If I understand it right then it would be enough to have a response of around 5kHz on FOH at most (unless it's a array system that is direcetd to front and sides as well, or having several tops to adjust sound direct to front and sides as well.
[sarcasm on]
ok, I think then I could lowpass my home stero system to around 5kHz because the highs are gone every time I'm off axis of the center of the cabs.
It then would be enough to have bass cabs where response rolls off around 3kHz at most.
There also then would be no need to repair a broken speaker in a 810 cab because the loss of loudness is nearly inaudible. There then also was no need to repair a tube amp because the player did not really notice that one of the 4 pentodes was gone.
A low budget grand piano made in china then would fit all the needs in a big concert hall because just the moment I'm on toilette the famous sound of a steinway grand piano is gone.
I bet most folks of the audience in a piano concert arn't musicians and don't hear a difference if the grand piano on stage is a steinway or something low budget made in china. And probably most folks don't worry about something like best seating place in a concert hall.
Never the less steinway is the most seen piano in concert halls all around the world.
[sarcasm off]
Every piano player knows that the perceived timbre when playing a piano isn't just the same like listening somewhere sitting at the audience. As the audience can't hear the same timbre like the player himself on stage would mean that a musical sounding performane of ANY instrument on stage does not matter.
I totally agree with
LiquidMidnight, the meaning of a tweeter isn't to stay clearly in front, or cut sharp through the mix on stage. IMO/IME well balanced sounds are charcterized thereby that the
missing of a component is more noticable then the pure
presence.