This is a fast, strong and inexpensive shelf for "bookshelf" speakers. The pictures are self explanatory, and should be all you need, but for those who don't have a tools/materials skill set, read on.
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Step 1: Make Them, Hang Them, & Add Speaker
Basically, buy 2 shelf brackets that have the long side shorter than your speaker is tall, (so that you don't see it when the speaker is on the shelf) and screw a piece of wood to it that is the size of the bottom of the speaker plus the space that the bracket takes up in the back. A bit smaller is OK. Plywood is preferable since it can't break along the grain that it doesn't have. Mark the position of the corners of the speaker and glue the blocks there. They will hold the speaker up over the bracket. If your wood is too thin for screws, use small nuts & bolts (machine screws), the bolts going in from the bottom, and not standing taller than the blocks. I glued some bits of tool drawer liner to the blocks to stop the speakers from sliding.
If at all possible, screw the top of the wall side bracket into a stud. If you hit wood, one screw will do it as long as it goes at least 1" into the wood (not including thickness of drywall or plaster). Don't screw it down so tight that the bracket digs into the wall, just snug against the surface. If you don't hit wood, then use any of the many types of drywall anchors that expand behind the drywall. I'd avoid the plug type, since they can pull out on impact in this application. Use a second anchor in one of the lower holes if you feel the need for extra strength or fear swinging speakers. In my picture, the shelf is mounted to brick. Plug anchors (like the conical plastic ones that come with everything) are fine for masonry.
FYI: If you mess up and trash your speakers I'm not responsible, period. As with anything and everything else, please use common sense, and get advice/help if you think you need it.