Hi and sorry I reply so late.
I've been at the worlds biggest LAN gaming mad for some days.

Anyway...
I use an inline fan with ducts. On top of that I use an oscillating table fan so spread the air over the canopy and a computer fan to pull the fresh air from the passive intake into the middle of the tent before the fresh air get sucked up THROUGH the plants.
The inline fan makes some noise but it is relativelly easy to build it into a simple muffler box.
I put a dimmer for lights mounted on the power coord going to this fan so I can adjust the speed of it.

All smell is scrubbed by a carbon filter.

The ventillation system is hooked up like this:
In the cailing of the tent the fan hangs on one side and the carbon filter on the other side. From the carbon filte runs a ducting to the cooltube to cool the 600W HPS and then it runs to the inline fan and out the top of the tent.
I use a 280cubic metre fan for this and running full out it does make a sound, even if noone is ther to hear it.
Something like 2-3 well ventillated gaming computers running at the same time.

The cost of the scrubber, ductings and fan would come to something like US$250 in Sweden. Money well spent since smell will never ever be an issue and a well ventillated grow area produces a LOT more weed.

I hope this helps a bit and if you want more info don't hesitate to ask.

Puffzter