Heh, a return to the days of knowing your phone was about to ring because your speakers started screaming about it. I hadn't considered that effect on the driver lines, but you're likely right that it will be less happy. That's testable at least.
Hey, those days are still around... GSM is just as powerful as ever, and home audio equipment is just as terrible at EMC as ever. At least a few streams I've watched online, you hear the distinctive bip-dit-beep-bip of a GSM transmission every so often...
The hope would be that having it enclosed would reduce ESD risks, though being acrylic it's not going to be static dissipative and I can definitely see the benefit of more capacitance from a chunk of metal even without it being grounded. The USB shield should at least be grounded at both sides.
If you have a USB port mounted in a plastic enclosure, then the only ground reference is the cable connecting it back to the motherboard. So, zapping the port, even if it's on the metallic shield part of it, still carries zappy energy all the way back to the motherboard. The cable is likely imperfect (the worst part being the transition from cable to header, where there's a full 1-2cm of unshielded connection), and that exposes the USB signals to ESD energy. Maybe not all of it, because it's kind of a secondary thing (it's seeing what energy is not being shunted by the ground wire), but it's still going to be a large percentage (in the 10s of % range), enough to be a hazard.
If the port is mounted into a big metal shield, that helps spread the energy out, but very quickly, the plate itself becomes charged, and where does the energy go from there? Well now you have a huge antenna that's inducing energy in everything around it. Even worse!
ESD testing is typically performed with a signal source on the order of 150pF, so it takes a big plate (i.e., about the capacitance of a human being in free space, oddly enough!) to have any effect on the amplitude.
What's more, ESD testing is performed in two phases: one to check direct effect (zapping connector shields, any exposed metal), and another to check indirect effect: a metal plate is set up near the device and zapped. Even this non-contact method produces considerable interference, enough to upset communications and cause failures of poorly shielded, sensitive ports (maybe not USB, but cables within the case, like SATA, sure). The equivalent "real life" scenario is, touching something metallic nearby, like a filing cabinet; the mini EMP from the spark couples into everything nearby.
What should the shielding look like?
Consider standing on the beach. Your goal is to block a huge wave incoming.
You set up a flat board, vertical, in front of you. Braced so it doesn't push away. The wave comes. It washes right around. Well, duh, that was pretty stupid, huh?
The physics of E&M aren't quite like water waves (quite a lot simpler, actually... E&M doesn't make turbulence!), but to a general idea, it still works out.
Suppose you get a few more boards, and stick them together, so that you now have a "C" shape around you. The wave comes, it crashes over the nose of your structure, and goes around it. The wave eventually washes in behind, but it's much less violent than before.
Add one more board and complete a square. Now you have a sealed column. The wave comes, it crashes around the column. Nothing happens, the water level inside remains constant (or it changes slowly, due to water seeping in through the sand or something). This is the ideal case, having solid metal shielding all around.
If you must have windows, the best place to put them will be away from the crashing waves. If the sides of your enclosure are insulated, ESD can't strike there. If the front, back, top and bottom are shielded, and the ports are only on the front and back (or whatever), the waves will tend to wash over those surfaces. They'll still wrap around the openings, but it won't be as strong as having a floating plate or something.
You'll still have no contest as far as outgoing radiation or incoming radio susceptibility (a window is a window, at those frequencies), but it's one thing at least.
Hmmm, that's a good point, though using the plastics that's buried mesh based adds some interesting problems to making a laser cut finger joint.
Would I be excessively optimistic in thinking that the kind of plastic used in static dissipative bags would be sufficiently conductive for EMC? That's reasonably clear and would solve some of the protection issues on things like the TFT lines. Google says they're typically less conductive than "conductive plastic".
Yeah no, you really need something metallized to do the job..
Hmmm, you mean as a mount plate still, right? For some reason I have this image of a plate with a motherboard sized hole for the board to sit suspended in.
Nah, I mean, a plate that's more of a web, with nodes at all the screw hole locations. Could do some artsy forms -- 'bubbles' missing from the plate, or a literal spiderweb style, or straight hard lines, or something more abstract, etc.
Tim