bridges - materials - setup etc.

A lot of creativity is shown regarding bridges on the CB instruments I've seen. The quintessential eye bolt seems to show up a lot, dog bones, ball point pens, bottle caps... all kinds of cool stuff. These obviously works great for plugged in CBs, [& for aesthetic "funk factor"] but what about acoustically? In most non amplified instruments some general rules of thumb I've observed: 1. Most are made of pretty dense material like bone, ebony, rosewood, maple, corian etc. 2. sometimes the body of the bridge is made with dense material like, ebony, rosewood or maple and capped with even harder materials like for banjos ebony atop maple and guitars bone on ebony. 3. Softer materials tend to absorb highs and denser materials accentuate them. I've used this to advantage on instruments like hammered dulcimers by capping the bridges with Delrin [a sort of self lubricating synthetic - I think it's generic name is acytal] this not only helped reduce friction to make tuning easier - it filtered out some of the high frequencies that HDs often have too much of anyway. One of the ways you lower the volume of traditional stringed instruments is by using a "mute." [And in spite of what one of my T-shirts says a banjo mute is NOT a 9 lb sledge hammer...;~) ] These are weighted clips that fasten to the bridge of say a fiddle or a banjo. This is helpful if we're trying to balance their volume with other acoustic instruments. But this also tells us that all else being equal, if you merely add weight to a bridge is reduces it's ability to vibrate freely and pass that vibration on to the sound board, and so the instrument gets quieter. With all that said, I'm guessing large eye bolts work against us if we're trying for optimum sound unplugged. An easy experiment someone might want to try is make a few bridges of different materials, but all the same height, and test them on the same instrument. If you have a cohort who's got the patience a blind listening test might be even a little bit scientific. Any takers? Recording the results and comparing that way might be cool too, but keeping all variables the same can be tricky. How about other bridge observations?

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  • A domino works great. They're extremely cheap too...I bought 20 for like $2 at Wally World. Cut them into 1/4" strips and slot them for strings, not too deep though, they seem to play better with smaller slots. They won't scratch your box and are pretty easily adjustable. One word of caution, they smell God-awful if you burn them with a dremel tool cutting bit so my best advice is to wear a gas mask. They also shed like corian when cut and a regular dust mask won't rid the smell.
  • I was using an oak bridge/saddle and it worked fine, now i have switched to a wood bridge(mahogany I think) and a small brass rod saddle. The sound is still good, to my ears not much different. Reason for change is the new bridge houses a piezo. I was worried the new bridge would dampen some beacause it is larger and covers more of the soundboard , but it did not effect it.
  • I have used deer antler..looks like bone..still stinks when you cut it.. connected to English walnut bridge then to top. sounds good.
  • one of my bridges is small steel handle, prolly a garden fence or a drawer, I used a hack saw to cut grooves in it. It seems to work well. The guitar it's mounted on produces a fair amount of sound, my strings are mounted in a block of oak that's almost flush with the back end of the box, so the strings are also tight across the corner of the box before they hit the bridge. Do you think making contact with the box affects the sound?
  • I think much of the reason for placing bridges close to the edge of the box is down to practical construction factors rather than sound. The box top (or bottom) can take larger forces close to the edge (I'd have to go into some maths to explain this properly but essentially it comes down to being closer to the sides of the box, which is where the support is). If you have no way of knowing for sure what load the box will take before it bows or gives way (and no one wants to find out by destructive testing!) then you play safe - especially if you've got a lightly constructed box or you're going for mor ethan three strings..
    Also, cigar boxes tend to be quite a bit smaller in area than regular guitar bodies, so it's more of a squeeze to fit in all the hardware and soundholes (if you're putting in a magnetic pickup and you want soundholes and your want control knobs and you want to have a clear area for strumming then the bridge can get pushed back to make room).

    However, it's an interesting question as to where you'd choose to put the bridge for absolutely optimum sound quality. I don't think it's as simple as being better the further it is into the centre. My gut feeling is there will be many different answers because boxes come in different proportions and sizes and probably trial and error is the only practical way to find out what works best. On top of that, sound quality can be a subjective thing, so each builder might have his or her own idea of what sounds best.

