Bought the 660 because it was one of the quietest I could find on Vornado site (thanks for dB ratings in specifications). Purpose is nighttime circulation, at lowest speed setting, in our bedroom 13x13. Received and used for a few evenings.  Lowest speed setting is truly whisper quiet while still moving air gently through room.   Though a bit pricey, worth a good evenings sleep.  Just ordered a Swan S for living room.