Lissajous Figures With Sound
To demonstrate the relation between "consonance" (musical intervals) and frequency ratios.
Two oscillators with loudspeakers and oscilloscope with scope/TV cart.
Two identical oscillator/loudspeaker setups are sounded and simultaneously input into the two axes of an oscilloscope to produce a Lissajous figure. Two pitches which are related by simple rational whole numbers such as 3:2 or 5:4 are musical intervals and produce stationary figures. Beats between two close frequencies are also visibly evident by this technique. Try two close frequencies and two related by a small whole number interval for contrast. Let your students judge their consonance.