quiet fans

I have a 2x2x4.5 ft. grow area available. I figured that I should go for a 250W HPS light (I don't have access to cheap LEDs) and 2 medium sized plants in Air Pots. My concern now is the ventilation. At first I thought of getting a 250 m3/h inline fan with a carbon filter, but I think they're...

While looking for Db information on various fans available I stumbled across these tests on youtube. Tested by hydromag under the same conditions. Various tests including Db , airflow and power consumption with each fan under different conditions. 1m of ducting with no filter Filter and 4m of...