An alternative is the lissajous curve, in which one frequency moves the line horizontally and the other moves it vertically.

(click on the interval name to see the curve)

Lissajous curves are a little more readable, especially for the most consonant intervals, but apprehension quickly diminishes as the relationships get more complex. An additional problem is that the lissajous method will not work for chords involving more than 2 notes (or perhaps 3 with a 3D lissajous figure).