Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Furnishings and Equipment (hierarchy name)
4. Sound Devices (hierarchy name)
5. sound devices (equipment)

Anotations

Scope note:

Devices used to teach the deaf to regulate vocal tones. These incorporated a spinning disk on which fifteen rings of alternating black and white spaces were displayed, the white spaces on the inner ring numbering 8, and on the outer ring 32, with intervals between. The numbers of the white spaces correspond to the vibrations of a diatonic scale. Alternating rings would appear as the user spoke, activating the flicker of a flame, causing a strobe effect as visual feedback.