Generator Noise

[matcommander]

Not sure if this post will get to the posts regarding generator noise, but here's my 2 cents: I've done a great deal of noise control in industry as an engineer, after being sent to a noise control school from the company I worked for.
I recently built a 'generator noise house' for my loud Briggs & Stratton generator on a quiet island off of Maine, USA. The generator is used only to back up my solar power if needed, which it mostly isn't.
Some noise principals: 1. Noise MUST be reflected before it can be absorbed. Passing through foam, fuzz, and fur doesn't work. Hard to believe, but that's the way it works. It has to do with Kinetic and Potential Energy in each pressure wave.
2. For a barrier, MASS is necessary for most frequencies we hear. However, for low frequencies, STIFFNESS is required (such as hard anodized aluminum, 3 layers on a passenger jet liner). After the noise is bounced back from these barriers, it can be absorbed by the foam, fuzz, and fur.
3. Thin layers of foam, fuzz, and fur absorbers are effective on high frequencies, but very thick layers are necessary for low frequencies, due to the long wave length (the sound is absorbed, or turned into heat energy, at 1/4 and 3/4 wavelength).
One of the most effective methods for reducing LOW frequency noise (this is most of the noise from your generator) is by CANCELING the noise using a 'Helmholz Resonator' effect. I cut 5/8" slots in one side of both cells of ordinary concrete blocks using a diamond blade on a circular saw. The blocks form the noise house walls, each course is cemented. Each course must have a barrier between it and the course above and below. I used 1/2" cement board and in some places, 2" solid concrete blocks. The slits face inward. Each pressure wave of sound 'funnels' into the slits, bounces off the rear wall of the blocks, and is cancelled by the next pressure wave entering the blocks. I added mineral wool insulation inside (not fiberglass, which isn't as dense and soaks up water) the blocks for the higher frequencies, which are absorbed rather than cancelled.
I added a "glass-pack" muffler-chimney for the exhaust noise, which gets rid of the heat and fumes of the exhaust. I made it from 4" and 8" stove pipe. The inner 4" pipe has many 3/8" holes drilled in it, and the outer 8" is solid, no holes. In between is packed with mineral wool. A 90 degree elbow is at the bottom where the generator exhaust enters, to bounce the sound around on its way up the 6'-high 'chimney'. It's incredibly effective, all I hear is a fast ticking noise coming out of the top.
I added a centrifugal 'squirrel-cage' style fan, plugged into the generator, to blow plenty of air into the house, as heat is a serious danger to motors and generators.
I left the front side open for my application, but this could be closed if there was PLENTY of ventilation, both supply and exhaust. The roof is plywood, but shingled, which provides plenty of mass above, but also plywood is a pretty good reflector of noise.
The outside of the concrete blocks should be painted with a thick latex paint, as the concrete is somewhat porous, and sound can get through it to some extent. Air passages are not good.
This is why a simple wood structure is not very effective, both from a lack of mass and stiffness and the air leaks.
To make it pretty, I used masonry bits and screws to attach wood 'battens' to the outside, then 1/2" plywood to those, and covered it all with vinyl sidiing.
Hope this helps. Matcommander

[mtv]

matcommander,

I've moved your post here, from the introduce yourself forum.

It's very informative.

Welcome to Austech.

[Tiny]

That's great, must be so quiet you'd have to check your incoming ammeter to know if it's running.
Like you I live on a stand alone power system & vary rarely use my generator, maybe once a year or 2 if we have a torrential rain event that takes out the hydro head pipe, as have solar & micro hydro.
Luckily my generator is in a very large shed far enough away with the door shut, it can't be heard inside the house.

[coalminer]

Sounds good