Hi RIU's and DIY'-ers,
Quite often I have read posts on taming/quieting fan noise, so I thought I would put together a couple of ideas and some pics for your consideration.
In my SCROG I have 2 in-line vortex fans @ 495 cfm's, they are fantastic, well built fans but within the mechanical cabinet of my box they sounded like friggin jets and resonated throughout the house.
So in order to tame these puppies down I approached the problem with the following considerations:
a) Elimination of as much Mechanical vibration and any remote chance of mechanical vibration as possible,
b) Isolation of fan equipment from the SCROG frame/box,
c) Muffling of wind noise within ductwork,
So with this in mind, these are some of the concepts I implemented:
1) The very first thing I did (after all my equipment like ballast, power bar, switches) were located in the SCROG mechanical box was to line the mechanical box walls with 3 layers of 1/2" Styrofoam, albeit a very basic start but it cut down considerably on the echo-y noise coming from the box.
2) Before I mounted the metal fan support frame to the fans themselves, I applied a bead of silicone caulking between the fan housing and the support frame and screwed them together. The silicone will reduce vibration from the fan transmitting into the fan frame.
Adding a dab of silicon between the metal joints and rescrewing the fan frame back together.
3) Next I isolated the fan feet from the frame of the box. I used a very dense rubber (available at most hardware stores) cut to fit the fan footpads. This will help to reduce vibration in the fan frame transmitting into the scrog frame. True that mechanical vibration from the fan can still travel through the mounting screws into the SCROG Box, however the point of contact between the fan frame and box was considerable reduced.
Note the red rubbber under the fan frame footings, this serves to isolate fan vibration into the SCROG frame.
4) Vortex Fans are brushed motors. In other words brushed motors (check your fan manufacturers web page for additional info) will readily accepted a speed controller (Fan dimmer or rheostat). It is important to control your fan speed for environment control inside the grow chamber (temp/humidity), however reducing the running speed from a 100% full bore to even 80% really reduces wind and fan noise. Why run say your cool tube fan at 100% when 60 % provides just as much cooling power. Place your hand near the light exhaust and turn down the fan speed till you feel slightly warmish air coming out of the exhaust, pending your set up you may find you can drop your light fan speed to almost 50%. (This of course begs that it does not raise your grow chamber temperature significantly, increase your fan speed if you find additional heat from the light accumulating in the grow chamber).
a. Note on Rheostats: DO NOT get a Rheostat for lights, check the package and it should be for fans only. Do not get the combined Light and Fan Rheostat, FAN ONLY. The Vortex fans draw 0.86 amps at full tilt, most light Rheostats are rated for 1 amp, this is not sufficient for an in-line fan. The one I found at Home Depot was a “Commercial Fan Rheostat”, for fans only and rated for 5 amps.
5) Tape, Tape and more Tape. Use Aluminium Tape (not duct tape as it does not form into the small recess as well as aluminium tape does) and tape each and every duct joint in your ductwork. Tape the duct to fan connection too. Duct work is not air tight by any means, improve your fan efficiency and eliminate any duct vibration by taping all the joints.
Aluminum taping of each and every joint to eliminate air leaks (increased fan effeciency) and to stop and duct rattles/mechanical noises.
6) Straight-line Duct Design: Pre-plan your venting design as best as possible to eliminate 90 degree bends. Not only does every 90-degree bend reduce your fans efficiency by some 10% (or more?), but increases the wind noise inside the duct considerably. I know from my own set up it’s impossible to have a completely straight duct line in a Scrog Box, however if simply changing the angle that your fan sits at, or the placement of the exhaust eliminates even one 90 degree elbow your system will be that much more efficient and quieter.
7) Use metal duct as much as possible. I know it’s impossible to use 100% metal duct for your set up as flexible plastic duct is a necessity, however plastic duct is deeply ribbed in the accordion type windings, this ribbing not only cuts fan efficiency (increased internal drag) but again creates a lot of wind noise.
8 ) Sound Insulation for duct and fans. Home Depot sells pre-fabbed duct insulation wrap for like $20 for 10 feet. I came up with a much cheaper and quieter alternative, Sleeping Bags! Go to your local Sally Anne or Thrift Shop and buy some used sleeping bags for like $5-$10 ea. (As an added bonus sleeping bags are suppose to be fire retardant/resistant!).
a. Measure circumference of your duct work and cut stripes of the sleeping bag with at least one side equal to the circumference of your duct work plus one or two inches. So my duct is 6”, the circumference is 19” and I added an 1” for a total of 20”. So cut stripes of sleeping bag 20” x however long you need to for duct wrap.
b. Use duct tape to “seem” the cuts over so as not have the stuffing leak out.
Sleeping bag strip, cut to duct circumference, seem taped and ready to be installed.
c. Wrap duct in the sleeping bag strips, use duct tape to hold in place. I went back with copper wire and banded the sleeping bag wrap every 6” to the duct for a nice tight fit
Wrapping and insulating the duct in progress.
d. I cut some pieces and custom fit these to the actual fan shells. The fan motors are internal and air cooled by the exhausting air, so no need to worry that you are choking the fans or causing them to heat up.
Duct sound insulation almost completed. I even wrapped the exhaust duct that leads into the chimney.
So there you have it, vibration, isolation and insulation should really knock down those jet turbines. I can stand next to my SCROG and the only noise I can hear come from the circulation fans I have inside the grow chamber (which is very, very low), there is no, zero, none, nadda noise from the in-line venting fans any longer! As a side benefit the reduction of fan noise also has a very high spousal appeal …() lol!!