I just found a nice explanation from L.A. recording engineer Ronan Chris Murphy as to why its not always a good thing to record vocals in a small vocal booth. I had considered adding one at much expense. Instead I employ a small absorber called a “reflection filter” around the back of the mic as shown here. This gives the mic more focus without complete isolation.

Jimmy McNally of the Instagators recording with an SE Reflexion Filter

Also Ronan touts the advantages of having a longer, narrower control room/tracking area instead of a small box control room. That is exactly what we have created at Barn Jazz, and the sound of the room is, I think, more open with plenty of room for bass frequencies to develop. Check his video blog out at Ronan Chris Murphy