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Thread: thinning the bridge?

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    Default thinning the bridge?

    I showed my new build to a local mando player, who liked it, but suggested sanding the bridge, (top and bottom) thinner, in the width, and told me that it had to do with fiddle set up. on the top part of bridge, where strings rest. He showed me his, and the round posts on either end, were almost sanded flat. again, he is talking about the width of the bridge, above and below the thumb screws. does this make any sense to anyone? , or just another opinion. seeems that it would brighten things up, but again, just an opinion. If so, could this also be considered in set- up?thanks
    Mike Marrs

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    Default Re: thinning the bridge?

    Can you provide some pictures?

    Thanks,
    Len B.
    Clearwater, FL

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    Default Re: thinning the bridge?

    no sorry ,can't, but what he did, was lay the bridge on a sander, either side, and thin the width of the bridge, top and bottom, sorry no pics, but I was just curious, if it had anything to do with the tone of the instrument
    Mike Marrs

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    Default Re: thinning the bridge?

    There is probably no reason not to try it... the worst thing you can do is bust or weaken the bridge. I suspect many of the opinions based on bridges are myth, and unless you are a high level professional you probably couldn't hear the diference anyway.
    Or build a few non-adjustable bridges and test them out with varying thicknesses.... I am presently using popsycle stick bridges on a couple of my banjos and one mandolin. You can't beat the price.
    Bart McNeil

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    Registered User Pete Summers's Avatar
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    Default Re: thinning the bridge?

    The fellow at Frets.com suggests that lightening the bridge improves tone, which sanding it thinner would do somewhat, I suppose. On my violin, the top of the bridge is very thin, which may or may not be a tone thing, but I figure the less wood the string has to slide over when tuning, the easier on the string if nothing else.

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    Default Re: thinning the bridge?

    Very interesting article....I have drilled some small holes in an ebony saddle to make it lighter and I didn`t hear one bit of difference in volume or tone so maybe like the fellow say you have to lighten it by 75% or more, I wasn`t anywhere near that maybe 25%....If working just with the saddle one would have to be real careful because the saddle might cave in....

    It is fun to try different things though, I am about to try and make a non-adjustable bridge from a piece of oak...I will try to lighten it like the article says....

    Willie

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    Default Re: thinning the bridge?

    On such things making a video before and after helps.

    Thinking about what could be having an effect (variables) helps as well. Overall mass, mass at ends, resonant frequency of the saddle, contact area with the adjustment nut. Maybe more things. Then take a bunch of saddles and work out these variables.

    I've done a lot of that kind of thing. It's a bit tedious, but surprises lurk in all those variables.
    Stephen Perry

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    Default Re: thinning the bridge?

    "The fellow at Frets.com" is Frank Ford. If I remember correctly, Frank did not say that a lighter bridge results in improved tone. What he said was that the lighter bridge resulted in greater volume, but that his friends preferred the tone with the heavier (i.e., standard Gibson adjustable style) bridge by a slight amount. Frank got his one-piece maple bridge down to about 3 grams, iirc.

    A little reality here. Violin bridges are very light; masses of only a few grams. They are very thin pieces of wood to start with, which would favor lower frequency bending motions, other things being equal. Even so, the lowest frequency normal mode of motion in a violin bridge itself occurs at around 3 kHz. The next one up is in the 6 kHz range. Now, whatever happens at 3 kHz and above is not unimportant in violins and other bowed string instruments. The bow imparts not only the "Helmholtz motion" (a "sawtooth" waveform in the lateral direction) to the string, but also even higher frequency components called "double slip" and "multiple flyback" motion. Which means that a violiin body deals with lots of high-frequency input from the strings, and its' design has evolved over time (especially in the 15th & 16th centuries CE) to deal with that input.

    Plucked string instruments are entirely different animals. The input to the instrument body from the string comes from a single pluck. The amplitudes of the lowest frequency components are relatively large, while the amplitudes of the higher frequency components are quite small. Which in turn means that the magnitudes of the forces applied to the top plate through the bridge are larger for the lower frequency components, and quite small for the higher frequency components. Iow, plucked string instruments are low frequency radiators to a comparable extent with bowed string instruments, but bowed string instruments are high-frequency radiators to a much greater extent than are plucked string instruments.

    What does all that mean for mandothingies? For one thing, mandolin bridges are pretty massive compared to violin bridges - even when comparing a maple one-piece mandolin bridge to a violin bridge. Bridge mass does matter, but I haven't sorted out just how much it matters. The bridge resonance frequencies (really normal mode frequencies) are another thing altogether. Mandoln bridges are very massive and stiff compared to violin bridges, and considerably shorter. I would predict that any modal frequencies in mandolin bridges would be way up there. In fact, Jim Rae and I did some accelerance spectra several years ago for several different types of mandolin bridges on a single mandolin. We did "control" spectra with the shaker on the instrument top - not on the bridge at all. The results: not anything in the way of "features" in the spectra up to 5 kHz or so. That means that there are no modes of motion up to at least 5 kHz. Not surprising, considering the differences in mass, dimensions, and stiffness between a typical mandolin bridge and a violin bridge. I did some subtraction and plotted some "difference" spectra, & saw only minor differences between the different mandolin bridge types, most likely due to differences in mass. I'd like to spend some time revisiting those results, if only I didn't have alotta things to do in front of that.

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    Default Re: thinning the bridge?

