6 SOL4 RUDOLPH KOENIG A PARIS (set number with Koenig trade mark and classification based the fequency of the fork, stamped on the wooden base). SOL4 253 v.s. (Koenig monograph and classification and frequency stamped on the fork). Hunterian Museum G.1986.119 (3) (type written on a small self adhesive label removed). DES ? after SHORE,John. 1711 London, England. MANU Rudolph Koenig. late19th early 20th century 27, Quai d'Anjou, Paris, France. DES HELMHOLTZ,Hermann,Ludwig,Ferdinand,Professor,von. circa 1856 Bonn, Germany. The vibration of the fork is mainained by an electromagnet consisting of two coils on a steel yoke with soft iron pole pieces. Behind the fork is a Helmholtz resonator in the form of a small brass cylinder with a small aperture and a shutter. When the shutter is held opver the aperture the sound generated by the fork is unreinforced and when the shutter is removed the sound resonates in the cylinder. This is part of a Helmholtz synthesizer used for research into the auditory system. Sometimes called Koenig's vowel sounds they are part of an original set of ten connected to a keyboard. By choosing a combination of various frequencies particular vowel sounds could be produced in what is called a Fourier synthesis.
This type of instrument was first described by Helmholtz in 1862.