Group III started to build several beta diaphragms for a capacitive microphone with spectral selection capabilities. They were tested using a four inch open speaker (without cabinet) close to them, moved by a headphone amplifier. Using a signal generator to provide different periodic stimuli, the diaphragms (different aluminum types tensed on circular wooden rings) were excited at 75 dbA-3cm, ir order to sense the movement to different sine waves —looking Chladni patterns. Key phrases: microphone design, chladni plates, acoustic testing of periodic waves.
