DnTw is the equivalent of Rw, but measured onsite. Rw is the value measured in an acoustic laboratory, while DnTw is measured on-site. An on-site measured value of DnTw + Ctr is permitted to be 5 points lower than the Rw + Ctr value. Where the BCA may call for an Rw + Ctr > 50, the same requirement may be satisfied by measuring DnTw + Ctr > 45 on-site.
