The fan motor for the Dust PROOF range of fans is extremely quiet The Acousti Fanand 153 Dust PROOF series use the highest quality double-ball bearings available for reliability Extra long life expectancy Sealed dust proof motor Supplied with a unique 3-speed fan cable One of the unique features of these fans is that the motor has been completely sealed from the outside environment. This prevents dust entering the motor & also reduces the amount of noise perceived to be coming from the bearings within the motor.