The 24Hz is merely the vibrating frequency of a mechanical function here.

You could go outside, pick up the end of your common garden hose and SHAKE it evenly while the water is running out in a downhill direction - and create much the same pattern.

The youtube poster is using a subwoofer, amplifier and signal generator set to the very low audio region, but in effect it is NOT being used to create an audio function here. It is being used to create a MECHANICAL function, in other words the excursions of the speaker cone outward and inward at the chosen frequency rate.

This particular phenomenon, along with certain other paramaters, such as modulating the pressure of the stream, is exploited in the various popular "Dancing Water" fountain displays:

http://www.bing.com/images/search?q=danc...n&FORM=IGRE

Just taking advantage of old Newton's laws, for every action there is an equal and opposite reaction, & etc...


--Mac