Official Luthiers Forum!

Where would you feel is the best place to put a bridge for volume, projection, and bass? I would think right in the middle of the lower bout to make the most of movement of air.So a longer scale would put you closer to middle if you measure from the sides to get closer to the middle of the lower bout with more flexing distance between the bridge and sides.

Isn't that one of the reasons shorter scale length guitars often have a 12 fret join instead of 14?

Darrin

It seems like most people agree that the middle of the lower bout is the optimum place for the bridge.

But hey, there are lots of killer sounding guitars out there with bridges way up by the waist.

My favorite guitar i have built was a 14 fret double O shape, with a bridge quite far north of the center of the lower bout.

The best place to put it is wherever you get results.

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Jordan Aceto
Ithaca, NY

That could be the reason for it Darrin.I was thinking on maby moving the waist farther north to put the bridge closer to center of the lower bout on a 14 fret scale.Sort of giving more room for the plate to flex more.

I disagree. The strings are pulling to one side, inducing torsion in the top. This moves the sweet spot away from the center, even if "sweet" is reduced to just maximizing volume.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I actually disagree with my own statement also, i was just stating that the "general agreement" seems to be middle of lower bout = good.

Like i said, i think wherever you get results that please you is the "correct" place. The best sounding guitars i have built so far have had bridges "north of center".

There are lots of great sounding instruments out there with bridges smack dab in the middle also, so i dont consider bridge location to be a "magic bullet".

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Jordan Aceto
Ithaca, NY

I'm thinking the farther the bridge is from the lining, the more air that will be pumped from the top plate.I realize braceing comes into play as well.

It all depends on how the bridge crosses your x-braces. If too far away from the braces the top will choke and distort. Moving the soundhole up a bit in order to have more wood in front of the bridge seems a better approach I think.
I've always thought 12 fret guitars sounded the way they do because of the shorter neck stock.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I think that the bridge should be at the 'acoustic center' of the top. That may or may not coincide with the geometric center of the lower bout. It all depends on how you brace the top.

Most of the sound seems to be produced by the top moving like a loudspeaker cone. The rocking of the bridge in response to changes in tension as the string vibrates does contribute, of course, but you have to remember that this force is usually much less than the transverse force of a string vibrating in the up-and-down direction. Also, guitar tops have to be built to resist that rocking motion, for obvious reasons, so this is mostly effective above the pitch of the open high E string, from what I can figure out.

Granted, if the top were uniform in stiffness in all directions, like the pie plate in a reso, you'd want to drive exactly in the middle. But it often isn't. Again, that's something you have under control, at least to some extent. I'd say that having the bridge a long way above or below that geometric center is likely to have some cost, but there's a lot of leeway.

I built a guitar a few years ago with a 20" scale length and a 14 fret neck. The bridge was about 2" below the soundhole edge, and it sounded OK. The relatively small bridge displacements of guitars with 'normal' scale lengths are well within the limits if you do it right.

I was thinking a 26and1/2" scale dread. And moving the x- brace back 1".

Maybe I'm wrong but it would seem to me that a 26.5 inch scale length would cause the guitar to be almost unplayable because of the string tension required to get up to pitch. I saw a Leo Kottke video
where he talked about a guitar with a long scale length. It was sitting unused because it was so hard to play.

Dave

Question that comes to my mind is if this was a significent inprovement in the function of the top would not all the major manufactures and top end builders been doing theis for decades if not centuries. i am not making fun of posing the question. Just giving insight on common deduction prior to the question. looking for ways to improve the tone or fuction and therby the tone is always a good thing.

I don't think the major manufactures are making great guitars for better tone.Do you? There braceing is awlful.There tops are too thick etc.,etc,etc,.Not to mention the paint jobs.Do you really thing they are building for better tone? I don't.

Dave, That's a good point.I'll have to look at that, as i didn't think it would be a problem.Mabey i'll string up a 2x4 and check it out.If it is a playability issue, i'll just move the neck in with a proper cutaway to get the bridge farther back instead of increasing the scale.

Tuning a guitar UP a half step or so will give you an idea of what the string tension will be like on a long scale guitar.

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Jordan Aceto
Ithaca, NY

Yes I do believe the good ones do. After all it is their business, now do they spend the time to make every production line guitar the best it can be and cosmetically clean inside? Well no they don't but if there is a change they can make to each and every guitar to improve there guitars and it is economically feasible to implement then yes they do those kinds of things every day. Now of course I am speaking of Martin, Taylor, Yairi and the other high end manufactures. Now they will never be able to spend the time to treat each instrument and make it the best it can be but the names I mentioned and a few others do care that their product is viable and well represents top line instruments with in a manufacturing model.

Could they be better yes but then you would pay $3k-$5k for the instruments you pay $600-$1.5K for today.

remember Alans quote!

When you design a guitar (acoustic) the bridge placement & brace layout need to be a working arrangement for both !

So lay it out like a speaker cone -stiff in the middle -flexible at the edges.
bridge & braces have to be designed to work together .

Mike

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Mike Collins

That would be what i'm looking at.Put the bridge in the middle of the lower bout just as the speaker cone is in the middle of the speaker frame to get the best sound.

