Instead of the Cello's strings, the Thermein-Cello has a flexible black plastic film fingerboard which produces a tone for as long as the finger is depressed, the pitch is efined by the position on the fingerboard and the volume is controlled by a lever. The timbre of the sound is controlled by two rotary knobs built onto the Cello's body.
The instrument was used throughout the 1930's by a number of musicians most notably Leoplod Stowkowski who commisioned Termen to design and build a bass Theremin Cello which was later abandoned due to the side effects caused by subharmonic frequencies on the orchestra's string section.