    So the best way to answer your question is to get building...

    MichaelS said:
    Question of bridge placement. I see alot of bridges on or near the edge of the box, I would think the bridge would work better further into the lid for better vibration and resonance, what do you think? Dose it matter?
  • Question of bridge placement. I see alot of bridges on or near the edge of the box, I would think the bridge would work better further into the lid for better vibration and resonance, what do you think? Dose it matter?
  • From what i have gathered after trying to find what might make a "softer" sound is that Bridges which are "steep" from the string to the body produce sharper sounds than a bridge that graduates out. So a bridge that is on top of, or built into, an "Oval" (Or possibly rectangle) shape, and gradually slopes down to the board after raising the strings, then affixed to the sound board will produce a softer sound.

    A look at some classical guitars seems to support this to some extent.

    Then comes the issue of where on the soundboard the bridge should be placed. I have always worked roughly on a third (+) from the tail, but it seems that many makers are choosing to locate it somewhat closer to the center.

    Of course this all "guitar" lore!
  • I have used the large eyebolts quite frequently.And noticed some boxes are louder than others.On a build I did a few months back(romeo and Juliet distressed) I used a tensioner removing the eyebolts and a lil grinding and it made a particle board top much louder than some of my cedar tops.It was not surprising to me because I am a fan of old vintage gibsons.I learned a couple of years ago that the old les pauls came with a lightwieght aluminum tailpieces(stopbar) Its said that by trading the zinc piece with the lightweight aluminum you find more transfer into the body of the guitar.creating more woody sustain in the instrument.I replaced my tailpiecxe on my les paul and was impressed with the difference.I have used a few aluminum tensioners now.And am very pleased with the volume from them.The only problem I have with them is they are hard on the top of the box when readjusting.and you have to grind the top of the rear of it down or it buzzes.Roughing it up.Or like I like to say adding a lil cbg charachter.The real plus is the volume! and the fact you get 2 eyebolts to use on other builds.i try to stick with the flat alum tensioners with the 3/16 eyebolts.I have also been using some other lightweight aluminum pieces like nuts.and my next 4 builds are going to have alum rod bridges.No matter what bridge i use I always make sure its flush with the top by grinding thru the threads.I lay the eyebolt on a board and rock the eye and grind till its flat. more connection more transfer.I have also learned over time that too big of a soundhole can knock your volume down.I believe if it lets out too much vibration the box doesnt sing right.Gotta trap some buzz in the box to keep it hummin.Maybe one day ill find a square inch formula for that for now im still learning as I go.
  • I just wanted to say the I think the bolt bridges are working very hard against us.
    I make a high bridge usually around an inch tall and try to get the angle of the strings coming down to the tail end as sharp as I can.
    I have been able to get them really loud this way.
    I use every bit of space the box allows to make this angle sharp so the strings are almost touching the edge of the box before they go to the tailpiece.
    I make my bridges from whatever hardest wood I can find and I shape them to a sharp point right on top and after they have been strung up for a day or two I hold them up to a light and if I can see light coming under the bridge I sand it till it fits perfect on top of the box.
  • Hey Randy,
    Thanks for your take on bridges and for that great jpg.
    I've noticed that a lot of the methods or materials I gravitate towards over time, ends up being a variation of some traditional approach that has proven itself over and over again across centuries of building a wide variety of instruments. I think bone is probably one of those materials - tho the "pay off" from it varies widely depending on the kind of instruments we're making.

    I noticed that the shim you used to raise the action on the bridge in your jpeg is tapered. It reminded me of a jig/gizmo I use to assist in setup. [I should probably post this somewhere with a photo, but I'll describe it here.]
    I've made a long tapering temporary bridge that I use to determine the finished height. Since it tapers I can put it at the correct location with the string tuned to pitch, then I pull the wedge out gradually - slowly lowering the action of the string while plucking it. I do this until the string buzzes and then push it back in, raising the action until the buzzing goes away. Then I know I've found the optimum height for that string. I measure the string height with calipers and make the bridge that tall for that string. Often the wound bass strings need to be a bit higher off the fretboard than the plain strings.
    Thanks again for the cool pic.
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