String Instrument Sound Production

Most string instruments have at least four strings and some have many more. There is usually a way to shorten the vibrating string to make different notes. Sometimes the strings are pressed against a fret board or fingerboard, which shortens the length of the string that is actually vibrating causing a higher sound. The shorter the vibrating string, the higher the sound. The longer the vibrating string, the lower the sound. Instruments like the guitar, mandolin, and banjo have frets—raised metal strips on the neck of the instrument under the strings—that help players know where to press down.

String instruments are tuned by turning tuning pegs or knobs that tighten or loosen the strings until they are at the prescribed tuning pitch (frequency).

Some string instruments produce sound when the strings are plucked. Instruments in this group use fingers, or in some cases picks, to pull on the string and then release it to vibrate. Instruments in this group include the harp, guitar, banjo, mandolin, and harpsichord.

Another common method of sound production is bowing. A bow consists of a wooden or composite stick with long strands of fiberglass or hair stretched tightly between the ends of the stick. Rosin is rubbed onto the hair or fiberglass and when it is pulled or pushed across the strings, the resistance provided by the rosin causes the strings to vibrate. Instruments that are commonly bowed are the violin, viola, cello, and double bass.

The third method of sound production is striking the string, usually with a hammer. This is what occurs on a piano or a hammered dulcimer.

Most string instruments play very softly and could not be heard very well without some type of amplification. It is the sound box, the largest part of the instrument, which acts as an amplifier for stringed instruments. Holes are cut in the top of the sound box to allow the sound to escape. If the holes are covered the sound is very muted. The only string instruments without a sound box are some electrically amplified ones like the electric guitar, and the piano which uses a sound board instead.