Saddle Break Angle Experiment

[Matt Mustapick]

Originally Posted by gitnoob

I don't disagree, but the net effect should be that break angle has a slight effect on the static deformation of the top, right?

I don't think so. I think these forces act on the bridge, which itself is essentially rigid and transfers these forces out to the bridge's external dimensions...the footprint of the bridge where it is joined to the top. Whatever the arrangement of stresses within the bridge, the forces the bridge relates to the top remain (essentially) unchanged, no? As an analogy, if I put tremendous force on a see-saw very close to the fulcrum that's no different than putting much less force further from the fulcrum. It would make no difference to the kids sitting on it. In my view, the forces imparted by the bridge are determined only by the dimensions at the borders of the system, not the details of the geometric arrangement within it. So that means the string height and the bridge footprint may matter, but not the other details...essentially.

[gitnoob]

I'm not quite seeing it yet -- I guess I don't see how the bridge can be isolated from the top. If the force distribution changes within the bridge (which we agree on), how can the top not experience that change, even if it's a small change?

[Matt Mustapick]

For instance on a seesaw,
torque = lever arm × force,

So if I apply 1 newton of force 6 feet down a lever arm, I will generate the same torque as if I'd applied 2 newtons of force 3 feet down a lever arm. So, very broadly, that's the basic concept I'm applying when I say that the arrangement of forces within the bridge shouldn't matter.

[gitnoob]

I think I get it.

My mental picture is of a constant pulling force on the string and a different force distribution between the saddle and the anchor depending on the anchor location and the angle between them. My "fulcrum" moves depending on that distribution.

[Matt Mustapick]

I see. In my view the fulcrum of the seesaw is analogous to the footprint of the bridge, which is not dependent on the details that determine break angle.

[steveyam]

Originally Posted by gitnoob

I won't give away the answer, but I believe it is something Alan has already determined.

The reason this should interest most people is that some guitars may seem like they need a neck reset because of the "low saddle." Maybe. Maybe not. If the only problem is a low break angle over the saddle, probably not.

Once again, great work Gitnoob. You deserve a knighthood for your experimentation and research. I look forward to Alan's findings too. It's objective, theory based research like this that is gonna help everyone understand, build and fine tune our guitars better.

One point, a low saddle (with a 'bad' break angle) is easily cured by simply deepening the bridge pin string slots with the appropriate tool. Very rarely is there a need for a reset.

[gitnoob]

Originally Posted by murrmac123

What I would like to know is, where exactly is that point?

I thought this was a good question, so I did one more experiment.

When is the break angle too low, and what happens at that point?

I didn't measure this angle, but looking at it, it appears to be pretty close to zero.



What happened at this point was interesting. There was still saddle contact, so volume seemed pretty good and there was no buzzing. Rather, the pitch went in and out of tune -- sort of a slow warble. I imagine that the string was sliding back and forth a bit over the surface of the saddle, effectively gaining a small bit of additional length and dropping in pitch as it slid.

[murrmac123]

Interesting experiment, gitnoob.

In the pic, it looks like the string winding is sitting on top of the saddle (can't tell for certain).

If the winding is in fact sitting on the saddle, perhaps you could try again using spacers in front of the ball end (old ball-ends would be ideal) to pull the string winding away from the saddle and see if that makes any difference to the pitch warble.

Or, you could wind the string round the pin and thread it through the ball end ...

[steveyam]

Originally Posted by gitnoob

I thought this was a good question, so I did one more experiment.

When is the break angle too low, and what happens at that point?

I didn't measure this angle, but looking at it, it appears to be pretty close to zero.



What happened at this point was interesting. There was still saddle contact, so volume seemed pretty good and there was no buzzing. Rather, the pitch went in and out of tune -- sort of a slow warble. I imagine that the string was sliding back and forth a bit over the surface of the saddle, effectively gaining a small bit of additional length and dropping in pitch as it slid.

Hmm. Don't forget hard strumming. It's different to just plucking a string in 'test mode'. Hard strumming will cause all sorts of movement, bad overtones, resonances, harmonics etc on a very low break angle.

This is an interesting thread. I had a neck reset done on my guitar a couple of years ago and did not notice any difference in tone. Before the neck reset, there was very little saddle left, just enough to keep the string off the bridge, and almost no break angle, especially on the high E. Now there is plenty of saddle and break angle, but I do not hear any difference in volume or tone. Just my experience.

