Room reflectivity at low frequencies determines bass elevation in measured steady-state curves

Evidence

In a measured steady-state room curves for loudspeakers one can anticipate that the bass will be elevated compared to the direct-sound, on-axis curve. The amount of the bass rise will depend on the reflectivity of the room at low frequencies, which is represented by the RT of the room. Figure 12.1 shows that the variations in bass can be considerable. The increasing directivity with frequency also means that listeners will be in a progressively more direct-sound dominated sound field at high frequencies. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1305