im assuming this s true for most inline fans of quality, but for my vortex 6" 465 cfm model any time you turn down the speed it buzzes. its not too bad of a buzz until you go under about 75% power. below 50% it buzzes like crazy. i think your best bet is to just get an appropriate size fan for your areas size so you would not need to use a speed controller. (by the way speed controllers can be found at harbor freight for about 13 bucks, same controllers that hydro stores sell just not with a brand on it.)

have you thought about using an inline duct fan from a hardware store such as lowes? theyre pretty cheap and they should get the job done just as well. ive never used one myself but they defintely look like a good way to do things on the cheap.
mushaboom Reviewed by mushaboom on . Inline Fan Decision Looking for a 6" 400+cfm fan, still undecided about which brand to go with, everything decent seems to be in $200ish range. I've searched but figured a poll would be alot easier to get opinions. I'll be running a speed controller for my 600w hps/mh to dial in perfect airflow and to reduce noise, and will be hung from ceiling mounted bungee cords. The closet system will go glass enclosed hood-> ducting-> fan-> ducting-> filter (unsure about insulated vs non ducting) with passive intakes. So Rating: 5