GUITAR STRING TENSION GUIDE
When you tune a string to pitch you are actually applying a tension till the strings reaches a given note. The string is built (material, structure and diameter)
to resist almost twice its announced tension without breaking.
The string is fixed at two ends: the tuners and the tailpiece (or string's anchor pont).
The portion of string vibrating lays over the nut and the bridge saddles. These are called "break angles". The portion of strings going from the nut to the tuning gears and from the bridge saddles to the tailpiece or anchor points are not directly involved in vibration but have an impact on the "feel" of your instruments especially when bending. Let's see how it works.
15% / 30% of the total.
While vibrating, the strings forms an elliptical pattern which is fixed at the anchor points (in the case of a guitar the nut and the bridge saddles)
and has its maximum width at the centre of the strings, which corresponds to the 12th fret position on the fretboard.
Pitch and all the rest being the same a heavier string will require greater tension and will be harder to bend. It will have a reduced vibration pattern, will deliver more sustain, more volume and a brighter tone with more attack.
Conversely a lighter string will require less tension, will have a wider vibrating pattern and will deliver a smoother tone with less volume.
over the 12th fret.
Variations in the strings length influence strings tension and "feel".
Therefore a longer scale will require more tension for the same pitch than a shorter scale.
This is why average, given the same gauge of strings, a Les Paul (628mm scale) will result to be smoother to play than Strats (647,7mm).
TENSION AND FEEL ON THE FRETBOARD
As we said before, every musical instrument has some portions of the strings beyond the nut and the saddles, which are not directly involved in the vibration which generate the note.
These portions of strings does NOT influence the tension but has some impact on how we "feel" the strings on the fretboard especially when bending notes near the nut and how we "feel" the attack of the strings while picking near the bridge.
For example changing the tailpiece angle on a Gibson Les Paul does NOT influence tension at a given pitch as some expect. In fact what happens is that lowering the tailpiece we actually increase the tension so, as an example, an A tuned strings may also result in a C. In fact right then it is but we will soon have to tune back to A using the tuning machines and this will return the string to the exact tension as before. With the tailpiece lowered.
So the rule is: everything else being the same to that pitch always correspond the same tension no matter what's up beyond the saddles and nut.
So how this portion of "dead" strings affects our instrument?
do not influence the tension but has an impact on the instrument playing feel.
Please check the images above where 4 different types of strings structure are shown.
Let's suppose to apply on the green "X" points (near the nut) the same bending of two steps.
Let's consider the portion of strings from the bending point "X" to the tuners (b,d,f,h).
Picture "1" shows a string fixed right over the nut and saddles. This is the typical Floyd Rose situation.
If you try to bend at point "X", the force you're going to apply with your fingers will be distributed in a portion of strings going from "X" to "b". Of the four cases this is the one who will require the higher effort to bend two steps.
Picture 2 represents the common situation where the strings extend beyond the nut and the saddles and are fixed for example on the right to the tuners and on the left to a tailpiece (Les Paul). In this case, by applying the same two steps bending, the energy is some way distributed on a longer portion of string (x-d). Tension is the same as before but we will have the impression of a smoother feel near the break angles.
Picture 3 shows same situation but with an increased breaking point angle. Length, pitch and therefore, tension are the same (x-f) but this time the bending will result a bit harder than in the second example.
Picture 4 shows an "off limit" case which may in some way remind of those old Jazz hollow body guitars. The strings extends a lot beyond the nut and especially the saddles (x-h). This example will produce the smoothest feel under bending.
Another factor which has some importance here is the friction at nut and saddles. In all last 3 examples the minor the friction over the nut and saddles, the better the tension will be distributed on the "dead" portion of strings. This will produce the smoothest feel while bending.
Some of the force applied for the bending will also of course dissipate from the bending point "X" to where the strings are anchored at bridge (a,c,e,g) but this portion has a lesser impact on the above (stil have some though).
WHAT DOES THIS MEAN IN PRACTICE?
All the above origins from two different factors: the longest the portion of non-vibrating string the more it will partecipate to extend during bendings and also the sharpest the angle at the friction points (saddle/nut/string tree) the less the strings will slide over them and so the less the non vibrating portion of the strings will extend to facilitate bendings.
pictured Tuscany Rush model.
Many of the modern guitar players techniques require lower notes on the instrument and this can only be achieve by adding strings on the bass side which are usually too big or too loose which cause problems in playing (touch must be soft where attack and force is required instead) and buzz on the fretboard.
This problem could be achieved by modifying the inner structure of the string.
By increasing the inner core diameter and reducing the outer winding coils diameter we will achieve a stiffer strings sounding deeper and still retaining an adequate stiffness which allows detuning without buzz for metal "drop tunings".
Actually by reducing the incidence angle over the nut and bridge saddles we will fell a better comfort on the fretboard with bendings and a softer attack at picking.
This can be achieved on the nut side by removing the string trees where possible using staggered tuners and on the bridge side by lifting the tailpiece on the Les Paul or by increasing the neck angle and reducing the height of the saddles over the bridge plate on the strat.
HINTS AND TIPS
All the below operations will contribute to a better "feel" on the fretboard: