High-resolution imaging of impulse response by high-speed polarization interferometer

Traditionally, microphones have been widely used for sound-field measurements due to their ability to accurately capture sound pressure at specific locations. However, their physical presence interfere with the target sound fields, particularly when precise measurements of subtle variations are required. To address these challenges, optical acoustic measurement techniques, such as the high-speed polarization interferometer utilizing parallel phase-shift interferometry (PPSI), have been proposed. PPSI has been successfully applied to the measurement of aerodynamic sound, sound radiated from fast-moving sources, musical-instrument sound, and determination of acoustic centers. Despite these advancements, PPSI has not yet been utilized for measuring impulse responses of loudspeakers. In this study, we propose high-resolution imaging of impulse response using PPSI. We measured two-dimensional spacial distribution of time stretched pulse (TSP) sounds emitted from a loudspeaker by PPSI and calculated the impulse response by convolving them with an inverse TSP signal in each pixel. We found that this method provides highly accurate, non-contact measurement of the spatial characteristics of impulse responses, offering valuable insights for improving speaker design and tuning accuracy.