44       There are three basic kinds of products: Absorbers: Products to absorb echo and reverberation only Soft Surfaces (acoustical foams, fiberglass, thick fabrics, cotton panels, rock wool) light weight Usually at least 1” thick Installed onto finished room surfaces Blockers: Products that are only designed to block sound transmission The heavier the better (8” of concrete will block more sound than 2” of concrete) The more mass the better The more density, the better Products that decouple hard surface contact will out perform mass alone. Composites: Products that will block sound AND absorb Echo Usually made out of something light AND heavy There are only a few products designed to do this. Put the soft surface toward the noise source.