Use the on installations into masonry, hat-channel type suspended ceilings where the space behind the speaker panel is open, or where a metal enclosure behind the speaker is required. This product is also useful to assist in installations where sound transfer from one floor or room to the next is of concern. Constructed of 1.2 mm thick metal, MBC back boxes are shipped fully assembled. Convenient knockouts for conduit are provided, 1 each on the top and bottom of the box. The knockouts will accept 1/2" (13 mm) conduits and loom clamps. The MBC back box is lined on all four sides with 3/4" (19mm) plywood to provide solid mounting surfaces for the speaker panel.