H. J. L. Struycken was a Dutch otolaryngologist, phonetician, and acoustician. After studying medicine in Groningen, in 1893 he started working at the Voorburg psychiatric hospital near Vught, where he attempted to distinguish psychiatric conditions from neurological speech disorders. His interest in phonetics and acoustics took Struycken to France and Germany, to visit clinics and approach instrument makers who could produce tuning forks for him to use in his clinical research.
Jules Antoine Lissajous was a high-school teacher, then held prestigious administrative posts in the education system of various parts of France. He had trained in physics, and defended his dissertation on vibratory phenomena in 1850.
Sigmund Exner is known for his work in comparative physiology and his studies of perception psychology from a physiological standpoint. He conducted important research on the localization of behavioral functionality in the brain, in particular studies on the functional architecture of the visual cortex. Exner investigated color contrast, hue adaptation, apparent motion, and the sensitivity of retinal regeneration. In 1899, he co-founded the Phonogrammarchiv in Vienna, an archive recording acoustic phenomena for scientific purposes.
Chladni was a physicist whose work focused on experimental acoustics. He invented the “Chladni figure” and various instruments. Until his death, he continued to travel and present his inventions and findings to a wide audience.