In response to Cathar's comments about silent fans, the Deltas do not fit the "totally inaudible" ranking. I've got a pair of the 70cfm 120x38 tri-blades. They're rated for 4 volt operation, and I've got my 2 operating just above their stalling speed as my only case intakes and exhasts. Since the rpm sensors fail around 650rpm about, I'd guess these are going around 600. There is no noticable bearing noise but the fan motors do tick. If your room is closed and very quiet, then you may hear these from from 6 feet or closer. If you've got an open window ambient noise will easily drown them out.
They may not be silent, but when taken to their lower voltage limits, they are VERY quiet. To me they rank with Panaflo L1A 120s when undervolted.
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