[rwskaggs]

As I ponder the mysterious workings of my guitars, I appreciate the hypotheses and experiments you are trying out here, Gitnoob. My imagination sticks in a rut without the sort of 'outside stimulii' you offer. Keep challenging us all!

[gitnoob]

Originally Posted by steveyam

Hmm. Don't forget hard strumming. It's different to just plucking a string in 'test mode'. Hard strumming will cause all sorts of movement, bad overtones, resonances, harmonics etc on a very low break angle.

Yes, movement is the key. You need sufficient downward force on the saddle to prevent movement of the string on the saddle.

The angle isn't the only factor in determining that. String tension is also a factor.

So the real question here should be something like: if you have a budget of 20lbs of force, how much of that force do you need to transfer to the saddle in order to keep the string from moving once you try to displace it with a pluck?

The answer appears to be "not much." I wonder if there's a way to get more specific.

[Alan Carruth]

I spent 'way too much time a few years ago measuring the strengths of the different signals that a plucked string puts on the saddle top. Basically, what I found largely confrims the math you can get from, say, Fletcher and Rossing, 'The Physics of Musical Instruments'. There are a couple of little non-linear effects in there that keep things 'interesting', but they don't usually matter (until they do, and then they can matter a lot!). Anyway, the forces you get from a string that bears firmly on a fixed and rigid saddle top are well defined, and can be calculated.

The question, then, is how much break angle do you need at the saddle to transmit all of the signal to the guitar? Basically, it turns out that it's probably not much more than the maximum downward angle you'd get at the saddle if you pushed the string all the way down so that it hit the fretboard. Any more displacement of the string and you just get buzzing. Any less break ange and the string can hop off the top of the saddle once per vibrating cycle. You'd hear that, so, if you're not hearing problems, you probably have enough break angle.

As for a number, I note that Benedetto uses a break angle of six degrees on his archtops. In that case, too much down force on the bridge can adversely effect the sound (I know because I checked it out).

On a flat top, as has been pointed out, the down force on the top of the saddle is balanced by an up force on the bridge where the strings contact it, so you've got a torque. This does change with changes in break angle, and the static distortion of the top also changes. Whether this effects the sound is a matter for further experiment.

The greater the break angle on the saddle on a flat top the greater the tipping force on the top of the saddle tending to break out the front of the slot. This can be minimized by tipping the saddle back; ideally to the bisector of the break angle. We've talked about that in another thread.

The bottom line for me is that we saw a statistically significant difference in people's perception of the sound of the guitar with a change in string height off the top, but not so with a change in break angle. We were able to find a couple of measurable differences in the sound spectrum when the string height was changed that could correlate with the altered peception. However, we could not entirely rule out the idea that greater down pressure on the top of the saddle transmitted slightly more energy to the top. It's possible that the 'low' break angle we used was too low, and that could acount for the slight measured differences from a very large change in break angle. As always, we need more data, and the question is whether it would be worth while to get it. Right now, I have to do something that pays for a while.

[PaulTensor]

Just putting my measly 2 cents in here. I was displeased with my instrument (seagull s6) with regards to its string height. It was properly humidified and the truss rod was just right. It seemed shaving the saddle was the common way to lower the action a bit. I didnt go overboard or anything and made sure it was perfectly level when I was done. With MY guitar and MY experience, doing this made the guitar play incredibly, BUT, was a detriment to tone and volume.

So many variables come into play. Lowering the saddle decreases break angle on the bridge end, but would increase it for the nut. Also, someone a ways back mentioned a greater upforce from the bridge pins. But thats assuming zero friction between saddle and strings which is impossible. Also, less of a break angle would increase torque on the top, so thats something to think about.

Lastly, isnt the ultimate goal to create maximum opportunity for vibration to occur? If we want the clearest path for vibration to occur, we would want the saddle smashed into the bridge as hard as possible. So we would want maximum downforce, regardless of any negating forces.

(one last rant. Im no physicist, but im pretty sure to have a true 0-net force (between saddle and bridge pins) an opposing force would literally have to be pulling straight up on the saddle. Which it isnt. I know all the forces eventually equal out, however, theres all kinds of vectors going with that which F's up thinking about this in simple terms.

All this science is slave to our ears, which is all that matters at the end of the day. But in my personal experience, diminishing that downforce by shaving the saddle made my guitar sound worse.

[ac2300]

You seem like a perfect subject to test our Power Pins, interested?