No one yet has answered my thought question of how two rooms, each with IDENTICAL louspeakers, placement, wall construction and acoustics, could still require a slightly different bass response. So I’ll answer:
A mastering room typically may listen at a slightly higher listening level than a mix room. And often may listen to more compressed material. As such, the bass response curve may not have to be turned up as high as in a mixing room.
This has proved true in my mixing and mastering rooms. They are far from identical rooms and speakers. The mix room is much smaller. Anyway, the bass response in the mix room is turned up +0.9 dB above flat measurement, below 125 Hz, and it sounds “just right”. The bass response in the mastering room is turned up only about 0.2-0.3 dB. Again, I think part of the reason is that in the mastering room we listen at a slightly higher level than in the mix room. ——-> Equal loudness curves, folks. That’s a reason.