that your g-string playability goes out of whack in concert with the weather. I suggest you are feeling the difference between a loose and tight soundpost. Since the post rests under the top on the g-side, when the bass tightens up (winter), the g side may feel high in relation to the other strings (though the general direction of the strings is downward). When the bass loosens up (summer), the opposite may occur. This happens especially with flatbacks. Next time it feels whacky, have your post tension (and position, and fit) checked out. You could also install a easonal ship under the string at the bridge when needed. Our astute members (above) have covered the bridge adjustment mysteries clearly and accurately. Kudos to all...
     
  11. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    "easonal ship" above, means, in English, "seasonal shim". Please excuse my typng...
     
  12. Jeff Bollbach

    Jeff Bollbach Jeff Bollbach Luthier, Inc.

    Dec 12, 2001
    freeport, ny
    ....and you have the nerve to correct my spelling! Learn to edit, Bud!
     
  13. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Now this is something I'm very interested in. How do I install an "easonal ship" (seasonal shim) at the bridge? What would it be made of, and could I do it myself? This is the only problem I've had with string height on this bass, and if I could fix it that easily, I'd be a VERY happy man.

    What I can't stand about the setup of many basses is a severe angle between the G and D strings. I imagine that so many are set up this way to facilitate easier bowing, but to me (a pizz player) it feels nasty when the D string is significantly higher off the fingerboard than the G....it feels funny to play, and it skews the volume toward the D string when I'd rather have them even or skewed a bit toward the G volumewise (on my bass, string height and tone are also handcuffed to each other). If there was an easy way to raise the G while leaving the D where it is, I'd grab it in a Yankee minute.
     
  14. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    Sounds like you need your bridge re-arched. I like about 1 mm extra space under each string as you go from g to e, for example, 5 mm g, 6 mm d, 7 mm a, 8 mm e. Sometimes the fingerboard is too flat for that set-up, if you plan to put a bow to it. Then you end up with a huge difference between g and d, which feels really yucky pizz. For a seasonal shim, stick a thin piece of leather under the string after smearing it with pencil graphite. This is not something I like to do, as the string can come bounding out of the slot with considerable force and no warning.

    The movement you describe in your bridge sounds like normal winter/down, summer/up. I think the lousy bridge and/or fingerboard arching just exaggerates the weird feel.

    Jeff--grease pencils at ten paces!!
     
  15. I've encountered this problem and agree with schnitenator the bridge is not correctly profiled to the f/b.
    I've solved it by adding an ebony dutchman insert to the bridge on the offending string. You walk a router bit into the area and cut a piece of ebony to fit that stands above the bridge arch. Glue it in, flush it off and recut a string slot - waalaa, you have a higher G string.
     
  16. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    Pete--I've never tried that. Doesn't the ebony insert brighten that string?
     
  17. I don't think there's enough of it there. I got the idea when someone brought a bass by with all 4 strings sitting on ebony inserts.
     
  18. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    I have seen new violin bridges with the ebony inserts- with such a small bridge I suspect that the effect is to brighten the response?