Here's my latest duct project. This duct , like my previous attempt, blows air directly on an Alpha heatsink. You can see a little fan mounted directly on the Alpha. This is a back-up fan, controlled by a Digital Doc 5, that only turns on when the temps get too high. Most of the time this duct, with it's 80mm variable speed fan, provides the only intake air to the whole case.
Other than the fan, I only used two parts. A Smart Choice Wall Offset Elbow....a drier vent part (BestBuy 7$). And a PlumbQwik Rubber Downspout Connector (Lowe's $2$). The vent is 4" in diameter, and I bent the fan end by hand .....an 80mm fan just fits and is held in place by crimping the aluminum. This holds it tight. Mounted in the case it is about 1/2" over the Alpha, and slightly offset to also blow on the ram.
The duct and the rubber sleeve were cut to fit with some small shears...very easily. The rubber sleeve is the only part that touches the case, so there are no vibrations. Right now there is a temporary mount...after the whole project is final, it'll be more secure.
There's a picture of the filter I'm using...same as before, a PowerCare lawn-mower filter. This duct could be polished and used in a case with a window...it looks good. But I'm going to cover it with some acoustic foam. Right now it's much quieter than my previous duct setup...Mostly because the fan is not in a direct line to the rear opening.
As far a temps are concerned, the cpu is about 1C less than before....but the ambient temps are up today...about 2C higher than my previous tests. The good part is the ram temps are down almost 4C, and the chipset temp is also down. So far, so good.