The Quest for Silence
Growing plants indoors requires decent ventilation—pure and simple. Without adequate air exchange in the room, plants suffer from all kinds of problems. There’s really no option to compromise on ventilation. Big powerful extractor fans will do a great job of venting all of your growroom’s stale humid air, and oscillating fans will move air around wonderfully to make sure every leaf has fresh CO2 touching it at all times. It’s a shame it’s all so darn noisy!
Introducing: the DIY Baron Wasteland SHUSH System
A decent ventilation system in your growroom will cause a constant electrical hum that vibrates right through the rafters, floorboards and walls, potentially causing neighbors concern and annoyance, especially if it keeps humming all through the night.
The uninterrupted whooshing sound of air being sucked through a carbon filter and ducting sounds strange, and those oscillating fans create a distinctive, rhythmic hum as they turn unceasingly from side to side. In some locations it would be unfeasible to grow at all because of the distinctive sound of the ventilation system.
Unfeasible unless we silence it all, of course.
Building your own silencer system is no easy task, but it can be done in a day. The basis of the DIY Baron Wasteland SHUSH System is a no-compromise, four-stage extraction silencing system involving:
- Insulated ducting
- A soundproofing box for your extractor fan, designed to absorb the mechanical noise
- An air expansion chamber to silence the rushing of air from your extractor fan
- An air baffle immediately outside the ventilation outlet to silence the air further and to help cool the hot, humid air
Soundproofing Fan Box
- A large sheet of thick plywood
- Some loose-fill acoustic insulation (commonly used to insulate lofts)
- 4 bungee cords
- 12 cabinet-maker style corner brackets
- 4 heavy-duty screw-in hooks
- 2 jubilee clips to clip around the extractor fan flange
- A large sheet of acoustic plasterboard (optional)
- A 25-gal. Rubbermaid-type container
- 6 standard, studio-style acoustic foam panels (the surface looks like egg cartons)
- Spray adhesive suitable for bonding plastic and foam
- Duct tape
- Enough fine mesh for two 1-ft. squares for a bug screen
Ventilation Outlet Air Baffle
- 1 sq. ft. of stiff wire mesh with small holes to use as a rodent screen
- Approximately 50 old bricks or similarly sized rough stones
- Some old junk that wouldn’t look out of place leaned up against the wall, such as old wood pieces
- Dust mask
- Old clothes
- Silicone sealant
- A little bit of DIY enthusiasm
Part 1: Fan Silencer Box
First we need to make our fan silencer box. This is a large wooden box that will suspend your extractor fan, packed loosely with insulation and then sealed up. Build the biggest box you can comfortably fit in your growroom. For an 8-in., RVK-style fan, you’ll need a 2-sq.-ft. box.
This leaves plenty of space around the fan to pack loosely with insulation. Although the box will be quite the behemoth, it can safely be used as a work surface afterward, so it will not waste space in your room.
Cut your plywood to a size suitable to make a box. We won’t go into this part too deeply here, as I’m sure you can handle it.
Essentially you will need six sides to form a cube, so divide the size of your sheet up. Don’t forget to compensate for the thickness of the wood for two sides so you can get a solid finish that will be easy to seal up inside.
There are a ton of online tutorials for this sort of thing. Don’t worry about fancy finishing; we are leaning towards function over form here. Assemble the box using the corner brackets, but leave the lid off. It should be nice and sturdy.
You can also use some screws through the base into the side walls to make it even tougher. Seal up the inside with silicon sealant to make it airtight—this will help dramatically with soundproofing. Measure the diameter of your insulated ducting, and cut holes in two opposite sides of your box.
The ducting should be a tight fit. Install your screw-in hooks inside the box towards the top of the circular holes.
You will suspend the fan on bungee cords here. Loosely fill the bottom third of your box with insulation. Wear your dust mask and gloves for this part!
Next, attach all four of your bungee cords to your extractor fan. The easiest way to do this is by using a jubilee clip commonly used to tether the ducting onto the extractor flange.
