To make your electricity generator more quiet is a good and very necessary idea. If you experienced a power outage then you know how noisy can be an electricity generator. One of the ways to cut down on most of the noise is to put the electricity generator in a soundproof box or enclosure.
Making a box big enough to enclose the generator is not a difficult task. Having proper ventilation for generator in this soundproofing box is more complicated.
1. Your box has to be larger than generator. Make sure there are 2 to 8 inches distance between the box walls and any generator component.
You should build the box from medium density fiberboard, which will absorb the vibrations.
2. You can use many soundproofing materials for the box interior. One of them is Mass Loaded Vinyl or MLV. Apply a thin layer of glue and line the interior box walls with MLV. Glue another layer of soundproofing material over MLV.
3. Ventilation is critical. Making holes in the box walls is the easy way to ventilate the interior of the box. However, if you are living in a hot warm climate you need a forced venting system. You can use a common blower fan mount on the box lid that will blow the air into the box cooling the generator. The blown air will escape through the ventilation holes.
4. Make sure the box will be steady. Use removable clips to hold your soundproof box on the generator pedestal.