We-2 The Doppler Effect (using a hand held speaker)
Published: Wednesday 15 March 2006 - Updated: Wednesday 30 March 2011
To demonstrate how the frequency of a moving sound source will change due to the source's velocity relative to the observer.
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The sound source consists of a battery operated oscillator driving a loudspeaker at constant frequency f. This is attached to a string and as it is swung above the head the pitch is heard to raise and lower as the device moves towards or away from the observer. The length of the string is 60 cm and a rotational frequency of 4 revs/sec yields a linear speed of 15 m.sec which gives maximum and minimum doppler frequencies of 1.04f and 0.96f.