Still, a clever idea to simply use a sub-woofer to kick the drops. I like it.
Anyway, I'm definitely going to try this.
It should work. I would try it but strobelights give me a headache.
Are you just saying that by using sound, you can break up an even faster stream, one that would ordinarily be too fast to break up on its own?
Just to clarify for everyone assuming that this is an optical illusion. It's not. The subwoofer is actually creating vibrations in the water stream that increase exponentially as the stream travels until their magnitude is larger than the diameter of the stream. At this point, the stream breaks up into drops. If you do this with a coloured stream of water (i.e. ink) and run a piece of paper under it, you will see individual drops of ink hit the paper.
There are two types of inkjet printers. The most common is what you see in household inkjet printers, it's called Drop-on-demand. You spit out a drop by doing something to the ink. Ofter you heat up a resistor, converting some of the ink to steam and pushing out a drop of ink.
The other type is called continuous inkjet. The way this works is you have a stream of ink, you stimulate it at some frequency which gives you drops at that frequency, and then you select some drops to hit the paper and others to miss.
The project I was working on used conductive ink and selectively charged the drops before sending them between two oppositely charged plates, sort of like a cathode ray tube with ink drops instead of electrons.
It was ridiculously cool technology, and a lot of fun to work on. The printer we were designing (never got to market in that incarnation) would have had paper going by at ~6 meters/second with very high quality, totally variable output. I thought we were going to disrupt offset printing in a big way. Sigh :).
 Ooo, found the patent. Great bedtime reading if you're interested: http://bit.ly/HXc6o2
It was a great project, but I'm much happier now doing the startup thing than I was being a physicist.
I recall seeing a tool for fine-tuning vinyl turntable speed that used that form of the trick - it was basically a cardboard "record" with spokes printed on it every (* grabs a calculator *) 4.02deg, so as to appear to be stationary when rotating at exactly 33.5rpm under light flickering at 50Hz. Thought that was ingenious.
I prefer the water and corn starch on a speaker  to get standing structures of weirdness.
Incandescent (filament) bulbs glow by black-body radiation as the filament heats. Mains cycles are too short for the bulb to flicker (though you can get interesting effects on slower, ~2Hz or thereabouts, voltage fluctuations).
Fluorescent and LED lighting actually flicker multiple times per second, though this can be tuned somewhat.
If you remember CRT displays and monitor flicker, the problem wasn't so much the flicker rate of the monitor, but the interference in rates and timing between your monitor and the overhead office fluorescent lighting. Setting refresh to anything other than (and preferably above) 60Hz (US) would resolve this.
I'm sure I remember my parents calibrating their turntable under incandescent lights, though... maybe it was their halogen up-lighter instead of their standard incandescent ceiling light? It definitely worked with one light in their living room but not the other.
It's also fairly well known that LED's response to voltage variation is fast enough to be of concern in highly secure data environments. Demonstrations have been made of reading line signal from modems, and even Ethernet and other high-bandwidth networking equipment status/indicator lights.
Cheap LED holiday lights don't even bother rectifying the AC voltage across the lights, so they are only on for half the cycle, giving them a very noticeable flicker. It's especially apparent as you scan your eyes past them.
In contrast, incandescents allow current to flow both directions, and will glow for a little while after current stops flowing, so they don't appear to flicker on 60/50hz mains current.
See the second image - http://www.1stdibs.com/furniture_item_detail.php?id=333935
I wonder how it would look if a different dye was injected into the flow every few seconds, just above the faucet. Presumably, the colors would appear to flow down as the water appeared to drop up.
Bass String Video: https://vimeo.com/4041788
The Phonotrope: http://www.jimlefevre.com/?page_id=200
There are plenty on YouTube. It is an amazing illusion.
I find it hard to understand how "a drop" seems to stay the same shape. I need to think a bit more about that.
so, you could have a mechanical system that hit the tube every /24th of a second, and you'd get some effect, but i think it would be hard to get the impact and recovery to be EXACTLY the same, or close enough you don't notice.
If you use sound to squeeze the tube, rather than pushing on it, the distortion and recovery are much more consistent, so you get the same pattern. I'd guess you don't have much control over where the drops actually appear. you'd have to wiggle the tube around on the speaker to get the right distortion.
The human mind is malleable and dynamic, not fixed like a 24 FPS camera lens (I imagine most humans don't have a fixed framerate for incoming sensory) - I do wonder if other critters with less dynamic minds would fail to some kind of trick.
I wonder too if it was this kind of dynamic ability that allowed us to disconnect from a fixed reality, thereby giving us contrast, the ability to analyze our surroundings, and therefore consciousness.
The matrix didn't go BSOD when Crysis launched, it wont go because of a reverse stream of water...
Since the frequency in the speaker is 24 hertz and camcorders can be set at 24 frames per second, it is likely that this is what is happening here-- the speaker frequency is causing pressure differentials in the water, the water's surface tension causes the succession of drops to form similar shapes, and the camera taking an image at the same frequency of as the speaker makes things look still because the drops are in exactly the same spot each frame.
You can notice on one of the lower bubbles further away from the spout the effect is less precise and the bubble seems to be changing shape or moving around.... this is because the effect of he speaker on the water decreases over time as the water gets further away and air turbulence causes the drops shape to pick up more randomness.
Another one is putting clear plastic wrap over a subwoofer, making it face upward, and sprinkling salt on the surface. The patterns it creates look like alien symbols as you explore the spectrum.