Beats With Two Tone Generators

Two tunable electronic tone generators can be used to demonstrate the phenomenon of beats.

The image below is the beat pattern produced by the two two small loudspeakers side-by-side that are driven by two tone generators.

When the two tones are close together in frequency, the ear hears what seems to be a single pitch, and the measurement above gives a frequency of 231 Hz. But the tone pulses in loudness at the beat frequency, the difference between the two frequencies. Measuring the period of the pulsing gives a beat frequency of about 8Hz. We don't get an accurate frequency of either tone, but we know that the two tones center about 231 Hz and that they are 8 Hz apart in frequency.