Place the keyhole hangers on either side of the back of the speaker box, approximately level, narrow end of the hole up. Mark the screw holes with a pencil.
Place a thumbtack under each keyhole hanger so the point of the tack extends out of the bottom-most part of the keyhole. Tape the thumbtack in place.
Align the screw holes in the keyhole hanger/thumbtack assembly with your pencil marks. Tape the keyhole hanger/thumbtack assembly back onto the speaker box.
Place the short level on top of the speaker box. Hold the speaker box against the wall where you want to mount it. Adjust the position until the level bubble indicates you have the speaker level against the wall. Push the speaker against the wall to force the thumbtack points to mark the wall. Set the speaker down on a table.
Remove the tape from the hangers and remove the tacks from the hangers. Place the hangers back on the speaker box, with the screw holes aligned on your pencil marks. Screw the hangers to the speaker box.
Screw two double-headed 2-inch screws into the marks you made on the wall with the tack points. Screw them snugly against the wall board. Lift the speaker to the wall and place the keyhole hangers onto the double-headed screws. It will hang level.