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So, I have this 4 KW RV generator enclosed in a steel shell much of which has some sort of insulation or noise damping fabric inside, but Id like to quiet the generator even more if possible. Ventilation and heat transfer takes place using a fan and shroud with screen mesh out the bottom, so I don't envision any heat transfer problem if I were to add yet more cover over the outer metal case.

 

WHAT KIND OF MATERIAL OR INSULATION OR SOUND DAMPING MIGHT I ATTACH TO THE OUTER SHELL TO REDUCE NOISE???????????? The muffler looks good and seems to work, I'm just looking for additional sound reduction.

 

I was thinking the 1/2 (has like aluminum foil on one side) or even 1 inch Styrofoam house insulation glued to the gennys outer metal case and maybe some on the lift up hatch door. It's protected from weather for the most part being under the RV aside from road dust and rain splash so Id think a product that could stand the outdoors will work, but not sure how well house Styrofoam insulation would stand up. They surely make some sort of insulation or noise damping material I could stick on the generators outer metal case??????????

 

John T

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Generally sound insulation in my experience (on ships) has a perforated metal finish on the noisy side. That "Traps" the noise inside. Also slots for ventilation/cooling would have an overlapping cover to prevent the sound waves going straight out of the slot. A mineral wool material about 1 1/2" thick is generally used.

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Thanks scouser, even though the stock muffler appears fine, I may add one more small car muffler in series (so long as not over flow restrictive) and see how that does. Still looking for the best "material" I might buy at Lowes or Home Depot to stick on the outer metal shell.

 

John T

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Be careful that whatever you add will not melt of burn.

 

Noise is actually just vibrations transmitted through the air or other media and sound deadening is basically an issue of absorbing or dampening vibrations.

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John I did some research on this about 2 years ago when I was considering building an exterior generator box. There are a lot of discussions around the internet by marine people for quieting engine, people that want sound dampening in their autos, survivialist types that want sound proof generators and house sound proofing for music etc. There are also you tubes of people experimenting with building generator boxes.

 

There are also specialty retailers that sell some of the materials such as mass loaded vinyl and a specialty foam type insulation. There were discussions online of folks attempting to get the same results withhome depot stuff and the results of their experiments. I cannot remember the details. I suspect you want mass loaded vinyl for your exterior covering. I do still have some links you may find interesting:

 

http://www.soundproofing.org/infopages/generator.htm

http://www.ehow.com/how_7597729_soundproof-noisy-generator.html

http://www.diymobileaudio.com/forum/general-car-audio-discussion/119256-mlv-homedepot-4.html

Dave and Lana Hasper

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Another way to quiet it down is to use duct board. It is a fiberglass board with foil facing on the outside. You can get it from Home Depot or any HVAC company should be able to get it for you. You cut it with a knife and you can even piece it together to make it fit. A quick search DUCT BOARD helps to visualize what it is.

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People use DynaMat in cars. I think it is expensive but there may be some non name brands out there.

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This is something I've looked into extensively over the last couple of years so I will try to give specifics. Unfortunately some of the info has been deleted.

 

There is a lot to it and details are very important.

 

Mass loaded vinyl is a good product to use

 

There is also a 3 layer noise reducing foam. There is a rubber septum in between the 2 foam layers. This product is used in the marine sector.

 

There is a noise reducing paint, spendy but a good product.

 

So here goes, There is a firm in Florida that makes generator enclosures from MLV, costs about 2k. This includes a 6" fan. They make a frame from pipe, something like boat stanchions then the side panels are wrapped around the framework and then the top is flopped on. There is overlap on all corners and it is held in place with Velcro. There is overlap on the sides overlapping the sides of the pan the generator is sitting in or on.. If you could imagine your generator sitting in a turkey basting pan, the generator cover sides overlap the sides of the pan.

 

Next, you need to make sure the air intake is offset from the exhaust. There should be no direct line of site so you can't see in the intake and out the exhaust. At the very least low air intake and high air exhaust with baffles on both.

 

Noise does not like to travel around corners, air doesn't care.

 

I'll try to find the deleted info and post it.

 

Another thing an 8" fan is better than a 6" fan. Volume is greater with less noise.

 

So many of the noise enclosures on UTube have a fan cut into the side or end of the box and a lot of noise comes out thru that hole. Or the generator on wheels has a mesh bottom.....that is a waste of time. You should try to attain at least 77db or lower..This is an ok noise level as told to me by some acoustical experts here in town. 85 is too loud. Fill or caulk even the smallest of holes or gaps with the appropriate caulking. Noise is like water, it will find a leak.

