Wanting to build heavy shelves on plaster walls (apartment)
In my apartment (old building, plaster walls, aluminum wiring) I'm hoping to build a fairly heavy shelf in my bedroom. Using triangle bracers, I'd like to make roughly a 40" wide shelf by maybe 24" deep to hold my DJ equipment. I was thinking of 2 shelves, the top to hold speakers, monitor, reciever, CD player, the bottom to hold turntables, mixer. I figure I have about 150lbs of sensitive equipment I obviously dont want to drop.
I'm not sure whats behind these walls. I figure studs, but its possible I dont have studs? Like plaster/lathe directly on masonry? The walls sure dont sound "hollow" when I knock on them.
What kind of fasteners do you think I should be looking at?
My rough plan right now is to run 3 vertical 2x4s going up the studs fastened in the middle. Then make triangle braces attached to the shelves/vertical braces. So weight would be supported in the middle and on the sides. I'm sort of flexible on width right now, I want it to be wide enough to hold my gear but I dont mind going wider if it means attaching to 3 studs to securely hold weight.
Also how can I be careful not to accidently drill into any wiring? I assume wiring is run vertically for the most part but I just want to be careful.