The way we do it in TV Studios....

We use a high volume/low speed meathod. Basically, instead of having a pair of small ducts moving air real fast (and loudly) we use a dozen or so ducts moving air reeeeeal slowly. But the volume of air is huge because there are so many ducts.

An ideal solution would be to have the fan INSIDE the box, not on the outer edge. And have a long duct connect it to the vent on the outside.
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Brad B.