How about a little more info when you start your posts. When people have to guess what your talking about, how are you going to expect a solid answer.I really hate to say this but why would someone put a vent fan in a box with no in or out air flow? I want to insulate the sound but I guess that was not clear to you guys... It is a duct fan for ventilation.... These fans can be loud I have heard and I want quiet... Don't reply if you don't know. I think we could save lots of our energy on here if the people that reply don't when they don't have an answer.....
For instance. What type of fan? Why put it in a box? Why insulate it? What are you trying to achieve?If you place an 8'' fan in a box and insulated the inside around the fan will the fan over heat???