Sound power is a poor estimator of bass performance in real rooms.
Evidence
Above the transition frequency region, and certainly above 500 Hz, all predictions perform well, but method 4 exaggerates the shape, indicating that more sound components are needed. At low frequencies method 1 stands alone as being too high, indicating that sound power is not a good estimator of bass performance in real rooms. The other three methods closely agree, but none can capture the extreme variability of in-room curves.
— Toole, Floyd E, Sound reproduction- the acoustics and…, 1317