How to Make a Soundproof Generator Box (DIY)

It’s always worth having a generator handy because they’re incredibly useful during power cuts or bad weather, but they have a reputation for being very loud. If you’ve ever wondered how to make a soundproof generator box, then you’re in the right place.

It’s really easy to build a soundproof generator box in just 8 steps, which are:

  1. Measuring out your materials
  2. Cutting out the pieces for your soundproof box
  3. Drilling ventilation holes
  4. Lining with soundproof insulation material
  5. Sealing gaps with acoustic caulk
  6. Fix on acoustic foam
  7. Building the soundproof generator box
  8. Putting the finishing touches

Soundproof Generator Box (1)

I’ll explain these steps in more detail below, but first I’ll go through a list of the materials you’ll need, along with which are the best soundproofing products to use in this kind of project.

Materials you’ll need for a soundproof generator box

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For this project, you’ll need a few standard building materials, some tools, and then some specialist soundproofing equipment. Make sure you have everything on this list before getting started:

  • Hammer and nails
  • Screwdriver and screws
  • Measuring tape
  • Saw (circular saw is best)
  • Glue
  • Acoustic caulk (Green Glue is best)
  • Right angle ruler
  • Ventilation ducts
  • MDF (medium density fiberboard)

Most of these items should be fairly easy to get; MDF should be available from your local hardware store, and you can get Green Glue (Amazon) online. Green Glue is ideal for this kind of project because it not only seals gaps but also dampens sounds escaping through the cracks. Check out my review.

What soundproofing materials do I need?


A soundproof box requires both dense mass and acoustic treatment, as this is the most effective combination that covers all issues. Dense mass makes the box heavier, meaning sound waves aren’t able to vibrate through it, and acoustic treatment helps to reduce echo and reverberation.

So what products should you use? Here are my top suggestions:

Mass loaded vinyl (MLV) 

Mass loaded vinyl is one of the best soundproofing materials in almost any situation, as it’s specifically designed for this kind of job.

In short, it’s what’s known as limp mass. This means that when a sound wave comes into contact with it, it simply dissipates. The technical term is deadening, as it doesn’t vibrate, which is how sound waves pass through a solid surface.

It’s also very dense, which adds extra weight to the box. This is helpful because the heavier an object is the more difficult it is for sound waves to pass through it. MLV is a popular product in all kinds of soundproofing jobs.

Acoustic foam

Along with sound deadening, you’ll also need a material that reduces echo and reverberation, as these both contribute to overall noise levels. Acoustic foam is ideal for this, and it’s essentially the stuff used in recording studios.

However, bear in mind that it should never be used on its own, but should complement other soundproofing materials. This is because acoustic foam doesn’t block sound, but rather it “improves” acoustic quality.

It does this through its open-celled structure, which traps sound waves and prevents them from bouncing off a flat surface. This is useful in this project because it effectively reduces the level of noise that’s able to escape from the box.

Although both of these materials are ideal in almost any soundproofing project, it’s worth bearing in mind that you’ll never completely soundproof a generator.

This is because you’ll need to leave air holes for ventilation, so obviously some sound will escape. However, this is a much better option than the generator overheating and blowing up.

How to build a soundproof generator box

Providing you have all the materials and tools handy, it’s time to start building your soundproof box. This method really isn’t difficult; the most complicated thing you’ll have to do is cut some wood. So let’s get started!

1. Measure the materials

It’s a fairly obvious place to start, but to know how big your box must be you’ll need to measure your generator. How big your generator actually is will be irrelevant if you have enough materials; you just need to know in order to cut the right pieces.

Don’t overlook the benefit of measuring everything twice before you start cutting pieces. After all, the last thing you want is to end up with pieces of wood that are too short for purpose.

It might be helpful to sketch a cuboid on a piece of paper and then write the measurements along the relevant sides. This will at least make it easier to visualize everything once you’ve cut your materials.

You’ll have to add a few inches on to each measurement to compensate for the soundproofing materials. For example, acoustic foam is about half an inch thick, and MLV could be up to 2 inches thick. So you’ll need to add around 5 inches extra to each measurement.

These are just rough guides; it’ll make sense to measure the thickness of your specific products before you start cutting, as they may be different.

2. Cut out the pieces

Cutting out the pieces

The next step is cutting everything out. Although you can cut just the wood now and then cut your soundproofing materials to size at a later point, I think it makes sense to cut everything to size at the same time.

Not only will you have the tools out, but you can check that everything is cut to the right size before you move on to the next stage.

Realistically any type of wood will be fine, but MDF is a good choice because it’s made of wood pulp and so is slightly denser than a standard piece of wood.

Use the right angle ruler to make sure all your lines are straight, and then cut the wood using a saw. The soundproofing materials can be cut with a craft knife as they’re not particularly thick.

