Abstract: Measurement of small oscillatory movements of an irregular surface involves the production of a speckle pattern therefrom by coherent light illumination, and the arrangement of a photodetector for direct response to such pattern, variations in photodetector output component at the frequency of the surface movement representing that movement. Another, stationary, illuminated irregular surface can be involved to produce a speckle interference pattern for response of the photodectector thereto and, in the case where the two surfaces are closely adjacent, a single beam can be used to illuminate the first and other surfaces predominantly and by stray light, respectively. This common beam illumination can be used in prior speckle interferometry. The first surface can be an eardrum oscillated by a sound wave, suitably of swept frequency or impulse form, with detection of the photodetector variations respectively being in synchronous manner or by Fourier analysis, respectively.