The speaker causes the hose to vibrate, shaking it 24 times a second. To the naked eye this looks like something of a blur, but if your camera is also taking a shot every 24 seconds the video looks like the water is frozen in space, with just slight changes to the position of the drops.
Adjust the frequency up slightly and the water appears to be falling with marvelous slowness – the shaking now occurs every 0.04 seconds instead of 0.0417, so the drops appear to be moving at 4% of their real speed.
Things really get interesting when you make the frequency just slightly lower than the required speed (have your tuba player go to F). Now the water appears to move upwards. This is known as the wagon-wheel effect, after the way wheels in Westerns can seem to rotate the wrong way when they are moving more than half way round between frames.
To see the effects without a camera, run the experiment at night using a strobe light.