Rudolph Koenig's sound analyzer

A few years ago a search of a sub-basement storage room in the Physics and Astronomy Building turned up an old instrument made by Rudolph Koenig. It is a sound analyzer, and was probably built at least 100 years ago. It has been partly refurbished, but has not yet been successfully operated.

This is one of numerous devices constructed by Koenig which make use of the manometric flame. In this instrument eight Helmoltz resonators (in the first photo, at the right or above) are each connected by rubber tubes to a flexible diaphram which modulates the flow of gas to a flame. The fluctuations in air pressure in the resonator thus result in corresponding fluctuations in the gas flow and hence in the height of the flame. A four-sided mirror can be rotated by a crank (at the left), allowing the observer to see the rapid fluctuations in the flame height. Each resonator responds to a different frequency range, and since the fluctuations of all eight flames can be seen simultaneously, the observer is able to get a qualitative idea of the spectrum of the sound impinging on the resonators.

Rudolph Koenig's sound analyzer

It is not straightforward to put a device like this into working order. The original diaphram membranes were all perished, and needed to be replaced with a material which has similar properties to the (unknown) properties of the originals. When new, the analyzer was probably used with something like coal gas which has very different properties from natural gas or propane, so it is necessary to adjust the gas orifices and/or use some alternative flammable gas. A more elaborate sound analyzer with 14 tunable resonators has been put into working order at the University of Toronto

The University of Toronto has quite a large collection of Rudolph Koenig acoustical equipment. I have been told that most of it was obtained following Koenig's display of equipment at the 1876 World's Fair in Philadelphia. The first head of the Physics Department at the University of Western Ontario, Dr. R. C. Dearle, came fresh from his PhD at the University of Toronto in 1919. It is quite likely that this sound analyzer came from the U of T to help fill out the physics laboratory at Western.

Below are links to various images, including larger versions of those shown above.

Back view
Front view
Closer view of the Helmholtz resonators
Back of resonators (out of focus)
Resonators from side (out of focus)
gas burners (out of focus)
burner and hoses
bevelled gears for turning the mirrors
top bearing supporting the rotating mirrors
Some of the original parts
Another view of original parts