Regarding ducts...

I did a quick search on ducts (and actually made one last week) but have a question. I actually didn't really make a duct, but rather, cut a hole in the side of the case and put an intake fan on it. I recieved in the mail today a 92mm duct from mnpctech.com.

http://www.mnpctech.com/FanDuct.html

That's what it looks like. Now, using this duct doesn't allow me to have a fan blowing into the duct, to the cpu fan. What I'm wondering is, do you get better temps with a fan blowing through the duct onto a cpu fan (requiring me to do a mod to the duct itself) or is it only necessary to have a duct going to the cpu fan and the cpu fan will suck in the cool air itself, without another fan blowing air through the duct. Am I making sense here? Thanks for your input.

probably the best option is a half-duct, that comes from the side panel fan and ends about half an inch short of your CPU fan intake.

Rationale:
You DO want the cool air getting into your CPU fan.
You DO NOT want any extra impedance; the gap in the duct makes sure that that cannot happen.

A straight, closed duct where the side fan is exactly the same CFM as the CPU fan would work well. Otherwise, leave a gap so that one fan is not fighting another, and no fan is fighting to breathe. Axial fans dramatically lose efficiency when they are fighting pressure. The gap prevents any pressure differential from arising in the tube ...

the wesson

PS For the same reason, any sudden narrowing in a duct tube really kills fan CFM. Also any turns, corners, etc are a bad idea. And a small or corrugated tube is a bad idea.

To actually answer your question -

you'll do better with a fan in the duct.

A fanless duct should have the duct opening right up against the CPU fan if possible.

the wesson

Alright. I just put the duct in there (the duct from the webpage, without a fan or anything, just a duct leading all the way to the cpu fan with a half-inch distance in between. My temps appear to have dropped about 1 C. I'll try to rig up a way to add a fan to it later. I put my hand inside the duct though, and I could feel the cool air being sucked in.

A passive duct is better than no duct and an active duct with a fan is better yet. Wesson had some sound advice.

Oh I agree. I'm figuring out how to add the fan to the duct now. Thanks for the help!

A passive duct can also work well if the entire case is sealed except for the duct, and all case fans are set to exhaust. Thus your case fans are helping ventilate the CPU.

In that case I would also not want to put the duct opening right up against the CPU, again because of pressure considerations.

the wesson

All I can say, is that whatever I had to say Wesson has already covered it.