Yet another math question

[Dave Bagwill]

Just as an addendum: Siminoff built a fixture that could restrain either the up and down motion of the bridge or the forward-backward rocking of the bridge (torque).

So he strung up a dred-sized guitar, brought it up to pitch (A=440) put it in the fixture and did the following:
1. strummed the guitar without inhibiting the bridge at all = 83db on a meter.

2. Then by inhibiting the upward/downward motion, he strummed again and = 81 db at the most inhibited.

3. then by inhibiting the torque, he strummed more and = down to 76db at the most extreme inhibition.

He was of course proving that the torque movement of the bridge is the vastly more important movement, which noone disputes as far as I know.

[John Link]

That's interesting Dave. So if we want a loud guitar, then facilitate rotational freedom of the bridge. Might explain why ladder braced guitars are so loud and well suited for unamplified accompaniment to the blues. I remember one you built for a blues singer that you posted a video of. It was very raucous.

Might also explain why the slab cut and smallish narrow maple bridge plates on some Gibson X-braced guitars work so well. They leave a lot of room for rotation and flex. Old Martins often display a marked S-curve from the tension on the bridge, suggesting that they are braced so they do not resist rotation that much. Despite the aesthetic/craft "problem" of the distorted top, they sound pretty darn good.

Strategies that might push volume:
1. Flat sawed, thin, narrow bridge plate.
2. Weaker bracing in the bridge area.
3. Taller saddle height.
4. Decoupling bridge from X-braces.
5. Thin lower bout.
6. Ladder bracing with lots of room around bridge with respect to brace spacing, like John How does.
7. ??

I have Siminoff's book and will look that section up.

[John Parchem]

Yes but Keeping in mind the freedom of the rotation of the bridge has to be limited by the structural requirements of the top. Over rotation of the bridge will slowly or quickly degrade the instrument.

The discussion helped me see a few things for the requirements of a pinned bridge. Providing extra structural support like CF trusses helps keep the instrument from folding at the neck\ body joint but provides no support against the torque that is causing the bridge to rotate. I have seen older guitars with a noticeable dip in front of the bridge and a bow behind the bridge.

I have played with a higher saddle on a classical guitar. I found there is a trade-off that depends on the sound one is looking for. I found the higher saddle provided a loud almost percussive sound at the start of a plucked note but it sharply died away. This make sense as the more energy that can be delivered into the top the more quickly the energy from the pluck will drain away.

[Dave Bagwill]

Another consideration is: how much tipping/rocking force is really needed? As Carruth points out, a saddle angle (not a string angle) of 10 degrees or so will tip the bridge much less. In fact, a saddle angle of 1/2 the string break angle will almost reduce the tipping propensity entirely - which is not a desirable outcome.
He uses a 30 degree string break, and a 9 degree saddle angle; giving plenty of rocking motion and all but eliminating breaking out the bridge in front of the saddle slot. It also helps with intonation, he claims.

Thoughts?

[ken cierp]

As Carruth points out, a saddle angle (not a string angle) of 10 degrees or so will tip the bridge much less. In fact, a saddle angle of 1/2 the string break angle will almost reduce the tipping propensity entirely - which is not a desirable outcome.
He uses a 30 degree string break, and a 9 degree saddle angle; giving plenty of rocking motion and all but eliminating breaking out the bridge in front of the saddle slot.

This seems to me to be a giant leap conclusion from many dimensional assumptions, so what are the --- top material thickness, brace thickness, brace height, bridge plate size and thickness, braces style (ladder/X), specific brace pattern, X location, bridge size, saddle slot location from front edge and pins, soundboard area, plus sound board material?

[Dave Bagwill]

I understand your concerns. But I think there is something to it.

edit: there are a number of guitar makers (examples below) who do tilt the saddle, but mainly for intonation reasons. As far as 'tipping' goes, I don't think that any variables matter; no matter what strings, woods, thicknesses etc., the tipping force will be reduced somewhat by the tilt of the saddle. maybe/maybe not beneficial?
I confess that I don't tip 'em, but SCGC, for instance, does, to help with intonation.

Another edit: from some other luthier group, on this subject:
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Bashkin
The bottom of a saddle shouldn't be angled, if the saddle slot is not! Some Luthiers angle their saddles back a bit, (and slot) to compensate for the forward pressure the strings will cause... Actually, I only know of one that does this.. Michael Bashkin...

Back - angled saddles
The saddle slot is cut at an 8 degree back angle, which has several advantages. First the string pressure is focused down towards the bottom on the saddle slot, rather than forward against the front edge of the slot. This minimizes the stress on the front edge of the bridge and therefore the likelihood of cracking in front of the saddle. Additionally, because of the direct downward string pressure, under-saddle pickup performance is enhanced.
http://www.bashkinguitars.com/images/f0 ... dle_lg.jpg

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Santa Cruz does this with there current models. The SADDLE SLOT is angled back about 10 degrees toward the bridge pins. So the base of the saddle itself is still flat.

One advantage of this, as I understand it, is that intonation corrects itself as the saddle is lowered.

Most folks agree that you want the base of the saddle nice and flat in the bridge slot, so you have even contact across the entire surface.
________________________________________________________________________________________________________RHolmes
05-31-2007, 08:16 PM
At the Taylor road show I attended last week the Taylor rep mentioned that they angle it approx. 8 degrees.
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Along with being properly compensated for excellent intonation, my saddles are precisely fitted to their slots and back-tilted. This allows string pressure to drive the saddle directly down to the floor of the saddle slot rather than pushing it forward. The result is more effective transmission of vibration, especially beneficial to the use of an undersaddle pickup. The possibility of the bridge splitting from forward pressure by the saddle (another fairly common structural failure with conventional bridges) is also virtually eliminated. - Todd Rose guitars
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" Recently I looked at the beautiful guitars of Bruce Petros in the US of A. He has a very informative website obviously to impress prospective clients but sites like his are great for luthier sleuths like us! He mentioned that he does indeed tilt the saddle back 10 degrees and he uses an exceptionally wide saddle., I emailed him and asked him about it (making it clear to him that I am a luthier and was interested from a design point of view ) and he kindly emailed back saying that his saddles were 3/16 of an inch wide, saying that it is good for intonation to have that sort of width and signing off that he hopes I have fun. The extra wide saddle gives a wide intonation range and the back angle increases the efficiency of the strings ability to transfer vibration to the bridge."

[ken cierp]

I see no harm in tilting the saddle -- I can't see the correlation regarding better intonation -- I must be missing something. Several of the imports have this feature and I think Ovation and Tak. (Kaman)
I looked at it and for me it complicates my manufacturing process. It does seem it may change that Apex force transfer -- but looking at the equation does more energy get lost, shot off as the secondary force factor?