The Disk vs. the Cylinder

Richard Koprowski of the Stanford Archive of Recorded Sound with an acoustical Edison disc player. Volume control on this mechanical device was provided by a fuzzy ball that could be shoved into the playback horn to reduce volume or removed to allow full volume.

Pull the cable, and the ball pulls back out of the horn, allowing sound to pass. Push the cable in, and the ball stuffs into the narrow part of the horn, muffling the sound.