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estebanana -> RE: New Guitar problem (Feb. 25 2014 1:23:24)
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quote:
I really don't understand this compensation thing at all. It seems totally arbitrary when you consider a technique as basic as vibrato. Players need to learn to play in tune, simple as that. Up high, down low, high action, low action, it all depends and makes huge difference before you go slapping your fingers on the fretboard, applying un even pressures with non machine like fingers. Then there is the fret height and finally string imperfections which is a huge factor. I can't see how a compensated bridge is doing a darn thing in the midst of all those playing variables. In that sense I am with mr. Reyes, but I guess I would really need to get a good sampling of guitars compensated and not, to focus a comparison.
If the string length was not compensated to fit the scale length you would hear it loud and clear as out of tune. It is a separate issue from player malfunction. You could not play in tune without a compensated scale.
There a few things at play in compensation which makes it less a science and more a trial & error problem - The diameter of the core of each string vs. how flexible it makes the over wound string is one factor. The diameter of a non over wound string and it's flexibility is another. The other factor is that pressing the string down does shorten it a bit. So the two combined factors that shorten a stopped string are: pressing it down and stiffening at the stop point.
Let's look at the part where the string stiffens at the stop point:
A string like the nylon treble G tends to play sharp, the reason is that it is a fat string in relation to how flexible it is. When you press it to a fret and stop it, the string does not actually stop at that fret because it's thickness creates a small length of string after the fret that becomes stiffer due to contact with the fret. There is a very, very small length of string that becomes like a little pipe due to contact tension with the fret and to compensate for that after length that tightens up and becomes harder the string length needs to be lengthened. The little stiff pipe section of string shortens the string length.
That is why G strings on Nylon string guitars often have longer compensation that the other strings. You can sometimes see wide saddles with a notch letting the G string ride farther back towards the tie block. All the strings do that physical hardening where they contact being stopped, and at the nut also, but the G string is biggest in diameter and sometimes requires a bit more compensation due to it's tendency to create a stiffer after length at the stop point.
Ok, do you get what I mean? I wish I knew the actual terms in scientific language for that phenomenon of stiffening at the stop point, perhaps Richard Jernigan knows the words?
If you got that far then there's more to compensation; and it is different in how one applies it for nylon strung guitars and steel strung guitars. The same principles apply, but because steel strings have different core to winding ratios than overwound nylon strings they flex at the stopping point in a way that nylon strings don't so they are compensated in a different order.
In general on both nylon and steel strung guitars the thickest overwound basses get more compensation. Theoretically nylon strings should get more bass compensation, but they seem to play in tune if all strings are compensated equally, with the occasional G string that needs a bit more. Steel strings need more bass compensation for the E and A, but the D with its small core can ride more toward the nut. Look at the long slant of a steel string saddle and you will see more bass compensation.
Ok so this is why, in some cases, changing the gauge of strings sets effects tuning. If the guitar plays sharp and you change the set to a smaller gauge core with a smaller G the guitar might play less sharp. The reason is because the smaller core in the overwound strings changed the amount of stiffness where the string is stopped.
So now you ask why does this matter? If you have not seen the problem yet, here it is, I'll say it again: When the string gets stiffer at the stopping point, it changes the vibrating length of the string relative to the scale. The compensation is to lengthen the string so when it is stopped, the length and scale length are more correct.
That is compensation in a nutshell. It's much more complex to try to figure it out so we generalize by making the saddle set back a few mm depending on how long the scale is and how high the action will be. A shorter scale like 650mm gets slightly less compensation than 660mm.
Some guitar makers have worked out compensated nuts where you go after the problem of the G string from both ends by setting G longer and the other strings at various lengths at the nut- in addition to saddle set back. Even the most analytical guitar makers will tell you that the system is not perfect.
I hope that was not confusing and spelled out some of the reasons why flamenco guitar saddles are compensated.
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