MB 600 cfm (Axial style) - 61dBA  (decibles)

SM 600 cfm  (Squirrel cage style) = High Speed 5.5 Sones / 62 dBA,  Low  Speed 3.8 Sones / 50 dBA

SM 600 cfm with 300 wire adaptor =  High Speed 5.5 Sones / 62 dBA,  Low  Speed 3.8 Sones / 50 dBA

SM 1000 cfm (Squirrel cage style) = 5.9 Sones / 64 dBA   

SM 1200 cfm (Squirrel cage style) ) = High Speed    5.9 Sones / 64 dBA
Low  Speed     4.0 Sones / 51 dBA