Sonometer is an instrument used to study the mathematical relations of musical tones. The instrument consists of a flat box with a string or wire stretched tightly between two thin, upright pieces known as bridges. One end of the wire passes over a pulley and is attached to a weight. When plucked, the wire vibrates and thus produces sound. The frequency (number of vibrations a second) of the tone increases as the weight is increased to tighten the wire. The frequency of a sound determines its pitch—the degree of highness or lowness of the sound as we hear it. A high-frequency sound has a higher pitch than a low-frequency sound. So adding weight raises the pitch.
The sonometer also has a third bridge that can be placed under the wire. Moving this bridge to different locations changes the length of the segment of wire that is plucked. The frequency of the tone increases as that segment is made shorter. A sonometer is also referred to as a monochord.
