Patent 7658592 was granted and assigned to Minebea on February, 2010 by the United States Patent and Trademark Office.
A fan housing is provided with slots formed in the enclosure of the fan housing. The slots are sized appropriately to filter the noise generated during operation of the cooling fan; e.g., tonal noise produced by the rotation of the blades. The slots may either be vented to the outside of the enclosure or closed off.