Strings of different thickness are used in a stringed instrument. why?

Answer 1

The size of a string is related to the pitch it is supposed to produce when played 'open'. Strings meant to make high pitches tend to be short and thin. Strings meant to make low pitches tend to be long and thick. There is a tradeoff between three features that determines pitch of an open strings pitch:

1. length: double the length of the vibrating part of a string and the pitch decreases by an octave. Halve the length of the vibrating portion of the string, and the pitch goes up by an octave. This is used to get more than one pitch out of a string (fingering).
2. mass density: the amount of material and its mass per unit length. If you increase the diameter of a string while keeping the material the same, the pitch decreases. If you reduce the diameter (make it thinner), the pitch increases.
   
3. tension: if you increase the tension on a string, the pitch increases. If you decrease the tension, the pitch decreases.

In designing an instrument (and there are still people who design stringed instruments!), these three aspects must be balanced to produce a set of strings which, when fixed at a common length and tightened to roughly the same tension, can produce low to high pitches, spaced so that fingering will fill in the notes in between. Likewise, keyboard instruments like pianos, must have every string engineered to fit each semitone from bottom to top, because there is no fingering to 'fill in the gaps'.

The result of this is that any instrument that has more than one string sounding more than one pitch will have different thickness strings. And, instruments which have pitches which are near, but different lengths (violin and viola, for instance) will either have different thicknesses if they are designed to have the same tension, or will have the same "weight" strings (same mass density and tension) but longer strings.

There is one workaround: as the mass density of a string rises (thickness) we reach a point where the string becomes unplayable: too thick. Long before we get there, we can change the material being used. Often, nylon or silk strings will be wrapped with a metal (silver, copper, various alloys) to produce low-pitched strings with reasonable tensions and diameters. This is why, on a violin, the top string is usually a single strand of metal, and the lower strings are wrapped with metals. The steel 'core' of the lower strings gives integrity, while the aluminum or other metals used in the wrapping adds mass.

Answer 2

Suppose we have a short, thin string for our highest note. There are THREE ways to lower the pitch: reduce the tension on the string, lengthen the string, or use a thicker string.

If the same thickness and tension of piano wire were used throughout a piano as in the highest octave, with the same tension, the length of the string would have to DOUBLE for each descending octave! This would result in pianos of about 60-foot length!!!

The accepted means of lowering pitch is by (a) lengthening the string (as is the case of a concert grand piano, of length 9 feet or more), and (b) thickening of the string by coiling the lower strings with copper coiling.

This was an interesting question, with a fairly easy answer! Thanks!

Best,

Fredrick Pritchard

Answer 3

A viola has the (left to right) C,G,D,A strings and the violin has G,D,A,E strings