I need to build a sound-deadening enclosure for my generator.

We lost pwoer for nearly 24 hours this past weekend. Thank goodness for the generator, because we had cakes to prepare and other things to get done (it was also my son’s birthday).

We have a gas powered 7KW generator and a transfer switch wired in so I plug a 220 plug in outside, and I can switch on about 10 breakers in the house, which is mightily convenient.

The downside, however, is that the generator is LOUD. I may have pissed off my close neighbor because I ran the thing for several hours (I turned it off overnight to sleep) saturday evening and then started it up again in the morning so we could get ready for church.

So, I want to build some sort of enclosure that will do three things:

  1. Keep rain off the generator
  2. Deaden the sound somewhat
  3. Allow airflow to the generator for cooling and combustion.

So, I turn to the dopers for materials suggestions and confiurations. What say you, dopers?

Is it possible to allow airflow AND deaden sound?

This may give you some ideas. It’s a silencer cabinet I built for my shop vac using plywood, acoustic foam panels, and a serpentine exit duct. It’s fantastically quiet.

No doubt your gen set has a cooling fan that moves air in a particular direction; as you design your enclosure, you may be able to take advantage of this prevailing breeze to draw air in and force air out. If there’s no well-defined airflow leaving the generator that you can use, then your enclosure will need an auxiliary cooling fan to force air through it any time the generator is on.

Unless you have access to fireproof materials, I’d suggest placing this whole thing far from any other structures on your property.

Perhaps some sort of cinder block enclosure with sides that have gaps (think checkerboard) so that air can move around.
Is it possible to move it to a more remote area and just run the wires back to it? Behind a garage, up on a roof?

I install them, and I can tell you that it has been common to have them damaged irreparably by sound enclosures.

I stopped selling them in areas where there are neighbors near by. They are basically loud lawnmower engines, and they’re loud, so I tend to only market/sell them in semi-rural areas where sound is less a concern. (While it still is to the homeowners, unfortunately)

I wish I could help you. My advice is to be careful. It’s easier than you think to damage them. You wouldn’t be the first to do it.

It is possible to move them.

Just make sure its done by a professional. (wire sizing, conduit selection etc are critical)

Mine’s in a sound enclosure/rain enclosure and it’s still loud. It’s a big Rubbermaid garden bin with exhaust tubing and 12V fans connected. And it’s held up to try to isolate the vibration. Helps a little. Not a ton.
Why not go ask the neighbor if he minded? You’re taking on a big project based on something you don’t have confirmation of. I bet he’d rather have an extension cord run over to his place.
We offered our neighbors a line, but they preferred to buy our gasoline to run their own generator.

I had the opportunity to snoop around a movie lot recently and saw a big generator like this one. The inside of the doors were lined with heavy felt like carpet underlay and fit very snugly. It wasn’t running so I can’t vouch for how silent it was.

So what type of damage are we talking about? Do they catch on fire? Do they restrict airflow too much, causing it to overheat? Do they feed the exhaust back as intake?

As for the other suggestions, I am not going to build something permanent like a cinder-block structure. I am surrounded by houses, so having a long wire (mine is 20 feet) only moves the problem to one of my other neighbors.

It might be a lot easier to just put a better muffler on it; here’s one source:

That can certainly help, but my understanding is that probably more than half of the noise is from the engine itself rather than from the exhaust.

Google on generator noise reduction for info on this topic.

There is a long distance between me and the next house, and he has a generator too, though I can barely hear his - mainly due to the distance.

I just use a long run that gets the generator behind a shed, perhaps you can do that, just get a structure between your house and the generator, and your neighbors also. Just positioning your car, or even a sheet of plywood between the generator and a house will make a big difference.

You are in a fortunate position of running it at full volume, so any serious noise reduction will seem very welcome even if you can’t get it to zero.

Here you go. This is what I was trying to remember.

Quiet your noisy generator with an automobile muffler

That’s what I was thinking of too.

There are 3 kinds of noise in my way of thinking: high frequency, low frequency and “ground transmitted”. I would add a muffler as described, rubber foot mounts, and open air walls around it with a roof that has sound insulation. Don’t enclose it at all. Think in terms of a small carport.

This is what I have been looking for…an article with pictures. So many folks simply say “hook it up to a car muffler” and leave the rest to the imagination. I am sure with a lot of trial and error, I could get this to work, but I would prefer not to waste a lot of time.

The generator itself is on rubber wheels and has rubber foot pads, so I do not think I am getting a lot of ground-contact noise. I do want to build something small to protect it from the elements, but building a small carport is probably out…I don’t have that kind of room, nor is assembling a carport in windy/rainy conditions something I want to think about trying, and especially not if there is a lightning storm around.

It took a combination of installing one of those “supertrapp” mufflers that Jack’s sells and constructing what amounts to a large phone booth out of celotex, aka sound board - this stuff is compressed sugar cane stalks or some such thing.

For this particular application, I was fortunate to have a clear demarcation of “people are on this side of this imaginary line” and “people are not on the other side of this imaginary line” so I was able to build a three-sided box eight feet wide, four feet deep and eight feet tall, open to the “no people” side. The net noise reduction was significant - the generator went from being obnoxious to a background hum, and it was even possible to go into the enclosure and move one’s head around the generator and discern the hiss of air intake and “kssshhh” of the generator head’s bearings amid the overall engine noise.

As raindog mentions, heat is a killer - even though this enclosure is 32 square feet and completely open on one side and had no roof, it still got pretty hot compared to ambient temperature in the enclosure.

In retrospect, given the cost of the retrofit muffler, all of the labor needed to finagle it into the generator’s frame and re-work the heat shielding, and the nuisance of having to build the enclosure, it may have been better to just buy a generator with quietness engineered in, such as the ones from Honda.

I don’t literally mean a car port but something bigger than a dog house. I’m thinking of a small shed in size but open so air freely moves around. Since I’m not an engineer I always over-engineer stuff so in this case I would want 3-4 feet of space around all sides with a doorway on each end and a free standing wall in front of each doorway.

As for the muffler design. You could extend the larger pipe and reduce it back down to the original muffler (if it’s a thin straight muffler) and put the car muffler OVER the original so you get the initial reduction of noise.

On a completely unrelated topic. The generator needs to be run on a regular basis to ensure internal parts stay lubricated and water doesn’t gather in the oil reservoir from condensation.

I faced a similar problem, although on a much smaller genset (2.8KW). I solved it by building this enclosure in my truck. The fan is driven by a temp guage (seen in upper left corner of the box). The exhaust vent can be seen here. The aluminum tubing in the first picture is used to siphon off a portion of the fan’s airflow and direct it onto the genset’s exhaust pipe, in order to prevent a hot spot from forming on the backwall of the truckbox. Here’s a view from outside the truck, showing the system when closed. I lined it with a sound-deadening adhesive from the “B-Quiet” company (safe up to 300C). I run it closed, and it has enough juice to run its fan and my camper’s 13.5M A/C. It makes about as much noise as a household dishwasher (with the truck’s tailgate closed – I think a lot of the sound goes up). I’ve used it in Yellowstone, with no complaints from fellow campers.

I realize this may not work for your larger setup, but perhaps you can glean some ideas from it.

On edit: I read some test literature (sorry, no link) saying that both Honda and Yamaha spent as much effort deadening the intake as the exhaust. Apparently the intake is a significant source of noise.

Pullin, that is very interesting. You didn’t replace the muffler at all, then?