Around 1930, an electrical vibrating reed (shown as light) pulsed an air control valve (area above light) from an air pressure tank ( outlines shown at left) into a horn speaker to amplify sound at speaker level to reproduce music tones.
Current speaker research is being on using compressed air and vacuum to amplify digital signal directly at speaker output. Digital speaker.
In the future, a speaker the size of brief case may give sound to auditorium.
Digital signal direct to power control units may be design to keep in mind.
