saddle design

[Mike Sandor]

I cut the slot in the bridge to fit a 1/8” wide saddle and piezo pickup. As the picture indicates, I used a thicker saddle blank and stepped it down to fit. Note that it is not fully inserted into the groove. When seated firmly in the groove, with the pickup, the stepped area shows about 5 thou. clearance. The question I have, are there any gains to leaving the extra width other than more room for intonation. I read that with more contact area between the strings and saddle, more string energy would be transmitted to the top. Then again, I see where many narrow saddles with a rounded over edge and minimal string contact to the saddle.
Thoughts?
Thanks, Mike

[Barry Daniels]

One question....Why?

Seems like a lot of extra work. Why not just route a larger slot in the bridge?

[Mike Sandor]

That was my original plan, but when I decided to use a pick up, I was advise to try to match the width to maintain consistant preasure. Not sure if that was the correct advise........

[Mark Swanson]

So just make the saddle as wide as the slot and call it good. There isn't really a big gain from a thicker saddle.

[Mario Proulx]

Bone has a lot of mass.

Mass makes a great mute.

Why do you want to have a built-in mute?

[Alan Carruth]

Mike Sandor wrote:
"I read that with more contact area between the strings and saddle, more string energy would be transmitted to the top. "

I doubt it. The forces that are generated at the top of the saddle by a vibrating string are well defined, and can be calculated pretty exactly (there's some non-linearity that complicates things, but it's 'small') for a 'stationary' bridge. Real bridges move, or you would not hear the guitar, but I digress. The point is that, so long as the string remains in contact with the top of the saddle throughout the whole vibration cycle, all of the force will be exerted on the saddle. It's possible that the saddle itself could act as a 'filter', if, for example, it's somewwhat flexible, and there's always the possibilty of poor contact with the bridge allowing for some relative motion, and reducing the power transmitted to the top. If the string does _not_ remain in contact, you'll probably hear it.

The main thing that keeps the string in contact is the break angle, and, as far as I can tell, that does not have to be very large to be effective. Archtops often use a 6 degree break angle, and some measurements I've got suggest that that's enough, although a _little_ more wouldn't hurt. Undersaddle transducers do seem to benefit from high break angles, as the static force makes them more effective for whatever reason.

Trevor Gore has mentioned that he feels the 'wrap angle', the amount of string contact with the saddle, makes a differece in the sound. This does not seem to be based on any objective data, but he's no fool. It's possible that more contact reduces sideways motion of the string across the saddle top by rolling or sliding. This might not, in itself, increase the force of the string on the saddle, but it it could result in the string producing two different frequencies as it vibrates: one from the 'vertical' motion of the string that's stopped at the saddle top, and a slightly lower pitch from 'horizontal' motion that makes the string lok longer as it rolls. Woodhouse, in England, has seen this effect for strings rolling on the fret tops.

Alan Carruth / Luthier

[Steve Senseney]

The comments from Alan are much more sophisticated than I can offer, with more experience, science and reading backing his information.

The problem I bring up is the use of the piezo.

I understand that the crystal (or piezo material) generates a current in relation to the pressure (or change in pressure) on the crystal. It the top is moving a great deal (as in a traditional acoustic guitar), a lot of the energy is sent to move the top. If the top is a solid body guitar, then most of the power in the strings would be more available to squeeze the piezo material.

This of course comes down to which sound do we want from the string/saddle/piezo combination.

So, what is the "best" for a piezo pickup? If we mounted the piezo at the top of the saddle (instead of underneath) would this be an improvement?

[Alan Carruth]

Top motion does alter the string forces on the top of the saddle, of course: I looked at that some in my 'string' paper that came out in 'Guitarmaker' in Issue 61, Fall of 2007, and that you can also see on my web site. The thing is that since it's top motion that makes most of the sound of the guitar the signal on the piezo actually mirrors in some respects the timbre of the instrument, so it's not a bad way to go to get something like an 'acoustic' sound. What you tend to get with a piezo on a solid body is a more or less 'flat' representation of the string forces, which may not be very interesting. A lot depends on the frequency response characteristics of the piezo pickup itself, of course. Resonances within the pickup elements, for example, may be the cause of the infamous 'quack', and it's hard to get rid of those entirely.

One big issue with any pickup technology on acoustic guitars is that every part of the instrument is making sound at some frequency. A single pickup, no matter how good, only looks at one spot, and sees what that spot is doing. I liken it to watching a ball game through a hole in the fence: you can only see part of the field. Two holes in different places, two pickups with different sensitivities, can often give a much better picture of the action. Even two- and three-element top transducers, which are usually piezos set up as acellerometers, can help a lot, but you have to get the placement of the elements right.

As an aside: the earliest piezo materials were crystals: Rochelle salt was one, and quartz is still used widely. The ones we see tend to be either ceramic (I've used lead-zirconium-titanate) or polymer ('Kynar'; polyvinyl-flouride). Common ceramic capacitors tend to be at least somewhat piezoelectric, which can be a real problem in some circuits. Anyway, the 'crystals' in our pickups are not generally crystals.

Alan Carruth / Luthier

[Bill Hicklin]

"The thing is that since it's top motion that makes most of the sound of the guitar the signal on the piezo actually mirrors in some respects the timbre of the instrument, so it's not a bad way to go to get something like an 'acoustic' sound...One big issue with any pickup technology on acoustic guitars is that every part of the instrument is making sound at some frequency."

Can that be improved by a dual system incorporating an internal mic, or is that just additional complexity for not much gain? (I've never tried to electrify an acoustic).

[Mike Sandor]

It took me a while to find my referance to this subject. The below is a quote from a article written by Ervin Somogyi,
"The average saddle is 3/32" to 1/8" wide. I use saddles that are 3/16" or more wide because it makes a saddle wide enough to offer adequate intonation compensation on a steel string guitar. The rationale for intonation compensation is the subject of another talk, but I want to say one thing about the contact characteristics between the strings and the saddle. If you have two virtually identical guitars one of which has the strings resting on a single high point of the saddle, and the other with the strings resting on a significant portion of the saddle’s top, I think you’ll find this second guitar works better. There is a better and more efficient coupling of kinetic string energy to the saddle by virtue of that extended contact. I can’t prove this, but I suspect if you pay attention to it you’ll get better results"
Easy enough to continue with the stepped saddle, and make a standard saddle and compare results,
Thanks,
Mike

[Celeste Hall]

If the strings are terminated with a tail piece like an arch top, then it would seem to me that saddle width would be an important in what and how energy is transfered to the top. If the strings terminate on the bridge itself, then all the energy at the bridge end of the string is going to end up in the top, regardless of bridge width (I am ignoring the energy loss due to imperfect molecular collisions). Not all the strings vibrational energy is going to be confined between the nut and saddle, in the arch top, the energy in the strings below the saddle is transfered to the tail block. In a flat top, the energy below the saddle ends up in the bridge, just like the string energy transfered through the saddle. The reason width and energy transfer relate is "energy flow density", energy per unit area. The higher the energy density, the more imperfect those molecular collisions become, and the less like a perfect solid our conduit becomes. The higher the energy levels, the less linear real materials act. At some point, we have to consider impedance interfaces and the reflections they cause. I don't have the data to model it as finite elements, but that might be fun and enlightening.

I am in the same situation as Mike, about to make a bridge with a piezo element below the saddle, and asking myself the same questions.