An empty cylindrical CD container is a ready-made acoustical resonant cavity. It requires only two additional holes: one in the base for a small speaker and one for a small microphone in the side. Because the top can rotate with respect to the base, the angular behavior of each resonant mode can be observed in addition to its frequency. The frequency is easily changed, and signals are readily displayed on an oscilloscope. The measured frequencies and angular dependence are in good agreement with theory.
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PAPERS| October 01 2009
Plastic CD containers as cylindrical acoustical resonators
Michael J. Moloney; Plastic CD containers as cylindrical acoustical resonators. Am. J. Phys. 1 October 2009; 77 (10): 882–885. https://doi.org/10.1119/1.3157150
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