I lime the S & P mixvent but they aren't as quiet as some may claim. For reference, I have 4" versions of vortex, can-fan, mixvent and s&p powerline series. Out of these four the can is quietest and the powerline the loudest to the ear. The can is also the largest by far and not suitable for many situations that would require only 4" fans. The speedster is a great speed control for the $. 17-30 bucks depending on source. It is non-linear though and when it seems you have turned it down 10% you have really lowered 30-50% depending on load and factory calibration of the units rheostat. Best way to figure value is with a kill-a-watt and note wattage change. Big however though, the powerline and some other fans including the mixvent I have (td100x) are louder when speed controlled. There is a resonant hum from the pulse wave modulation used to control speed. Essentially you can picture a bicycle crank being turned and it's effect. At full blast the rider pumps continuously thus smoothly turning the drive wheel. The rider feels little deccelerative effects as they are constantly moving forward. But if the rider moves with repetitions of pumping .25 seconds and coasting .25 seconds, they will essentially oscillate in feeling a forward-backward movement. This is what the fan blade does since it is balanced to spin at full speed. The sound becomes apparent at real 60% or lower which is more like a 10 -15% reduction on the speedster or similar devices. This is not a malfunction of either the fan or the speed controller, but just incompatiblity between the devices. It is safe to lower untill the hum becomes apparent. Can-fan and vortex are fully speed controllable without hum. There is a blue plastic sunleaves fan that I have had the chance to play with the 6" version. If the 4" is similar, will be a good contender. The model slips my stoned mind now but it is the blue plastic one so not too hard to miss. Don't let plastic scare you as it is extremely efficient at vibration damping. Much more so than steel. Can-fan and vortex each use vibration damping paint which is noticably better than the powerlines. Sorry for the breadth and scope but my girlfriend got busy with Christmas wrapping and I'm bored as all get out. :::::edit::::: I am high. You are going 6". Never tested can, vortex is like a rocket engine, sunleaves is nice, my out of state buddy saw my stuff and told me to gets mixvent. I havnt visited him or seen the 6" version.