Comparison of acoustic, electric and laser contactless displacement measurements applied to observe nonlinear behaviour of diaphragm movement in dynamic loudspeakers

Dynamic loudspeakers introduce distortion into reproduced auditory signal, especially in case of operation with high power or low frequency. Assessment of distortion by measuring current of voice coil should allow to compensate or prevent the product of distortion. The paper contains a comparison of displacement capture by optical triangulation displacement sensor, acoustic signal acquired using microphone, voltage and current. In case of processing low frequency signals, acoustic signal captured by microphone is dominated by harmonics of the fundamental frequency, and the laser displacement sensor provides more accurate information about the diaphragm displacement. Harmonics recorded in current have the same character as the displacement signal for low frequency, but for frequencies above the resonance, acoustic signal is a better source of displacement information.