It is of the utmost importance, if the violin is to sound at its best, that it be strung with strings of the proper size. Violin strings of the same kind are made slightly different in thickness, since some violins sound better with thin, others with thick and others with medium strings. For ascertaining the exact size of strings a little instrument called a string gauge is used. This consists of a thin plate of brass or other metal fitted with slots of different size or with tapering slots marked with numbers, into which the string is slipped, and the proper gauge ascertained. The correct gauge once learned, strings of the proper size can be ordered from the dealer by number. Strings of the same gauge should always be used when once the best thickness has been learned.
An expert professional violinist learns by experience the exact size of strings which suits his violin best, but the student or amateur is rarely competent to judge in this matter. It would be worth many times its cost for him to take his violin to his teacher or any good experienced violinist, for the latter to experiment with, in order to ascertain the size of each string E, A, D, G, which suits the violin best. The size of the strings makes a very great difference in the tone of the violin. Many violins which sound comparatively well with thin strings would be insufferable with very thick. Again, it does not follow that all the strings should be proportionately thin or thick. Very few violins are perfectly even in tone, and the violin often has to be humored as to the size of strings. Some violins might stand a comparatively heavy E and D, but require a thin A, in fact every violin is a law to itself, and much experimenting must be done to get at the exact size of each string which make it sound best. One of the prime essentials of a good violin is one with a perfectly even scale, from the open G to the highest note on the E, but such violins are very hard to find and command a very high price.
The great violinist Spohr says on this point: "In order to obtain a full and powerful tone, the largest strings the instrument can bear are generally preferred --such as will easily and quickly produce all tones without at all damping the sounds of the instrument. But if a violin loses nothing in the quality of its tone by using smaller strings, those of middling size are to be preferred, for, besides their full and effective tone, the player has more command over his instrument, and can add elegance and taste to his performance. The relative proportion of the power of the strings must be such as to give every one an equal share of richness and volume of tone. Experiment is the only guide in this matter. An unevenness in the tone of a string, which could not be remedied by the sound-post and bridge, may sometimes be equalized by the greater or less tone of another string. When the size of the strings is once fixed, let it not be changed. A frequent alteration from small to large is detrimental both to the player and to the instrument. The strings which are purchased ought therefore always to be the most suitable to the instrument, for which purchase a string gauge can be used."
The average violin pupil pays very little attention to the relative size of the strings as best suited to his violin, and, as a rule, buys strings without paying any attention to their gauge. In this he makes a great mistake, for the tone of his violin would be vastly improved by being strung with strings of the proper size, and as a result his playing would also be improved, for, being accustomed to drawing a good tone from a string of a certain size, he would not draw as good tone if a string of different size were substituted, at least not until he got accustomed to it.