9 Ideas and Plans on How to Build Soundproof Generator Box

Do you use a generator at home, camp, or work to power tools, lighting, or for emergencies? Listening to it roar for hours can be nerve-racking. So can be the complaints from family and neighbors. Have you considered building a soundproof generator box? I did!

A soundproof generator box should suppress the noise from a generator from 85dB or 90dB to levels closer to an inverter generator between 48dB and 60dB, or less.

In this article, I’ll discuss 9 ideas and plans I considered when looking at building a soundproof generator box.

How to Build Soundproof Generator Box

What to Consider When Designing the Generator Quiet Box

There’s a lot to consider when designing and building a soundproof box for a generator. Making something soundproof usually means making it airtight. That may not be as practical or as easy as it sounds.

Generators need to get air for combustion to happen, and to keep it from overheating. They use fuel to generate electricity, so there needs to be a port to expel exhaust.

A gas, diesel, or propane generator should only be run where there is adequate air circulation. It produces not only electricity but also carbon monoxide. You need to decide if it will be a permanent structure, portable, or collapsible for storage. Additionally, does it need to be weatherproof; and finally, what is the budget?

How frequently the generator will be used is another detail. If it’s used daily in one location or carted from site to site affects the design. For generators used only once or twice a year, then you may have to consider adding fuel stabilizer to the fuel.

Another consideration is starting and stopping the gen-set. Access to pull cord or key start, choke, or primer and even the gas shut-off valve are design requirements. Additionally, do you start it in the box, put it in after starting, or have doors or movable access panels?

You also need to be able to connect the power cords to the generator. That means you need either a hole for cords to fit through or an external panel that links to the generator. There are many factors to plan around, so let’s take a look at building one.

Things You Will Need to Build Soundproof Generator Box

Building a soundproof box for a generator needn’t be difficult or impossible. Once you determine whether it will be a permanent, portable, or collapsible structure, you’ve made a good start.

The dimensions of your gen-set help to identify the minimal size required – 2” or 3” around each of the sides and top should be added for your interior dimensions.
Now you’re ready to look at building materials, which also depend on what your structural plan looks like. The materials should help stop the sound, not create an echo box.

  • MDF or Medium Density Fiberboard will block more sound than plywood.
  • Green glue sandwiched between layers of MDF will decrease vibrational sound transfer.
  • Acoustic caulking at seams and corners will further block noise.
  • Foam mats can be used under the generator, and to line the walls and lid to block sound.
  • Mass Loaded Vinyl (MLV) is also a great liner for the box, the thicker, the better at blocking noise.
  • Flexible metal duct pipe and ventilation materials for air intake, cooling, and exhaust.

The design and function of the generator box will identify other materials that may be needed, including hinges, receptacle boxes, and even wheels.

How to Build a Soundproof Box for a Generator: Step by Step

Generator noise control for a permanent or portable soundproof box is similar. The following steps work for either and offer the potential for enhancing sound control if the structure is permanent.

Remember, for structures to be portable, you need to be able to lift and carry them. Additional layers will decrease noise, but also mean more weight.

Step 1: Measure the dimensions of the generator. Determine the thickness of layers being added to line the inside, and then add 2” to 3” to all sides. Depending on how extension cords plugin and the diameter of the flexible duct tube, you may need to adjust the measurements. A plan with accurate dimensions will make a big difference in the build.

Step 2: Layout the cuts for the top, sides, and bottom (if required) on the MDF or plywood. Measure twice, cut once. Use a circular saw, table saw, or have the lumber store do the cuts for you. Label the pieces with a pencil, so you know what is what.

Step 3: Select the top piece and trace your duct pipe opening near one end. The second vent can be at the opposite end of the top, or near the top of the side furthest from the one already drawn on the top.

Heat rises, so the higher the vents on the box, the better. Cut out the two ventilation holes. If the top is to be hinged or removable, the top ventilation may need some reworking.

Step 4: Layout the box pieces, so the sides are inside up around the top; which is also inside up. If the top will sit on the sides and be screwed down, draw a perimeter line around the outside edge of the top to accommodate the thickness of the sides and any layers being added. Do the same with the two long sides or two short sides where they will join together.

Step 5: Layers help dissipate noise. Roll out the MLV and cut it to fit the sides and top, accounting for the perimeter overlap lines. Glue it directly to the MDF or plywood surfaces.

