Critical distance measurement of rooms from the sound energy spectral response

At any point in an ideal room, the standard deviation of the acoustic energy spectral response from its mean is shown to be a function of the direct-to-reverberant acoustic energy ratio at that point. This function yields a method for measuring critical distance, at which these energies are equal, which is more powerful than the traditional total energy response method. The new method uses measurements made within the critical distance; it does not require that the reverberant energy be uniform in the room. Calculations made for computer-simulated rooms show that the method is valid for rooms having a wide range of average absorption coefficient. In some cases, results can be obtained with the new method where the total energy method fails.