String Music Instruments Including the Guitar and Violin
String Instruments Including the Guitar and Violin
A string instrument is a musical instrument in which strings are set in vibration. These include the guitar, violin, and banjo, among others.
String instruments make their sound by resonance, but the resonance needed is in two fifferent forms.
A major difference between a violin and a guitar is the bow causes a triangular wave shape instead of the sinusoidal shape.
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Resonance in a String
When a wave is plucked or bowed it begins to move back and forth. The disturbance moves along the string while additional wave crests and troughs follow in a continuous manner. When the disturbance reaches the end of the sting, it reflects. If the string length is just right, the reflected wave will cancel the forward moving wave at points called nodes, and reinforce the forward moving wave at points called anti-nodes. A standing wave will be set up. Whether or not a standing wave will set up depends on the string length and the speed the sound moves. The speed depends on the composition and thickness of the string, and the tension in the string. Turning the frets will control the tension in the string.
Because strings in instruments are subject to thermal expansion, tuning fir the room in which it is to be played is essential.
The Complexities of the Vibrations
Vibrating strings cannot send sound very far. The sound must be assisted at the instrument. This is done by having the bridge carefully placed so as to vibrate with the strings. This is transferred to the front plate. The vibrating front plate sets up a resonance in the box, utilizing resonance in a tube. The vibrating air in the box can start the back plate vibrating.
Inside the Box
Resonance in a tube occurs when a wave moving through a tube, and the wave reflected at the end of the tube, pass each other so as to create a standing wave, which means at some points there is always a cancellation, or a node, and halfway between the nodes the waves add to each other to produce an anti-node.
The important thing to remember is it is all about the resonance, the nodes and the antinodes, that make the quality of the sound.