Generator Bay - Sound Proofing

[Mark Scott]

I'm looking to insulate/sound deaden the generator box. I've seen on several conversions two types of material used.1.) Reinforced foil attached to a sound deadening material and 2.) a black egg crate/ waffle design foam. I'm sure both have advantages/dis-advantages. I'm looking for a sources to investigate. Any help with product or company names is appreciated. I am currently using a 20kw generator , Kabota by SouthEast Power in a "quiet box" that is not as quiet as I would have thought it to be. The muffler is contained in the "quiet box", it produces somewhere near 100db of noise. Maybe this is "acceptable", I'm sure I've heard them much quiter than that. Thanks in advance for your help. Mark

[Kristinsgrandpa]

www.soundown.com

There was post on the BNO about sound insulation about a year or so ago.In the post there was some info about the best sound insulating material.

From some tests, one of the best was concrete, and someone was trying to use some tile backer board because it was partially concrete and stiff enough to not let sound pass. I never did hear the outcome of the test but am curious as I haven't done my genset compartment yet.

The soundown website has some good info, and will sell you whaterver you want. From what little bit I read you have to have deep pockets.

At bussin 05 I walked around the campgrounds listening to gensets and talking to owners abut their silencing material. The foam seemed to be the best, although thickness was the key.

Ed

[boogiethecat]

A different take on how to soundproof things, if you have the room...

If you can create a completely enclosed housing for your genset made with fairly heavy steel walls, like 060 thick, and create air inlets and outlets that make the air go a foot or so, take a 90 degree bend and then enter or exit the housing (basically if light can't get directly in or out around the corners, neither can sound), you're almost there for a really silent genset.

Then all you have to do is line everything with a sound reflection absorber (which is really inexpensive) rather than big bucks stuff like lead lined, etc.

I did exactly this with my 15kw generator trailer... I took a quick look at how the silent MQ type generators work (like the 20-100kw units that they you rent) by going to a rental yard and opening a lot of "quiet" generators and takning note of how they were built.   I basically duplicated how they all seemed to be made, and ended up with an amazingly silent unit with very little expense or trouble.

For the sound-deadning material, take a look at McMaster-Carr's catalog.  I bought this stuff- 5692T49, $11 per foot (each foot is 54" wide) adhesive backed and skinned.  The same stuff is a buck less per foot if you provide your own contact adhesive (3M 77 works ok, but I like "foam & Fabric adhesive" that I get from a local auto upholstery store a lot better)
If you look carefully, they give you a "NRC" number (noise reduction coefficient) for each of their products and intersetingly this stuff is one of the least expensive and has the highest NRC number of almost of them, .80 .  There are a few with higer NRC numbers but the cost is a LOT more for them, and this stuff works like a charm.

The big trick seems to be that the enclosure is well sealed and/or gasketed (use 1/2" wide neoprene weather strip gasket material on all doors and panels that are removable) wherever there may be line-of-sight ways for the sound to get out.  With my 3x3 foot door opened and the generator running, you have to yell to be heard if you're within 15 feet of the thing.  With the door closed, it's as quiet as can be, right next to it.  If the door is even cracked open a tiny bit, it gets really noisy really fast!!

There you are, another possibility that works...
Cheers

[DrDave]

I use 1" fiberglass duct board, a 4X8 sheet is about $35.00 and is foil on one side.

I also used 1/4" lead/poly-plastic sound absorbing material I got from a surplus place on
solid surfaces but it tended to reflect sound.

The duct board is easy and it sucks up all kinds of engine and fan noise if the raw side
it towards the noise. Kinda nasty to work with and is not flameproof but mostly what
is these days.

I also discovered that the air intake noise or "resonance" on the small diesels is hard to
deal with. The trick there is to move the air cleaner and have the air tube path make a couple
of 90 degree turns. I use small radiator hoses that are pre-bent.

Also consider noise dampening. some noise gets carried through most mounts and causes
the chassis or bay door to retransmit noise. The trick is to make a set of mounts that let
the whole generator assembly "float" on the mounts, you should be able to wiggle the genset
case/frame if you did it right.

Just some ideas....

[NJT5047]

My Yamaha genset was noisy to the exteme.  Even buzzed the RH side of the bus.   Mounted in the AC condenser compartment so not much room to work.  Found that the noise was being transmitted through the flex mounts that were OEM with the EDL6500.  Already had 1" Rubetex foam glued up in the box, but removed the genset and covered the whole floor with foam, mounted the generator back on top of the foam with rubber isolated mount bolts.  Made a huge difference.  Not as quiet as some, but soooo much better.  Muffler is below the compartment hanging in automotive mounts.   While this is a lot smaller genset than you have, it is also a 3200 RPM unit and will make a ton of noise.  In the orig enclosure, it was only 68 dbs...getting back to about that now. 
Be suspect of the flex mounts.  They can transmit a ton of noise. 
You may benefit from an automotive style muffler.  Often quieter than genset muffs.
Rubetex was glued up (and down) with 3M R320 adhesive.  Rubetex does not burn.  I was concerned with this and did a burn test with a torch.  It will melt, but the instant the flame is removed, there was no flame. 
I wouldn't wrap a muffler with this stuff, but it'll insulate any panel, and it isn't expensive.   WWGrainger carries both foam and adhesive. 
Good luck, JR