saddle design question (Full Version)

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X -> saddle design question (Jul. 10 2019 2:05:04)

Hi, luthiers,

Guitar nerd with physics background here curious about two things:

1. Came across this pic of a grooved saddle:

http://www.graphtech.com/products/brands/nubone

which reminded me of my very first guitar ever, an archtop with the f-holes and such a saddle. My question is, why have the grooves disappeared on today's saddles? It would seem to me that allowing the string to vibrate parallel to the soundboard would mean the vibrating length is more than intended, though the error is admittedly small, probably about half a millimeter in a 650cm string. Am I wrong?

2. (See other thread)

Thanks, guys, I'm thinking of commissioning a personal guitar and really want to know. And BTW, I did search the archives before posting this.



constructordeguitarras -> RE: saddle design question (Jul. 10 2019 16:05:13)

Grooved saddles are from the 60's when it was cool to be groovy. [8D]

But seriously, I suspect that a grooved saddle puts more strain on the right hand--not such a problem if you're playing a steel-string guitar with a pick. And we position the bridge to compensate for changes in string length that occur during playing.



X -> RE: saddle design question (Jul. 10 2019 23:17:41)

Hello, Ethan,

Thanks lots for your attention. However I don't think I explained myself well. In my opinion, my question really has nothing to do with compensation.

Consider this: If I pluck a string, the string vibrates in many directions. We can think of the vibrations as of two kinds: vibrations parallel to the soundboard surface, and vibrations perpendicular to the soundboard surface.

The string length for the perpendicular vibrations is fixed (for an open string) by its end points, at the nut and at the saddle.

The string length for the parallel vibrations is also fixed at the nut, but since the end at the saddle isn't fixed in place by a groove, the string will tend to slip back and forth over the saddle, so that its saddle end point has effectively moved towards the tail block, and the length of the vibrating string is effectively longer (the note will play flat).

Compensation will not fix this, because the problem of saddle slippage will be present however you compensate.

As I said, the error is very small and it probably adds to the timbre of the note, but it's questions like this that distract me when I should be practicing my picado.



Andy Culpepper -> RE: saddle design question (Jul. 10 2019 23:27:36)

The grooves have not disappeared, they were never there to begin with. Violin bridges are usually grooved because of the extreme curvature of the fingerboard and bridge and the relative softness of the bridge material. Some archtops have violin-style bridges so maybe that's why yours was grooved. But yeah, guitar saddles don't have grooves unless someone messed up the string spacing, or they were worn into the saddle over time.



Andy Culpepper -> RE: saddle design question (Jul. 10 2019 23:31:04)

quote:

The string length for the parallel vibrations is also fixed at the nut, but since the end at the saddle isn't fixed in place by a groove, the string will tend to slip back and forth over the saddle, so that its saddle end point has effectively moved towards the tail block, and the length of the vibrating string is effectively longer (the note will play flat).


You're overthinking it. You would be talking about something on the order of hundredths or thousandths of a millimeter, not even close to half a millimeter.



constructordeguitarras -> RE: saddle design question (Jul. 11 2019 1:18:13)

There are several other more severe causes of guitars being out of tune. And have you noticed that there are three string lengths anyway (EE, BA, GD)? In the profound words of a cabinetmaker I worked with: "It is what it is."



timoteo -> RE: saddle design question (Jul. 11 2019 5:47:12)

quote:

The string length for the parallel vibrations is also fixed at the nut, but since the end at the saddle isn't fixed in place by a groove, the string will tend to slip back and forth over the saddle, so that its saddle end point has effectively moved towards the tail block, and the length of the vibrating string is effectively longer (the note will play flat).

Your model is wrong. So not only are you overthinking it, as Andy said, but you're also underthinking it because you've simplified things too much.

When a string is plucked, you're effectively increasing the tension of the string, which pulls the top of the saddle forward toward the nut. The whole bridge rotates, pushing the top of the guitar down into the body in front of the bridge and pulling the top up out of the body behind the bridge. That's what makes the sound!

And while any minute wiggle back and forth along the saddle may effectively lengthen the string, that's part of the compensation that Ethan mentioned - the saddle is positioned so that the string sounds right, it's not entirely positioned based on an exact mathematical calculation.



JasonM -> RE: saddle design question (Jul. 11 2019 15:49:26)

How about those little brass looking spring spacers instead of a regular saddle. I’ve seen them on this Conde and also a Manzanero:
http://www.condehermanos.com/en/tienda/guitars/special-models/al-di-meola

Looks like they have grooves and let you adjust string spacing, but I don’t know much about them.



Richard Jernigan -> RE: saddle design question (Jul. 11 2019 22:40:29)

quote:

ORIGINAL: timoteo

When a string is plucked, you're effectively increasing the tension of the string, which pulls the top of the saddle forward toward the nut. The whole bridge rotates, pushing the top of the guitar down into the body in front of the bridge and pulling the top up out of the body behind the bridge. That's what makes the sound!



It's a little more complicated than that. In fact, it's a lot more complicated than that. There are two more components of force on the bridge beside the force along the length of the string. When the string is plucked it sets in motion a lateral displacement, perpendicular to the length of the string. When the lateral displacement wave reaches the saddle, it exerts a force perpendicular to the string length (and the change in tension) on the saddle. The lateral displacement force can be resolved into two components, one that tries to move the saddle--and hence the soundboard--up and down, the other component which tries to move the saddle sideways.

If the break angle at the saddle is acute enough, and the string tension is strong enough, the sideways force never overcomes the static friction, and the string doesn't slip along the bone. This is the case in every successful guitar I have examined in detail.

Under the same circumstances, the string never leaves the saddle in the upward direction, so the effect is to move the bridge-and the sound board-up and down. It is this component of force which is most effective in producing sound, though the other two each play a role.

More in considerable detail, with a lot of measurements in Al Carruth's great paper, "String Theory": http://www.alcarruthluthier.com/Downloads/stringTheory.pdf

RNJ



X -> RE: saddle design question (Jul. 11 2019 23:33:52)

I'll look through the Carruth paper this week, Richard. I'll have to pick up luthier jargon like "break angle" to fully understand it, but it seems like my kind of paper. I'll come back and repost after I've read it

But to summarize: the consensus here is that grooved saddles add nothing to a guitar's sound. It was never explicitly stated, but I guess the there's also a consensus that neither do they detract.



Richard Jernigan -> RE: saddle design question (Jul. 12 2019 0:25:16)

Break angle: The string changes direction when it passes over the saddle. "Break angle" is the angle made by the string in this change of direction. The more acute the break angle is, the more downward static force is directed by the string against the bone.

If the break angle were too obtuse, when plucked the string could slip sideways on the bone, or it could lift off the bone. Either case would immediately be noticeable due to the loss of energy transmitted from the string to the bridge, or the buzz of the lifiting string.

RNJ



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