Generator Soundproofing Material: Building a Soundproof Box

Soundproofing Material for Generators
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General Tips for Building a Generator Soundproof Box

You have just bought a generator for electrical emergency purposes or for camping. The problem is that this machine produces so much noise that it could easily disturb your neighbors or even your own sleep.

This is a reason why most people who own generators wonder if they could soundproof their generators.

But before embarking in the process, you need to understand that you cannot completely soundproof a generator. This is because the generator needs intake air in order to run, and it needs to release exhaust. Generators also produce a lot of heat, so it’s very important to provide for a way for the heat to escape the generator soundproofing box.

Closing all the holes can ruin the generator, by causing it to overheat. (Newer generators actually have a built-in carbon monoxide detector, so will shut down if not properly ventilated.) Of course, overheating can significantly reduce the life of the generator as well. Therefore, you cannot totally block all the vents where air passes.

So, the best you can hope for is to significantly reduce the noise the generator makes.

The good news is that air and heat can leak through any unsealed gaps, including around corners, while sound travels in waves – essentially a straight line. So, you can provide ventilation holes, and still control the noise, by “baffling” the sound – putting up barriers that it needs to go around. The more baffles the better.

There are two ways to provide noise reduction – via sound absorption, and via sound blocking. We’ll use materials that accomplish each of these strategies, for maximum effect.

Materials for DIY Generator Enclosure

What is the best soundproofing material for generators, specifically for your DIY generator enclosure?

The best generator soundproofing materials are those that absorb and/or block sound, while being resistant to the heat a generator produces. In case it’s not obvious, sound-absorbing foam designed for indoor use is not an option, since it melts easily. You’ll always want to keep generator safety in mind.

There are a number of choices of sound absorbing materials for generators, which are also heat resistant. The only hard and fast rule is, don’t use metal for any part of the generator box, since it tends to vibrate, and will actually generate noise itself. In general, the harder the surface, the more it will only reflect sound, rather than absorb it.

An excellent choice for the main generator box walls is medium density fiberboard. You can buy it a home supply store, or even online. Plywood can be used, in a pinch, but it has downsides. First, its surface is hard, so it doesn’t provide much sound absorption. In fact, it can even vibrate and generate noise itself. Secondly, it’s heavy, so will be more difficult to move around, if necessary. Fiberboard provides much better sound absorption, and is considerably lighter weight, so is a much better soundproofing product for our purposes.

You don’t really need a frame for your “quiet box” – it’s sufficient to glue the sections together, then screw them together, for extra strength. If the box will be heavily used or abused, however, it’s a good idea to build a frame using either 2×2’s or 2×4’s.

If your generator isn’t going to sit on the ground, or on a really hard surface like concrete, for example, if it’ll sit on a wooden floor, you’ll want to set it on vibration pads, to keep the sound from transmitting through the wooden floor.

So, here are the materials we’ll use:


  • 2×2 boards (or 2×4 boards)
  • Small fan

Tools to Build a Generator Soundproofing Box

  • A measuring tape
  • Marker or pencil
  • Right angle ruler
  • Circular Saw
  • Power Drill or Screwdriver

Planning Your Generator Enclosure

The most important thing you need to consider is the purpose of the generator itself. Is it for household use only, or is it for camping? The answer to this question determines the type and size of the soundproof box you need to build.

Permanent generators are meant to produce electricity for the house and appliances. If this is the purpose of your generator, then the soundproofing box needs to be sturdier to withstand outdoor weather and other elements. It can also be larger and heavier, since you won’t be moving it around.

In many cases, people add brick enclosures to reinforce the soundproofing box, but I don’t recommend it. For one thing, since brick is so hard, it doesn’t absorb sound at all, but just bounces it back. There are better choices.

If your generator is portable, that is you bring it camping, for instance, you have to build a soundproofing box that is sturdy enough to withstand sun and rain. You’ll also want to install a handle onto the generator box to make it easier to lift during the trip. And, of course, it needs to be light enough to move around easily. (The generator is very heavy, of course, but it typically has wheels.)

How to Easily Build a Soundproof Box for a Generator

1. Measure everything

The size of the soundproof box depends on the size of the generator. Bigger generators may need bigger boxes, of course.

Obviously, the first step is to measure the generator. This is to make sure that you are constructing the correct soundproof generator box, with sufficient room around it for air flow. Making the correct measurement is really important. Getting the wrong measurement can jeopardize the whole project.

