The effective radiation area SD is one of the most important loudspeaker parameters because it determines the acoustical output (SPL, sound power) and efficiency of the transducer. This parameter is usually derived from the geometrical size of the radiator considering the diameter of half the surround area. This conventional technique fails for microspeakers and headphone transducers where the surround geometry is more complicated and the excursion does not vary linearly versus radius. The paper discusses new methods for measuring the SD more precisely. The first method uses a laser sensor and microphone to measure the voice coil displacement and the sound pressure generated by the transducer while mounted in a sealed enclosure. The second method uses only the mechanical vibration and geometry of the radiator measured by using a laser triangulation scanner. The paper checks the reliability and reproducibility of conventional and the new methods and discusses the propagation of the measurement error on the T/S parameters using test box perturbation technique and other derived parameters (sensitivity).
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