A direct measurement of the acoustic ratioQ—i.e., the ratio of reverberant sound energy density in an enclosure to the direct sound energy density—by a correlation technique is shown to be possible. Results of such measurements in several rooms are found to agree fairly well with values obtained from the reverberation time through the formulaQ = 4πTR2/13.8V, which is based on the Sabine theory of the diffuse reverberant sound field.