![Image](http://members.home.nl/taselaar/niels/shockhorror.jpg)
The duct opening is 4x12cm. The fan is a Nexus 120mm, ducted (I love ducts) to my cpu heatsink. The results are shocking! (Prime 95 until temperature stabilizes)
No duct:
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fan rpm 510, max diode temp ~67..68 degrees c
fan rpm 660, max diode temp ~50..51 degrees c (max speed)
With intake duct:
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fan rpm 540, max diode temp >79 degrees c (eek, I took it off.. would've gone higher!)
fan rpm 720, max diode temp ~71..72 degrees c
The fan speed increase is caused by the duct and the resulting pressure situation, despite the opening being 48cm^2
The temperature difference is huge. 4cm is about the maximum height I could use 'inside' the case, it would really make the case too wide going to 12cm for instance. Anything in the way of direct intake paths can dramatically decrease cooling efficiency!