Yup. Sorry, Q, but the aluminum foil shielding thing for speakers is really an urban legend.
Aluminum foil is pretty good for RF and electrostatic shielding, but it can't touch DC or LF *magnetic* interference. The interference you get from unshielded speakers is from the permanent magnets that forme the motor structures: that's a DC field, and it will go through aluminum foil like it's not there. The AC fields from the signal in the voice coils that is driving the speakers is almost never strong enough to do anything to a monitor. Even if you have them turned up to 11, that wierd ripple pattern on the screen is probably from either your eyeballs or the shadow mask shaking, rather than from the AC magnetic field!
To "shield" against magnetic interference, budget speaker designers usually use teeny little magnets, and then design the speaker basket to try and trap as much of the field as possible right there. Then, they *might* put some high-permeability stuff like mu-metal foil inside the cabinet to try and trap other stray flux lines (or, just use a pressed-steel case, for some of the cheapo computer speakers). But realistically, "shielded" speakers are usually fairly feeble speakers. There certainly are some relatively good ones, but the usual case is that really good studio monitors need potent motor structures (especially for the woofers), which means big magnets, which means that your tube will turn green and pink if they are within a foot or so. All the foil in the world won't do squat in that case.
The best solution? Get an LCD flat panel, since LCD displays don't care at all about stray magnetic fields from monitors. And then choose your monitors for their sound, not their shielding. Seriously: compromising the monitor quality to keep the screen from turning green may not be in your best long-term interests!
