The classical demonstration experiment on acoustic beats using two signal generators and a dual trace oscilloscope is an important ingredient in teaching the subject.1 This short laboratory note aims to point out what may be the simplest demonstrative experiment on acoustic beats to carry out in a classroom without employing any lab apparatus.
References
1.
D. E.
Boucher
, “A visual and acoustic demonstration of beats and interference
,” Phys. Teach.
37
, 177
(March 1999
). 2.
P.
Gluck
, “You can illustrate beats without the usual tuning forks
,” Phys. Educ.
39
, 241
(2004
). 3.
S.
Kadri
, R.
Jaafar
, W. Z.
Adii
, and A.
Nazihah
, “Physics demonstration of sound waves using Visual Analyser
,” Lat. Am. J. Phys. Educ.
7
, 10
–15
(2013
).4.
Visual Analyzer is a free software including wave generator, oscilloscope, spectrum analyzer, and minor tools. See http://www.sillanumsoft.org/prod01.htm.
5.
J.
Groppe
, “The hope of Audacity® (to teach acoustics)
,” Phys. Teach.
49
, 99
–102
(Feb. 2011
). 6.
J.
Kuhn
, P.
Vogt
, and M.
Hirth
, “Analyzing the acoustic beat with mobile devices
,” Phys. Teach.
52
, 248
–249
(April 2014
). 7.
Audio Tester is a shareware software including wave generator, oscilloscope, spectrum analyzer, and other tools. Software is downloadable at http://www.audiotester.de and may transform a PC having a high-quality sound card into a complete audio lab. Wavegen is a wave generator having the fundamental feature to send the signal to a single selected channel (left or right) or to both channels (Menu: Setup/Sound parameters). The twofold opening of the same software on the same PC causes no particular drawbacks. The shareware version has no limitations in use, except it automatically shuts off after 12 minutes.
8.
D.
Halliday
, R.
Resnick
, and J.
Walker
, Fundamentals of Physics
, 9th ed. (Wiley
, New York
, 2011
), p. 459
.9.
10.
Another subjective effect of psychoacoustic nature, so-called binaural beats, is an auditory processing of artifacts or apparent sounds. It can be caused by specific acoustical stimuli in some subjects. The effect on the brainwaves depends on the difference in frequencies of each tone in each ear. So these subjective phenomena happen without physical superposition of acoustical perturbations. A popular introductory paper can be found in
G.
Oster
, “Auditory beats in the brain
,” Sci. Am.
229
(4
), 94
–102
(1973
). 11.
12.
D.
Olson
, “Musical combination tones and oscillations of the ear mechanism
,” Am. J. Phys.
37
, 730
–734
(July 1969
). 13.
J. C.
Runge
, “Combination tones
,” Phys. Teach.
17
, 49
–51
(Jan. 1979
). © 2015 American Association of Physics Teachers.
2015
American Association of Physics Teachers
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