Meridian and Lexicon pre-pros use the same approach, measuring in the time domain and correcting for low frequency ringing. Neither system operates above 250Hz nor do they make any attempt to flatten frequency response.

In receivers, newer Denon models do some similar stuff with the Audyssey system they've licensed; newer H/K units also do the same with their EZset/EQ system designed using some of the research from the audio legends at Harman (Floyd Toole, Todd Welti, Sean Olive).

Wayne, since you post at SMR, I'm surprised you haven't read more about how the Lex EQ system works. You can also read some discussion about this subject here .