In another thread, Riley (bigcat) showed a drawing of his room that's narrower at one end. Usually a room should get wider and / or taller in the rear, but in this case that's not the best solution. As it happens, someone else today asked me why it's better for a room to be larger in back than in front. So I figured it's worth a brief explanation:
I can think of three reasons to have angles in an audio room:
One reason for angles is to avoid flutter echo, that "boing" sound you get when sound reflects repeatedly between two parallel surfaces. This applies both in rooms where you record as well as rooms where music is played through loudspeakers.
Another reason is to deflect early reflections toward the rear of the room as an alternative to absorbing them. This applies mainly to playback rooms, though I could see a situation where reflections could be intentionally aimed away from distant microphones in a studio's live room.
To answer the main question, if a listening room gets small in the rear, reflected sound will have a sort of megaphone effect as it comes back to your ears. But if the rear wall is larger, the direct sound spreads out (gets weaker) as it travels toward the rear and has less energy per square foot when it reaches the wall. Then again, the reflected sound will narrow again and get stronger, so my last point might be wrong. I'll be interested in hearing opinions or ideas from others about this.