A stringed instrument may be the easiest type of musical instrument to make at home. A few basic elements are all that's required. Depending on the skill level and time investment of the maker, finished products can range from the disposable, cardboard toy variety to those worthy of professional performance.
One basic element required for your instrument is a resonating chamber. Think of the body of a guitar--a nice hollow wooden box with a hole where vibrating air can pass. The vibrations permeate the wood, and the air in the chamber resonates (vibrates in sync) amplifying the sound. Amplification is the main purpose of the resonating chamber. The quality of the sound produced will be affected by the material used to construct the chamber as well as its size and shape.
For your resonating chamber, you could use anything that can vibrate--a shoebox, a foil-covered milk crate, a gourd or a washtub--and that has a hollow area inside where air can vibrate.
Strings can be made from rubber bands or fishing line. You could use shoelaces or twine, or you could buy actual guitar or violin strings, which are made of nylon or steel. Using strings of varied thickness will help to alter the pitch of the tones produced. Arrange strings in ascending order from the thinnest to the thickest. Strings must be attached to the resonating chamber--the body of your instrument--in such a way that they vibrate freely, while their vibration transfers through a solid material connection directly into the fabric of the chamber itself. A bridge on a guitar elevates the strings from the body so that they will vibrate freely while providing this solid connection, so that the vibration of the strings transfers into the wood of the body. The tension of the strings holds the bridge in place.
The simplest homemade string instrument is a shoebox with rubber bands stretched around it, and a pencil used for a bridge. Five rubber bands of five different widths will create five different notes.
String Length and String Tension
On a guitar or a violin, tuning is accomplished by adjusting the tension of the strings; the higher the tension, the higher the pitch of the note. These instruments have winch-like mechanisms which allow the strings to be wound tightly with the simple turn of a knob and which then hold the added tension, preventing slackening. Create rudimentary versions of these with butterfly screws and nuts, and you'll be able to tune your instrument with a screwdriver.
In a typical washtub bass, one string is bolted or tied to a metal washtub. The opposite end of the string is attached to a long broom handle. The free end of the broom handle is wedged against the top of the inverted washtub. By pulling the broom handle, the player can change the amount of tension on the string, thereby changing the notes played. This is an example of a simple, homemade musical instrument which can be used in lively, melodious musical performance as in the case of many an accomplished jug band.
Different notes on a single string are also played by changing the length of the part of the string that vibrates. If you press a guitar string down against the middle of the neck of the guitar, only the bottom half of the string vibrates. A shorter vibrating length of string produces a higher note.
The concept behind a guitar slide is useful for rudimentary instruments. The slide is simply a small cylinder of steel or glass which is placed on top of the strings. As you slide it back and forth along the strings, the length of the vibrating part of the string changes, thereby changing the note played.