3. Drill ventilation holes

Generators kick out a lot of heat when in use, so you’ll need to add some vents to maintain appropriate air circulation. At the very least, you’ll need to drill some large holes, but I’d recommend using some household vent covers (Amazon link).

One should go on the lid of the box, and another on the side opposite the lid vent. The lid vent is best placed towards one side; for example, the lid vent is in the right-hand corner, so the wall vent will go on the left side of the box.

Mark out a template for the vents on the appropriate sides, and then cut these out. A jigsaw would be best for this job, but you could also use a hacksaw or similar small-bladed tool.

Once you’ve cut the holes, screw the vents in place.

4. Lining with soundproof materials

soundproof materials

Place your pieces of wood in the correct layout for how they’ll be assembled later (similar to how a flat pack box looks pre-assembly) and then get your pieces of MLV. If you haven’t cut these yet, do so now and label accordingly.

Next, glue these onto the inside of each piece of wood, as you’ll obviously want the soundproofing to be inside the box. Just use normal glue to stick the sheets down, and then leave this to dry.

You can add another layer of MLV if you want, as the more mass you add the more soundproof your box will be. However, a single layer of MLV will provide plenty of soundproofing, so this is your decision.

Obviously remember to cut holes in the MLV for the vents; otherwise, they’re effectively useless.

5. Seal gaps with acoustic caulk

Before adding your next layer, you’ll want to go over the MLV and make sure it’s completely stuck down. After all, sound can escape through even the tiniest holes, so paying attention at this stage is definitely worth it.

Green Glue is ideal for this job because it’ll fill in any gaps and also help to stick the MLV down. Run some caulk along the edges, stick them down and wait for them to dry. Repeat this until you’re happy that you’ve sealed every gap.

6. Fix on acoustic foam

Adding acoustic foam into your soundproof generator box will massively reduce the level of sound within it. Acoustic foam is open-celled and very soft, which means sound waves have a hard time bouncing off its surface.

Adding a layer of this on top of the MLV compliments it well. Think that you’re working from the outside in, and so the acoustic foam will prevent some sound waves from reaching the MLV, which should then block everything else.

Acoustic foam generally comes in panels, so cut these to size and stick down with some regular glue. Be careful when doing this and go sparingly with the glue.

This is because the glue can block the foam’s cells, which would reduce its effectiveness at trapping sound waves. You’re generally fine using glue for this job, you just don’t need very much of it.

Same as before, stick down any loose edges with Green Glue and don’t forget to add foam to the box’s lid (cutting holes for the vents where necessary).

7. Build your soundproof generator box

Now that you’ve got all the sides ready, it’s time to build your soundproof generator box. This should really be an easy step because you’re just assembling 5 pieces of wood.

Fix the walls to each other first, using your right angle ruler to make sure they’re straight. It might be helpful to get someone to hold things while you measure and fix them.

The easiest way to do this is to fix 2 sides together at a right angle, repeat with the other 2 sides, and then join these 2 right angles together. This saves you having to mess around with 3 wobbly pieces at once.

Fix the sides together with nails or screws, and then seal the joins with Green Glue. Do this both inside and outside for the best results.

Finally, attach the lid. If you’re happy with a box that you can lift off your generator, then nail it in place and seal the joins inside. However, another option is to attach it with hinges.

Just bear in mind that doing this will reduce its soundproofing ability by a small amount. This is because even if the lid sits flush to the sides, there’s still a tiny gap between the 2 surfaces that sound could escape through.

8. Add the finishing touches

Now that your soundproof box is essentially finished, you can add any finishing touches and troubleshoot any minor issues. This is a good time to check all the joins to make sure they’re completely sealed with caulk.

Also, it might be worth adding a ventilation duct (Amazon link) to your vents, but this will depend on what kind of vent you installed earlier. Rather than fitting a vent, adding a duct hose can actually help with soundproofing.

This is because sound waves travel in a straight line, so adding a vent hose that you can bend will reduce the amount of noise that’s able to escape through the vents.

Whichever option you choose, you need to ensure that your generator has enough airflow. Without enough air, it could blow up or catch fire, and no amount of soundproofing is worth that.

That said, a simple vent or ventilation hose will be enough to provide the right airflow. If you have a large generator then it might be worth fitting a few more vents, as it’ll require more air than a smaller generator.

This is also a good time to paint the wood with sealant or similar in order to make it more water-resistant. Any kind of fence or shed paint will be fine for this.

Some final thoughts

Building a soundproof box for your generator isn’t a difficult task, and the results definitely make it worth a go. What’s more, all of the materials are readily available and aren’t expensive. Just make sure you don’t overlook ventilation!

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