Bridge Question

Discussion in 'Setup & Repair [DB]' started by rake, Jul 17, 2005.

  1. rake


    May 4, 2004
    Is there a reason that bridges have a large chunck of wood cut out of them? Has anyone ever tried a completely solid bridge? I would think that it would transfer more vibration to the body than bridges with only 2 contact points. Would it make no difference at all? Obviously I'm rather ignorant when it comes to DB construction, but any comments or explanations would be appreciated.

  2. Your logic makes sense, and I'm currently using it in reverse: I'm experimenting with a prototype solid body EUB and I'm making the bridge as light and flimsy as possible, with lots of holes cut out, to emulate some of the flex of an acoustic and compensate for the rigid body.
    Seems to me a more rigid bridge would be an advantage on an an acoustic instrument.
    But I'm only speculating - would like to know if there's a reason (other than tradition) for bridge design.
  3. Doug Westlake

    Doug Westlake

    Jul 6, 2005
    The bridges on violin family instruments are, from an engineering viewpoint, up againts two limits; mass and flexibility. Both these qualities absorb sound, starting with the highest frequencies first. If the bridge is too heavy, it will not move in response to high frequencies, which have less energy than low ones. If it is a bit too flexible, the movement will absorb highs, but still effectively transfer lower frequencies. When you're shaping a bridge 'by ear', it will sound better and better as you remove wood, up to a point. This is because you're removing mass. When you reach the point where the bridge begins to get flexible enough to absorb the highest frequencies produced by the fiddle, an audible 'roll off' of the highs will begin to be heard.

    All this can be inferred by looking at the basic construction of a violin family bridge. What look like decorative holes actually make the bridge into a structurally solid 'X' shape which is both as stiff and as light as it can possibly be. Also, the practice of exactly quarter sawing the wood ensures that the bridge is as stiff as it can be. Furthermore, one side of the bridge is more exactly quarter sawn than the other, which means that side aims directly towards the center of the tree. That side is stiffer than the other, and is traditionally faced towards the tailpiece to best resist the bending forces of the strings. If highest stiffness to weight ratio were not the deciding factor of bridge design, almost any design would work. But, hundreds of years of empirical development have arrived at a very narrow, and specific design that meets the requirements.
  4. Fascinating, Doug - and very clearly put too. I feel all ... enlightened!
  5. Doug Westlake

    Doug Westlake

    Jul 6, 2005
    Well, thanks Doug, I'm feeling encouraged! Guess I'll pontificate a bit more. I think that one of the main reasons EUB's and other electric fiddle family instruments sound so...different than their acoustic cousins is right there, in the bridge area. Anything with a soundpost, bass bar and F holes towards the lower end of the 'C bout' has a bridge that moves in wickedly complicated ways. When you mount that bridge on a solid platform (like the top of a EUB), you greatly limit that bridge's movement, which limits string interaction and produces a much...simpler sound.

    I think the best way to provide for that complex bridge movement on an EUB would be to mount it on a piece of thin wood that is supported only at the front and back, and free at the side edges the way any instrument with F holes' soundboard is. That way the bridge could rock, roll and tilt just like an acoustic instrument. Just thinning the bridge would be forcing all that movement to occur in the bridge itself, which might sound ok...but I have a feeling that letting the bridge move in the normal way will sound much more like a doghouse is s'posed to sound!