More plys is better than less. If the face veneer is paper thin it's probably less than ideal. (There might not even be a face veneer at that price.) Make sure it looks like the plys are glued together well, I've seen stuff that bubbles up between the plys over time and you can physically rip the plys apart with your hands.
Above all, void free is highly desirable. By looking all the way around the sheet you should be able to see if there's voids or not. Sometimes they fill the voids (like BB fills problem areas with football shaped patches) and that's ok, but if you see big holes in the plys at the edges you are just asking for trouble if you use that.
So no, it doesn't have to be the most expensive plywood. But there are things to look for. You don't want construction grade but you don't need furniture grade.
Also if weight is an issue, go for sanded pine. BB is much heavier but it's also stronger. Pine is pretty soft. It's still strong compared to mdf but you can dent it with a fingernail. Duratex is pretty hard so if you use that for a finish that isn't an issue.
Also as I mentioned, 1/2 inch pine starts to twist and warp almost immediately as soon as it's cut up. The smaller the panel the more it will warp. Unless you want to straighten panels as you build, don't cut it until you are ready to glue it.
At $10.35 a sheet that's probably construction grade, so probably only 3 ply, probably no face veneer, probably badly glued plys and probably very rough face and full of voids. But check it out at the store, you might be pleasantly surprised. But I doubt it, that's very cheap. Arauco is pine and it's very nice, I think it sold for about $20 - $25 for a 1/2 inch sheet last time I saw it for sale.
Last edited by diy speaker guy; 04-13-2015 at 01:26 PM.