When measuring for your generator soundproofing box, you’ll need to allow extra space on all sides, for sound absorbing material, and possibly heat dissipation, as well as to give the generator space to “breathe”. The minimum additional space between the generator and the closest wall surface should be 3 inches or so.

Before cutting your materials into pieces, make sure to check and recheck the measurements. Sometimes it takes several times to make sure everything is perfect. The carpenter’s rule “measure twice, cut once” will serve you well.

To make sure that all measurements on every side are intact and correct write all the measurements for later reference.

2. Cut the Soundproofing Materials (and Framing)

Now that you have all the measurements, it’s time to prepare the medium density fiberboard (MDF).

My recommended one is this Medium Density Fiberboard, which you can buy this on Amazon, of course. Note that this fiberboard is 1/8 inch thick (thin, actually), so you’d definitely want to using lumber framing.

Using the right angle ruler and pencil or marker, mark everything on the fiberboard (and optional framing lumber). Then check your measurements several times oto make sure everything is in place.

Using the circular or table saw, cut the fiberboard or other sound absorbing materials (and framing lumber, if you’re framing) according to the measurements you made.

Make sure you make markings on each piece of the material. This will help you save time during the construction.

3. Making Ventilation Holes

Before making the ventilation holes, make sure you have the ventilation duct. Now, measure the diameter of the duct.

Then, after making the measurement, draw circles on the fiberboard that correspond to the size of the duct.

There are two things you need to remember as to where to place the holes.

First, there should be one hole on the top of the fiberboard. But do not make a ventilation hole right in the center of the fiberboard. Instead, make the first hole near the side of the board.

Second, place another ventilation hole on the wall. Then make circles on the fiberboard that will be used as the wall of the soundproofing box.

Optionally, you may want to install a small fan for considerably better airflow (and a smaller hole). If so, you can cut one hole for the exhaust, and one hole the right size for the fan.

4. Assemble the Generator Box

After making all the pieces ready, it is time to put them together. If you want to use a frame, now is the time to screw the frame sections together.

Then, you’ll want to glue the fiberboard pieces together. You can either glue them and clamp them into place, or glue them and screw them together, it doesn’t really matter. You just don’t want to screw them together first, then glue them, or you’ll get poor glue coverage, and probably messy drips of glue everywhere.

Using the screws, connect the pieces together. At this point, the generator sound isolating box should start to take shape. The walls and the ceiling should be in their respective locations.

5. Installing the Mass Loaded Vinyl Insulation

As we mentioned, the box itself can be constructed out of fiberboard. To really beef up the noise reducing effect of the box, you can line it on the outside with Mass Loaded Vinyl soundproofing barrier. This is vinyl embedded with a “high mass element” – a fancy way of saying very dense mineral. Usually, it’s barium sulfate, not that you would care. Mass loaded vinyl very effectively blocks sound.

Note that, unlike the fiberboard, which absorbs sounds, mass loaded vinyly actually blocks the sound. The make an excellent combination – fiberboard on the inside to absorb sound, MLV on the outside, to contain the sound.

After making sure that the measurements are correct, it is time to cut the mass loaded vinyl. Then glue the pieces in their respected areas on the soundboards.

When installing the MLV, you’ll want to make sure that the generator box is completely sealed (except the vents, of course). So, wrap it around the edges when possible, and seal the other edges with acoustic caulk.

6. Seal the Edges of the Generator Box

Caulking is the best way to seal the edges or corners of the soundproofing generator box.

When it comes to caulking, I only use Green Glue Noiseproof Compound. For me, this is a perfect sound absorbing adhesive for generator boxes. This is not just a regular glue. It is in fact, an acoustic material. Rather than hardening, like some caulks, acoustic caulk remains soft and flexible, so actually absorbs sound itself. Needless to say, this glue helps accomplish your goal of making a perfect soundproof generator box.

7. Install the Venting Duct

This is the last thing you want to install. The venting duct is very important to provide breathability for your generator.

Without a vent, the generator may overheat. This may cause danger not only for the machine but more so for the people around.

A lot of venting ducts installed help to void the catastrophe. If you constructed the box the way it should be, you’ll have peace of mind.

One last warning (if you opted not to install a fan): check the temperature. You can stick a meat thermometer through a small hole to monitor the temperature, or just go ahead and install a small fan and forget about the heat problem.

