[mpd]

MPD's $42 Super Stealth Fan Muffler DIY Tek w/Loads of Pics
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There is nothing more annoying (or downright scary!) than a grow room or cabinet that isn't quiet stealthy. Security demands that we keep things quiet so that nosy people find something else to be nosy about or so that stealth cabinets remain that way. The purpose of this thread is to show you how I designed and built a cabinet muffler designed to reduce the fan noise in my customer growing cabinet to absolute zero. Nothing heard from outside!

I don't know how it will work for your particular fan, but I guarantee you it will be a lot less noisy. You may have to mount a fan box (PM me and I'll help you do that too) and a pre-muffler to make sure your noisy centrifugal fan doesn't give away the game. Follow along and take advantage of the time I took to document this project.

I bought all of the supplies at the local Lowe's. You can find the same things at Home Depot, so either place will work just fine.

First, the material list:

1 - 3" x 5' section of water pipe - $9.18+tax.
2 - 4" to 3" pipe reducers/couplers - $13.22+tax.
1 - 16" by 48" fiberglass wrap insulation package - $5.58+tax
1 - roll of duct tape - $2.99+tax
1 - Tyvek Painter's Smock (Dupont) - $3.99+tax
1 - 1" Hole Saw - $5.87+tax
1 – 3/16” Drill Bit - $1.99+tax
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You will also need the following:
An electric drill that will accommodate the bit.
A jig saw or hack saw (to cut the pipe)
A hammer
A cardboard shirt box top
A tape measure
A Sharpie marking pen
A pencil
A ruler
A sheet of paper 8-1/2"x11"
Scotch tape
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I will provide an overview of this muffler project by going through the specifications first, then the actual tek. This is a 12" plastic and fiberglass muffler designed to create an exhaust noise dead zone on the output side of my custom grow cabinet. Silence is important because my grow cabinet sits right in our family room with a 40" HDTV on top of it. This is a focal area in the house and we can't have any noise from the fan system going! I have noticed a slight amount of humming that is covered by the television, but when the television is off you can hear a slight background hum like you would hear from a refrigerator, only less so. So enter the muffler project. This will sit between the fan and the aluminum can filter which will sit in a box and the box will be connected to the outside of the box. Can filters slightly increase the noise of the fan, so we need to eliminate the noise on that side of things. If the fan still makes noise after that I will create a pre-muffler for the intake side of the fan.

So the operation here is to create a muffler body out of a piece of 3" pipe by drilling 1" holes along the pipe. We will then wrap it extra tight with fiberglass insulation. We will wrap the fiberglass insulation with Tyvek (smell insurance) and then wrap the entire body of the muffler with a layer of cardboard. Reducer/couplers on either end will complete the project!

So, let's get started!
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Step One – Create the Drilling Template
The object of this step is to create a template that will be used to mark the pipe so that starter holes can be drilled and then (eventually) the 1” holes will be drilled. A regular 8-1/2” by 11” sheet of paper wraps around a 3” pipe perfectly – did you know that? Well, if you follow this tek you will soon see this for yourself. The template is a grid and the grid is made up of 8 rows of 6 holes (48 total holes to be drilled). To lay out the holes we lay them out in 1-3/8” by 1-3/8” square boxes. They won’t quite fit correctly across, so you have to first take a ruler and mark off an 1/8” on each of the LONG SIDES of the paper (note the picture below). Once that is done you can start laying out your rows of “hole boxes”. When you are done you should have a grid of 48 boxes on your paper. Once you have the boxes you need to find the center point of each box. Once you have marked the center point you have to punch a small hole in the center. This is so that the Sharpie pen can be used to mark through the paper and on to the pipe itself. I used the pointy end of a common compass to do this task. When you are done it should look like what I have here in the picture (more or less).

Picture of Paper Template

Step Two – Measure & Cut the Pipe
The object of this step is to measure and cut the pipe to the right size. You will need the pipe, the Sharpie marking pen, the measuring tape and the jig saw (or hacksaw if you don’t have a jig saw). Now I set up my project on a sawhorse for stability and I want you to be careful when you are cutting things, so use a sawhorse if you can. Take the pipe and from one end measure off a 12” segment. Mark all the way around the pipe and then take your jigsaw and cut the pipe so that you have a 12” piece to work with. Set the remaining 4’ section of pipe to the side. You are done with it.

