How to reduce generator noise?

I tested some automotive mufflers on my Onan 4K and even when the exhaust note was cut way down, the mechanical noise was still significant.

When you are dealing with a multi piston, large generators (4K+) there is just a lot of noise. I am debating on buying a small 2K just to run my refrigerator and small appliances. I still appreciate having a nice big genny to run my A/C, but a smaller and quieter backup that burns less gas really does sound appealing.

Jose

tpi wrote:
Problem with generator noise is to get a 3 db reduction (half the sound energy) takes considerable effort and half the sound energy translates to a hardly noticeable difference. Kind of unfortunate property of sound energy and how we hear it.
....

100% correct!

While a 3dB reduction is half the sound energy, it is barely noticeable by the human ear.
A 10dB (1/10 the energy) is a significant reduction in noise, and hard to do.

When we (work) had to use the quietest possible generator, we used a Honda EU series. (EU-6500)
When even that was too loud, we used a 4KW inverter and a HUGE battery system.

No, the generator use I'm talking about is mealtime use in, say, a Provincial Park, where there are no hookups. I feel like we're disrupting the entire campground whenever we run it, so we don't use it as much as we'd like to.

tpi wrote:
Certain conditions ensure generator running such as hot weather and air conditioning. But if you're running it frequently in cooler conditions you may want to approach this from a standpoint of minimizing generator operation through a few 12 volt mods and accessories. Briefly: knowledge of 12 volt operation, use of propane appliances, battery maintenance and capacity, LED lighting, and solar.

+1, are you running the air conditioner all day or something else?

Problem with generator noise is to get a 3 db reduction (half the sound energy) takes considerable effort and half the sound energy translates to a hardly noticeable difference. Kind of unfortunate property of sound energy and how we hear it.

For me I'd limit it to ensuring the rubber mounting system is working and no direct sound is transmitted into the RV. And maybe the matting discussed on areas where it wouldn't impede airflow.

Certain conditions ensure generator running such as hot weather and air conditioning. But if you're running it frequently in cooler conditions you may want to approach this from a standpoint of minimizing generator operation through a few 12 volt mods and accessories. Briefly: knowledge of 12 volt operation, use of propane appliances, inverter, battery maintenance and capacity, LED lighting, and solar.

These are all great suggestions. Thanks so much for your thoughtful replies! And Handbasket, you're right, our Onan is only a 4K model. I was thinking of our previous RV. Oops.

GEN-TURI

Some of the noise is from the RV maker's low-cost installation. I'm really surprised such a small RV uses such a large Onan. Be that as it may, get the _installation_ manual from Onan for your model. It'll give you the minimum requirements for the air intake opening, and minimum compartment clearances.

My Tiger CX has a rear compartment mounted Onan 2800. I was able to get it down to under 58 dbA @ 23', mostly by doing 'Onan-allowable' things.

I added the Onan resonator, and a SuperTrapp spark arrestor.

I used 1" thick rigid fiberglass furnace insulation, smeared with silicone goo for weatherproofing. That was used both to insulate the compartment, and to reduce the 'way-larger-than-required air intake opening in the door. The latter made the most difference of all the steps I took, IMO; it was sure the most bang for the buck.

I put .20" rubber washers around the mounting bolts, between the truck frame & the Onan's base pan.

My compartment is under the end of the couch, with a small space above. I use that to store extra blankets, so they help with sound management in the interior.

Most of the remaining noise is mechanical, exiting with the cooling air around the exhaust pipe. Do not restrict this air flow. I installed a flat f'glass baffle about 12" down. It's open at both front and back to allow the hot air to escape.

I can stand right against the rear of the RV and carry on a conversation with someone standing on the opposite side of the exhaust without raising my voice. There's a brief burst of louder noise when the generator reacts to a sudden heavy load like the A/C compressor cycling on. Otherwise, it runs at the same noise level, loaded or not.

I do a roughly quarterly safety inspection of all my 'self-engineered' arrangements, more frequent in the summer.

Jim, "Statistics mean never having to say you're certain."

Inside or outside noise, or outside noise coming in?

As mentioned, exhaust or transmission of vibration?

Mufflers, directional end exhaust, or isolation rubber mounts, depends what you're trying to do.

Anything that impairs the free-flow of air is going to have a probable negative impact on the operation of the generator. I would hesitate a long time before I modified the venting.

You could enclose the remaining sides of the box with sound absorbent material, that would reduce the sound directly transmitted into the rig. There would still be the sound that comes out via the vents, that includes the exhaust noise.

You could also look into an improved "muffler" system. They do exist, but what you would need to do could with your setup I don't know.

Personally (I am an Electronics Engineer that worked in sound generation/propagation for many years), I bought the quietest generator I could find. Reducing noise inside the generator was a winning formula for me.