Most rooms don’t need acoustical treatment.

Believe me, almost all untreated rooms sound terrible.

Right on the spot....

But even  if i dont doubt that all HFT are  very good, we can do it ourself at no cost with basic acoustic science... I know, i did it myself.... I say that for those who cannot afford to bought them, not to denigrate good engineering....

Having the money i would have probably bought them... But i did not need them now....

This post should be called “most people don’t use room treatments but they should”. The room is the most important piece of the puzzle on putting together a great sounding room. Book, furniture, etc... are not replacements for a true absorption panel or an actual diffuser. If you have a dedicated room you must treat it correctly to get the best out of your equipment. If you have cheap stuff then it won’t matter much

+1 Millercarbon (best point)

Yes, and no. Past a certain point, the nuance any given system may behold can be more achievable with focused attention on surfaces and corners where treatment could be of considerable benefit. 

All rooms need treatment asap.

Diffusers?  What about 1d (lateral) vs 2d (scatter).

wouldnt 1 d be best if ceilings are flat?  Why bounce scattered waves off a ceiling???