I was reading the extremely positive review of Earthworks' Sigma 6.2 monitor speaker on Stereophile which can be found here:
http://www.stereophile.com/fullarchives.cgi?859
The author (and editor) John Atkinson made this interesting comment in the review:
"But even the Earthworks couldn't...
Finally a time and phase accurate speaker from a pro audio manufacturer. Take a look at the Earthworks Sigma 6.2
http://www.earthworksaudio.com/ns/monitors.html
Check out the near textbook perfect step and impulse responses, and the high quality components (Solen inductors and capacitors)...