I just received a used Honda EV-4010 generator, and installation requires an enclosure (which I can easily make from sheetmetal; however, I'd like to add sound-absorbing sheets to the enclosure to further silence the already-quiet genset.

Any suggestions?

HI Rusty:

I use the marine stuff that is either 1/2 inch or 1 inch that is used for sound insulation in marine generator applications. I get mine from West Marine but I am sure most marine shops carry the same or something similar. One sheet weighs a lot!

It has a high density layer of something and it really insulated the noise and heat. It has a glue back that activates when the paper is taken off and the adhesive is exposed to air. I used this stuff around and over the doghouse of my SOB (454) and it made driving conditions livable! I also lined my genset housing and you could barely hear it after done.

I intend to put this material around the engine room of the Barth when I get back from AZ. It will reduce the noise at idle a lot. (have no complaints while driving) I am going to add this over the top of the genset and up the front of the firewall in front also.

J.C. Whitney sells a similar product in two thicknesses, though theirs is not self-adhesive. From experience with products having the word "marine" in front of them, the odds are Whitney's stuff is less expensive, though it isn't cheap.

I've used marine soundprofing in the past that had a layer of lead foil sandwiched between layers of dense foam. The Whitney stuff is similarly constructed, but the core is something other than lead foil. I've used both successfully, but it would be comparing apples & oranges to rate one above the other. Both were effective in the installations I had, but one was a sealed engine compartment, the other a RV genny compartment open on the bottom.

I used the marine stuff on my doghouse, a reinforced metalic skin on both sides with a very dense foam core. I got it thru some swappin' but I heard it'a very expensive. I attached it to the doghouse with spray adhesive, then tin tabs and staples to make sure, then sealed all the joints with duct tape. The clutch fan is barely noticable any more and the engine noise is very low. I had enought to do the inside and outside except the top surface on the outside, where I used a cork floor underlayment, then carpeted the whole thing. HUGE difference in heat and noise! Oh yeah, also installed weathersripping at the meeting surfaces and got rid of the piano hinge for a 4 point Southco rubber latch setup that holds the cover down very tight, eliminating the hot air on the leg problem.

After some research I found the following material which I intend to use to line an enclosure for my diese genset.
http://www.b-quiet.com/ultimate.html
Based on their sound data I expect to see about a 50% reduction in noise which should make it almost imperceptible at 15 feet from the unit. I looked at JC Whitney but could not find acoustic data to compare with this so I went with a lab proven product. Hope this helps.
Tom

Rusty, I haven't tried this yet but have been considering its use to isolate my engine bilge.
http://www.tecnifoam.com/index.html
Tim

Thanks for the info, folks - very helpful!

I did find http://www.marinefoam.com/ which looks pretty good (and very expensive as well) - it's a bit thicker than some of the other choices, which look like they'll be more economical and just as effective.

It gets complicated. Material has both NRC and STC ratings. Each rates different characteristics. STC is sound transmission coefficient, which is how well it blocks sound. NRC is noise reduction coefficient, which is how well it absorbs sound.

A doghouse needs max STC, since you want to block sound entering the cockpit.

A genset compartment wants both. You want STC to block sound into the RV. A high STC material on the sides of the compartment also reduce outside noise somewhat.

You also want to be a good neighbor as well as benefit yourself by minimizing outside noise. This is where NRC comes in. A genset has to breathe air in and out, so there will be passages for noise to get out. Insulating the inside with high NRC ratings will absorb much of the sound before it can get out. Much sound travels line of sight, so strategically placed baffles can help here, too. Air goes around corners pretty well, much better than sound. So, baffles do not hurt air flow but help trap sound. Even suspending a batt of high NRC material underneath a genset's cooling air outlet can make a big difference.

So, different ratings address different methods of measuring sound reduction capabilities. You want both. In my own case, the noise inside does not bother us too much, so we are going go look more at NRC.

Owens Corning 703 is pretty decent stuff. Thicker batts have an NRC of 1.

I bought some of the JC Whitney stuff, and it delaminated sitting on the shelf in the shop. But it is good looking, otherwise. Has a heavy layer between two layers of foam. Constrained layer technology and all that. Converts sound into heat.

More good info! The EV-4010 comes with very comprehensive installation data, and in fact, I intend to "soundproof" the sides, top and back of the enclosure, and to make an easier-to-remove baffle for the front. Since the radiator is behind the generator section, much of the already-minimal engine noise can be muffled with stuff in front of the engine. The requirements for the opening for adequate cooling are quite modest.

And I had expected to use both STC and NRC components (recommended by several of the websites) - just replacing the Kohler with the EV-4010 does most of the work.

The EVs have a whine that will come out the air outlet of a well-insulated enclosure. I have a friend who built a rearward outlet duct and lined it with high NRC fiberglass material. Made a big difference.

BTW, if you are looking at add-on mufflers, forget the small 3S Supertrapp. I have one as well as its dedicated resonator. It makes only a small difference. Go for the larger 5S.

I didn't realize that your generator is in back, our mechanical layout must be very different between the 28 ft and 30 ft breakaway. Mine is in the front and thanks goodness it is, any less weight in front, the front wheels would be off the ground all the time. In fact, I am looking at ways to move the coach batteries (4 T-105s and the inverter) up front, it will be a lot of work but should result in much less tail wag!

As El Segundo Bill says, it gets complicated. He had J. C. Whitney stuff delaminate in his garage. I have a scrap left over from installing the genny in my previous S,O.B. four years ago, & I can't make it peel with out tearing the material. Of course, we never see anything like SoCal temperatures here.

There's more variety of soundproofing materials out there than I ever thought possible. The 1" J.C. Whitney stuff I have is identical in cross-section to the "Ultra Barrier Plus" Rusty is considering. The 1" J.C. stuff actually measures 1 1/8" thick, while the Ultra Barrier advertises it's 1 3/8." Price-wise, $94.99 for 12 sf @ Whitney equals $7.92/sf. $149.50 for 16 sf of the Ultra Barrier equals $9.34/sf.

The "B-quiet Ultimate," that Tom is considering comes out to $4.58/sf. Incidentally, that website lists a lead-lined product similar to what I used years ago in a marine installation, but they don't make it now, the price of lead is too high.

It would be interesting to have several people use different materials & then compete to see who got the most sound deadening for their buck.

I was just at West Marine and MAN, the prices have gone up! 2 years ago I paid $60 for a 34 X 54 sheet of 1/2 inch and $80 for a 34 X 54 sheet of 1 inch thick stuff. Now it is $110 and $130!

Gotta look for something cheaper and better!

You might check out Dynamat http://www.dynamat.com/
I think Autozone & O'Reilly have it.

"..thanks goodness it is, any less weight in front, the front wheels would be off the ground all the time. In fact, I am looking at ways to move the coach batteries (4 T-105s and the inverter) up front, it will be a lot of work but should result in much less tail wag!

Check your shocks and shock mounts before putting much weight in the front. The early Breakaways had problems with "breaking away": the front shock mounts would fail. This was a big topic at a Barth rally I attended in Nashville back then - don't remember the year.