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Old 02-03-2007, 08:48 PM   #1
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Instructions for quieting a Generator

Guys,

I just came across a site that has instructions on how to quiet your generator. It includes all of the stuff that you need to quiet down a Coleman generator (probably the loudest of them all), with a 10 HP B+S motor.

http://www.alpharubicon.com/altenergy/gensetquiet.htm
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Old 02-08-2007, 07:54 PM   #2
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Thats good stuff. I was think myself about getting a muffler for a motorcycle or a atv and adapt it to fit when I do get a generator.
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Old 02-09-2007, 02:45 PM   #3
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The guy, that wrote the article, said it quieted his Coleman (I think) generator, quieter than a Honda. Now, that's really something to brag about.

I'm also going to try it as soon as I get a gennie (I think I can pick up a used gennie for a very reasonable price).

Good luck on yours. If you get to convert yours before I do, let us know how well it works.
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Old 02-28-2007, 09:12 AM   #4
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I don't know if I said this anywhere on Skoolie.net, but I used a car muffler on a noisy genset maybe 7 years ago.
Basically added a $20 muffler similar to what this guy did. The car muffler is so large and has such a low internal resistance (relative to the genset exhaust pressure/volume) that it just absorbs the noise.
I too used flex exhaust tubing to allow the genset to move and not stress the muffler connection.

The muffler can be permanently mounted to the frame, maybe using a heat shield between the gennie and muffler, and a cage to protect the muffler from damage, and the folks from the hot muffler.

BTW, you can wrap the muffler, exhaust tubing etc. with a high-temp insulation, and that may have the benefit of increasing the efficiency of the genset....don't know for sure, but they do that a LOT with high-performance car exhausts, and it does help THEM.
The insulation would help absorb even more ambient noise from the genset mechanicals.
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Old 02-28-2007, 08:03 PM   #5
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Ryan, what kind of genset did you do this with and did it make a drastic difference in noise?

-Richard
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Old 03-01-2007, 10:15 AM   #6
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It helped a LOT with noise.....the idea was to set up a friend's house for possible Y2K problems (no problem, obviously), and the quieter, the better. If no one knows the unit was there, they're not likely to steal it.

It was an ancient but rarely run Sears Craftsman gennie, when my buddy got it used it had probably been run only once; the paint on the muffler was barely blistered!
I used a generic small car muffler he bought at Meineke, and a few exhaust ells/flex pipe/fittings. I hammered out a flange on a stub of exhaust pipe, pop-riveted that to the gennie muffler, and went from there.
The enclosure we made from 3/4 sheet ply, lined with rigid insulation, cut a few holes for ventilation, with a small fan screwed on there to keep stuff cool. The fan plugged directly into the gennie: if the gennie ran, the fan ran.
The relatively immense capacity of the car muffler easily absorbed the small engine exhaust noise. With the muffler designed to control 500+ CFM of exhaust, it barely slowed the 150(?) CFM of the gennie running flat out....no back pressure increase to speak of.

From about 15 feet away you could hear the mechanicals running (without the enclosure), from 40 feet you hardly heard a thing, IF you were listening for it....otherwise it was QUIET.

Y'now, they do something like this for Burning Man, I've seen it in photos. Build an enclosure, it absorbs some noise, reflects the remaining noise upwards.
Some also dig a hole and plant it below ground level so any noise not absorbed by the ground is radiated upward.
I remember seeing at a hobby show, a guy cut a 55 gallon drum in half crossways; he lined it with fibreglas, and rewelded the base back on it. Then he plumbed the exhaust from a model airplane engine into the drum. Used indoors, you heard the prop whistling, and the engine sucking in air through the intake, and the mechanical rattle of the ignition as it fired....that was about it.

BTW, I was watching TANK OVERHAUL on cable last night (DVR), and the M18 tank destroyer they worked on had a neat feature: the rear engine compartment hatch folded down, and when down, it acted like tracks to pull the engine (on rollers) out for changes or repairs. Doing something like this on a bus would make installation and maintenance a breeze. The compartment cover can also be the access tracks/ramp.
Mounting the gennie on a heavy plate, and having that plate on heavy rubber isolators will keep it quiet (absorb some mechanicals normally transmitted through the base of the gennie) as well. Some years ago I found out you can buy noise isolators tailored to specific frequencies, so if you know what freqs the gennie is putting out, you can absorb that completely.

I've written about noise and gennies somewhere else, can't remember where. Basically, noise is absorbed by changing it's frequency, or deflecting it away.
Heavy objects absorb the noise because it's natural frequency is too LOW to have a resonant reaction to the offending noise.
Other materials absorb the noise (insulation, for example) because it's energy gets lost in the random frequencies that the insulation is made of.

Some mufflers use a noise-cancelling principle, where they make the noise reflect back on itself; one interesting effect of this is in tuned exhausts like on 2-stroke engines. The noise is also used to extract the exhaust pulses, making the effective exhaust pressures (and horsepower losses) lower, even increasing extraction, WHILE STILL KILLING THE NOISE....horsepower GAINS are the point here.

Another trick is like most auto mufflers use: make as many 90 degree bends as possible, and pass the exhaust pulses through holes; it makes the pulses tend to cancel each other out. Those bends absorb energy.
This type of exhaust robs horsepower though, unless you use a REALLY big muffler to keep flow levels up. That's why back in the day I used an International Harvester truck muffler in my '68 Mustang: it fit the same, but the huge intake/exhaust pipes cut back pressures while still absorbing noise. Kinda like a Stealth Bomber......

Hope this answers the questions, and any more you may have.

Ryan
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Old 03-01-2007, 07:13 PM   #7
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The head mechanic at the bus garage where I work suggested to tie the exhaust into the bus' muffler. He said he saw a setup like this once and it was really quiet.
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Old 03-02-2007, 09:08 AM   #8
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the geni in that article is the exact unit that i have and don't use because it's too noisy.
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Old 03-03-2007, 02:59 AM   #9
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Hey guys,

I'm sorry I haven't go on recently. I'm not ignoring ya'll, I'm busy looking forr another job (too many hours in the present one)

Anyways, here I go:

Ryan, I really didn't want to take away from your post (I do remember seeing it and liked it), I just saw the article and thought it was neat. The biggest thing I liked about the article was the pics of the gennie and the mods. They also gave part numbers for the mod.

BTW, I wouldn't have even noticed the article if it wasn't for you making me aware of the idea (I really don't have too much of an imagination, or so says my ex)

Rick, the idea sounds great, using your bus muffler, but trying to connect to it would probably be a pain for me. I don't weld much and I would have to get a shop to do it for me. Could you imagine what I'd get from the techs there? Remember, I'm in Houston and they have even less of an imagination than I got
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Old 03-03-2007, 03:03 AM   #10
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Hey Jason,

I was wondering if you ever tried putting a muffler to your gennie? The reason I ask is because if the unit is still noisy, it probably wouldn't be worth modifying.
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