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Old 09-14-2011, 11:12 PM   #1
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Is there any way to quiet a generator?

Does anyone make an exhaust muffler for generators? I f Honda can make a quiet generator, why can't Onan?
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Old 09-14-2011, 11:23 PM   #2
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Most of the noise you hear is not the exhaust, it's mechanical and very hard to quiet down and still keep enough air flow.
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Old 09-14-2011, 11:24 PM   #3
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Originally Posted by Mr_D View Post
Most of the noise you hear is not the exhaust, it's mechanical and very hard to quiet down and still keep enough air flow.
So over all which is better the Honda or the Onan?
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Old 09-15-2011, 07:45 AM   #4
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They are two different animals. No reasonable comparison between a portable and a frame mount.
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Old 09-15-2011, 09:41 AM   #5
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They are two different animals. No reasonable comparison between a portable and a frame mount.
I had the opportunity to take the case off my Honda 3000i and the way they quite down the exhaust is it just dumps into the case at one end. This would not work on a motor home. As the OP said the noise is mostly mechanical and vibration.

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Old 09-15-2011, 09:45 AM   #6
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How loud is an ONAN.. True story:

A few years ago I agreed to provide power for my ham radio club's field day, I mean I have 5500 watts, they needed perhaps 500 of them tops (multi station operation)

So I parked the RV in the middle of the field.. Ran my HD "house power" cord I use when Detroit Edison fails me at home and added somn more 30 amp lines on that (RV type, winding up in the old 8-outlet box I used back in my trailer days.

As we plugged in the first of the stations the Field Day Chairman says "You can start the generator now"

It was running. We were less than 200' from it and he could not hear it.. (I could but I have "Tuned" hearing (Long years of trying to listen to a voice under noise on a radio has taught me to filter my hearing) but I had to "listen hard" to hear it.

In the motor home it is kind of a low purr.

NOTE: I run with a Gen-Turi in place.. (I mean I had to run it 25 hours straight) the Gen-turi does not make is "Softer" but it does deepen the note making it less annoying and it moves much of the noise up out of the way so it's not as noticble.. The A/C blower inside will mask it completly,,, Just run the blower on HIGH, not auto, not off. but FAN (or Cool) mode on high.
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Old 09-15-2011, 10:12 AM   #7
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You might also consider lining the generator bay with dynamat or something similar.
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Old 09-15-2011, 11:57 AM   #8
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You might also consider lining the generator bay with dynamat or something similar.
That might be an interesting idea.
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Old 09-15-2011, 12:18 PM   #9
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The Hondas are quiet primarily because they are an inverter type generator rather than direct AC generation. That means they can run at lower RPMs when the load is less than 100%, so much less noise. A direct generator has to run at a constant 3600 RPMs no matter what the load, so they are always loud. Newer ones are less so than previous generations, though.

Honda also help by making a their engines to very tight specs, so less NVH. But you can buy a honda-powered genset (e.g. from Northern Tool) and it is nowhere near as quit as the Honda "i" series gensets, and that's because of the direct vs inverter difference.

Onan makes inverter gensets, but they seem to be only the diesel models. My Onan 7500 Quite Diesel makes much less noise than my previous Onan gas 5000.
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Old 09-16-2011, 07:12 PM   #10
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The Hondas are quiet primarily because they are an inverter type generator rather than direct AC generation. That means they can run at lower RPMs when the load is less than 100%, so much less noise. A direct generator has to run at a constant 3600 RPMs no matter what the load, so they are always loud. Newer ones are less so than previous generations, though.

Honda also help by making a their engines to very tight specs, so less NVH. But you can buy a honda-powered genset (e.g. from Northern Tool) and it is nowhere near as quit as the Honda "i" series gensets, and that's because of the direct vs inverter difference.

Onan makes inverter gensets, but they seem to be only the diesel models. My Onan 7500 Quite Diesel makes much less noise than my previous Onan gas 5000.
I thought the Onan twins ran at 1800? There's a really old single cylinder Onan that ran at 3600.

It's the inexpensive geni's that run at 3600. That's one of the big things that make them so darn noisey... That and the much lower volume mufflers commonly seen on them.
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Old 09-16-2011, 09:07 PM   #11
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I've worked for many years, prior to retirment, in the VIP airplane part of Boeing. The lesson I learned was that most noise comes from vibration being transmitted from a vibrating compnent to a large surface that can magnify the noise.

The first step in any noise reduction plan is to isolate the source from its attachments to structure. Use airbags, elastomer loops, polyurethane doughnuts, steel braided isolators. whatever. Usually, that will get rid of 80% of the problem, as far as the occupants of the vehicle are concerned.

Next is insulation and re-direction. In an RV set-up, where you're trying to minimise annoyance to people close by but outside your rig, you need to look at isulation, padding the enclosure of the generator so it doesn't send structural vibrations out to others.

Re-direction, moving the output source of the noise so that it doesn't bug your neighbors might be as simple as one of the commercial, heavily insulated exhaust systems that put the outlet above roof level while you're docked.

My team was so successfuol on one project (a 747-400 VIP for a head of state) that his main complaint was that the cooling fans in the entertainment cabinet in the executive bedroom were too noisy. That bedroom was in what is normally the first-class compartment of an airline 747, where aerodynamic noise is usually the worst.

Really, noise reduction is a relatively simple process of minimising the biggest noise-maker first, then working your way down the chain to where the remaining problem becomes trivial.

Implementation is where it becomes more difficult.
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Old 09-18-2011, 11:16 AM   #12
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Figured I throw in my 2 cents worth regarding generators.

We're planning on getting one of the gen-turie exhaust diverters for our on board onan. A friend has one and they work very well.

For our auxilliary generator though. I took an old cardboard box a new tv came in. I cut tabs into the bottom of it so I could secure it with rocks, then cut a slit in one side. I set it around the baby gen in a C shape. It gets plenty of air and helps with cutting down on the noise. You gotta face the opening away from you. It's not a honda, nor is a invertor style gen, so it's not super quiet. 65db the cardboard is more of a sound deflector than anything.

Now if I can just figure out why the generator has crapped out on me from make electricity. A whole different post I know.
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Old 09-18-2011, 11:45 AM   #13
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Actually Onan makes many very quiet generators. My last three MH's had onan gas generators. 4 kw models. One claimed to be quiet but it was not really. On our new mh the generator is 8 kw and much much quieter than the gas rigs. It has a better enclosure and runs at lower rps I believe because it is diesel. On my last two MH's I bought sound material which helped the interior sound but not dramatically. I tried many different things and just could not come up with many improvements. There have been dozens of threads on this subject and no one has come up with a really great solution. RV.net has many threads if you do a search.

I have stood next to some very large generators that just purred and are even quieter than my 8kw. Recently I tried to quiet my 8 KW down even more. I too have the genturi exhaust which actually helps in two ways. The exhaust fumes don't roll under the mh and annoy us when sitting outside and the hot exhaust is redirected upward so it reduces the fire hazard. The noise being redirected helps quite a bit too. You can definitely tell the difference when standing near the exhaust. Not the genturi does not make a complete enclosed exhaust system. There is a gap between the muffler and the genturi but the noise and fumes still go up extremely well.

As an experiment I tried covering the generator temporarily with blankets etc just for a test. I have a db meter so have an excellent reference besides the ear. No help covering the generator. That said perhaps taking the metal covers off and lining the inside of the metal with a thing noise dampening material would help. The largest source of noise is the intake and cooling air. I experimented with some material to have the intake and exhaust go through chambers so the noise would get bounced against the sides. There was a good deal of noise reduction doing that but I am concerned about heat so didn't pursue that a lot more. One thing that actually helps a bit is to place a rug under the generator which absorbs some of the wind noise. I might try building a small box with noise dampening material to place below the generator but have a gap like the genturi to prevent any heating issues. Sounds like I will be experimenting more. No pun intended. Good luck and keep us posted if anyone comes up with the golden bb.
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Old 09-18-2011, 11:46 AM   #14
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Wolfie, what you just demonstrated was that sound is fairly directional. Is also fairly reflective. You can cut the sound down by putting a sheet of plywood between the sound source and the sound recipient.

Ken
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