Room acoustics basics

Earl Geddes wrote what might be considered by many a definitive book on the subject of acoustics. 

Odeon Room Acoustics Software. Their site is very informative. 

Here's a relatively recent (2014) book on acoustics that might be valuable.

Acoustics of Small Rooms

https://digistar.cl/Forum/viewtopic.php?t=557

I found this to be a very interesting read.  It touches on many of the accepted theories of room design and adds some new thoughts.  It includes a room dimension calculator so you can plug in different numbers and see how they change the room.  I like comparing the same numbers on the Bonello formula to see how close the two charts can get.