PURPOSE: Model for beats between mistuned audio oscillators.

DESCRIPTION: Two transparencies of equally-spaced lines and spaces are used to model beats. One transparency has been reduced about ten percent so the two transparencies represent two sound waves of different frequencies, where (for example) the dark lines represent the compressions and the white lines represent the rarefactions. Aligning the two transparencies on top of each other on the overhead projector creates waves which go in and out of phase as time progresses: when they are in phase the sound is loud, but when they are out of phase the sound is soft, creating beats. Note that the scale of the beats (at the right) produced by superposing the two transparencies is greater than the scale of the photograph showing the two individual transparencies (at the left).

SUGGESTIONS:

REFERENCES: (PIRA unknown.)

EQUIPMENT: Two scaled transparencies of parallel lines and spaces with overhead projector.

SETUP TIME: None.