Rudolph Koenig was one of the more prolific and colourful instrument makers in the renowned nineteenth-century precision instrument trade of Paris. Beginning his career as a violin maker, in 1858 the young Prussian immigrant shifted his talents towards the growing field of acoustics. Altered Sensations is a portrait of his vibrant atelier, a place of construction, commerce and experiment. For over forty years it was also a popular meeting place for scientists, artisans, musicians and teachers. Using archival and collection research from across North American and Europe, David Pantalony has traced the material and social influences of this space on the development of modern acoustics. In particular, he has detailed the manner in which Koenig modified, extended, spread and challenged Hermann von Helmholtz's Sensations of Tone. A large part of the research on Koenig comes from the actual products of his workshop which survive in museums and collections around the world. The second section of Altered Sensations provides a Catalogue Raisonné of Koenig’s entire line of instruments, including their history, details from specific examples, locations, and references in the literature. This catalogue will serve as a practical guide for curators and researchers as well as a comprehensive overview of nineteenth-century acoustical practice.