PURPOSE: To demonstrate diffraction and interference of sound.
DESCRIPTION: A small loudspeaker plays music with lots of bass, but the bass is not very loud. When the speaker is held up behind a hole the size of the speaker in a board about two feet square, the sound becomes much louder, especially the bass. A loudspeaker produces two distinct sound waves: one from the front and one from the back, which are out of phase with respect to each other. In the absence of the baffle, these sounds both diffract in all directions, and, because they are exactly out of phase they interfere destructively, especially the bass. The baffle forestalls the diffraction and thus reduces the magnitude of the interference.
REFERENCES: (PIRA 3B55.30)
EQUIPMENT: Audiocassette deck with cassette, small speaker, and baffle.
SETUP TIME: None.
Go back to Lecture-Demonstration Home Page.