Superposition of multiple sources, constructive and destructive interference, and array beam forming are common topics demonstrated in undergraduate acoustic classes. The student learning experience is enhanced by building a system with speakers and measuring the resulting amplitude at various angles with a microphone. This experiment is often performed in an anechoic chamber to achieve quantitative agreement between theory and experiment. We have developed a simple tabletop apparatus using inexpensive ultrasonic transducers that yields comparable results without the need to use an anechoic chamber.
REFERENCES
1.
H. F.
Meiners
, Physics Demonstration Experiments
(Ronald
, New York
, 1970
), Vol. 1
, pp. 508
–509
.2.
M.
Correll
, “Ultrasonic transducers for interference experiments
,” Am. J. Phys.
32
, iii
–iii
(1964
).3.
S. C.
Bloch
, “Electromagnetic and acoustic interference analog
,” Am. J. Phys.
33
, 164
–165
(1965
).4.
L.
Kinsler
, A.
Frey
, A.
Coppins
, and J.
Sanders
, Fundamentals of Acoustics
, 4th ed. (Wiley
, New York
, 2000
), pp. 195
–199
.5.
6.
For a discussion of decibels and acoustic source levels see
D.
Chapman
and D.
Ellis
, “The illusive decibel, thoughts on sonars and marine mammals
,” Can. Acoust.
26
(2
), 29
–31
(1998
).7.
SensComp Global Components, “
Application notes
” <http://www.senscomp.com/application_notes.html>.8.
APC International Ltd. <http://www.americanpiezo.com/index.html>.
9.
H.
Blum
, “Acoustic interference demonstration
,” Am. J. Phys.
42
, 413
–414
(1974
).10.
E. O.
LaCasce
and E. E.
Hays
, “An oceanographic Lloyd’s mirror experiment
,” Am. J. Phys.
52
, 1121
–1125
(1984
).11.
R.
Urick
, Principles of Underwater Sound
, 3rd ed. (McGraw-Hill
, New York
, 1983
), pp. 62
–64
.2009
U.S. Government
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