Some obscure but important philosophical difficulties with the standard method of measuring transmission loss by the reverberant room method have led to reexamination of the basic concepts. An equation is derived relating transmission loss to the “total loss area”H2of the receiving room.H2is found to be measurable within a negligibly small uncertainty, using familiar sound‐decay techniques, providing thatT2/T1, the ratio of “natural” reverberation times of the receiving and source rooms is properly adjusted. It is shown that the equations commonly used in the existing standard method require knowledge ofA2, the total absorption of the receiving room, implicitly excluding transmission through the panel.A2is not generally measurable without prior knowledge of the transmission loss of the test panel. These and other considerations result in the proposal of a new procedure.