If you have a portable generator, you’ve probably noticed that the loud noise they make is hard to ignore. You could spend a few hundred dollars for a quiet inverter generator but a generator quiet box is a great solution.
With a few off the shelf items and a little elbow grease, we have a DIY solution to quiet your generator. It also costs a fraction of the price of a newer, quieter generator model. You’ll find the process outlined below, step by step so that it’s easy to follow.
It has been tested on a 10,000 Watt generator and, once in place, our quiet generator box solution will make an ordinary fuel generator run at the same noise level as an inverter.
As a side note before we begin; this method also works with loud air compressors too. It will also make even the quietest portable generator even quieter.
Designing the Perfect Generator Quiet Box
The best DIY solution is to create a quiet box for your generator or compressor.
For those who may not know, a quiet box is just what it sounds like, a box that has been insulated and soundproofed to keep all the sound inside of it. That means your generator can sit in the box and do all of its loud work without that loudness leaking out and reaching you.
Just because this is a DIY project, that doesn’t mean you should cut corners when it comes to planning. Like any other project, we should have some specifications that our quiet box needs to meet. We decided on seven spec criteria in total, take a look at them:
- The quiet box must dampen the generator’s emitted sound by a minimum of 50%, to inhibit more than 50% of noise by making sure the box is sufficiently insulated.
- Assuming the generator isn’t used frequently (for example, only during a main power outage) then the box must be easy to assemble/disassemble for easy storage. It should be able to be stored discreetly and conveniently in a workspace, garage, or bedroom.
- Assembly and disassembly must be fast, meaning there should be no screws or nails required for these processes. You shouldn’t have to break out the toolbox to set this quiet box up.
- Sound leakage occurs where mating and interconnected surfaces aren’t airtight, so the sound is carried out of them. This means the surfaces of the box must be airtight.
- The generator needs cooling, so there needs to be air intake and output ports built into the box with ducts running through them.
- The generator quiet box should be functional in both the interior and exterior, assuming it’ll be sheltered from rain and other harsh weather. If outside, it should also limit carbon monoxide exposure for neighbors and bystanders.
- The design should be modular and flexible so that many people with many different generators can follow this guide and make a different but functionally identical quieting box for their specific generator model.
Most if not all of these specifications have already been addressed in the steps below. That said, it’s a good idea to keep these in mind and refer back to them during your DIY project to make sure that your quiet box is as rigorous and functional as it should be.
Step 1: Measurements
Before you do anything, you need to know what numbers you’re working with. This means measuring your generator or air compressor.
Remember to leave a few inches on every side of your generator as they’ll be needed to accommodate the thickness of the box, the insulation on the interior of the box, and any ventilation equipment that may be necessary.
It's better to make a quiet box that’s a bit bigger than you need. Extra ventilation space and wiggle room is always a good idea.
You may even have multiple devices you want to be quietened alongside your generator, like a compressor, so you can even consider making one large quiet box to keep all of these together and quietened.
Write down the measurements of your generator and the quiet box and keep them somewhere in sight, you’ll need them visible and in your mind for the next step.
Step 2: Cutting the Sides and Top
Now it’s time to start making the generator quiet box.
You need to decide on which material you’re going to use.
Cement backer board works well but we’d suggest using a fiberboard, which your local hardware store will have or you can even buy it online.
Just make sure you've got your measurements spot on so you order enough boards for the job.
Fiberboards are great at soaking up sound and preventing that sound from spreading deeper into your home.
You’ll need enough of this MDF sheet to create five pieces, those being four walls and a top for your quiet box. If you’ve bought sheets of MDF online, you’ll have to wait for them to arrive before continuing. Make sure they comply with the measurements taken in step 1.
When you have the sheets in your possession, you should separate them into five equal pieces if necessary. This can be done with any saw but the smoothest cuts are achieved with a table or circular saw if you have access to any of them.
Once they’re cut, label each piece with a pencil so you know which ones are walls and which one is the top piece, which will save you some confusion later in the DIY process.
You don’t want to buy too little of this material as that’ll mean another store visit or another order online.
Getting two medium-sized pieces to fit together is often more expensive than just getting a larger piece and cutting it down, so don’t worry too much about getting a larger sheet if you do.
Step 3: Make Ventilation Holes
You’ll also need to acquire ventilation ducts. It’s a good idea to have these ready before you get to this step as you’ll want to measure them.
As you’d do when making any holes for DIY purposes, you should measure the diameter of these ventilation ducts and mark that diameter by drawing two circles on the MDF box.
The first of these should be on the roof of the quiet box, towards the back of it so that it’s not sat at the center.
