Well beams by themselves? Maybe, but certainly adding furniture, carpet, etc, all contribute to sound absorbsion and breaking up standing waves.

Picture a 20hz note, which travels something like 55ft per second, hitting a number of beams and partially breaking up and reflecting sound. Some of which get absorbed into couch you are sitting on.

Now picture and empty cement room with nothing in it. The empty room would sound boomy, because that note traveling at 55ft per second would hit the back wall of your 20ft theater room unobstructed, bounce off the front wall reaching your ears twice in less than a second..

Also, the waves would crash into each other causing standing waves or cancellation of sound. Depending were you sit, this can be bad..

If you were in a room with no wall or infinite sound aborbsion you would get the true image of what came from your speakers..

Most people do not have theater rooms like this..