String height above bridge: How tall is too tall?

[ChalkLitIScream]

Im aware that ideal string height above the soundboard is 0.50''.
I did some calculations, and to get my high E string to have a .50'' string height, the saddle protrusion would be 0.20'' (my bridge is flat and is 0.30'' high). for the particular string, i understand that this height is safe.

Now with my high E being 0.5'', the tallest string height (D string) would be 0.57''***, and saddle would protrude 0.27'' from the bridge). Would the tension exerted in this scenario be safe?

I plan to use a bluegrass gauge strings, tuned 2 steps down, giving a total tension of 136lbs. ( I occasionally may tune to open D, with a total tension of 153lbs)

(For reference, standard light gauge (12-53) has about 156lbs of tension, standard tuning)


Thanks all.


***the string height would not actually be 0.57'' as the D string is slightly lower than the highest part of the saddle. Actual height would be about 0.55'' for the D string.

[Rodger Knox]

That depends on a couple of things. The usual problem with high saddles is splitting out the front of the bridge, so how far back the slot is from the front of the bridge is important, and will determine the "safety" of that projection.

There's also the rule of thumb that there should be as much saddle below the top of the bridge as there is projection above it. It doesn't sound like you have that much depth in the saddle slot.

The simple solution is to route the saddle slot with a little back angle (6° to 10°) to reduce the tipping force.

[Bruce Sexauer]

Assuming you mean off the top rather than the bridge, 9/16” usually works okay, and 5/8” makes me have trouble sleeping. Off the bridge 3/16 is a lot but still works, usually. 1/4 will tend to break things.

[ChalkLitIScream]

Roger, Bruce, thanks for your expert replies.

There is .24" of bridge in front of the saddle slot on the treble side and graduates to .35" at the bass side. What say ye?
The saddle slot is 3/16 deep, giving me a suggested saddle height of 6/16. The saddle I had in mind would be .46" tall. That's a little over 20% more and be .085 taller. Would this be testing my luck?

[Rodger Knox]

The slot is pretty far back, that should work OK. It's not that the height of the strings off the top is too high, it's more that the bridge is a little thin.

[Alan Carruth]

As Roger says, it would help some if you could rout the slot a bit deeper, even if you can't angle it back. The fact that the slot is so far back from the leading edge of the bridge really helps. Other than that, don't do anything, such as ramping the slots, that increases the break angle. If they're already ramped I'd fill them in to move the break point back as far as possible from the saddle top. The 'need' for anything more than about 15-20 degrees of break angle is, as far as I can tell, a myth. It's the break angle over the top of the saddle that produces the tipping force that causes bridges to split out in front, not the height of the strings off the top.

Having the strings higher off the top will affect the tone, however. The 'ideal' height off the top is probably a matter of opinion, although a half inch is pretty normal.

[martingitdave]

How tall is too tall?:

When your hands hurt.

I have (essentially) two of the same guitar. One has a high setup and sounds amazing. But, I can't play it for more than an hour. So, I got a used on and had it setup for lower action, flatter fret board and added a pickup. The result is easier to play and sounds good, but can't compete acoustically with the stock guitar.

[ChalkLitIScream]

Originally Posted by martingitdave

How tall is too tall?:

When your hands hurt.

I have (essentially) two of the same guitar. One has a high setup and sounds amazing.

I'm trying to have a tall saddle and very low action. That's ppossible by adjusting the neck angle. I always thought that you either could have a guitar that plays great but doesn't sound as good as it could, or have a loud guitar which will end up maiming your fingers, haha. Its possible to have both, but now it seems that you can have a loud guitar that plays great...but only for a few minutes before it implodes ya can't win.

[yellowesty]

On the last two guitars I've built, I've used a floating fretboard extension and a bolt-on neck. That means that the saddle height (and, therefore, the height of the strings over the soundboard) is a separate issue from the action (the height of the strings over the fretboard).

As a far less experienced builder than many on this forum, this design gives me a lot of flexibility (and error recovery) in my builds. I use a slightly recessed (by the thickness of the sides) butt joint between the neck and the headblock, so adjustment of neck position (and, if necessary, angle) can be made easily after finishing and stringing up.

I'm surprised that this approach is not more common.

[ChalkLitIScream]

Thanks for chipping in Alan. read a similar post a few days ago and it drove your point about the forces that may crack my bridge.

Ill try to summarize what I learnt here:

-saddle slot should be deep enough to house (atleast?) half of the saddle's height. exposing too much saddle above the slot can cause cracking

-need sufficient amount of bridge between the saddle slot to prevent cracking. I will trust that .24'' material is sufficient.

