A simple system consisting of a battery-powered audio source on a string swung in a nearly horizontal circle is investigated. Our analysis of the measured signals shows that there were many echoes of the sinusoidal variation of frequency due to acoustic images of the source.

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PYTHON is available from ⟨http://www.python.org⟩.
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The SCIPY package and documentation is available from ⟨http://www.scipy.org/⟩ and can be used to compute the sonograms and inspect them interactively using the pylab.specgram function. The authors would be happy to share further details with interested instructors.
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