All,
I'm noticing my generator (7.5KW Onan DK model, 1800 rpm) seems to be a little on the loud side. That is for a water-cooled genset. I am wondering if anyone has taken any sound proofing/noise attenuation measures for one of these generators. I am considering lining the sheet metal around the genset with engine compartment soundproofing material.
Anyone tried anything that works well? I'd be interested in listening.

This is what I initially ordered for my Honda (also liquid cooled), but because of clearance issues with the enclosure, couldn't use it so another Barthmobiler got it and I went to one much less efficient.

Anyone heard anything if this product:
http://www.quietcoat.com/index.html

If any coating would work it would be my first choice due to hoses (rear engine to front radiator, fuel etc) currently fastened to the generator bay: center line genset between driver and passenger seats belowdecks.
A spray/paint/roll on would be ideal as I could just pressure wash and paint. This product claims up to 20DB noise reduction/80% absorption of noise.
I found this product from from stereo installer links. I've asked the vendor if it will handle the heat inside a watercooled engine compartment. Fortunately my radiator is on the side of the coach leaving the genset bay not involved with the primary cooling for the engine, and I suppose somewhat cooler.

Treating a gong or a cymbal with a coating to dampen the vibrations is not like applying sound insulation to the inside of a box full of clanking, vibrating machinery. Any heavy coating on that gong/cymbal would dampen the vibrations, & make them clink instead of clang.

You need something like the material Rusty pictured to reduce the amount of sound that penetrates the coach interior, but it's hard to do much to attenuate the sound that escapes to the outside. As long as you have to circulate air through the generator compartment. The sound will escape wherever the air can.

J.C.Whitney sells several varieties of material for this purpose, & I used their thickest variety to good effect on one installation, though I barely had room to install it.

To reduce the noise inside the coach from our genset (and road noise) we had two nice form fitting carpet floor mats made up for the front area under and between the seats. This is on top of the original carpeting.
The wifey then thought it was a good idea to put down some matching bound remanents for under the pilot and co-pilot seats and in between them. To keep them clean and nice, since a lot of wear would occur. We are now up to three layers!
You must remove these to get to the genset access door between the seats. With the genset running its easy to hear the difference.
This doesn't do anything much to reduce the clanking noise the neighbours must endure! But we seldom use the genset anyway.
Don and Patty

I hope this works but hopefully Bill will help me fix it if it does not. See my earlier post at: http://barthmobile.com/eve/for...071057082#2071057082 for the full story of solving this problem. It has been two years since it was completed and is working flawlessly. After checking very hot operation I added a squirrel cage fan to the underside opening in the frame to add cooling air as a supplement to the pusher electric fan. We operated this set up for 30 days after Hurricane IKE when our neighborhood was hard hit and we went to California and also had no problems.

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Originally posted by olroy:
Treating a gong or a cymbal with a coating to dampen the vibrations is not like applying sound insulation to the inside of a box full of clanking, vibrating machinery. Any heavy coating on that gong/cymbal would dampen the vibrations, & make them clink instead of clang.

Yes. Sticky coatings and Dynamat are examples of this. Stainless sinks often have a coating or a constrained-layer sticky pad to dampen vibration. I line the insides of speaker cabinets with my own resonance-damping concoction, as well. The difference is stunning. This approach would be good for gen compartments made of sheet metal, but should only be part of a sound reduction program.

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You need something like the material Rusty pictured to reduce the amount of sound that penetrates the coach interior.

Yup, that's good stuff. It has a high STC rating, which means not much sound gets through it. To some degree, it also helps outside, as it stops noise from traveling through any surface to which it is applied. A high STC material is also good for doghouse insulation, both noise and heat.

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but it's hard to do much to attenuate the sound that escapes to the outside. As long as you have to circulate air through the generator compartment. The sound will escape wherever the air can.

No, it's not really hard, it just requires a different approach and different materials. Sound does indeed escape through air passages. One method of attenuation is to line the compartment with a material that is rated with a high NRC. There are reasonably priced materials that have an NRC approaching 1.0. These will absorb the sound while it is still inside, so less sound will get out.

