The Panther low-speed cooling fans range in form factor from 60 to 92 mm. They operate by converting a conventional low-frequency signal to a high-frequency signal. By operating at switching levels above 20 kHz, they produce a soft commutation resulting in quiet operation above the human audible range. At a fixed low speed, a Panther fan has a 1× to 3× decrease in sound pressure in decibels over a standard dc fan of the same form factor. Available sizes include 60 by 15 mm, 60 by 25 mm, 80 by 25 mm, and 92 by 25 mm. Dual ball-bearing fans are available for OEMs and range in price from $4 to $6.