You probably already have a couple kicking about. Make sure they are on tight! Drop the fan inside the box after double checking you have it positioned in the correct direction for the air flow. Position your fan inside the box and stretch each bungee cord up to clip onto a hook.
Keep your dust mask on. The fan should now be securely suspended inside the box. Next, feed in your ducting and attach to each end of the fan. Use more jubilee clips.
You can trail the power lead out through the same ducting hole. Seal up the gaps around the ducting and the box before filling the rest of the box with loose insulation. The insulation works better at attenuating sound when it is loosely packed, so don’t cram too much in. Fill the void above the fan, too.
Screw on the lid, and fire up the fan. You will be amazed at how quiet it is. The vibration will be killed as well as the mechanical noise.
Although this works incredibly well, you can improve it even further by double-layering it with acoustic plasterboard. Just cut to size and screw it on the outside of your box. You’ll find the plasterboard usually comes in sheets the same dimensions as the wooden board.
This step is optional; you most likely won’t need it. Next we need to do something about that pesky air-rushing noise, so it’s time to build our air expansion chamber silencer.
Part 2: Air Expansion Chamber Silencer
Those fans move a lot of air, fast! The air expansion chamber slows the rush of air out, relieves the air pressure and dampens the sound.
First you will need to cut a circular hole in one side of the plastic box for your insulated ducting to poke through. Cut it offset from the center. Make it a tight fit and pull the ducting in just enough to hold it in place. Secure with tape.
Next, cut a hole for your final vent to the outside world in the lid of the box and cover this hole with your mesh bug screen.
Ensure the vent hole is not positioned directly opposite the ducting, as we want the air to swirl around inside the box, not pass straight through. I prefer to make this outlet hole in the lid, as it is easy to fix to your external wall, and joining the two halves together is as simple as snapping the lid back on.
Carefully glue the acoustic foam tiles onto all inside surfaces of the expansion chamber including the lid. You can easily cut it to shape with scissors to ensure a tight fit around the ducting inlet and the vent outlet.
The acoustic foam achieves two things: the rippled surface disrupts the flow of air, slowing it down, and it also absorbs the sound of mechanical whirring from inside the ducting.
Attach the vented lid to your wall vent hole. You can just screw it onto the wall. Seal up the gap between lid and wall with some silicon and close up the chamber.
You should seal around the sides of the lid too to preserve full efficiency. Now, securely attach your stiff wire screen to the outside to prevent any rodents from having a party in your ducting.
This set-up is now almost completely silent, but if you stand immediately outside the final vent, there is still a whisper of airflow, as well as detectable warm air.
Part 3: Sound Baffle and Air-cooling Maze
Energy is never lost, it just changes state. Every time sound is forced to turn a corner, some of the noise is converted to a miniscule amount of heat.
Likewise, every time hot air comes into contact with something cold, there is heat exchanged and the air gets cooler.
If we build an elaborate, open maze using bricks or stones immediately outside our vent, the hot air will be broken up, slowed down and also cooled to an ambient temperature in one smooth move.
Stones hold their temperature much longer than air, and remain cool in the shade even on the hottest days. You can use any large rocks. Rough ones with uneven surfaces will work better at silencing the noise and cooling the heat. Differences in size will also help absorb a wider frequency range for better sound performance.
Build up your maze outside the vent making sure you leave enough space for the air to travel around unimpeded.
Think about how much space you need to leave. If you have a 10-in. vent opening then you must allow at least the same amount of air gap at every stage, otherwise it is going to increase the pressure, speed up the air and make it noisier again.
Leave a few inches of expansion room immediately outside the vent and then start building up the rocks. Leave gaps of an inch or so between every rock and keep on building it up until you don’t hear anything at all.
Building your own silencer system is not for the faint of heart, but is something you only need to do once for a lifetime of peace of mind, and you get a real sense of achievement, too. Just keep it to yourself—SHUSH!
Written by Baron Wasteland