Sound synthesizer

From Ccpi

Helmholtz's sound synthesizer, also known as a vowel synthesizer, is a large group of instruments for mixing timbres of various harmonics, specifically to produce vowel sounds. It usually consisted of between eight and ten electrically-driven tuning forks, each attached to a Helmholtz resonator, forming the first harmonics of the fundamental tone. Each tuning fork is on a magnetic circuit, driven by a current rendered intermittent by a master tuning fork, which is identical to the largest fork in the group. This master fork actuates the largest fork once per cycle, the second largest fork once every two cycles, etc.

The volume of the individual tones is controlled by a keyboard. Each key opens and closes the slit on a given resonator, causing that fork's tone to sound or silence.