PURPOSE: To demonstrate the interference of standing waves in a stretched wire.
DESCRIPTION: A long hollow cavity supports two stretched strings held in tension by a tuner. The tensions in the two stretched wires can be separately adjusted, creating different fundamental frequencies. Stops can be inserted along the wire to observe the frequency as a function of length, or to show the frequency ratio between two similar wires with the same tension but of different lengths.
http://physics.kenyon.edu/EarlyApparatus/Acoustics/Sonometer/Sonometer.html
The differential Sonometer was invented by the French acoustical apparatus manufacturer, Marloye, ca. 1840. This has two strings, which may be used to illustrate beats if the two strings have almost the same frequency. If one string has twice the frequency of the other, octaves may be demonstrated.
| A Sonometer is a device for demonstrating 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:
a. the square root of the tension of the string, b. the reciprocal of the square root of the linear density of the string, c. the reciprocal of the length of the string. The usual sonometer is horizontal and the tension is supplied by the weight of the masses hung on the ends of the wires after they pass over the pulleys. This arrangement has the defect that the strings and bridge cannot be seen by the class. It is better viewed by the class when it is vertical. |
EQUIPMENT: Differential Sonometer, as photographed.
SETUP NOTES: For more history on this device see:
http://physics.kenyon.edu/EarlyApparatus/
http://physics.kenyon.edu/EarlyApparatus/Acoustics/Sonometer/Sonometer.html
Click on "Acoustics" and then "Sonometer".
Updated by JZ in 6/23/2005