Dynamic Measurement of Transducer Effective Radiation Area

The effective radiation area S D is one of the most important loudspeaker parameters because it determines the acoustic output (sound power) and efficiency of the transducer. This parameter is usually derived from the geometrical size of the radiator considering the diameter of one-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 with the radius. New methods for measuring S D more precisely are discussed. The first method uses a laser sensor and a 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 the geometry of the radiator as measured using a laser triangulation scanner. The reliability and reproducibility of the conventional and the new methods are verified and the propagation of the measurement error on the T/S parameters using the test-box perturbation technique and other derived parameters (sensitivity) is discussed.