 

Re the noise cancelling paint. If used on metal, it should be applied INSIDE the meta box or pan or whatever. You want to prevent the noise from GETTING to the metal. No sense putting it on the outside. This from the firm that sells it. It is expensive....100 to 200$ a gallon as I recall.

 

Dynamat is good stuff but you will need more than just that. A good design and good product will reduce the noise to an acceptable level.

 

The noise is coming from 3 areas, intake, exhaust and clattering of the motor itself.

 

Roger

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WOW Thanks all for the great and exact type of info I was looking for. Armed with this new knowledge I'm headed to our local suppliers to see what's available (now that I know what I'm looking for lol). Any onboard RV Generator I've owned is never as quiet as a Honda, but with the type of coverings described and I still think I will add yet another muffler, I should see improvement. When dry camping in a quiet peaceful Natl Forest or BLM if there are neighbors too close, I just hate to fire up the genset and don't usually have to (have plenty of solar and batteries and inverter) unless the first wife needs the hairdryer or microwave for extended time.

 

John T

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We added another muffler AND tailpipe. The tailpipe runs up beside the truck stack. The result was not as much as we hoped. The biggest cause of noise now is coming out of the air intake. A mesh covered hole about 6" X 20" in the bottom of the cab. Engine thump and clatter are now the biggest problems I have to deal with.

Intake low, exhaust high, baffle both. Insulate inside the engine pan, not outside. Insulate inside the generator box cover and if possible add a MLV cover with cut outs or vents in the appropriate places.

Caulk, plug or fill even the smallest of gaps. Will it be perfect? No, but it will be a lot better than it is now. We dropped the db's from 85 to 77 which is huge. With further improvements the db's may come down another 5.

It can be done, we did it and you can to.

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  • 1 year later...

A lot of the noise is windage noise.  It takes special inlet and outlet baffles in the airstream to stop this type noise.  

I worked with low noise AC units some, and it was a very interesting design problem.  Higher frequency sound and lower frequency require different sound attenuation techniques.  

It is very difficult to add sound attenuation material on an RV generator that will have any meaningful effect.

Ken

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  • 2 months later...

Hi John, I dived into this several years ago. I had a Coleman 4kw genset that was LOUD! I bought a "quiet" muffler for the B&S engine for nearly $80, didn't help according to my ears. I built a wood frame box and insulated it with 2" fiberglass non-faced insulation. Put a temporary fan in the  end where the intake was; my ears still were not happy.

I went to a sound expert at IU and asked for advice. He said most of the noise remaining was actually from the engine proper, and he didn't give me any hope for further noise reduction.

Now that Coleman genset is gone, wood box burned. I bought a Boliy 3600 invertor genset  which is already quieter than a Honda 4000, and much lighter (78#) to carry/move around.

Durn, I had about $300 invested in that quieting exercise too.

 

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as to exhust noise. add a stack to it.

a 4in pvc say about 12-15 feet up. ( can use slip fit peces to gain length) about a foot or two above the higest poit of your rv. supported?? but it is open at the bottom to allow cold air in. 

add a fitting to your gen,  steel tubing ( electral comdut). a 1/2 larger dia than the exhaust on the gen. curved part into the "stack" not touching (would melt the plastic).  tubing goes up the center of the pvc a good foot and stops.

use brackets to attach the two parts. ( steel exhaust, plastic stack).

convection keeps the hot exhaust going up and out. benafits of no exhaust in camp. and a bit less noise. but any box you build around the gen is going to make it run hotter. so you will need a oil cooler to help fight heat. or burn out the motor.

 

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I also went down this road with an old generator that I had.  I built a very nice enclosure that greatly reduced the noise of the generator (7500 watt Champion).  I was able to get the noise down to the equivalent of a small Honda inverter generator, but I could never properly control the heat in the box.  No matter what I did (louvered vents, fans, exhaust ports, etc.), I could never keep the heat down enough in the box to make me feel comfortable running the generator in it.  I put a few hundred dollars and a lot of my time into the project before I finally gave up on the whole thing and sold the generator.  This was all for my last 5er that did not have a built in generator.

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I've build sound enclosures that have reduced engine noise to a hum.  To go further than that is exponentially more $.

Tuning the insulation to the type of engine, air sealing, baffling, isolation and correct grade of muffler is what I've seen missing from many enclosures. 

 

 

 

 

 

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How many hp does a say, Ford 5.4 pickup V8 develop at idle? Enough to power a RV genset? 

Ya I know, I can hear my Honda 2000 half a mile away in the quiet desert but can’t hear my neighbors pickup idling over their in the next camp spot...

"Are we there yet?" asked no motorcycle rider, ever. 

 

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