I apologise - I gave an incorrect link previously - should have been this one
Yes they are expensive £19 (I am using 9 of eveything in my build - the ££££ - ouch) but when you power them up you realise why - they are unlike many fans you will come across - they have some real grunt and the air volume they move is awesome - leave them running face down on a desk and they will almost take off!!!
Spec - an Air Flow 36m³/h and high static pressure (they can move static air quickly from startup =grunt)
Many fans (computer type - black case) have 4 wires. This normally indicates that they have an inbuilt speed controller and often a speed sensor output.
The inbuilt speed controller uses a square wave signal @ 25khz - you vary the duty cycle of the PWM signal to change the speed - this is an industry standard spec
You may well hear you computer fan run at different speeds - that will be using the system described above
So the catch is how you get your 25khz control signal - I use a standard microprocessor board to supply the 25khz signal. I am able to remotely change the speed of the fan to shape how much smoke is exiting the system