Picture of Cut Pipe

Step Three – Mount the Template & Mark the Holes
The object of this step is to get the template properly mounted on the pipe and then get the hole locations marked using our Sharpie. Take the sheet of paper and align it on the pipe so that the template is in the middle (more or less – no need to be anal about it unless you want to). Tape one end and then wrap the sheet all the way around the pipe until the lines line up at either end, then tape the other end of the template.

Picture of Pipe with Template Mounted

Once you have that done you can go ahead and take your Sharpie marking pen (or other permanent pointed magic marker) and mark each hole location so that you have the pen marking the paper and the pipe. You are now ready to drill.

Picture of Pipe and Template with Guide Holes Marked with Sharpie Pen

[IndicaCowboy]

Very nice.

[mpd]

Step Five – Drill the 1” Holes
The object of this step is to finish the drilling operations by drilling out the pipe for all (48) 1” holes. Put the hole saw in your drill and start drilling them out. I found that you have to disassemble the bit after each drilling to get the plastic plug out. I did this by hammering the bit out of the hole saw each time. It is a real PITA, but in the end it was done. Yeah, you will probably have to recharge your drill battery halfway through like I did, but if you have a regular power drill you don’t have to worry about running out of power.
Picture of First Row of Holes Drilled Out

Picture of Completed Pipe – all 48 Holes Drilled

Step Six – Cut & Wrap the Fiberglass Insulation
The object of this step is to get the fiberglass insulation wrapped around the holes section. I cut a 10” wide section out of the bat. The bat/wrap is 48” long and as I wrapped the initial turns I use my fingers to firmly push the fiberglass insulation into all 48 holes (not too firmly, you don’t want to tear the insulation bat, you just want it to be sticking a bit into the hole) and then wrap the remaining turns firmly and tightly. When you are done it will look like this (note how the ends of the pipe stick out and are not covered with fiberglass bat).

Picture of Wrap Laid Out

Picture of Muffler Pipe Wrapped with Fiberglass Wrap

Once you have done that you turn the pipe around so that you can tape down the bat. Run the tape firmly (not TOO tight dammit!) around the ends and the middle so that what you have when you are done looks like what you see below.

Picture of Muffler Pipe Wrapped with Fiberglass & Taped

[mpd]

Step Seven – Tyvek the Muffler
The object of this step is to create a minimal stink barrier in the muffler. We do this by cutting the leg out of a Dupont Tyvek painter suit and using it as a sock over the muffler body.

Picture of Tyvek Suit

Take one leg of the Tyvek suit and pull it over the muffler body. Leave enough so that the ends can be taped down on the neck of the reducers. Mount the reducers on the pipe first. Once you have the reducers on the unit should look like this.

Picture of the Muffler with Reducers Mounted

Now tape down the ends of the Tyvek wrap to the reducers. There will be some extra material along the side. Roll it tightly and run a piece of tape along that side to keep it held down. When you are done the project should look like this.

Picture of Muffler with Tyvek Wrap in Place

Step Eight – Mount the Cardboard Wrap & Finish the Project
The object of this step is to mount the cardboard outer shell and tape it in place as the shell for the muffler, thus finishing the project. I used the top of a Christmas box and you can use a standard cardboard box top for a shirt box (like from the cleaners) to get you what you need.

Picture of Cardboard Box Top

Once you have the box top, CAREFULLY separate the corner pieces so that the cardboard box top lays flat. You are going to tape the end to the muffler. You will notice the genius of this design is to make it workable for cabinet grows and easily put together.

Picture of Cardboard Box Top Before Taping Box Top

Wrap the cardboard around the muffler body and tape all the seams. Your completed project should look something like this.

[mpd]

Picture of Completed Muffler

And that is how this tek is done.

[microsmyname2]

right on man good shit!

[benzo]

Wow, very nice ! Do they make 6in water pipes ? If I wanted to scale this up ? Or would I have to use reducers ?

And where in your exhaust line do you place this ? At the very end ?

Edit: re read and saw you place between the fan and scrubber.

Thanks for spending the time to make this.

[mpd]

No, you can easily scale this up.

[the gnome]

have you given it a test run yet?
how's it perform?

[mpd]

It positively kills all noise. I have my set-up as intake plenum to insulated duct, insulated duct to muffler, muffler to uninsulated duct, uninsulated duct to CAN filter, CAN filter to uninsulated duct, uninsulated duct to output plenum. I am sitting approximately 3 feet away from the box with the fan running full out and I cannot hear it. The only way you know it is there is by turning everything off and standing right by the box with your hand on the box so you can feel the slight vibration put out by the fan. The sounds is about a 1/4 of what the noise is from a modern refrigerator/freezer in your house.

It really works great.