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.

Adriaan Daniël Fokker was a prominent Dutch theoretical physicist. He is known in theoretical physics for the Fokker-Planck equation and his work on the theory of relativity. In the years around 1930, however, Fokker also became interested in room acoustics and the tuning of musical instruments. He designed several sound reflectors, which amplify the sound reaching the audience, especially in churches, but his work on musical instrument tuning is what made him more widely known.

Cornelis Zwikker was a Dutch physicist and one of the initiators of the Dutch Sound Foundation. After studying chemistry, mathematics, and physics in Amsterdam, he worked with Philips in Eindhoven until 1929, when he was appointed professor of theoretical and applied physics at the Delft University of Technology. Zwikker was responsible for the acoustic design of many buildings, among them the studios of the Dutch broadcasting organization AVRO.

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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.

Image Source: Dresdner, Albert: Industrielle Vertreter der Industrie und des Handels in Wort und Bild, Berlin, 1899.