Hi Michael,

I think when you speak of any change in the path of the major manufacturers, (and to some extent, the buying public), you have to allow "tradition" to weigh heavily in the equation.

If you knew that you could build guitars that sound pretty much the same as your best guitar, but that would never need a neck reset and would never belly, would you do it? Before you answer "yes", would you do it if it meant moving the soundhole into one of the upper bout corners, and if it meant using a tailpiece with a modified pinless bridge? In other words, if the guitars no longer look like any Martin or Taylor model, would you build guitars that strayed far from tradition, sounded about the same, but greatly increased their longevity?

It's taking a while for high-end hand builders just to educate their buyers about the benefits of an adjustable neck (something the major manufacturers still have not done), and that is a feature that can be completely hidden within a traditional guitar. So, it doesn't surprise me that none of the major manufacturers are making any modifications to their tried-and-tested true, traditional styling with traditional engineering. Why should they rock their own boat?

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Mark ;that's what works for me !
I've made classicals for 30 years & the bridge is smack dab in the sweet spot !
I've learn to take advantage of that location !
It seemed so logical that all I make are 12 fret steels now !!

Some times a 14 fretter ~
But the 12 fret ones are so hot !!

Mike

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Mike Collins

As Laurent said, if you locate the bridge closer to the center of the lower bout you need to close the X a little to support the wings. This factors in another variable regarding tone. I've been using a bridge that is almost 6 3/4 long on my 12 fret parlors so I can splay the X more. I don't think I'd do it with a belly bridge though. Seems to work, folks like the way they sound.
http://www.thepodium.com/p-16608-kenned ... arlor.aspx
Hopefully they won't all start exploding in a couple of years.
TJK

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Mike Collins wrote:
"remember Alans quote!
[snip]
So lay it out like a speaker cone -stiff in the middle -flexible at the edges.
bridge & braces have to be designed to work together ."

A guitar top moves air in the same general fashion as a speaker cone, but it's not a speaker cone. For one thing, a guitar top has to withstand the pull of the strings, which a speaker cone does not. Stiff center and loose edges is one way to go, and gives a particular sound, but you can also use a looser center, within reason, and stiffen the edges some too. Thats how scalloped bracing works, and we all know what that sounds like. Of course, you can unload the thing and use a speaker cone; which is what resos are about. There are lots of ways to do it, but my point simply was that it's the top moving in and out that makes most of the sound, not the rocking of the bridge, and you have to dfesign accordingly depending on the result you want.

Interesting, I just finished a Siminoff book and if I didn't misunderstand, he states the opposite of this........that most of the sound comes from the bridge rocking back and forth. I'm new to luthrie but I must say I'm surprised how little agreement there is how things work.

To the original poster's topic, just a thought but wouldn't glueing the bridge in the middle of the lower bout and pulling 150 lb of string tension there limit movement.......right where you would like the most movement?

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Formerly known as Adaboy.......

Darryl,

I read the Siminoff book too, and he showed how he determined that the bridge was primarily rocking (fore and aft), and my fuzzy understanding (don't really know where I got it) is that archtop guitars (but not flattop steelstring guitars) primarily transmit vibrations via a pumping action. Again, I know where I got the notion that "stopped" (typically bridged) steelstring flattop guitars primarily rock the bridge - it was Siminoff's book.

So, I'm betting that Al Carruth has set up his own experiment and came to a different conclusion - and I'd love it if Al would show us how he arrived at that. Maybe if we keep bugging him...

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Regarding the 26.5" scale, it will work.
I built my first guitar on a 12-fret 000 platform with a 26.5" scale, the neck joining the body at the 13th fret. Bridge location remained the same as the original design.
I use a lot of slacked tunings so the tension never bothered me. Even in standard the tension is not that different -with lights, less than a set of mediums on a 25.4" scale-, on the other hand the player experiences a bit more "left hand fatigue" with the longer scale in the first frets. When strung with mediums I tuned the guitar in Eb or D and capoed at the 1st or 2nd fret.

The idea is to have the bridge in the middle of what? The geometric centre of the whole body, the lower bout? Does it really matter?
Steel string traditional bracing splits the top into small discrete areas, this is the heart of where the tone comes from. Locate the bridge where your bracing calls it, or vice-versa.
I never thought 12 fret guitars sounded "better" than 14 fret designs, but yes, they sound different.
Look at Baroque guitars or vihuelas, the bridge is way down the lower bout, not in the centre either. They also have an excessively short neck (by today's standards) and virtually no bracing.

I wouldn't take verbatim, and probably not very seriously, most of the theoretical work out there. (i.e. the episodical breakthrough about Stradivarius and the Cremona makers.)
Most of the time it sounds more like guesswork, or religion, than science.
The guitar is a seriously complex system, there are millenniums of plucked string instruments tradition and history behind us, and a whole population of ghosts and restless souls who were as obsessed as we are by the mysteries of luthiery, and worked hard at it.
The guitar as it is now did not come out of nowhere and its entire design makes total sense for what it is designed to accomplish. Yes we can add a little bit of wood here, remove some there, but the overall design is mature. Subtleties and details are what makes the difference.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/