Now, let's look at the problem of the sound that does get out. Sound travels best in a straight line. If we can force the sound to turn a corner, and line the walls of the passage with high NRC material, much of the sound will be absorbed on the way out. This can also be accomplished with baffles, or false walls, with the material applied. Many good professional designs for movie shoots use this technique, and it is stunning just how quiet they are for their output. My air intake and outlet is on the underside, so I can reduce my noise by just laying a carpet on the ground underneath. An experiment using cardboard boxes to raise the carpet closer to the genset underside yielded a measurable reduction in sound, as well. So did hanging a curtain of carpet from the edge of the MH to the ground. I hung a curtain of carpet to separate the intake from the outlet, just to be sure no hot air was being sucked back in, and that cut a db or two, as well, because the carpet absorbed some of the sound. All of this illustrates how sound hitting an absorbant material is absorbed. The air turns the corners without significant restriction, if there is enough area.

I have a friend who, as a result of some campfire discussions, built an air-scoop-looking thing over his air intake. It is lined with high NRC material, so not much noise gets out. He only mounts it when parked. It is quite effective. My air inlet is blocked with a piece of high STC material, which is quite effective. There is enough open area underneath for enough cooling air to get in as long as I run only one air conditioner. Temps got a little high in there with two ACs running in 100 degree plus OAT.

I know some of this is not terribly useful to DP owners, as the genset is not well-enclosed, though. I have taken measurements on the same genset in a Barth and in a Country Coach. The CC was several dbA louder, owing to its greater open area up front. This illustrates how sound can be reduced with only a little interference in the travel of sound waves, with no insulation, even. Anything is better than nothing.

One other thing.....It can be beneficial to go over the genset and look for anything that can rattle. I gobbed a little silicone rubber here and there on sheet metal to quieten down some of the mechanical noise. An up pipe, like a Gen-Turi can help a little. I knocked a db off by welding in a motorcycle glasspack muffler. A small disk diffuser muffler dropped another DB.

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J.C.Whitney sells several varieties of material for this purpose, & I used their thickest variety to good effect on one installation, though I barely had room to install it.

I still have a partial roll of that stuff. It is coming apart as it sits on the shelf. The mineral-loaded vinyl layer is coming unglued from the foam.

Before I replaced the air-cooled Kohler propane genset with the Honda liquid-cooled, I measured the sound levels.

The sound-dampened enclosure dropped the noise by 3 to 5db. I still have to fix an aluminum plate to the center of the grille in front of the genset air intake to further dampen the sound in front.

I had a layer of that lead filled noise insulating, High heat meterial that came from the factory (Barth RSV) but I was not satisfied with the noise at tailgates and the like. Spent 400 bucks on this 1 1/4" adhesive foam high heat noise deadening crap and I swear I notice no difference! n What a project it was too! I will see if I can post some pics but I will say from the get go that I did not bother noise insulating the bottom because I think it needs more air flow. The squirrel cage idea is what I figure will work best but it will have to wait til next winter. (There is enough foam left over to finish the project.) I believe the manufacturer of that foam stuff is Tecnifoam. I even insulated the outside door and built an artificial wall that recessed one inch into the compatment, and was oversized to allow air to come in and the noise would have to by default hit the foam on its way out of the door. (pics to follow)

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Originally posted by Kris & Tina Jones:
I had a layer of that lead filled noise insulating, High heat meterial that came from the factory (Barth RSV) but I was not satisfied with the noise at tailgates and the like. Spent 400 bucks on this 1 1/4" adhesive foam high heat noise deadening crap and I swear I notice no difference! n What a project it was too! I will see if I can post some pics but I will say from the get go that I did not bother noise insulating the bottom because I think it needs more air flow. The squirrel cage idea is what I figure will work best but it will have to wait til next winter. (There is enough foam left over to finish the project.) I believe the manufacturer of that foam stuff is Tecnifoam. I even insulated the outside door and built an artificial wall that recessed one inch into the compatment, and was oversized to allow air to come in and the noise would have to by default hit the foam on its way out of the door. (pics to follow)

I don't know the specs of your material, but there are two ratings. One, STC, rates the material on how well it keeps sound from traveling through it. The heavy vinyl layer, either lead or mineral-loaded, makes this material good for that purpose.

The other rating is NRC, which rates the ability of the material to absorb sound before it leaves the area through the openings that must be there.

Each material does a different thing. Since our gensets have openings for intake and exhaust air, we can't block the sound completely. We can put high STC material of damping material on the metal walls of the enclosure to prevent sound going through the walls, and we can line the enclosure and make baffles lined with high NRC material.

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I will say from the get go that I did not bother noise insulating the bottom because I think it needs more air flow.

The bottom is where most of the noise comes out. ........I closed off my door grill with high STC material, and my meter now tells me that most of the noise is coming from underneath.

An artificial wall of high NRC material hanging underneath will help that a lot. I have jerry-rigged a carpeted piece of plywood to good effect. It also absorbs any oil my genset might dribble, as it has a Corvair engine.

