Who said “ flat freq response “ is the best?

Recording engineers don't record anything flat
first there are really no flat microphones
Actually we use our ears to get the overall sound we prefer
It is never flat. Our control rooms were rolled off top and bottom forcing the engineers to boost base and treble. A perfectly flat recording in a flat room sounds terrible. Forget about frequency response and listen to what you like
Alan

if it measures good and sounds good, then it's good.  
if it measures good and sounds bad, then it's bad. 

in other words, who cares how it measures, get an EQ to compensate for room interactions, and of course just about every other record you play. 

KlarkTeknik DN360 and minidsp 2x4hd.  Yes to both. 

Who said “ flat freq response “ is the best?

If you want to hear it the way it was recorded and intended to be listen to, then flat is best.
If you don’t like it, buy a equaliser and do what you consider to be the best.
http://www.schiit.com/products/loki

Cheers George

@kalali 

06-24-2018 12:41pm

This discussion begs this question: would two different speakers with identical frequency response curves sound the same in your room? I'm betting the answer is no.

There are so many other variables. Impulse response, compression, dispersion (power response)  and distortion among a few of them. 

ESL's have often really mediocre FR but their lack of reflections make up for it in detail and imaging.