They are the quietest fans going.
No not silent but getting closer than any of my previous fans.
20dB
Once I make an acoustic box for it add acoustic ductining, fit the exhaust silencer it should be undetectable.
When i had the cab set up before I was using a KSA 4" Acoustic fan inside a DIY acoustic box, insulated ducting, fan silecer and a DIY acoustic silencer.
My friend also a grower, couldn't hear it and was amazed ( I could just about hear it but I knew it was there), this fan will be even quieter!
I am also going to get a rhino Pro 5" filter and a Varic fan speed controller.
The fan is bigger than I need but is also quieter than the 4" version.
I will reduce the fan speed to make it even quieter and the bigger filter will also reduce the strain on the fans motor making it quieter.
I will also at some point build another exit silencer and then it should be silent.
Add to that I am using a passively cool grow light and everything should be as quiet to here a pin drop!!!