Pick up an S&P fan at hvacquick.com. They are pretty good, cheap, and quite, i use 3.
see the ballast on the fans...
and about the shelf...i use one but i wanted by cab fully contained. I jut helped a guy here in Vegas build a cab and we placed all fans, AC box, dehumidifier in the attic. We did a 4x4 vert setup /2 600s so we needed the height. Remotely placing all this stuff cuts down on noise as well. So there are 4 4"ducts going from the cab to the attic, to make it look cleaner all 4 were ran inside a single 8" duct. I dont have pics but will try to get some. I even have my C02 tank in there...
see the door that's insulated over fan/ballast chamber to stop noise. Also make sure there is decent airflow...