Run a bead of acoustic caulk around the edges of the MLV to seal any cracks. Cut out around the vent pipe holes and seal the seams there too.

Step 6: Use a closed-cell vinyl or rubber foam (vinyl nitrile, neoprene, EPDM, or SBR) padding or mat for the next layer. Cut it to size and glue it to the MLV layer. Some pads are self-adhesive, so it may be easier to use. Cut out the vent hole and use acoustic caulking to seal all edges too.

Step 7: It’s now time to assemble the box. MDF can be brittle, so pre-drill and countersink for screws. Secure the sides together, and then fasten the top to the four sides. Turn the box upside-down, and use acoustic caulk to seal where the sides meet, and where the top meets the sides.

Step 7a (optional): To further decrease the noise, coat the outside of the box with a layer of Green Glue, and cover with a second layer of MDF or plywood. Secure the two layers together.

Add handles to the sides or ends to make it easier to carry. The box will be almost twice as heavy but will mute more sound.

Step 8: Installing the vents is an important step. Without a good supply of air, the generator won’t work properly, and can also overheat. The gen-set also needs to exhaust the air used for combustion.

Soundwaves travel in a straight line, so using flex exhaust hose bent in opposing directions or ductwork with multiple angles works best to interrupt the sound. Use brackets to secure it to the top and sides, so it doesn’t move.

Secure one pipe system to the exhaust hole, and another piping system to the intake hole. Caulk around the pipes where they go through the holes on the box.

Step 9: Turn the box upside right. Over the vent holes secure some metal screen to keep bugs out, and then fasten an angled vent cover over the top of the hole.

The cover will keep moisture out and also deflect sound that may escape. The power cord would go under the edge of the box after it’s plugged in.

Step 10: Plans that include a bottom may also have hinges on one end to tilt the top to allow fueling and starting, and wheels for ease of movement.
Each design will be a little different to suit the generator, materials available, budget, and the builder’s skills.

Permanent soundproof boxes may incorporate a box within a box, a layer of Rockwool insulation, even a layer or two of 5/8” drywall sandwiching a layer of Green Glue. If it’s not portable, the options are greater.

Ideas and Plans on How to Build Soundproof Generator Box

1. Generator Quiet Box (Baffle Box)

This is a portable sound-reducing cover for a generator. The video explains how it was built, and you get to hear the difference in noise with and without the quiet box covering the gen-set.

The box sits over the top of the generator. One end has two cut-outs for air intake, cooling, and exhaust. The three closed sides and top mute the noise, but the open end isn’t.

The Quiet Box has a 2” x4” frame covered with 1/2” plywood and lined with the quiet board. L brackets are used to secure and square the joints. All gaps and seams are filled with spray foam to decrease sound movement around the quiet board. Once the generator is started, the cover is lowered or tipped over it, and the noise reduced.

 

2. Portable Generator Enclosure Plans

Portable Generator Enclosure Plans
A plan, material list, and instructions on how to build a 5’x7’ generator shed. The base is 7’ by 4’ -9”, so it could hold a good size generator. Framed in 2×4 and clad in T1-11 plywood to look like board and batten, it could be painted to complement other structures.

The front wall is designed to open outward as two equal doors for ease of access.

The shed style roof also lifts to open in two equal sections and is finished in shingles. The shed is uninsulated and has no vents, so it isn’t soundproof.

However, it could easily be insulated and lined with MLV and drywall or MDF to make it more sound friendly. Vents with twisting pipes could also be added for intake and exhaust to mute generator noise.

Build this generator box

 

3. Enclosure for a Generator

Enclosure for a Generator
This enclosure is a permanent structure to house a standard generator used to run fridges, freezers, and the air conditioner when the power goes out. To protect it from the weather, keep it secure from theft, and reduce noise, it was built on a concrete pad with walls made of concrete blocks.

The cores were filled to increase the density, which also muffles more sound.

The bottom course is 1/2 blocks on their side, so the cores act as vents – cover with screen to keep bugs and rodents out. The T&G pine front is hinged to the top, so it lifts for access. The plywood top is also hinged at the back to the cinder blocks.

Two bathroom fans were installed in the top to run from the generator and remove heat and exhaust. A half plastic barrel was used to cover the fans. The whole unit was painted to blend with the shrubbery.

Build this generator box

 

4. Quiet Generator Box

The generator is housed in a plastic yard storage box with lift up lid and double door front. Rectangular vents are cut near the bottom of the two sides and in one door panel, and covered with metal vent covers.

