Construction material for portable generator sound-deadening box

[joshuabardwell]

I am planning on building a sound-deadening box for a portable generator. I'm curious if y'all could suggest some hardware-store material that would be a good choice, that might not be obvious. As I understand it, the best material would be MDF, because of its density, but that's a no-go because it disintegrates as soon as it gets wet. I have heard that plywood is a poor choice because it basically just resonates like a drum and doesn't really baffle the sound much. One person on the Internet suggested the silver insulation panels, but I'm skeptical; they contain air, for thermal insulation, so it seems like they would have too low a mass to be effective at sound deadening. Another person put fiberglass batting on the inside of his box, which I'm skeptical of for the same reasons.

Any input y'all might have would be welcome.

 

[aczlan]

3/4" plywood with sprayfoam on the inside, then tin inside that.

Aaron Z

 

[wyeguy]

Don't know about sound deadening, sorry, but if I was doing this I'd also consider fresh air for engine operation & venting the exhaust. Maybe you've already got this covered. Good luck!

 

[joshuabardwell]

Don't know about sound deadening, sorry, but if I was doing this I'd also consider fresh air for engine operation & venting the exhaust. Maybe you've already got this covered. Good luck!

Yup. I've done a lot of research into various construction techniques. It's tricky to keep the generator from overheating while not opening up big holes that let the noise out. I don't have any solid answers there. I'm just going to try stuff and see what happens.

 

[joshuabardwell]

3/4" plywood with sprayfoam on the inside, then tin inside that.

What's the purpose of the tin? To keep the spray foam insulation from being knocked off?

 

[aczlan]

What's the purpose of the tin? To keep the spray foam insulation from being knocked off?

That and spreading the heat around enough that you don't get hot spots that light the foam on fire.

Aaron Z

 

[joshuabardwell]

I have done some looking into spray foam insulation, but I think I must be looking at a different product than you're suggesting. Everything I'm seeing is way expensive, and requires specialized equipment. Can you point me at a specific foam product?

What's the benefit of the spray foam over, for example, the silver insulation board?

 

[pwright]

You might look into the sound deadening and thermal barrier stuff they sell for vehicles.

 

[ericb2400]

short stroy from many years ago when i was not as smart as i am now I was chosen to drive the truck to pull the tlr in a Christmas parade. we put christmas lights on the tlr + flood lights etc etc. Generator in bed of my truck. It is a chrismas parade so we wanted the generator to be quiet. Made a temporaroy box out of blue foam inslulating board. Had 1.5ft clearance all arouind for air space and brathing holes cut in the box also. long story short. It got hot in the box. the gas tank swelled becaous of the heat, when i uncovered the generator, gas was shooting 20+ft out of the vent hole in the gas cap. :shocked: Once it cooled down etc, the gas tank was still distorted. I will never box a generator again. I would rather listen to it than risk what could have happened that day.

 

[PILOON]

Staple old carpeting on the inside of a plywood housing, that will help a lot.
Felt is also good.
For cooling, a computer type muffin fan while quiet will move lots of air. You can get them in 12 VDC as well as 110AC (and barely draw 1 amp).
Make the exit opening the same size as the fan you select and orient inlet and outlet in opposite sides/corners.

 

[CurlyDave]

IMHO you will be far better off to just buy one of the ultra quiet generators. They are pricey, but they work.

Unless you are an engineer, running a generator inside any kind of home-made noise suppression device will bring you grief and danger. If these were easy to make, they would be on the market.

I am an engineer, and my solution was a Honda eu2000.

 

[joshuabardwell]

I will never box a generator again. I would rather listen to it than risk what could have happened that day.

I appreciate the feedback, and I definitely plan to do thorough testing to ensure adequate cooling before using the box unattended. I plan to use an IR thermometer to measure temperature at various points during normal running, and then when in the box. I'll probably also install a 120v pancake fan, since there'll be a ready source of 120v power when the genny is running.

All that being said, the real question I have is: did the blue insulation board work to quiet the generator?!

