Optical methods of measuring loudspeaker diaphragm movement.
The principles of making measurements of the vibrational behaviour of lightweight diaphragms, using optical methods employing coherent-light interferometric techniques, are discussed. The use of a frequency-shifted reference beam (Doppler interferometry) is described, and simple methods of obtaining such a reference beam are considered. Results of measurements made on the diaphragms of loudspeaker drive units are discussed and methods of presenting these results are outlined.
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