Strutt|Building Acoustics|Reverberant Level (From Room Constant) calculates the reverberant sound level based on the Room Constant `R`, as follows:
`L_(p,rev)= L_W - 10log(4/R)`
Note that calculating `L_(p,rev)` using `R` is the 'exact' calculation (provided that the sound field is diffuse); the alternate approach (Reverberant Level (from RT)) is an approximation for situations where the average absorption coefficient in the room `alpha_(ave)` is low.