 

[joshuabardwell]

IMHO you will be far better off to just buy one of the ultra quiet generators. They are pricey, but they work. Unless you are an engineer, running a generator inside any kind of home-made noise suppression device will bring you grief and danger. If these were easy to make, they would be on the market. I am an engineer, and my solution was a Honda eu2000.

No way that the quiet is worth the price of an eu2000 to me. If the box doesn't work, I'll just suck up the noise.

 

[forgeblast]

I have bought foam kits through Foam it green .com . I am wondering if you need to make a box but what if you went with something that looks like a dug out (3 sides sloping roof) to bounce the sound away from you.

 

[MarkV]

Would a better muffler on the generator be an option? Mine is also crazy loud and have thought of after market mufflers, I just don't use it enough to bother.

MarkV

 

[dmccarty]

One way to minimize sound transfer is to disconnect one side of the wall from the other side by offsetting the 2x studs. A picture is worth a gazillion words, look at the bottom of this page, How to Soundproof a Wall

You use two sets of 2x studs, one set for each side of the wall. Wall covering is attached to only one set a of studs so there is no direct sound transmission through the wall. Insulation is added for more sound deadening. I thought about doing this for interior walls in our house but figured it was overkill. I think we have more sound transfer through the slab than the walls.

These types of walls are insulated to cut down the noise but that is also going to cause a build up of heat. Not sure how to safely deal with the heat issues. Then there is that pesky exhaust and air supply to worry about.

The huge generators at work sit in metal inclosures on a side of the building sorta away from people. When those gensets are started, they make a heck of a racket.

Later,
Dan

 

[s219]

A great sound insulator is fiberglass batting behind perforated metal or perforated masonite peg board. The holes really knock down mid and higher frequency noise and the fiberglass damps the rest.

A good rule of thumb is that you want the absorber to be about the size of the wavelength of sound you're trying to attenuate. So low frequencies (deep noises) need big structures, while high frequencies need small structures.

The most effective way to quiet the generator would be to figure out what noises it's putting out, and then target the most annoying ones first. But that takes a sound meter, which is not a typical piece of equipment for most of us. I'd probably experiment and see what works best.

 

[3930dave]

Coupla thoughts...

Just had the doghouse off my van. Full size vans aren't popular anymore, but maybe some of the Michigan guys who hang out here know who can supply the doghouse insulation. Appears to be some type of fibre, covered with heavy "tinfoil".

As discussed, the thermal engineering is non-trivial. Consider investing in some thermocouples - they aren't that expensive. Fluke used to sell a thermocouple adapter (essentially just a calibrated amplifier) so they will direct read Temperature on a DMM. With a good DMM, you can direct read the Tcouple output, look up a table, and convert to Temperature - PITA though vs. the cost of an adapter.

Sensors, Thermocouple, PLC, Operator Interface, Data Acquisition, Rtd is one source for Thermocouples, Fluke too.

External fuel tanks, at least during testing, should help on the safety front.

Did some research a while back.... the best bang/buck muffler implementation I saw was using a 600cc street bike muffler. (600s being the sweet spot in the street world, lots of guys drive the bike home from the dealer and pull the stock exhaust. Ergo, lots of virtually unused 600cc mufflers are for sale, and therefore cheap).

The example I saw was on a Yamaha genny, that a guy built to run at Glammis. Essentially built a tripod, and had the bike muffler firing straight up. Good solution, low cost, and mostly comes down to having some intermediate metal working skills.

Pls keep us posted how this goes.

Rgds, D.

 

[buickanddeere]

Obtain a quieter generator and a longer extension cord.
A acoustical baffle only needs one side and a top. Find the foam with the points and pits. Probably on eBay.
As previously stated. Heat is everything

 

[joshuabardwell]

I have bought foam kits through Foam it green .com . I am wondering if you need to make a box but what if you went with something that looks like a dug out (3 sides sloping roof) to bounce the sound away from you.

I am thinking that direction too. Simply redirecting the sound, vs. enclosing the genny entirely, would help with the air flow and heat issues.

Would a better muffler on the generator be an option? Mine is also crazy loud and have thought of after market mufflers, I just don't use it enough to bother.

From what I have read, putting a muffler on a generator isn't much worth the trouble, because so much of the generator's noise is from the motor itself, not the exhaust.