Bridge designs for acoustic properties

I've read a bit about the pros and cons of different bridge designs which are typically used on classical instruments (violins, cellos, double bass etc). It seems most of the considerations were to do with the way in which strings cause the sound board to vibrate.

When I look at guitar bridges I'm left scratching my head. Obviously they work, they've been designed the way they have for centuries and they sound fine. People continually pay top dollar for them.

My question for those who understand guitar design and acoustic resonance is, why wouldn't acoustic or arch top guitars have a bridge like the ones on classical instruments?

A good question, and one I have no immediate answers to. I have a few thoughts though.

Some of it might have to do with relative string tension and 4 strings vs 6 strings. Violin strings have variable tensions ranging from an average 17.5lbs for an E to 10lbs for a G. It comes to an average 50.5lbs in total for 4 strings. A set of D'Addario Phosphor Bronze 11-52s has a total string tension of 144.5lbs and for 12-53s that's around 156lbs.

Those bridges are fairly high. To get one to even fit on a normal guitar, the neck angle would have to be a lot steeper than standard. Most classical style guitars have a fingerboard that's parallel to the top. You'd also need to string from the back of the guitar.

There are also issues with tuning stability with that type of bridge. As it's tall and only held in place by friction, any tuning can move the bridge from upright, which then affects the intonation. On fretless instruments the player can make small changes to finger position to change the pitch of the note. You can't do that on a fretted instrument. String bends are also going to affect the bridge position a lot. Get the bridge beyond a certain angle and it's likely to collapse.

I think you'd also have to have an arch top to make it work. I've been told by luthier friends that it's very easy to 'overdrive' an acoustic guitar top with too high a saddle and put too much energy into it, which the wide flat top of a standard acoustic makes it easy to do. So an arch top with it's greater inherent strength might be the only type of guitar where it's even feasible. The higher the bridge is, the greater the downward force of the strings is and the stronger the top needs to be. So for an acoustic guitar to cope with a similar break angle to a violin, it's top would have to be a lot stronger (and less resonant as a result). The bridge itself (if a classical type) would have to be a lot stiffer and stronger to cope with the extra tension.

The curve of the 'classical' bridge looks like it also plays an important part in the way it works. Violins etc have a pretty small radius board. If you try and match that bridge style with a much flatter (and classical guitar necks are simply flat) board, then the bridge needs to be curved to suit. So forget any big string bends.

The bridge (according to Wikipedia) acts as an acoustic filter and helps make the instrument sound like it does. So a guitar with a violin style bridge might sound very different and more 'nasal'.

So to have that kind of bridge and make it work effectively, I think you'd end up having to make a lot of changes to the basic construction of a guitar, and effectively you end up with something that resembles a large viola/small cello. The guitar is simply a very different instrument and sounds the way it does because of the way it's built, bridge included.

That's not to say that there can't be any experimentation and maybe someone will come up with a new bridge style without changing the fundamental construction of the guitar.

Also don't forget that decent classical instruments cost an awful lot more than a decent acoustic guitar does. If you ever aspire to playing in a classical orchestra even at a semi-pro level, a decent basic violin is going to cost you at least £20k/$36k, and the bow about the same. As the instruments get bigger, the cost goes up. Yes, you can get $100 Chinese violins on eBay but they sound horrible. If you start making guitars along the lines of a violin/cello, then expect the costs to spiral as there is just so much more manual work required.

Thank you for your well considered response. I'd not thought of over-driving a flat sound board, and that totally makes sense.

I've seen mandolin bridge designs where they had two feet (as opposed to one long piece in contact with the sound board). The saddle was also free to swing like a T shaped see-saw like the classical bridge. The main difference was that it was much shorter and a bit wider like you'd expect on a guitar bridge.

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Now I'm wondering if I should muck about with this kind bridge design for my incoming fretless ES-5V...

Some floating archtop bridges are fairly similar to that, but obviously even more solid still.

You may find that a bridge that maximises acoustic volume may reduce the sustain of the guitar. More of the string energy is being dissipated as sound energy, so the note length should (according to my logic) reduce accordingly. If you are using the guitar mainly acoustically, this may be a benefit. With a pickup, less so. It may even encourage feedback a little sooner.

Still, I'd go ahead and try. It's removable and replaceable, so no harm done if it doesn't work out. Obviously you only get a basic intonation adjustment with that type of bridge by slanting it, unless you have it a lot wider so you can form some ridged sections with the ridges in different places. But the more you widen the classical design it to make it stronger and less tippy, the closer you get to a basic archtop floating bridge!

Note that string height adjustment will be a one-way process by deepening the string slots (or rubbing some height off the feet).

But a comparison of different bridge types could certainly be fun and informative.