Before installing acoustical tiles or paneling over an irregular surface, you must create a level plane, using ceiling- or wall-width furring strips. These are lengths of wood, usually 1 x 2 or 1 x 3 inches. They may also be needed when installing new siding or shingles or plasterboard over uneven walls.
It simplifies the task to make a scale drawing on graph paper. Plot from the center of the area outward: strips on 12-inch centers are usual for tiles, on 16-inch centers for paneling.
Nail furring strips at right angles to the joists or studs, using two 21/2-inch nails at each juncture. Check every two strips with a level. Hammer shims (thin wedges of wood) under any spot where the strips are not level. On a masonry wall, use masonry nails or adhesive, as advised in the paneling instructions or by your paneling dealer.