Koenig's Apparatus for the Analysis of Sound

This late 19th-century apparatus (image 1) is part of a sound analysis device. It imitates a design by Rudolph Koenig for what is considered the first spectrum analyzer. It is displayed alongside a flame manometer and a rotating mirror (image 3), which would have formed crucial parts of this analysis machine.

Description

The object in image 1 consists of ten Helmholtz resonators arranged in a wooden frame, and was acquired from the Wheatstone Laboratory, King's College London, in the 1980s. The resonators were made by Rudolph Koenig in the late 19th century, but the maker of the frame is not certain. Most probably this apparatus was assembled at King's as a more affordable version of Koenig's apparatus for the analysis of sound, using a standard set of resonators.

In Koenig's design (image 3) each resonator has one end open to the air and the other end attached to a rubber pipe. That pipe is connected to a 'flame manometer' capsule, consisting of two hemispheres separated by a thin rubber diaphragm. One hemisphere is connected to the resonator via the pipe, and through the other hemisphere flows a flammable gas, which burns at the end of a narrow jet pipe at the top. The pressure of the gas in the capsule is dependent on the pressure of the air in the other hemisphere, which in turn is dependent on the vibrations of air within the resonator. Thus, during resonance, the gas flame vibrates in sympathy rendering visible the presence of the given frequency in the sound under investigation. An experimenter would then sing or make a sound in front of the open resonators and observe the vibrations of the flames in a rotating mirror, acting like a stroboscope, which made it easier to see the vibrations (image 4). Flame manometers were also used with the "Trombone de Koenig", as well as for many other acoustical experiments.

manometric_flames.jpg