One of the concerns with rooms is that in America we tend to build rooms with dimensions that are multiples of 4 feet, the typical size of building materials available. That is good economically, but not necessarily so when it comes to sonics. Take a typical medium room size: 16' L x 12' W x 8'. I've come across a lot of these here in Albuquerque. This gives big bumps in room response at 70Hz, 84Hz, 100hz and 116Hz which are problematic in that the 70Hz and 84 Hz lie in "the mud" factor in low frequency response. You know, that Boom Box kind of LF. The 100Hz and 116Hz bumps make bass sound thick and mask a lot of low frequency articulation.
Go here to find a great calculator that you can play with and learn a lot:
https://amcoustics.com/tools/amroc?l=16&w=12&h=8&ft=true&r60=0.6What is handy about this calculator is the ability to hear what problems are generated by convergent modes. It is a video game for audio nerds like us.
I plugged in the dimensions listed above. By varying the dimensions 1' at a time you can see and hear the difference that say a false wall can give.
Also, check out 'Tools' for a quick education in acoustic room theory.
Here is a site that deals with how to trap using Helmhotz resonators to suck out the really nasty room modes.
http://web.archive.org/web/20010803052829/www.headphone.com/EditorialHeadroom/RoomTubes.aspThis has been around for years and is a great resource.
Small changes in room dimensions can reap huge gains in room response and room gain.