l shaped members the upper base member 42 has an open upper end and comprises an array of apertures 50 which extend at least partially about the upper base member 42 the apertures 50 provide the air inlet 18 of the base 12 the upper base member 42 houses an impeller 52 for drawing the primary air flow through the apertures 50 and into the base 12 preferably the impeller 52 is in the form of a mixed flow impeller the impeller 52 is connected to a rotary shaft 54 extending outwardly from a motor 56 in this example the motor 56 is a dc brushless motor having a speed which is variable by the controller 44 in response to user manipulation of the dial 22 the maximum speed of the motor 56 is preferably in the range from 5 000 to 10 000 rpm the motor 56 is housed within a motor bucket comprising an upper portion 58 connected to a lower portion 60 the motor bucket is retained within the upper base member 42 by a motor bucket retainer 62 the upper end of the upper base member 42 comprises a cylindrical outer surface 64 the motor bucket retainer.