Prefer a Ready-made Soundproof Generator Box?

Of course, you don’t need to build a soundproof box from scratch – there are a few ready-made soundproof generator boxes available. Noisy generators are a widely known problem, so of course, manufacturers have come up with some solutions, over a range of prices.

Maybe you don’t need to fully eliminate noise from your generator – say, it’s for temporary use during a power outage, or you’re off camping somewhere where there are not a lot of other people around. In that case, a simple padded tent, like the Portable All-Weather Generator Rain Shelter will work just fine. It muffles some of the sound, which may be just enough for your needs, while serving as a rain cover, and it’s inexpensive.

At the other end of the price range is the Zombie Box, which they say is the world’s first patented noise control system for generators. It provides excellent soundproofing, provides plenty of ventilation, and is solidly built, so it will typically outlast any generator you put in it. Unfortunately, it’s expensive. They start at around $1,000, and go up from there.

What Makes Generators Noisy?

Well, not all generators are noisy. Most of the quieter ones are the new models.

There are many factors as to why some generators are quieter than others:

1. The Use of Inverter Technology

The newly produced generators are equipped with the latest technology that keeps them less noisy while functioning.

The main difference between the old and the new models is the use of modern electronic systems that produce power.

Not only that, the new models are more efficient and versatile than the older models.

However, some new generator models are less capable of producing power as much as the traditional generators do.

2. Power

This may be obvious. The more powerful the generator gets, the noisier it becomes.

So the power output and noise come hand in hand.

Even the new models of larger generators still produce louder sound than the smaller ones.

3. Soundproofing

There are some brands that come with noise reduction technology built in. But many brands come without any kind of soundproofing. Most of the generators with noise reduction are, of course, expensive ones. As an aside, note that the more expensive generators also have remote starters, so they’re easier start once they’re boxed in – no need to open the box in order to pull a manual starter rope.

4. Generator Location

The closer you position the generator to where you are, the noisier it gets. So the simplest thing you can do is to place the generator away from the house.

However, this is not possible if you have limited space in your backyard.

Aside from that, you don’t want to have disturb your neighbors.

While placing the generator away from your house will help reduce the noise, you might need extra cable as well, although this isn’t much of a drawback.

There is one important thing you need to remember in placing the generator outdoors. That is to make sure that the surface is sturdy enough for it to be stable.

Avoid using a platform that vibrates. This will only worsen the noise. Find materials that will keep the generator stable and do not vibrate.

How to Reduce Generator Noise without Building a Soundproof Box?

The good thing is that there are many ways you can do to minimize the generator’s noise without even building a soundproof box.

Some of these techniques are more effective than others. But, if done right will surely reduce the sound of the generator. The amount of work needed may also vary.

Some tactics may require more labor while others are economical and less arduous.

Here are the techniques. It is up to you to choose which best suits you.

1. Place the Exhaust Pipes Vertically

One of the reasons why generators are noisy is the horizontal positioning of the exhaust.

To reduce the noise, position the exhaust pipe vertically. This way, the sound will project upward to the air allowing it to scatter.

The other option is to point the exhaust away from your house. But make sure it is not disturbing your neighbors.

2. Block the Sound

One of the best ways to lessen the sound is to deflect it. This is done by building or putting something that blocks the sound waves.

Figure out what materials you can use to build barriers. You could use a pile of sacks of sand. Or, you can use hollow blocks to block the sound. There are maybe many free materials from your garage you can use. Just make sure they’re either fireproof or will be a safe distance from the generator.

One clever suggestion I’ve seen is just to leaning sections of sheetrock or OSB up against the frame of the generator at a 45 degree angle, pointing down to the ground. This reflects the sound into the ground, and reduces the noise very significantly. Oriented strand board is a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands in specific orientations. Because the wood strands don’t run in the same direction, it reduces the sound better than plywood. Sheetrock works just as well, and is basically fireproof (except for the paper wrapper). In any case, if you choose to use flammable material, keep generator safety in mind – be sure to keep it away from the hot surfaces, and keep an eye on it.

3. Change or Upgrade the Exhaust Muffler

A muffler can make a huge difference in reducing the sound. In most cases, bigger mufflers do a really good job at a sound reduction.

Final Thoughts

There are many ways to soundproof a generator. The best is to build a soundproofing box.

For more information about soundproofing, you can visit my Soundorooping Guide.

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