I'm making a custom case for my mini-itx board, and I've been trying to decide what style of vent to use on the top for a large fan. The two options I've been toying with are either an open cutout with a typical fan grill/guard, OR make the typical hex grille cutouts.

Any thoughts? Do I have to worry about EMI escaping through a large fan opening using a fan grill/guard? (120 - 140 mm fan)

Thanks

A radiator grill like this one in black powder-coat stainless steel, the HEXX Black from Phobya for 120/140mm fans could look good

For both thermal and acoustic reasons it's important to let the air path (the top vent) be unrestricted. Here's something to read:

http://www.pugetsystems.com/labs/articl ... -Noise-107

Nice article. So case manufacturers were always working hard to to give us a quality product and not just trying to be cheap, lol.

That was a pretty good article, thanks. I appreciate the suggestions. Seems like I can't go wrong with the wire fan guard, and the honeycomb vent doesn't seem too bad either.

Most ITX builds doesn't need a very fast rotating fan either, which lessens the turbulence/resistance effects of grates. But in general I'd go with nothing more than the fans own plastic guard or a cut down(like every other ring or so) wire grill. EMI is not a problem unless you have something sensitive in the general direction of the hole, and also depends on what kind of parts are nearest the opening. Any chance of designing the opening elsewhere than on the top? I'd generally prefer to have a side or rear vent in order to lower the risk of whatever things coming into the system from above, if there's a real chance for choice. Convection inside a case is such a weak force anyway if there's to be an exhaust fan rotating at any speed.

The top vent could be considered a side vent depending on how you orient the case (horizontal - top vent, vertical/upright - side vent) Not sure if that counts?