-break angle affects how much force the strings apply, 'trying' to pull the saddle forward. too much can cause the bridge to crack. changes with the saddle height relative to bridge (not taking ramping into account)

-tone. higher string height gives more torque applied to the top, and is the main reason Im trying to change the geometry of my guitar.


Feel free to chip in. Im quite enjoying this physics lesson!

[Alan Carruth]

In the extensive experiment I did comparing the effects of changing string height above the top and break angle as independent variables, I found:
1) as long as there's enough break angle to keep the strings on the saddle top all through the cycle of vibration, the actual amount of sound produced was not changed either by altering the break angle or the string height off the top, and
2) changing the string height off the top does change the timbre of the sound.

When you pluck a string you're putting in a certain amount of energy, and that's all there is to work with. Assuming the efficiency of the box (which depends on how it's built) is the same, and the strings stays in contact with the saddle top (so that it transmits all the force), you'll get the same amount of power out of it. I used a mechanical plucker that produced the same force on the string within 2% every time, and allowed for precise control of the place and direction of the pluck along the string. Setup 'A' had the strings 11mm off the top with a 25 degree break, 'B' was the same height off the top with 6 degrees of break, and 'C' was 18mm off the top with 25 degrees of break. I did six plucks on each open string for each case, with the pluck in the same spot and the direction perpendicular to the plane of the soundboard.

In recordings of the output made on my computer with the same setup each time there was no difference in the rise and fall times of the signal, nor in the maximum amplitude. It looked as though the total energy in the sound was the same each time for a given string, no matter that the bridge setup was.

What did change was the relative amount of power in different overtones, but only when the string height off the top was changed. There were three 'signals' at the top of the bridge:
1) 'transverse', where the up and down motion of the string pulled the top up and down like a speaker cone,
2) 'tension', where the twice-per-cycle tension change of the string pulls the top of the saddle toward the nut, rocking the bridge, and
3) 'zip tone', a longitudinal compression wave in the string which pushes and pulls the saddle top similarly to the tension change.

The 'transverse' signal produces most of the sound, since it is a larger force signal than the others, pushes the bridge in a way that produces more movement for a given force, and is also more effective at producing sound than rocking the bridge. Altering the string height or break angle doesn't change the way this works.

Moving the strings higher off the top gives the string rocking signals, the 'tension' and 'zip' signals, more leverage to rock the bridge, and this produces more power at those frequencies. The 'tension' signal, acting twice per cycle of the string, introduces a bit more of the second partial, and sometimes the fourth. The 'zip tone' is normally dissonant, and also high pitched, so a little bit of it can make a fairly large change in the timbre, and there was more of it when the strings were higher off the top.

Again, as far as I could tell, these changes in the signal did not add to overall power output. Since the 'total available horsepower' of the string is established by the plucking force and location, and the guitar is only so effective at changing that into sound, an increase in output at one frequency is likely to be balanced by decreases elsewhere. I will say that measuring the actual power output and efficiency of a guitar is a tricky thing do do. I only know of one such measurement, and I'm certainly not able to duplicate it. At any rate, it seems to me that timbre changes due to altering the height of the string off the top are changes in the mix of frequencies in the signal, and not so much in the actual power output, as far as I could tell.

[lar]

very interesting Alan.

So the string height changes the tone of the guitar but not the volume (hopefully I'm paraphrasing correctly).

So the 'zip' and 'tension' frequencies are relatively high? Say the string is vibrating at 440 hz, then these two frequencies would be 880hz?

You were plucking 1 string at a time I assume, as opposed to strumming. Did you pluck all 6 strings? And you were plucking perpendicular the top, to get the most output I assume. Any idea how a typical guitar player plucks strings? It's not perpendicular but is the plane of the vibration typically 20deg, 40deg, off the perpendicular? I'm sure it changes whether its a strum, finger, or a flat-pick, so maybe there isn't a single answer. Or is it more of a circular motion?

[Imbler]

Alan,
Thanks for your patience in answering all these questions. I read every response from you even when you have previously addressed it, as it seems to sink in a little deeper each time!
Mike

Originally Posted by Alan Carruth

In the extensive experiment I did comparing the effects of changing string height above the top and break angle as independent variables, I found:
1) as long as there's enough break angle to keep the strings on the saddle top all through the cycle of vibration, the actual amount of sound produced was not changed either by altering the break angle or the string height off the top, and
2) changing the string height off the top does change the timbre of the sound.

