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.
Wolf, Oskar. 1871. Sprache Und Ohr: Akustisch-Physiologische Und Pathologische Studien. Braunschweig: Friedrich Viehweg und Sohn. https://reader.digitale-sammlungen.de/de/fs1/object/display/bsb11002822_00005.html.
Cardamo, Girolamo. 1554. “De Subtilitate, Libri Xiii”. In Hieronymi Cardani Mediolanensis Medici De Subtilitate Libri Xxi, 273–289. Nürnberg. https://archive.org/details/hin-wel-all-00000138-001/page/n316/mode/2up.