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#1
Old 04-04-2010, 11:24 PM
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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?
#2
Old 04-04-2010, 11:40 PM
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Is it possible to allow airflow AND deaden sound?
#3
Old 04-04-2010, 11:51 PM
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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.
#4
Old 04-05-2010, 12:07 AM
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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?
#5
Old 04-05-2010, 02:17 AM
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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.
#6
Old 04-05-2010, 02:18 AM
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Quote:
Originally Posted by Joey P View Post
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?
It is possible to move them.

Just make sure its done by a professional. (wire sizing, conduit selection etc are critical)
#7
Old 04-05-2010, 02:47 AM
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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.
#8
Old 04-05-2010, 03:18 AM
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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.

Last edited by Holden West; 04-05-2010 at 03:19 AM.
#9
Old 04-05-2010, 10:19 AM
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Quote:
Originally Posted by raindog View Post
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.
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.
#10
Old 04-05-2010, 11:58 AM
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It might be a lot easier to just put a better muffler on it; here's one source:
http://jackssmallengines.com/quietmuf_index.html
#11
Old 04-05-2010, 12:17 PM
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Quote:
Originally Posted by Turble View Post
It might be a lot easier to just put a better muffler on it...
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.
#12
Old 04-05-2010, 12:18 PM
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Google on generator noise reduction for info on this topic.
#13
Old 04-05-2010, 01:59 PM
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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.
#14
Old 04-05-2010, 02:24 PM
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Here you go. This is what I was trying to remember.

Quiet your noisy generator with an automobile muffler
#15
Old 04-05-2010, 02:38 PM
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Quote:
Originally Posted by Turble View Post
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.
#16
Old 04-05-2010, 02:59 PM
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Quote:
Originally Posted by Magiver View Post
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.
#17
Old 04-05-2010, 11:22 PM
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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.
#18
Old 04-06-2010, 02:09 AM
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Quote:
Originally Posted by crazyjoe View Post
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.
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.
#19
Old 04-06-2010, 01:39 PM
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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.

Last edited by pullin; 04-06-2010 at 01:41 PM. Reason: Wanted to add sound source info
#20
Old 04-06-2010, 02:51 PM
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Pullin, that is very interesting. You didn't replace the muffler at all, then?
#21
Old 04-06-2010, 03:06 PM
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Originally Posted by gotpasswords View Post
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.
That might be an easier route.

Run the big noisy generator during the day just when tons of stuff must be powered. In the evening/night, use a small portable Honda or some such to run a few lights, a computer or two and the fridge or what not.

Those smaller Honda generators are amazingly quiet.
#22
Old 04-06-2010, 03:16 PM
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Yeah, I did some quick googling on those super-quiet Honda generators. For a 2KW unit (enough to run some lights, the fridge, and the gas furnace) it's $1200. I paid 600 for my 7KW unit. The best comparable unit they have is a 6.5KW unit, which is FIVE GRAND.

I think I'd rather do some trial and error on a muffler than spend a $1200 - $5000 dollars on something to replace it.
#23
Old 04-06-2010, 03:18 PM
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Oh, something else I just noticed, most of those smaller generators only have a 120V output. My transfer switch expects 240V
#24
Old 04-06-2010, 06:05 PM
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Quote:
Originally Posted by Turble View Post
It might be a lot easier to just put a better muffler on it; here's one source:
http://jackssmallengines.com/quietmuf_index.html
We did a thread like this a few years ago and offered the same advice from the same website as you did. The OP installed the super-trap muffler and claimed it didn't help much at all.
I think the best way to handle this situation is to buy a more expensive generator that's already quiet. Like a Honda. Those things just purrr away and are very quiet.
#25
Old 04-06-2010, 06:11 PM
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Originally Posted by crazyjoe View Post
Yeah, I did some quick googling on those super-quiet Honda generators. For a 2KW unit (enough to run some lights, the fridge, and the gas furnace) it's $1200. I paid 600 for my 7KW unit. The best comparable unit they have is a 6.5KW unit, which is FIVE GRAND.

I think I'd rather do some trial and error on a muffler than spend a $1200 - $5000 dollars on something to replace it.

Ok, I see most of what I just posted was already stated up thread. in a hurry here!

Anyway, if you build an enclosure simply plug a kick-ass fan into one of the outlets and have it blow over the generator as it runs. The cool thing is the fan will only run when the generator runs. As if I had to mention that.
#26
Old 04-06-2010, 08:50 PM
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Originally Posted by crazyjoe View Post
Yeah, I did some quick googling on those super-quiet Honda generators. For a 2KW unit (enough to run some lights, the fridge, and the gas furnace) it's $1200. I paid 600 for my 7KW unit. The best comparable unit they have is a 6.5KW unit, which is FIVE GRAND.

I think I'd rather do some trial and error on a muffler than spend a $1200 - $5000 dollars on something to replace it.
By the time you build an enclosure, dick around, and end up messing up your 600 dollar built in china wonder, that 1200 dollars or so won't sound (heh) so bad. And I suspect the really small Hondas are a bit less than that even.

Like I said you've got a powerful/loud one to run during peak times. Get you a tiny wisper quiet honda to run CRITICAL stuff during non peak times.

If you want to live like normal when the power is out AND expect no aggravation or noise for 600 dollars total, IMO you are expecting way too much.
#27
Old 04-06-2010, 09:47 PM
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Meet it in the middle - if you want power, you want it quiet, and you don't care if it's on wheels or not, have a look at Kohler's line of LP-fueled residential generators. A 12 KW model will set you back about $4000, but is rated for 65 dB at seven meters away, and it self-starts in under 15 seconds. (You'll want to upgrade your transfer switch to one that works automatically)
#28
Old 04-07-2010, 08:24 AM
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Originally Posted by crazyjoe View Post
Pullin, that is very interesting. You didn't replace the muffler at all, then?

Sorry crazyjoe, was away from the computer 'till this morning. In answer to your question, I didn't modify the generator in any way. The muffler points at the back of the truck box, and I use the ducted part of the fan to dissipate the heat. The temperature control is almost superflous, though. The fan ends up running almost all the time once it heats up in the box.
#29
Old 04-07-2010, 09:56 AM
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Originally Posted by billfish678 View Post
By the time you build an enclosure, dick around, and end up messing up your 600 dollar built in china wonder, that 1200 dollars or so won't sound (heh) so bad. And I suspect the really small Hondas are a bit less than that even.

Like I said you've got a powerful/loud one to run during peak times. Get you a tiny wisper quiet honda to run CRITICAL stuff during non peak times.

If you want to live like normal when the power is out AND expect no aggravation or noise for 600 dollars total, IMO you are expecting way too much.
600 total? How about the 800 I spent getting the transfer switch wired in by a professional electrician?

And I don't expect no aggravation or noise, I don't need a whisper quiet generator, I simply need one that doesn't rattle your fillings out with noise.

And as I said, the smaller generators don't have a 240V output, so I would not be able to run much without running extension cords (safety hazard) all over the house.

Comparatively speaking, if I mess up the $600 generator after spending $100 on trying to soundproof it, I am still only looking at a pittance compared to 4 - 5K for one of these quiet generators.
#30
Old 04-07-2010, 11:59 AM
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Originally Posted by crazyjoe View Post
600 total? How about the 800 I spent getting the transfer switch wired in by a professional electrician?

.
The fact you spent more on the wiring/switching than you did on the generator might be the first clue as to the real problem.
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