The second ventilation duct should then be on a side piece. You can pick any of the four as long as it’s opposite the placement of the first ventilation duct. Assuming the first is towards the back of the top piece, you’ll want your second hole on the side piece furthest away from it.
Cutting ventilation holes can be achieved with a wide variety of tools. A reciprocating saw stands out as the fastest and most convenient option.
Step 4: First Layer of Soundproofing
By now you should have the basic quiet box sides and top arranged in front of you. It should look like the disassembled box and have the two ventilation holes that we will fill later. For now, it’s time to get the first layer of soundproofing insulation onto the sides of the box.
The best way to dampen and deaden any sound that comes out of your generator is to cover the box sides with material that soaks it up. That’s why it was important to leave some space when measuring out your quiet box so you can fill that space up with sound-dampening materials.
Your first layer should be MLV, Mass Loaded Vinyl, which is a handy sound barrier material that’s commonly used for soundproofing in other settings.
If it works for professional soundproofing, it’ll work for keeping your generator quiet.
Where foam is used to absorb sound waves, material like MLV is better for blocking and deflecting the sound outright to stop it from escaping the quiet box.
It's common for MLV and similar soundproofing material to have some kind of adhesive or glue on one of their sides but you should still look into a soundproofing compound.
These are viscous sealants offered by companies like Green Glue that not only stick the vinyl to the piece of MDF but can add even more sound insulation to your quiet box.
It’s also useful to use Green Glue or a similar soundproofing compound for the next step.
MLV can be expensive so if you want to go a little cheaper then use a high density foam instead.
Step 5: Second Layer of Soundproofing
Once the MLV is in place, you should look for material to make your second layer of soundproofing.
Look at vinyl nitrile, sometimes referred to as VN, for your second layer. This is a closed-cell synthetic rubber that absorbs sound and should be available online or at your local hardware store.
Like with MLV, it’s often used for soundproofing and may be in high demand if you live in a certain area. Shop around and get the best price to make this DIY project as cost-effective as it can be.
Once you have the material, cut it to size and glue it to the vinyl layer already in place on every piece. Use Green Glue or a similar product once more to seal the edges and caulk any cracks or spaces in the sound insulation.
After it’s fully sealed up, you should have the five different pieces with one side covered by the MLV and the VN.
Step 6: Assembling the Generator Quiet Box
It’s finally time to assemble the quiet box.
This isn’t too difficult. You’ll assemble your quiet box like you’d assemble any wooden box, with nails or screws. Make sure you have a trusty hammer and a pack of nails or screws and use them to attach all four walls.
If you expect to modify the quiet box in the future, you’ll probably want to use screws so that the design is future-proofed for upgrading. Whichever you pick, use them to secure the top of the box once all walls are in place.
As a bonus, you can make the top hinged to make altering the box or removing the generator even simpler in the future. You’ll need a little more DIY know-how to do that, of course, but the Internet is your friend and there are plenty of online tutorials on how to hinge a box lid that can help you.
Note that if you do this, you may have to install the vents differently so that there are no obstacles to the lid.
Step 7: Add Ventilation Ducts
Your generator isn’t going to last very long if there’s no ventilation. Generators get hot anyway but an enclosed generator is much easier to overheat.
That’s why it’s important to not just create a quiet box but to also provide a ventilation solution so that the generator doesn’t overheat and become dangerous.
When choosing your ventilation ducts, it’s a good idea to pick ones that have a lot of bends and kinks in them. If you know anything about how sound travels, you know that corners do well to limit how far sound waves travel.
Those curves in the duct will help to keep the sound inside the box instead of having it all spill out from its ventilation holes.
Speaking of those holes, thread the ventilation ducts through them and make sure they’re secure and won’t be shaken loose by any residual vibrations from the generator. The openings of the box should be placed near some exterior ventilation to guarantee that clean air is getting inside the ducts.
Adding a fan that you can power from the generator will help with ventilation.
There are a few variations on this design you could play with. Experimenting with soundproofing materials and ventilation orientation will also help reduce the noise.
Conclusion
Having followed all of the steps above, you should now have a functional quiet box that can house your generator and reduce the noise pollution from it.
If you've got a sound level meter you'll get a good idea of the kind of generator noise reduction your box is giving you. The proof is in the hearing though.
If you've built your generator quiet box well then you shouldn't need an electronic device to tell you. You should notice about a 50% reduction in how loud it sounds to you.
This was all done for much cheaper than what it would cost to buy an inverter generator too, or even a professional pre-built quiet box. That being said, this box will be great for making an inverter generator quieter too.