Here are those pics I promised. I have to correct myself on one thing, The noise inside (I have been recently informed) has indeed been reduced. The outside noise is still quite noticeable because the botom is exposed.

Note: There are 5 layers here. A double sided adhesive, a semi dense foam, a hard black plastic, a dense foam, and a sealer


Note: This is the false wall I was talking about.

Thanks for all the feedback, I am loaded with quite a few ideas. My biggest problem is that my 'engine bay' for the generator is not dedicated to the generator alone: being centerline between the driver seat and passenger seat, and between the main engines front radiator and rear engine I seem to be having to deal with lots of coolant lines, gen and main engine, fuel lines, numerous air lines and electrical bundles. Basically a very 'busy' compartment and not many flat spaces to simply apply sound insulating blanket material. I may have to go with a coating... I can't see enclosing the genset in a cabinet, access for maintenance is tenuous at best already.
I once purchased a 'noise blanket' that installed over a rotary compressor on my home a/c that significantly quieted it down. I may look into that technology and come up with a soft and velcro'd together 'enclosure'.
I'm still gathering ideas and open to suggestions.
I did find out (and corrected my earlier post) that the genset is at 1800 rpm thank goodness. I'm not sure but think it's loaded with 10-30w Schaeffers synthetic, I'll be dropping in 15w50 Schaeffers synthetic, that might drop a DB or two.
Any thoughts on a little STP: Rusty? I know you don't care too much for it....
A thought just occurred to me; can I apply an acoustic absorbing coating 'directly' to the gensets diesel engine??
I'll start a new thread....

I woouldn't recommend 15W-50 - engines are designed for certain viscosities. 10W-40 should be acceptable, as would straight 30. There is no reason to use STP - is time has come and gone - 40 years ago.

Engine oil should have no appreciable effect on engine noise; if it does, other, major, problems exist.

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Engine oil should have no appreciable effect on engine noise; if it does, other, major, problems exist.

I would have to think that if an engine were running 5w10 and you dropped in 40W or even 15w40 there would be a measurable drop in DB's, certainly this is observed easily in aircooled engines. To Wit: On my Dixon ZTR w/16HP Briggs I just dropped in 15w40 and it had been running straight 30w put in by the dealer. I recognized a noticeable lower level of noise from the noise-maker. I have no DB meter and therefore claim Layman Shadetree Mech Ignorance...
Possibly this 'soothing and smoothing' of the engine noise is much greater on air cooled engines than in a water cooled.

Not trying to jerk your chain Rusty, I just have a few air-cooled engines and as I live in Texas and in summer we run the higher vis oils down here and when I've switch from a lighter weight in these air cooled's, the difference is sometimes dramatic. Certainly some of this sound dampening would translate over to a water-cooled engine as well, no?

Again, I have just enough knowledge about these things to be dangerous to myself and others, yet enough boldness/foolishness to publicly display it...

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Originally posted by Stratosurfer:

I would have to think that if an engine were running 5w10 and you dropped in 40W or even 15w40 there would be a measurable drop in DB's, certainly this is observed easily in aircooled engines. To Wit: On my Dixon ZTR w/16HP Briggs I just dropped in 15w40 and it had been running straight 30w put in by the dealer. I recognized a noticeable lower level of noise from the noise-maker. I have no DB meter and therefore claim Layman Shadetree Mech Ignorance...

I just have a few air-cooled engines and as I live in Texas and in summer we run the higher vis oils down here and when I've switch from a lighter weight in these air cooled's, the difference is sometimes dramatic.

I have noticed this on air-cooled motorcycles, particularly those with roller bearing big ends. A roller-cranked Porsche was the same. I don't remember any difference on Corvairs, however. Even though they were air-cooled, I suspect the shell bearings were inherently quieter than roller bearings, with just fewer parts to rattle around.

Radial engines operated in cold weather often had an oil dilution system that thinned the engine oil with gasoline for easier starting on cold mornings. I can still remember how noisy the engines were until the oil thickened. We were not allowed to use any power at all until the oil had been at so many degrees for so many minutes. An old fighter pilot told me that it was about ten times more rattly when the engine was right ahead of you, rather than out on a wing.

That was way before I owned a sound level meter, though.

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Certainly some of this sound dampening would translate over to a water-cooled engine as well, no?

My own take on it is that the thinner oil lets things rattle around a little more, and would be more noticeable on an air cooled engine, due to the lack of a heavy block and the water jacket.