Is room treatment a science?

"Is a $4,000,000, 2000 seat auditorium trial and error or scientific.?"

It depends how they went around the volume of bodies expected to be in and material that clothes would be likely made of while there.

yes, it's a science. But you can diy, cheaply and simply and hear an improvement/difference.
It's easier to take brightness and echo out of a room, I would think, than the other way 'round.
Having a large rug on the floor helps.
Artwork on the walls helps.
Seating arrangement helps and the style of seating helps too.
I really notice a difference by pulling the curtains across the sliding glass doors. Stops reflection and harshness..

That Geddes book is a gold mine! If only I had known- and it had come out a dozen years earlier! Lol!  Oh well at least I got the solid wood exterior door with weather seal!! 

Yes, room treatment it is a science.  Do yourself a huge favor, and download REW software and learn how to use it and interpret the data.   Start by optimizing the position of your speakers and listening position, then begin to add treatments addressing first reflection points, slap echo etc.  Sometimes, you can get surprising improvements by careful positioning of room treatments other than the listening position.  

You can do a certain amount without measuring, but it can be slow progress.   Most of us can discern small differences for the better or worse by ear.  But after a while, it can get to be mind boggling to keep track of.  There are so many variables.   I like graphs that I can archive along with notes on listening impressions associated with a given room configuration.  I can tell you my room is orders of magnitude better than when I started, and I never would have gotten where I am now without REW.  If you invest a little time and effort you won't be sorry.

Millercarbon wrote, "That Geddes book is a gold mine! If only I had known - and it had come out a dozen years earlier!"

Yes it is a gold mine, under-appreciated probably because it has "Home Theater" in the title.

I’ve been in Earl’s home theater room several times (mostly listening to two-channel). It is one of only two systems I have experienced which can pull this off: It can play so loud that you literally have to shout into the ear of the person next to you in order to be heard, but the sound is so clean that it doesn’t hurt your ears! This actually makes it kinda dangerous, as the SPL can be much higher than you realize. The only other system I heard which could pull this off was over ten times the cost.   The combination of natural timbre, smoothness, imaging precision, and spaciousness in his room is amazing.   And his bass is pretty good too! 

Duke