Official Luthiers Forum!

I don't play, much less build, nylon string guitars, but on steel string guitars, I have no doubt that the string doesn't "stop" cleanly/completely at the saddle(nor the fret). The steeper the break angle, the more complete/clean the 'stop', much like a musician can improve/alter his/her tone(and intonation) by paying attention to how they fret a note(finger pressure and placement). On guitars with very low or nearly non-existent break angles(older guitars with the saddle cut down to nothing) I've even noticed a distinct intonation issue dependent upon how hard a note is played(plucked); played lightly, it would intonate correctly, but played aggressively, the intonation would go flat, suggesting that the string's active length would no longer "stop" at the saddle. On inexpensive guitars that aren't worth the cost or bother of a neck reset and still had decent action with the cut-down saddle, I've cured the above and improved the overall tone by simply slotting the bridge(slotting the pin holes) to bring the strings closer to the saddle, providing some reasonable break angle. Even at the same height above the soundboard, there was a very noticeable change by changing the break angle.

Even capo placement(are capos ever used on nylon strung guitars?) can have a dramatic effect on tone; while placing the capo mid-way between frets can appear to work just fine, listening closely(and with a responsive guitar, of course) while moving the capo closer and closer to the fret does change the tone, to the point where many of us will place the capo right -over- the fret. Using a high quality capo with a small and hard sleeve, like a McKinney or Elliot, allows it to be placed right over the fret without muting the open notes(a bit of trial and error is necessary to find the 'sweet spot'...). A lot of us first learned of this through Tony Rice, BTW. Many would think that as long as the notes(fretted or capo'd) aren't buzzing that all is fine, but fact is, getting a clean/buzz-free note is just the beginning...
Soft rubber and/or spring-loaded capos need not apply(and shouldn't even exist, in my opinion, but I digress...).

As for the ideal bridge height, as well as string height above the soundboard, that will depend upon the whole of your build and design as well as its intended use/goal, and not any -one- factor.

On flamencos, quite often. But indeed rarely on classicals.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Sondre asked:
"Can someone explain to me how this works? Is it true for non-pinned bridges?"

I did my experiments on a classical guitar, so it's a fixed 'stop' bridge, but not one with pins. Anyway...

Keep in mind that the down force of the string on the saddle top is matched by an equal upward force behind the saddle. One way to think of it is to project the back string backwards until it hits the top. That could be seen as the effective location of the up force. For a low break angle that point will be pretty far back from the saddle, and it moves toward the bridge as the break angle gets higher. You could imagine the string being attached back at the tail end of the guitar, in which case there would be no upward force directly on the top at all, and the string would be trying to make a straight line from the nut to the saddle top to the top at the tail. This would push the bridge down, as you can see that it does on any guitar with a tailpiece.

Whatever you think of this model (and I'm not as sure of it as I'd like to be), it's hard to argue with data (unless you have better data!). On my test guitar I used an 18-hole tieblock. This allowed me to tie the strings off two different ways:
1) the 'normal' tie, where the string goes through the center hole in the front of the tieblock, and
2) a 'high' tie, where the string goes over the top of the tieblock, and into the center hole.
With a normal saddle height, this gave two different break angles: about 25 degrees and something like 6 degrees.

I also made a tall saddle, which put the string height off the top at 18mm as opposed to the normal 11 (don't try this at home!). With the tall saddle the break angle is 25 degrees using the 'high' tie. Thus I had two cases with the same break angle but different saddle heights, and two with the same saddle height and different break angles.

I clamped the guitar down around the edges, and measured the displacement of the top with and without string tension for each setup at two points, 50mm in front of and behind the saddle on the center line of the top. In each case the bridge rotated toward the nut by a certain amount, and also pushed downward. If you account for the amount the bridge was depressed in each case, you can find a 'centroid' of rotation: a fixed point behind the saddle that was not rotated either up or down relative to the top depression. It was closer to the saddle, and the same distance back, for the two 25 degree break cases, and further forward for the 6 degree break angle.

I also looked at the vibration modes of the top, and saw changes in each case. Naturally the high saddle made the most difference, but there were small changes with alteration in the break angle as well. This is consistent with changes in local stiffness caused by distortion of the top. Again, the changes due to break angle by itself were small, and they seemed to be pretty much inaudible in the listening test. Still there were changes (which surprised me!), and there is always the potential that they could make a difference in the sound.

Now you know as much as I do.

Well, Mario, I have only seen Tony Rice once, live, but have watched him on countless videos, and it seems to me that out of all the notes he plays, less than 5% of them are on open strings, and furthermore, at the speed at which he plays, it would be impossible for the listener to detect any tonal difference in the open strings when he does play them...which is not to say that your capo placement is not without merit, but I sure as hell ain't going to trade in my Shubb for an Elliot any time soon just to get a 5% improvement in tone...

and it seems to me that out of all the notes he plays, less than 5% of them are on open strings, and furthermore, at the speed at which he plays, it would be impossible for the listener to detect any tonal difference in the open strings when he does play them...

You're ignoring the time he spends playing rhythm, which is in fact, the majority of the time, and the main reason for using the capo in the first place. Face it, once out of first position when playing lead, the capo is no longer necessary, and most lead playing is done "up the neck" and no longer in first position. The capo is mostly used because the open strings lend a lot to the rhythm's tone and, especially, drive, versus the use of closed(barre) chords. Tony discusses it to great lengths in one of his earlier teaching videos or(gasp! I'm showing my age!) tapes.

Alan, thanks for taking the time to explain! I believe I managed to wrap my head around it now.

Sondre

I'm thinking if you change the break angle without altering the height of the strings above the top then you would have to move the anchor point of the strings which would, in turn, somewhat change the rotational forces applied to the top.

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Steve Smith
"Music is what feelings sound like"

I don't know enough to disagree with Mr. Carruth very often, but I'm pretty sure that last statement is incorrect.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon