Low volume listening dynamics

@wolf_garcia , actually the (2001?) update flattens the low level curves somewhat. At least above 100Hz. Below that, room effects dominate anyway. So listening 10 or 20 dB below your normal listening level should reduce room distortion in the bass, but won't otherwise affect the balance enough to compensate for the tone control distortion. IMO.

But that bass boost can be fun sometimes, can't it?

I have 4 pairs of speakers with low-ish efficiency ratings (82 dB, 85 dB [2], and 86 dB). All 4 pairs sound nice but rather anemic at low volume levels. They really need some juice to hear what they're capable of and it's frustrating when you want/need to listen with the volume turned down and that magic is gone. My nicely efficient Omega's (94.5 db) sound wonderful at low volume levels. I no longer experience any of that frustration which annoyed me so.

Did I get an update in 2001? Was it from Fletcher or Munson? And I have a great sounding room likely due to a  high sloping ceiling and my impeccable taste in furnishings.

I always found that low level detail was a strength of tube amps. I dont really think the efficiency of the speakers is as critical as others on this thread.

Would that all had your good fortune, Wolf. It's ISO 226 (2003), on the 70th anniversary of F-M.