Near-Equal Frequencies Produce Very Slow Beats

When the clamp is positioned near the bottom of the tuning fork arm its effect is very small, so the frequency difference between the two tuning forks will small and the beat frequency very low.

Discussion

The closer the clamp is to the bottom of the tuning fork arm, the smaller the effect it has on the vibration frequency of the tuning fork. In this movie, the clamp is placed lower than in either of the two preceding movies. Because of this, the beat frequency here is the lowest.