Is a larger Carbon Scrubber Quieter

Looking to upgrade my 4" carbon filter and 170 cfm fan. Biggest concern is STEALTH. Is a larger carbon scrubber quieter than a smaller one? My 4" was pretty loud wide open with no fan speed controller. What quiets these filters the most, dialing the speed down? Would a 8" filter with 700 plus CFM be quieter than a 6" filter with 325 CFM. I was looking at hyper fan with built in speed controller, and Vortex S line with 100 percent speed control. Are these quieter than traditional can filters? Is there anything out there higher end than those, and quieter? Would a muffler make things even more quiet?

Build your own muffler. Theres a ton of diy threads on,those things. Im sure you could build one for under $50 easily.
http://billpentz.com/Woodworking/Cyclone/MufflerBelliveau.cfm

Therea a link to a nice one. You can make one similar for cheaper than that. Instead of that styrofoam material you can use polyfill (pillow stuffing) . Just be creative. A muffler will help though

Oversized insulated ducting,ie; 6" insulated ducting for 4" fan,8" insulated ducting for a 6" fan,etc

Would be a start as...

1) Insulated ducting cuts down on the noise of the air rushing around in the ducting

2) Eliminates radiant heat of all the hot air moving around in the ducting from radiating out,further heating the growspace.

3) If oversized,it reduces the velocity of air rushing around in the ducting (allowing for better/improved airflow) even further reducing the noise of the air rushing around in the ducting.

Another good addition to that would be to use a duct muffler after the fan.

And another good addition would be to build an acoustical dan box out of 3/4" MDF and lining with acoustical foam on the inside walls of the box and around the fan.