since the motor has strong cyclic components to its noise why don't you
look into some kind of simple Active Noise Control with local speakers
and car amplifiers.

Maybe you could knock off another 5 with this.

Very good installations can do about 15 dBa

Paul

Ignoramus24281 wrote:

A while ago I posted some questions on soundproofing a generator. For
details of the generator, see

http://igor.chudov.com/tmp/onan/Diesel/

particularly, check out the "Enclosure" link.

Unshielded, the genset produces 85 dB at 10 feet.

I finally have satisfactory results. The enclosure itself reduces
noise by 5 dB. If I put another sheet of plywood in the direction that
I need to block the most (my neighbors), the noise goes down to 76 dB,
giving the total of 9 dB reduction in the needed direction.

The other directions are less important because the house and the deck
and the shed are going to shield/scatter most of the noise. (see the
link on the above mentioned page to see where the genset will go).

I am going to call it a success and stop the soundproofing work. Maybe
I will add some sound dampener substance to the engine panels.

On a related note, I sealed the top with epoxy, and will probably use
"deck treatment" on the rest. This enclosure will be normally covered
by a heavy duty tarp, when not in use.

Thanks to all!

i