Best material(s) for a baffle box?

[--Ever--]

I'm curious what type of material (eg eggshell, audio foam, the hard thick mat stuff) is best for sound dampening the kind of sound coming off a generator (eu2000i).

I'm versed in baffle box designs, including many of the posts here and on RV forums. I figure 3/4" plywood or MDF will suffice for the frame. But I'm yet to see if there's been any testing on the actual material that's best to use.

Side question - when making a "directional baffle box," Ie one that has has one side open, is it best to aim it outwards or, instead, up?

Examples:

http://www.amazon.com/FatMat-Thick-Self ... +dampening

http://www.amazon.com/Acoustic-Eggcrate ... pening+egg

[Pootzen]

Carpet remnants seem to be the go-to cheap solution according to this thread: viewtopic.php?p=250192

I plan to build a basic box with a side hinge and open top with carpet stapled to the inside for my generator this year.

[Elliot]

Even my EU3000 could use some baffles. Last year it annoyed me quite a bit, and thus no doubt others. It may be getting louder with the years.
How can we make sure any carpeting will not shed small pieces of the nap along the cut edges? These make nasty moop.

[Pootzen]

Even my EU3000 could use some baffles. Last year it annoyed me quite a bit, and thus no doubt others. It may be getting louder with the years.
How can we make sure any carpeting will not shed small pieces of the nap along the cut edges? These make nasty moop.

Good point, I'm going to bring a baffle for my brand new Yamaha 2400 this year (noise + security). I'm thinking I should duck tape the edges of the carpet remnants. I did the same thing for the blocks of insulated foam I brought last year and it worked great (just had to make sure the edges were completely sealed ahead of time, that stuff flakes everywhere).

[trilobyte]

I use and would recommend using any carpet or thick fabric material that you've got. Foam (the soft kind, not the rigid stuff) also works well, if you've got it. Make sure it's got breathing room - if the material's getting darkened from the exhaust, it's too close IMO. Pointing up can work, I've also pointed it in a direction that faces away from other campmates/neighbors. Since ours is a Honda EU2000i it's quiet enough that I don't have to worry about it throwing over a distance. The baffle will also give you the added benefit of security (since it obscures the make/model from people passing on the street) and acting as a wind/dust break, which is good for the generator IMO. If you've got a spare couple pieces of wood, put the generator on that instead of directly on the playa to further remove it from the dust.

[--Ever--]

Thanks for the replies so far!

I figure carpet works. Just looking for something a little more "pimp my box" if you know what I mean (and, that's what she said).

It's funny. After reading all the posts on the forum about how Hondas are so quiet, I still had someone complain about our eu2000i. The one that they dropped their tent next to.

[Pootzen]

There comes a point at which people have to take responsibility for their own choices. I camped across the street from a sunrise coffee camp and most definitely learned my lesson.

Trilobyte - thank you for tip, I'll use the leftover plywood cut for the baffle box to make a base.

How important is it to have a couple inches of clearance at the bottom (like this box)?



My plan to buy a single sheet of 4' x 8' plywood and have it cut like so:



4 parts - 3' x 2'
2 parts - 2' x 2'

This configuration should give 7.6" x 3.75" clearance on my generator (without a lid like the one above).

[FlyingMonkey]

There comes a point at which people have to take responsibility for their own choices. I camped across the street from a sunrise coffee camp and most definitely learned my lesson.

Trilobyte - thank you for tip, I'll use the leftover plywood cut for the baffle box to make a base.

How important is it to have a couple inches of clearance at the bottom (like this box)?



My plan to buy a single sheet of 4' x 8' plywood and have it cut like so:



4 parts - 3' x 2'
2 parts - 2' x 2'

This configuration should give 7.6" x 3.75" clearance on my generator (without a lid like the one above).

How are you dissipating heat & exhaust? Do the openings on the bottom provide enough venting & fresh air intake?

[Elderberry]

Good question.

[FIGJAM]

(without a lid like the one above).

[BBadger]

I don't understand why you guys are bother with a roof unless you're afraid the generator will get stolen (use a lock?) or maybe too much sun? You're just reducing airflow, reflecting the sound out the openings, adding more surfaces to vibrate and transfer sonic energy, and overall making a more complex structure.

You're on the playa, not in a building complex. Rarely is there anything taller than one storey where sonic waves aimed upwards would intersect with other structures. Instead of a roof, try to build a (taller) structure with that wood to channel the sound upwards. Use the sky as an endless sound dump for your noise.

The walls of your structure matter too. You're not going to be able to reflect all the sound towards the sky, and there will also be sound coming out of the air ducts on your baffle. Carpet, while cheap, usually doesn't work very well alone because it doesn't have much mass. You need a combination of mass and absorbing materials so that the waves don't simply pass through your walls, and so the energy gets converted to heat. The more mass, the greater the attenuation (see the link near the bottom).

Consider making some real sound baffle panels such as these. Also consider using two layers of plywood in order to give your structure mass and a small intermediate region between the two walls to disrupt vibrations. Sound may still get reflected downwards towards the ventilation ducts, so concentrate on that area for sound absorption.

Anything that generator comes into contact with will transfer vibrations and sound to the environment. Try placing your generator on a vibration isolating surface, such as a box of sand (make sure it doesn't MOOP). Raising the generator off the ground will also give it some ventilation and may help block a direct line of sight (sound) to the ventilation ducts.

Here is some other good information on (commercial) generator enclosures and the properties of materials and construction that can affect performance.

[Pootzen]

Here's what I ended up building...

[FIGJAM]

It needs some carpet in the INSIDE too!

[Pootzen]

Oh, right, forgot the carpet... thanks!

[gyre]

I would think a slight tilt outwards at the top would direct sound better.

Don't confuse isolation with absorption.

[Elderberry]

When you start trying to angle things, it just makes it too complicated. The box works fine. Somebody posted some pretty scientific calculations of angles, and sound, etc. for the perfect box somewhere on here, but you'd spend all your prep time just trying to figure it out and build it to those specs.

[gyre]

I need a baffle box to keep.
Was it bbadger that posted some interesting design ideas?
If you want to burn it, it severely limits materials and time.
I think any angle would be an improvement, besides stopping standing waves.

/\instructions
Cut two sides with the top longer than the bottom
Cut two pieces to attach to the ends.
Make them wider at the top, but they do not need to be identical to the first two.
That's it.

Mass density law says the material is crucial and the denser the better.
Reports are that almost everything helps though.
Absorption can actually make sound penetrate better, so an open box is sort of a balancing act as far as carpet goes.

Layers of different material will decouple even when glued together with a flexible glue.
Do NOT screw them thogether.
Plywood / soundboard / sheetrock / plywood / repeat is a proven approach.
More effective when the surface is the hardest material, as far as isolation goes.
Typically sheetrock on both sides in a studio.