Idea for a small 250w set up but looking for input

Hey guys, I've got an idea for small 250w hid set up. I'll be building my own tent/box for this. I'm thinking 2.5' X 2.5'X5.5'. I figured that would be enough space for 1-2 nice plants. Venting is a problem I'm running into. I have no problem buying a fan but stealth is somewhat of an issue. It doesn't have to be SILENT, just quiet. Since I've never done this before I don't really know how loud a 4" inline would be. Was wondering if anyone had experience with these http://www.ventingdirect.com/soler-and-palau-td-100-4-100mm-inline-mixed-flow-duct-fan/p934765?source=gba_934765

I don't have neighbors so my fans are loud and obnoxious.

The inline fan you marked is extremely similar to the one our graphics shop uses with their thermal printer. It sucks all the inks fumes out of the machine and is mounted in the showroom. Quiet is an absolute and those fans run pretty silent.

It is borderline for air movement, the room you propose is 35 cubic feet and the fan pushes 100 CFM. Right on the edge, but should work.

Personally, I overbuild, but I spend a lot more for my yields than average.

Without a muffler my 4" HTG fan is as loud as a window AC unit. I'm running a single plant in a GL60 tent which is close to the size you wrote about and It's good for 1 plant 2 wont fit very well but it's the perfect 250 watt set up. My current i'm scrogging a ladyburn 1974 and it takes up the entire tent check link in my sig.

Is it the sound of the fan or the sound of air turbulence through the ducting? Do you have the fan attached to the tent or is it hung with bungees as I've seen some do? I was thinking about making a box lined with acoustic foam for the fan and using insulated ducting, seems like that would cut down on the fan noise and the turbulence withing the ducting.

i made my fan i too a bunch of pc fans bought carbon and used aluminum foil anf fishtank parts and made an awsome silent carbon filter had to make three of them for a 2 plant grow box
o not amazingly efficiant

You are on the right track with the insulated ducting, this will take a lot of the sound out itself. A carbon filter while super important for smell control can also help to reduce fan noise.