[Steve]

Designed to reduce the perceived noise from 19-inch-wide server and rack-mounted equipment (including blade server chassis) with clever design, the patent-pending, self-ventilating cabinet reduces the Sound Power Level (SPL) by up to 90%. It's extremely useful in instances when servers have to be located in rooms where employees work, and the 42U chassis is capable of dissipating 3kWs of heat.

http://www.hexus.net/content/item.php?item=5579