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Seldaniel
11-02-2009, 03:01 PM
I have tried like mad to find this answer elsewhere, and having no success, return to you guys!
I recently purchaser a gasoline powered portable generator to power my home during power outages. ( Yes, I know, the power will never fail again!)
It is too loud.
Searching for mufflers for it taught me two things, first, the best answer from the ‘camping crowd’ is to get two small car mufflers and some pipe, point them at the sky, then drink a lot, because it will work partially, as lots of sound comes from the motor, so it is really a waste of time. But they do not know you guys, and you are the smartest people on earth.
Being intelligent and or stubborn, I call your attention to the fact that the manufacturer sets the engine speed at 3600 rpm in order to deliver a consistent 60Hz power, and that works out to 30 cycles per second.
30 cycles per second is woofer territory, and I know Helmholtz resonators are good for fixed frequencies, but can’t find out how to design one, either to place nearby, or to incorporate into the exhaust system. I did find some neat stuff about using them in the intake, to smooth out the flow and increase engine power. They spoke of muffling intake noise, but gave no specifics.
Size is of little concern, within reason.
Thanks,
Seldaniel

louped garouv
11-02-2009, 03:08 PM
all of the gentleman i know (throwing parties in the national forests) build a non air tight box that goes over/around their generators to contain the noise as much as possible...

they generally also make somewhat long runs of properly sized power cords to their amps & equipment racks....

hjames
11-02-2009, 03:13 PM
How big is this thing? I gather its propane powered? (My inlaws in Richmond, VA have a similar near-full house backup system for medical gear for their parents ...)

There are external motor sounds to mask, as well as internal sounds and exhaust noise.

Have you built an enclosure for the generator yet? I would think a baffled enclosure with accoustic inner walls (think sound chamber) would take a lot of the sound annoyance away.


Another supplement would be negative feedback - mike the system, invert the signal, and play it back in close proximity to the motor to null out the sounds ...




I have tried like mad to find this answer elsewhere, and having no success, return to you guys!

I recently purchaser a gasoline powered portable generator to power my home during power outages. ( Yes, I know, the power will never fail again!)
It is too loud.

Searching for mufflers for it taught me two things, first, the best answer from the ‘camping crowd’ is to get two small car mufflers and some pipe, point them at the sky, then drink a lot, because it will work partially, as lots of sound comes from the motor, so it is really a waste of time. But they do not know you guys, and you are the smartest people on earth.

Being intelligent and or stubborn, I call your attention to the fact that the manufacturer sets the engine speed at 3600 rpm in order to deliver a consistent 60Hz power, and that works out to 30 cycles per second.

30 cycles per second is woofer territory, and I know Helmholtz resonators are good for fixed frequencies, but can’t find out how to design one, either to place nearby, or to incorporate into the exhaust system. I did find some neat stuff about using them in the intake, to smooth out the flow and increase engine power. They spoke of muffling intake noise, but gave no specifics.

Size is of little concern, within reason.
Thanks,
Seldaniel

BMWCCA
11-02-2009, 03:31 PM
I recently purchaser a gasoline powered portable generator to power my home during power outages.
It is too loud.

You cheaped-out. Buy a better one! ;)

http://www.cumminsonan.com/www/common/images/residential/products/rs12000med.jpg (http://www.cumminsonan.com/residential/products/)

Cummins now offers a complete line of Cummins Onan residential emergency standby systems. Clean, quiet, and neighborhood friendly, all models run on either natural gas or propane. Permanently installed outdoors, the residential emergency power system is no more conspicuous than a central air conditioning unit and is linked directly to your permanent fuel supply. During a power interruption, the Cummins Onan residential emergency standby system will automatically deliver the power to keep homes running smoothly. And it will reset once the power returns. It's that easy.

1audiohack
11-02-2009, 08:04 PM
30 cycles per second is woofer territory, and I know Helmholtz resonators are good for fixed frequencies


That is a more complex issue, exhaust pulses are inpulses and are very broadband. The 30 CPS is more an audible indicator of RPM than frequency fundamantal. For the most part with mufflers physical size is king for noise abatement. Have a glance at something like Walker commercial and stationary power mufflers.

We have a SpinTron that is used for valvetrain validation as well as other things, it will "motor" a nonfiring engine, with or without pistons. You would simply have to witness it to believe how mechanically noisy an engine can be in the absense of induction and exhaust noises! And it is hard to believe how loud the induction side can be. You have very little control of that. Once you spark it, it only gets worse.

The mechanical racket is where a secondary enclosure will help you the most. What ever noise you "contain" will have to be converted into heat to be "disposed" of with insulation and mass. If you are not worried about your neighbors, or don't have any in rifle range, you could build a three sided reflective (bare plywood) enclosure and direct the noise away. You could do some easy tests with a sheet or two of almost any wood product to see if you can get it down to where you can live with it. Add thick fiberglass as needed.

All the best,
Barry.

Seldaniel
11-03-2009, 03:30 PM
Thanks to all.
I do not need a bigger one, and wanted a portable model so I can loan it out or use it at my other place.
Sound panels and an enclosure are part of the plan, but because it is air cooled, I can’t go too far.
Barry wins for getting closest to the answer I was looking for, and his answer pretty much settles it for me. – There will be no artfully made magic resonator keeping things whisper quiet. So I will go as far as to point a large car muffler up at the sky, build absorptive panels with rigid fiberglass, and hope for the best.
Luckily I have cords and capacity to keep the closest neighbors refrigerators running. That ought to buy a few friends!

Thanks again,
S