    Quote Originally Posted by bmac View Post
    There is probably no reason not to try it... the worst thing you can do is bust or weaken the bridge. I suspect many of the opinions based on bridges are myth, and unless you are a high level professional you probably couldn't hear the diference anyway.
    Or build a few non-adjustable bridges and test them out with varying thicknesses.... I am presently using popsycle stick bridges on a couple of my banjos and one mandolin. You can't beat the price.
    Well it is a banjer. Who the heck could tell the difference?
    Breedlove Quartz FF with K&K Twin - Weber Big Horn - Fender FM62SCE
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    Default Re: thinning the bridge?

    Thinning as the OP describes will reduce the surface area contacting the top, and in turn effectively increase the pressure exerted on the top (?). So many factors at play here than mass alone.
    Like Stephen pointed out, on an adjustable bridge it also reduces the area of transferral through the thumbwheels. As to opinions about what effect this has I will bow to the knowlege and experience of the likes of Stephen and Dr Dave.
    Last edited by Ben Milne; May-22-2012 at 10:32pm.
    Hereby & forthwith, any instrument with an odd number of strings shall be considered broken. With regard to mix levels, usually the best approach is treating the mandolin the same as a cowbell.

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    Default Re: thinning the bridge?

    So many things and their effects are beating together in instruments that systematic experimentation (real experimentation - with a goal, a system, etc.) really proves useful and isn't difficult. Keep everything the same except one variable.
    Stephen Perry

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    Default Re: thinning the bridge?

    I guess I pitched the level of my earlier post too high. Will try again, this time digesting & simplifying it some.

    1. The OP was responding to a suggestion by a friend who made the usual seemingly obvious comparison to violins. Violins and mandolins do have some superficial similarities. They are both small boxes with holes that pump air in the holes at a few low frequencies and radiate sound from the outside of the plates at much higher frequencies. There are also some very pronounced differences, however. The most profound is that they are driven differently, one repeatedly by a bow, the other by a single pluck. And, the differences in structure necessary to respond to those different drivers are similarly profound. To paraphrase someone famous, where mandolins are concerned, forget violins; they "ain't no part o' nuthin".

    2. As I stated above, I did systematic experiments with mandolin bridges. I had a few of Red Henry's one piece bridges, kindly supplied by Red. I had some 3-piece all- wood adjustable bridges of my own design, with a sliding wood wedge for the adjustment. I had some conventionally adjustable (i.e., threaded posts and adjusting nuts) bridges of my own design, and some conventional Gibson-type adjustable bridges. All were carefully fitted to the top plate of a single mandolin. And here is the important part: I found no signs of any resonances in any of the bridges up to at least 5 kHz!. Now, with hindsight, that's not too surprising. A violin bridge is a very tall, thin little piece of wood, and its lowest resonance is up at ~3 kHz +/- a few hundred Hz. Mandolin bridges are much thicker, shorter pieces of wood, which means that they are much stiffer, And being much stiffer means that any resonant frequencies would have to be much, much higher than they are in violin bridges, which is exactly what I found. And because plucked string instruments, including mandolins, are driven primarily by forces from the lower frequency string modes, any forces from string modes above 5 kHz will have tiny magnitudes and be inconsequential. So, forget bridge mode resonance frequencies in mandolins; they "ain't no part o' nuthin". Now, mass is somewhat more important. The lower mass resulting from lightening a bridge can result in more volume, but it may also result in more volume for some harsh high-frequency components for which you might not like the effect on the sound of your instrument.

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    Default Re: thinning the bridge?

    [QUOTE=Martian;1053683]no sorry ,can't, but what he did, was lay the bridge on a sander, either side, and thin the width of the bridge, top and bottom, sorry no pics, but I was just curious, if it had anything to do with the tone of the instrument[/QUOT

    If this were a violin well, maybe. Violin bridge thickness is very important but as Dave says, a mandolin ain't a violin; it is a different animal altogether. People keep doing the violin envy thing I guess. Their names are similar, violin - mandolin. Guitars. Now there is a darn close cousin. Lets talk about guitar bridges.

    Seriously, I do have a question for Dave and the other mandolin builders.
    I lower the string height on the treble side of the bridge more than the bass side in part because of the thickness of the strings but also because the fretboard has a radius. Does this make sense?

    This is not the case on my old bowl back with a flat fretboard. (and one piece bridge...).

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    Default Re: thinning the bridge?

    I don't see the connection between a radiused fretboard and lower string height on the E-string side. I do usually set instruments up w/ a lower string height on the E-string than on the G-string, but I do that for flat fretboards as well as for radiused fretboards. What matters is the height of the string above the frets, regardless of fretboard radius. The amplitude of an E-string under typical playing force is less than the amplitude of a G-string under the same playing force. That means that the E-string height can be lower than the G-string height for no buzzing under a given set of playing conditions.

    There is no single set of string heights that is right for everyone. Players who frequent jams and are trying to be heard may play harder, and consequently want a higher string action in order to play hard without buzzing. Players who are trying to raise the level of their playing and play more difficult works, licks, etc., may want a lower string action for ease of playing and responsiveness. What seems to feel good for me, regardless of fretboard radius, is about 0.065" - 0.070" for the G-string at the 12th fret, and about 0.045" - 0.055" for the E-string at the 12th fret. For someone else, that may be all wrong. That is what bridge adjusting posts and nuts are for. And through all this, I have left out any discussion of neck 'relief', which would be a topic for a different thread.

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