This video demonstrates the principle of the manometric capsule and the Koenig analyzer, which can be used to study sound.

The capsule is made of two small chambers separated by an elastic membrane. A gas is introduced into one of the chambers, feeding the flame through a small nozzle. The other is connected with a funnel and a rubber tube. The flame can be observed in a rotating mirror, and appears as a continuous band of light. If a sound is produced close to the funnel, the capsule membrane vibrates. The vibrations modulate the flow of gas and produce oscillations in the flame. In this case, the mirror appears as a jagged band whose shape depends on the frequency of the sound.

Resonance. A bronze cup is made to vibrate by means of a headband, and produces a sound. If the natural frequency of the cylindrical cardboard box corresponds to that of the sound produced, the latter is reinforced. The box acts as a resonator.

Koenig’s harmonic analyzer makes it possible to determine the frequencies that make up a complex sound. A series of 14 Helmholtz resonators cover a range of frequencies from 96 Hz (SOL1) to 1280 Hz (MI5). They can be connected to the manometric capsules through rubber tubes. The flames lit on the capsule nozzles are observed by reflection on a rotating mirror. If one or more of the frequencies in the sound produced correspond to the frequencies of the resonators, the flames of the capsules vibrate. The flames that remain static light bands appear as solid, whereas those that vibrate appear as jagged bands.