How to Soundproof A Generator
Soundproofing a generator is a relatively simple task, provided you keep ventilation in the forefront of your design. There are 2 methods that come to mind when silencing a gasoline or a diesel powered generator. Both methods require a box or enclosure to be placed on top of the generator itself.
The first method would entail the construction of a box made of something other than wood. Some alternatives that are readily available are materials such as Homasote, or soundboard, MDF, (Medium density fiberboard) or even Hardy board. Now granted, wood is the most common building product available to the public as a whole so wood can be used if these other products are not feasible. The soundproofing itself will negate the negative properties of the wood.
The box or enclosure will have vent holes usually at the top for air in and at the bottom on the other side for air out. It is always best to have the ventilated air travel through a series of bends and turns in the ducting. The flexible ducting found at Home Depot, or Lowe's is great for this purpose, also, venting the outlet duct far away from the enclosure is always advisable.
Now the inside of the enclosure should first be lined with a 1-Lb mass loaded vinyl MLV, (The American Mass Loaded Vinyl is perfect for this application). The MLV would be glued directly to the inside walls of the enclosure. There will be 4 sides and one top section that needs to be covered. Next you will need to caulk the seams of the MLV with an acoustical caulk such as OSI-175. Do not be sparing with the caulk, as it is an integral part of the soundproofing design.
The final step will be to glue a layer of "closed cell vinyl nitrile foam mat" directly to the layer of MLV. (As usual, America mat is the perfect choice). It would not hurt to caulk the mat as well, but contact cementing the seams and joints will be fine. Make sure that your vent ducting is flexible and has lots of hard curves and bends in it. Sound likes to travel linearly, and dissipates rapidly if forced through curvy winding ductwork. A small computer fan or something similar can be used at one or both ends of the duct ports.
The second method is pretty much the same as the first, but instead of doing all the ducting; you construct the enclosure using 2 separate boxes. One box should be 3" to 4 " shorter than the other (on all sides) so it will fit inside of the larger box. Here's how this works. Take the larger box and cut out one of the side panels where the smaller box will slip inside of the larger box. The fact that the smaller box is 3 to 4" shorter; it will provide an air gap where the ventilation, both in and out, will travel. Now granted a little sound will escape, but with both enclosures soundproofed as described above, the results of quelling your noisy generator should be remarkable.
If you have further questions on soundproofing an industrial or a camping generator, please do not hesitate to call or e-mail me personally. Thanks for reading and learning. Remember, Knowledge is Power!
As Always, Dr. Bob