When you pluck a string you're putting in a certain amount of energy, and that's all there is to work with. Assuming the efficiency of the box (which depends on how it's built) is the same, and the strings stays in contact with the saddle top (so that it transmits all the force), you'll get the same amount of power out of it. I used a mechanical plucker that produced the same force on the string within 2% every time, and allowed for precise control of the place and direction of the pluck along the string. Setup 'A' had the strings 11mm off the top with a 25 degree break, 'B' was the same height off the top with 6 degrees of break, and 'C' was 18mm off the top with 25 degrees of break. I did six plucks on each open string for each case, with the pluck in the same spot and the direction perpendicular to the plane of the soundboard.

In recordings of the output made on my computer with the same setup each time there was no difference in the rise and fall times of the signal, nor in the maximum amplitude. It looked as though the total energy in the sound was the same each time for a given string, no matter that the bridge setup was.

What did change was the relative amount of power in different overtones, but only when the string height off the top was changed. There were three 'signals' at the top of the bridge:
1) 'transverse', where the up and down motion of the string pulled the top up and down like a speaker cone,
2) 'tension', where the twice-per-cycle tension change of the string pulls the top of the saddle toward the nut, rocking the bridge, and
3) 'zip tone', a longitudinal compression wave in the string which pushes and pulls the saddle top similarly to the tension change.

The 'transverse' signal produces most of the sound, since it is a larger force signal than the others, pushes the bridge in a way that produces more movement for a given force, and is also more effective at producing sound than rocking the bridge. Altering the string height or break angle doesn't change the way this works.

Moving the strings higher off the top gives the string rocking signals, the 'tension' and 'zip' signals, more leverage to rock the bridge, and this produces more power at those frequencies. The 'tension' signal, acting twice per cycle of the string, introduces a bit more of the second partial, and sometimes the fourth. The 'zip tone' is normally dissonant, and also high pitched, so a little bit of it can make a fairly large change in the timbre, and there was more of it when the strings were higher off the top.

Again, as far as I could tell, these changes in the signal did not add to overall power output. Since the 'total available horsepower' of the string is established by the plucking force and location, and the guitar is only so effective at changing that into sound, an increase in output at one frequency is likely to be balanced by decreases elsewhere. I will say that measuring the actual power output and efficiency of a guitar is a tricky thing do do. I only know of one such measurement, and I'm certainly not able to duplicate it. At any rate, it seems to me that timbre changes due to altering the height of the string off the top are changes in the mix of frequencies in the signal, and not so much in the actual power output, as far as I could tell.

[Bruce Sexauer]

In my experience, increasing string height above 7/16 increases volume at the expense of sustain, and increases clarity at the expense of midrange. Strictly subjective observations.

[Alan Carruth]

lar:
The 'tension change' signal is at even multiples of the string fundamental. For the low A with a fundamental pitch of 110 Hz, the tension change signal is at 220, 440, 660, and so on.

The 'zip' pitch varies a lot depending on the string length, material and construction. For steel and nylon strings it is often somewhere between the 7th and 8th partials. Winding lowers the zip pitch, and also the fundamental of the string, so the multiple stays pretty similar.

"You were plucking 1 string at a time I assume, as opposed to strumming. Did you pluck all 6 strings?"

Yes; each one six times, to see how much variation there was.

" And you were plucking perpendicular the top, to get the most output I assume.e sense"

Partly; it was also the easiest way to do it with my setup. As much to the point, it was more 'pure' in some sense: it might have been hard to separate out effects from sideways motion. It would have been nice to have looked at a bunch of different angles, but such things take time. As it was I did 108 plucks, at ten minutes or so of setup for each. Then came evaluation of the data, which took much longer.

" Any idea how a typical guitar player plucks strings?"

All sorts of ways. One book on Classical playing spends a lot of time talking about how to get perpendicular motion.

"It's not perpendicular but is the plane of the vibration typically 20deg, 40deg, off the perpendicular? I'm sure it changes whether its a strum, finger, or a flat-pick, so maybe there isn't a single answer. Or is it more of a circular motion?"

The string doesn't usually start off with a circular motion, but it can become so through feedback from top motion. Strings that are not really round, or even just have scratches on them, can follow very complicated trajectories.

'Volume' is a subjective term; two signals that have the same amount of power can have very different perceived volume, depending on the mix of partials, among other things. For example, since 'normal' hearing is most sensitive between 2000-4000 Hz, a sound with a large proportion of energy at those frequencies can seem loud at low power. That's why the high pitched 'zip' tone can be so audible, even when there is not much energy in it.