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A sonometer is an apparatus made of a hollow box having two holes. A string is attached to it by which the transverse vibrations of strings can be studied. It is also called the monochord because it often has only one string. On the wooden rectangular box are two fixed bridges, near the ends, and at one end is a pulley. A string,wire is fastened at one end, run over the bridges and the pulley, and attached to a weight holder hanging below the pulley. Weights can be added to the holder to produce tension in the wire, and a third, movable bridge, can be placed under it to change the length of the vibrating section of the string . It is commonly used in Melde's experiment. A sonometer demonstrates the relationship between the frequency of the sound produced by a plucked string, and the tension, length and mass per unit length of the string. These relationships are usually called Mersenne's laws after Marin Mersenne (1588–1648), who investigated and codified them . For small amplitude vibration, the frequency is proportional to:

  • The square root of the tension of the string
  • The reciprocal of the square root of the linear density of the string,
  • The reciprocal of the length of wire of sonometer