h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Positioning the Bridge on a Mandolin - A4195352
Author: Gnomon - U151503

A short entry on a technical subject. I hope it's not too specialist.

What do you think?

It seems just the right balance of economy and detail

I'll sit down later this evening and pretend I'm brand new to the subject and try the instructions

OK, so now all the mandolin players on the site have commented, what happens next?

It gets edited (Its a good entry by the way)

I've had a go on a mandolin. Twice indeed, to my certain recollection. Not that I ever realised the bridge was movable.

Still, that makes me enough of an expert to ask questions, right? So why *is* the bridge movable? Why couldn't that lazy old mandolin-maker just have fixed it in the right place, and saved us all this trouble?

So *that's* what I need to do to my mandolin... Tuning it relatively using the 7th fret gives strings that are hopelessly out of tune.



Ah... sadly my mandolin doesn't have a moveable bridge - I can only adjust the height. Perhaps I need to fiddle about with that instead?

Anyway, a useful little Entry (but not for me! )

Why is the bridge movable?

I think it is because the exact position depends on the thickness of the strings, and the mandolin maker doesn't know what sort of strings you are going to fit. Perhaps pailaway could confirm this.

I have to grudgingly admit that Pinniped's question is a good one, although I have one for him - how do you play mandolin with only flippers, seal-boy?

There's some builders forums on the mandolin cafe that I searched last nite and as far as I can tell, you're right, Gnomon. If the strings were dimensionless, then you'd never have to move the bridge from the starting position that you identify. However, all of the strings have varying widths and the first four are even worse because they have wound cores, so you have to tinker. The length needed to produce the correct open note is slightly longer than the theoretical length - and is longer with increasing string diameter. Some mandolins do have glued bridges, but this is uncommon and I've never seen them on higher quality mandolins. It's more common for a builder to set up the instrument for a particular set of strings.

Of course, that still begs the question of why. After all, guitars almost always have glued bridges. It's probably because guitars are lots longer from nut to bridge and so are more tolerant of slight variations, whereas mandolins are not.

Electric guitars tend to have movable bridges, and the bridge can be adjusted independently for each string.

I wonder if that's because minor difficulties with tune get amplified, and so electric guitars are even less tolerant in that respect and require even more exquisite control.

even now, I'm picturing jimi hendrix bending his guitar across his thigh and wondering if there was any sense in the last post.

I think it is because electric guitars are a huge business compared with acoustic stringed instruments, so they get all the good gadgets.

In addition, they're basically planks of wood, so you can screw any sort of heavy metal thing to them and it won't affect the resonance.

This reads fine to me, but I know I'm not your likely audience.

Now if you wanted help with positioning your mandolin on a bridge...

>>how do you play mandolin with only flippers, seal-boy?<<

I never said I played it. I only said I had a go on it

Gnomon, I think you've hit the nail on the head - it's got to be the mass that determines the best bridge to use, and the cost that determines what actually gets used.

It's a spring-mass-damper system and the mass has to be tuned to the mandolin for best results. Well, an elastic membrane - mass - damper system. And the ideal bridge would have just the right mass and just the right contact area, which the bridges we're used to seeing approximate - given all of the usual trade-offs, whatever they are.

However, I'll bet the glued bridges are less expensive. So, if you're mass-producing instruments and you're competing for giving a better price, then the cost difference probably becomes significant, whereas if price is not the single determining factor, then you go ahead and put a more expensive bridge on and charge more.

Just a thought



As for you, sir - had a go on it? You mean like using it for a sled? I can see that.

Ok, I've tried the experiment of reading this as if I were as clueless as Pinniped.

If someone were attempting this for the first time, I wonder if just a little more needs saying about actually moving the bridge? ie, place the mandolin on a table, grasp the bridge on each end with thumbs and forefingers, and make small incremental movements. if the bridge proves too hard to move, slacken the strings down one or two notes as the procedure works whether the instrument in proper tune or not. if it's really impossible to move, it might be glued down.

Also, a warning about keeping the bridge vertical and not tilted, so that the base remains fully in contact with the face of the mandolin.

Your last sentence: "You'll end up with a mandolin that plays beautifully in tune." is true if you remind the reader to give the instrument a final tune after the bridge is properly positioned.

Good points all, pailaway.

I'll try and make some changes in a few days, but I'm heading off on holidays until Saturday night, so I won't get a chance before then.

Have fun

For when you get back - I asked a this guy - http://cohenmando.com/ - who's made a study of mandolin acoustics if he knew whether the use of movable bridges vs fixed ones was more a matter of tradition, or of physics. Here is his reply:


The original motivation was probably that first the Neapolitans, later Orville Gibson, and still later Loar and Hart, wanted to "violinize" the mandolin. Their thinking was that since the violin was already acoustically "perfect", making the mandolin morphology (and also that of the archtop guitar) more like the violin would improve the acoustic volume and sound quality of the mandolin. Not very good thinking, since the mandolin is a plucked stringed instrument, and no amount of shape shifting is going to make it into a bowed stringed instrument. However, they did succeed in making new varieties of plucked stringed instruments, with their own characteristic sounds.

There are some physical differences between the way that a fixed bridge drives a top and the way that a floating bridge (e.g., violin family, mandolins, archtop guitars) does the same. There are a few descriptions of it in the literature. You can also get some idea by looking at Fletcher & Rossing's text, "The Physics of Musical Instruments", 2nd Ed, Springer, NY, 1998, in chapters 9 (Guitars & Lutes) and 10 (Bowed string instruments).

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Don't worry GB, I'll get my own back.
I've already started on the definitive Entry on 'How to Traverse the Ice-Shelf using Musical Instruments'