Damping factor

The damping factor of a power amplifier is a metric used to describe the amplifier's ability to control the loudspeaker. It's basically calculated by dividing the amplifier's output impedance into the loudspeaker's input impedance when the speaker is operating near resonance. It's a really important number to know when you're making a decision on matching an amp to a speaker - yet you rarely ever see it mentioned these days? I have been wondering as of late why? Is it because no one cares? No one knows what it means? I don't have an answer to these questions but they're good questions. The long and short of this is that an amplifier with a low damping factor has trouble controlling a connected loudspeaker where an amp with a high damping factor is the boss in the amp/loudspeaker control battle. Moreover what's detrimental to achieving a flat response from the speaker is when an amp has a low damping factor not all frequencies produced by the speaker are flat causing bumps and dips in its response. Tube amplifiers, because they require an output transformer, have notoriously low damping factors which is one of the reasons they sound so different on various loudspeakers - some of this good, some of it bad - but all a matter of personal taste. I would encourage a broader discussion on the topic as well as hope that more manufacturer's of amps and loudspeakers publish both their imedance curves as well as damping factors. It might spark some good conversation as well.