Rudolf Koenig

Karl Rudolf Koenig (Königsberg, 1832 – Paris, 1901) was a German physicist who, although he trained under Helmholtz at the University of Königsberg, directed much of his work towards the construction of precision instruments rather than towards theoretical acoustics. His role is today essential to understanding how research moved from improvised experimentation to the reliable apparatus that equipped the laboratories of the period.

After taking his doctorate in physics, Koenig apprenticed with the Parisian violin maker Vuillaume. He completed that apprenticeship in 1858 and settled on the Quai d'Anjou, where he remained until the end of his life. There he made tuning forks of great accuracy for his tonometer, which could cover the entire audible range of frequencies, as well as clock tuning forks, sirens, compound sirens and improved Helmholtz resonators. The reputation of his workshop spread to universities across Europe and the United States. The French government commissioned from him the apparatus for establishing the normal pitch at 435 Hz, and he refined Léon Scott's phonautograph, the forerunner of Edison's phonograph.

His research, published in various articles and summarised in Quelques expériences d'acoustique (Paris, 1882), focused above all on beats between harmonics, combination tones and phase in the quality of musical sound. Unlike Helmholtz, who used reed harmoniums and sirens, he advocated the use of pure tones; to achieve them he sounded large tuning forks with a cello bow, since the higher modes of a tuning fork are not harmonic. Many of his results clashed with those of Helmholtz, and comparing the two is today a fruitful way of understanding experimental acoustics in the nineteenth century.