4 Mounting Blocks for invisible loudspeakers. For use when there is insufficient cavity space for an Amina cavity backbox (less than 75mm). Allows installation of Amina loudspeakers into plasterboard with a rear cavity depth of just 30mm – Please note, rear of loudspeaker should be covered using soft insulation material where mounting blocks are used to prevent ingress of debris over time.where no Backbox is used.