The harp produces sound when its strings are plucked, causing the strings to vibrate and move air through space. The strings are attached to a soundboard, which also vibrates and moves air, resulting in audible sound waves.
The harp produces different sound tones based on the length and thickness of each string. Thinner, lighter strings vibrate rapidly, producing higher-pitched tones. Thicker, heavier strings vibrate more slowly, producing lower-pitched sounds. In terms of length, shorter strings vibrate more quickly, while long strings vibrate more slowly.
In order to produce sound vibrations, the strings of a harp must be tensioned to the soundboard and neck. Tensioned strings are either attached directly with knots or indirectly with a fixed plug, tuning ring or tuning peg. Harps with tuning pegs allow the player to fine-tune the frequency of each string by manually adjusting the tension. Higher string tension produces higher notes, while lower string tension produces lower notes.
Pedals allow further pitch customization. Each pedal is connected to a metal rod, which is attached to a hook mechanism. Pressing the pedal causes the hook to pull up on a string, increasing its tension and pitch by a half step. With the introduction of the seven-pedal, double-action harp in 1801, the harp became capable of producing any key.