A round hole near the top of one side has a T pipe inserted for the exhaust, and a chimney attached. The exhaust is connected to the generator using a muffler and pipe, which quiets the noise even when the doors are open.

On the side opposite the exhaust, a 900cfm fan was installed to pull heat and fumes out. The fan is protected with a modified roof vent with a thermometer to monitor the outflow air temperature. A weatherproof receptacle is fastened beside the fan. The inside of the box is lined with a reflective thermoplastic material. A shut-off switch is mounted to the front.

 

5. DIY Portable Generator Sound Enclosure

This is a video showing a portable wheeled box for a small 1000W RV generator. The box is manufactured from OSB and 1” x2” pine. It has a hinged lid for access to the generator.

The whole box is lined with the quiet board. A fan mounted in the lid blows air into the closed box, and out a covered vent hole between the handles. The box has handles and can be moved like a wheelbarrow. The noise difference is noticeable in the video.

 

6. Best Lightweight Generator Quiet Box? – DIY

The quiet box fits overtop of a generator and quiets the sound. It’s a plywood cube structure with a handle centered on top. The 2” x2” pine frame is covered with lightweight foam tile backer-board on the outside and inside and the space between filled with fiberglass insulation. The bottom of the gap is closed in with 2×2 to keep the insulation in place and provide rigidity to the bottom.

The inside seams and corners are also caulked to prevent sound seeping out. The handle is attached through the two layers and secures to a wooden block. The whole cover weighs about 12 pounds. A pipe extension is added to the generator exhaust, and a channel is cut through the side so the cover will fit over it. The air intake is also through the channel.

 

7. Honda EU2000i Inverter/Generator Baffle (Quiet or Silencer) Box

This video shows a finished wheeled baffle box for an inverter/generator. It has a hinged top and an exhaust vent made of a metal dryer type vent. The vent lines up with the generator exhaust. The box is made of 3/4” plywood screwed together. The discussed plan includes the addition of a fan to pull air into the box for cooling and combustion, but it hadn’t been installed.

A hasp holds the lid closed, but straps to prevent the top from rotating open 270° were missing, but planned for, as were handles for lifting the box into or out of a vehicle. Part 4  shows the finished product with a cooling fan, handles, and outlet. It discusses the problems of heat and identifies the need for ventilation to move the heat out of the box.

 

8. Generator Shed Plans

portable generator sound enclosure
The article includes a set of plans, material list, cut list, and instructions on building a 4’x4’ shed for a generator. The framework is 2” x4” with a sloped shed-style shingle roof. One end of the shed is hinged to provide access to the gen-set for fuelling and operating. The walls can be T1-11 sheathing and painted, or plywood with siding. The floor and roof deck are 3/4” exterior grade plywood. It recommends that all seams and gaps are sealed.

The project isn’t vented or insulated. However, it would be easy to insulate the shed and finish the interior to decrease sound transfer. Intake and exhaust ventilation would have to be added as would an exterior electrical outlet. The article does mention that the shed could be placed on 4×4 skids for ease of moving to other locations.

Build this generator box

 

9. Generator Noise Reduction Box

This is a video showing the construction of a 3’x5’ generator box on casters. The base is 3/4” plywood, and the sides and top are 3/4” OSB. There is an 8” air space created with an interior wall at each end of the box. The walls have an off-set opening to allow airflow and to baffle the noise. Biscuits and screws are used to connect the pieces. Bathroom ceiling fans installed in holes cut in both ends helps circulate airflow through the baffled ends.

An electrical receptacle and an on-off switch are mounted beside the front access panel, and 2” x2” pine is used to trim out the top opening. 4” thick acoustic foam is nailed to the inside back wall, top and front and 2” foam attached to the baffle walls to absorb sound. An exhaust hole is cut in the back and through the foam. When closed up, the sound meter reading is 54dB down from 80dB when the box is open.
The gas tank was removed and attached to a frame on top of the generator box to make refueling easier.

 

Conclusion

A generator is a useful tool for homeowners, contractors, cottagers, campers, and RVers; especially when there is no electrical power. The biggest concern for most, however, is the noise. Building a quiet box for a gen-set doesn’t need to be difficult, just remember air needs to go in, and exhaust and heat out.

Hopefully, the suggestions and ideas presented help with your soundproof generator box design. If you found this article informative, pass it on. Your comments and suggestions are always appreciated.

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