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Speaker Bar
# 3B55.10

Description: A variable function generator drives two speakers which are mounted on the ends of a 8 ft board. The generator will be preset to 3 kHz. The speaker bar is set on a pivot. Direct the students to plug one ear and listen for variations in intensity while you slowly turn the turntable. Alternately, have the students move their heads back and forth while plugging one ear. (The speaker does not move.) A set of switches allow either speaker to be turned off.

Purchased/Built: built

Setup Time: 15 min

Quant. in Demo Room: 1

Demo References
The Video Encyclopedia of Physics Demonstrations Disc 10-20 Speakers in phase are mounted at the ends of a rotatable bar.
Meiners 19-5.2 The pattern from two speakers 3' apart is investigated with a microphone and microammeter.
Sutton S-102 Two speakers fed from the same source at the ends of a 12' bar. Project the pattern into the room and move the bar.
Meiners 19-5.1 Two speakers mounted at the ends of a board on a turntable are fed the same high frequency audio signal.
Freier and Anderson Sl-3 Two speakers 2m apart are driven from the same oscillator while students move their heads around to hear the interference pattern.
The American Journal of Physics AJP 42(5),413 Use high power speakers and a 50 Watt amplifier.

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