Dining room speakers - cutting holes

I didn't take any in progress pics of this. This room is all plaster, so we had to take extra precautions before making holes for some ceiling speakers. I made a backing out of quarter inch plywood to fit in the joist bay, and attached a 2x4 on each end of the plywood. I attached this in the attic to the joists. Of course, I put one of them in the wrong place, even though I'd already drilled a hole for the centre. So I had to rip that one out, and rebuild it. I used a compass to mark out the hole, then cut the plaster out first with a razor knife. Then I used plaster washers to keep the plaster attached to the lathe. Then I used a jigsaw to cut the hole, throught the lathe and the plywood (after drilling a hole to get it started). The plaster still cracked a little, but was way better than without using the plywood and the washers.

Here it is with the wire ready, after finishing the plaster work. It has a coat of concrete fill, and will need a couple more coats to finish it. I'm going to add some styrofoam insulation above the soft of speaker box I built in the attic. The 2x4s hold back the vermiculite as well. We'd like to add more insulation in the attic as well...