Portable generators are often very noisy. A part of the noise comes from the engine itself, but some of it comes from the exhaust system which can be muffled. There are two approaches for cutting down on the noise of the generator, first the use of an after-market or even a make shift muffler and second the addition of a quiet box around the unit.
The addition of a muffler will help with the noise from the exhaust but will not deal with any engine noise. The best way to find a suitable muffler for the generator you own is to do an internet search for products made for that specific model. Some larger brands do have mufflers you can buy, while others will need a little bit of creativity to fashion something that works.
Many on line forums have suggested that a common lawn mower muffler that one can buy at a home improvement type store can be fitted to do the job. This means installing it between the “spark arrester” and the muffler mount.
Beyond installing a muffler or if a muffler will not work, you can also add a quiet box to your generator to quiet the sounds. This will help to quiet the noise from the engine that might not be fully masked by a muffler. One thing to keep in mind when doing this, most generators rely on air flow for cooling, so you have to make sure the box is not cutting off the air flow by either being too small or not vented if it needs to be smaller.
You will also need to make sure the exhaust is not collecting inside the box, so it is better to fix the way the exhaust system is hooked up so it runs outside of the box.
In order to build your own quiet box, some basic supplies will need to be gathered. This includes two by four lumbers for the frame, plywood for the basic structure, some type of fasteners like nails or screws to fix things together and some sound canceling materials you can find at most home improvement type stores. The sound barrier material will need to be heat resistant as well since the generator can make heat within the box. Generally fiberglass veiling works. You will also need the basic power tools you probably have in your garage to cut the materials and fix them together.
Make sure you add vents as not only does the generator produce a lot of heat, it need to get fresh air to run properly as well as let the exhaust out. You can access videos on websites like YouTube to see how the quiet box comes together. After a little bit of searching on line you may find there are as many ideas about how to make the best quiet box as there are different kinds of generators.
It seems there are a variety of ways to design a quiet box from something very portable that just fits over the generator to small permanent structures that resemble a dog house. It really depends on where the generator is going to be used and if it is regular use in a single place.
A more portable type of design would be great for generators that are used for things that require them to be mobile like an RV vehicle or for a generator that is only used for emergencies. Whether you opt for a moveable design or something that is fixed in place, neighbors will surely appreciate the muffled effects of the quiet box because without it even a small generator can be very noisy.