Instruments may be widely classified under three categories:
- String instruments: examples include tanpura, violin, viola, veena, guitar, mandolin etc., which produce music through the strings.
- Wind instruments: examples include flute, recorder, saxophone, trumpet, nagaswaram, morsing etc which produce sound by blowing air into their mouth pieces.
- Percussion instruments: examples include mridangam, ghatam, tavil, dhol, pakawaj, drums, etc, which produce sound when they are hit on their designed surfaces.
Now let us try and understand as to how do these instruments produce sound and the factors affecting the quality of the sound it produces. In other words, let us see how music and physics are inter related and how best physics help us understand music.
String instruments produce sound when the strings are plucked either by fingers as in veena, tanpura, mandolins, guitars etc, or by a bow as in violins. When the strings are vibrated through any of the above methods, sound waves propagate along the length of the string. The body of the instrument which is generally hollow, acts as sound box, couple the vibration of strings to the surrounding air, making it audible.
The pitch of the notes produced by the instrument, characterized by the frequency, depends mainly on three factors namely Tension in the string, Length of the string and the thickness of the string which characterizes its density. The tension in the string is generally controlled by loosening or tightening the string. Tighter the string means more is the tension and higher the pitch and vice versa. Length of the vibrating string is generally controlled by stopping the fingers at different lengths from the point where the vibration starts. Shorter the vibrational length, higher is the pitch and vice versa. Thicker the string, lower the pitch.
Wind instruments also basically work under the same principle but for the fact that the physics of an air column applies better than the physics of a stretched string. The instrument basically acts as a hollow tube in which a column of air is set into vibration by the musician blowing into its mouth piece. The rest of what happens is physics of a resonating air column.
Percussion instruments like mridangam, ghatam, drums etc., are generally tuned to a specific frequency. The body of the instrument will be hollow which resonates the sound through it when the surface of their stretched membrane is hit. Larger the surface area of the membrane, lower will be the pitch and viceversa.
Further References for detailed understanding: