sound-damping towers for generators

Fex · Post by **Fex** » Fri May 18, 2007 9:21 pm

If our camp has a genny I would like to case it in a sound chimney. Who's done this? I've got a couple of questions before I construct one.

1: Is 8 feet tall enough to shunt the worst of the din up out of earshot?
2: How much open space around the machine do you want to keep the heat from building up?
3: Is it necessary to put a draw fan in to keep it cool or will an inch of open space at the bottom allow enough airflow while still keeping the sound mostly contained?

I've got materials to make an excellent sound barrier but I want to make sure the dimensions of the chimney are sufficient to do the job and still not put the machine at risk.

MikeVDS · Post by **MikeVDS** » Fri May 18, 2007 10:07 pm

I have not done one before but if you find someone who's an expert on these they'll need more information. Some thing probably needed will be the size of the generator and the max load and durations you'll put on it. Also how loud is it currently and how loud is acceptable. Model and make could also help.

1. Sound does not travel in a straight line and can do seemingly weird things. The higher it is the more efficiently it will filter out sound. At some point the returns are not worth the cost, which is what I think you're looking for. Unless you're doing yours based on someone elses well tested design or get an audio engineer to spend a chunk of brain power on the project you'll just have to test and see what is acceptable to you. If you're willing to modify it after built, you can do your own study so you can feel confident you have a good design worth sharing with others.

2. Heat will always build up. Depending on the outside temperature and the load you're running and how well you insulate your system with the chimney, you'll reach some temperature. You obviously know there is some temperature that you don't want to exceed because it could hinder or damage your generator. To really find this you'd need to know the rough heat output of your machine. Without knowing anything about it it's impossible to guess. Also the maximum temperature it can safely operate at. Make and model go a long way for that. Then you wrap it in an insulated box. Material, thickness and rough design would be needed to find out how well it will trap the heat.

3. This depends on your findings from #2. You also did not mention that it needs air to operate. I'd guess that you could put something in a box and have it run out of o2 before it overheats, so don't forget about that.

I'd recommend finding out what some other people did and copy one that looks good as close as you can. Or just play around and see what works out for you. You can get a digital thermometer for cheap and watch the temp if you're worried about that. If you're watching them temp you can start with a well insulated design with a short stack at first. If your temp stays within range then you're not over insulated. If it's too loud add to the stack. If that doesn't help much you may need more insulation or different materials, which you'll have to run the temperature tests again.

Why the stack anyway? I have not seen anything like that before. Because it needs to breathe I'm picturing two boxes with the insides lined with that spiky sound proofing material. The inner box would have the corners cut off and the outer box fits over it with the centers of the sides cut out. I honestly don't know if that would work well but looks good on my mental paper. If it needed air flow it would be easy to add a small box fan or too as well.

dragonfly Jafe · Post by **dragonfly Jafe** » Sat May 19, 2007 4:41 am

...also seek to avoid a "transmission-line" effect, where you create a long tube open on one or both ends, with the generator's low frequency noise starts resonating (thus making things even worse)...

8 feet is right in the middle of the 1/4 wavelength bass freqs....

And the walls need to be very stiff or very flexible (and/or heavy), otherwise they will just be sounding boards. Plenty of braces to prevent those big panels from flexing, etc.

I gave up with massive heat-mongering enclosures and finally bought a honda EU2000....

Ron · Post by **Ron** » Sat May 19, 2007 2:36 pm

After much experimenting with putting noisy generators in all kinds of sound dampening constructions I found that none of them really work like they're advertised. My camp is biting the bullet this year and paying more for a quiet generator, having given up on the whole notion of making a noisy one quiet.

Ron

Post by **mdmf007** » Sat May 19, 2007 4:51 pm

Ron theres an easy way to make a noisy gen quieter -- Get more extension cord, and make it someone elses problem!!! Lol - thats not very burneresque but would work.

later

gyre · Post by **gyre** » Sun May 20, 2007 12:51 am

How about this?

http://www.fischerpanda.com/
57 db

The stack is an interesting idea.
If it is tall enough, airflow could be superior to an open engine.
The standard approach is to use a water cooled system with the engine in an enclosed box.
Silencing the exhaust and intake as much as possible will help any generator.

If the stack is rigid close to the engine, you might get away with sheet metal ductwork with insulation glued to it.
Rubber would damp the metal as well as help with reflection.
There are two approaches, isolation and absorption.
Isolation works best but in an open arrangement, you can't rely on it.

For stack effect, the taller the better.
Paint it flat black too.
The purest form of solar power.
The stack will work better if it is round as much as possible.
If nothing else a baffle with sound absorbers will cut harshness some.

phil · Post by **phil** » Mon May 21, 2007 4:52 pm

mdmf007 wrote:Ron theres an easy way to make a noisy gen quieter -- Get more extension cord, and make it someone elses problem!!!

Yeah, had that happen to me. Some jerks camped by us, put their generator right next to our shade, then put their shade off a ways. They used the generator to run their blender for drinks. They'd come over, crank the generator, run the blender, smiling at us as they did, then turn it all off and go back in their shade for drinks.

Post by **mdmf007** » Mon May 21, 2007 5:05 pm

Glad you knew I was kidding. My mates and I had a similar instance 4 years agobefore we started dragging 20 of our buddies out.

So we show up in 02' in kyles vw camper. Pop up the shade and throw down the carpet and lawn chairs. Whole camp set up took 4 minutes. We were on the outer ring at about 7:30 It went well for three days and we had tons of room, one night we come back around dinner time and there are 2 cars parked about 4 feet from the rear of our van and the driver side. They have an old generator that sounds like a lawn mower, and their cars trapped us so we couldnt move. I look at one of the aghast and he just looks at me. I say "sorry We parked so close to your campspot 4 days before you got here. I would have moved had I known we were in your spot. "

So there are asses all over.
later

unjonharley · Post by **unjonharley** » Mon May 21, 2007 6:01 pm

I offered to fix guys generator next to me last year.. I had a 3lb hammer in my hand at the time.. He elected to move the genny to the street side of his camp..

Lassen Forge · Post by **Lassen Forge** » Tue May 22, 2007 12:55 am

phil wrote:
mdmf007 wrote:Ron theres an easy way to make a noisy gen quieter -- Get more extension cord, and make it someone elses problem!!!
Yeah, had that happen to me. Some jerks camped by us, put their generator right next to our shade, then put their shade off a ways. They used the generator to run their blender for drinks. They'd come over, crank the generator, run the blender, smiling at us as they did, then turn it all off and go back in their shade for drinks.

And they didn't even invite you over for drinks?!!

We have the Genuine Apokiliptika Silencing Kit for that - comes in 10 and 12 pound varieties. Guaranteed to work, or your money Back.

Available at your local No-Value Hardware, or at Home Despot, in the "War Hammer" department...

phil · Post by **phil** » Tue May 22, 2007 9:31 am

> And they didn't even invite you over for drinks?!!

Nope, just the noise.

I'm thinking a 5-lb bag of sugar would be more mystifying than brute force.

MikeVDS · Post by **MikeVDS** » Tue May 22, 2007 9:38 am

I gave up with massive heat-mongering enclosures and finally bought a honda EU2000....

I can also vouch for those Honda EUx000s. A camp member got one for this year and it's quieter than a lot of computers. They are pricey but I might have to get one myself. If you watch ebay and craigslist you can sometimes find them at a decent discount (which will still be pricey).

Ugly Dougly · Post by **Ugly Dougly** » Tue May 22, 2007 10:00 am

A note on erecting styrofoam towers on the playa: they call the wind Maria, and very damn thing turns into a kite.

I would polite tie a string around the gas cap to remind them that I had access to their fuel supply when they weren't looking, before wasting good sugar on such a stunt.

gyre · Post by **gyre** » Tue May 22, 2007 3:11 pm

Sugar in gas is a myth.

I know someone with a new diesel looking for best offer now.
Should be very quiet, electric start.

I think a better muffler would help most generators.

unjonharley · Post by **unjonharley** » Tue May 22, 2007 3:51 pm

FeX, Did you buy a Coleman powermate?.. If so Your screwed..

The best sound damper I have seen on the playa is this: Two sheets of ply wood cut in half to form four sides.. Then old sofa pillows attached around the inside top.. Set this up in your backyard and test run.. On the playa when the dust is blowing and when the genny is not in use, Cover the damper with a tarp.. This is to cut drifting dust.. If you run it to long some one will come along and cut your head off.. and for christ sake do not bury it like some damn fools have tryed.. Now go play in the street like a nice boy

MikeVDS · Post by **MikeVDS** » Tue May 22, 2007 5:13 pm

Sugar in gas is a myth.

I imagine that a 5 lb bag of just about any solid granules in a small generator would clog the fuel filter and both the tank and filter would need to be cleaned out.

unjonharley · Post by **unjonharley** » Tue May 22, 2007 5:19 pm

MikeVDS wrote:
Sugar in gas is a myth.
I imagine that a 5 lb bag of just about any solid granules in a small generator would clog the fuel filter and both the tank and filter would need to be cleaned out.

\/
The film from the top of a yogurt cup will do the trick.. Or a few turning from the dril press.

gyre · Post by **gyre** » Tue May 22, 2007 5:27 pm

Sugar would have the same effect as any random material.
Nothing special though.

Captain Goddammit · Post by **Captain Goddammit** » Tue May 22, 2007 7:54 pm

gyre wrote:I think a better muffler would help most generators.

Friends and I have experimented extensively with different mufflers on loud generators, up to and including running the tail pipe into a garbage can full of water. We've welded on car and motorcycle mufflers, tried boxing the generators, all of that stuff.

It really doesn't work, they're loud and obnoxious, and everyone around you will wish you weren't there... to put it mildly.

We now own Honda EU-series quiet generators.
No one has ever bitched, or even mentioned anything at all about these things running, and I have an electric fridge, so I run a genny around the clock at BM.

Yeah, they cost a bit more, but what good is a cheap set when you can't stand to turn it on? We're not rich guys who can drop big $$ on BM stuff without thinking much of it. This is one of the things that you won't regret stepping up for. Damn near as important as quality booze for your margaritas.

Damn near.

gyre · Post by **gyre** » Tue May 22, 2007 8:54 pm

The intake counts too.
But the overall construction matters, it's just not easy to fix.

The one I posted is supposed to do 57 decibels.
That doesn't seem too bad.

Any muffler must be solid and too large can allow some rumble.
Most generators run in a narrow rpm range so a muffler can be spec'd just for that.
Harshness is hard to measure but much can be done there with absorption.
Borla uses multiple small tubes and the same thing can be done if joints are knife edged.
SPD in cali has those fittings.

Zhust · Post by **Zhust** » Wed May 23, 2007 4:02 am

Fex wrote:If our camp has a genny I would like to case it in a sound chimney.

*shrug* Who is Green Man?

Ugly Dougly · Post by **Ugly Dougly** » Wed May 23, 2007 10:46 am

Sugar makes the gas taste a little sweeter.

Fex · Post by **Fex** » Fri May 25, 2007 7:37 am

jaycerochester wrote: *shrug* Who is Green Man?

WTF? Where'd that come from?

dragonfly Jafe · Post by **dragonfly Jafe** » Fri May 25, 2007 7:40 am

...maybe that the best way to quiet a generator is to not have to run it...