FORMANT CHANGER AND SPEAKER DRIVER
I’ve made two devices that allow you to take the output from an inexpensive electronic keyboard and mess with it acoustically. In the Formant Changer (the small image on this page), the output goes to a speaker playing into a wooden box. By opening & closing the lid, and by involving the small chimneys in various ways, you can continuously shift the overtone content of the sound. In the Speaker Driver (the main image on this page), the signal goes to the driver element of a speaker (speaker cone removed), which rattles against a hand-held piece of tin foil. A piezo pickup takes the highly filtered, distorted sound from the tin foil and sends it to a regular loudspeaker.
In the audio clip, Speaker Driver is heard first, then the Formant Changer.