Filling enclosures

[avatar307]

Sometime ago, I posted a message here asking a question about calculating the volume of 4th order enclosures. Sreten replied, giving some much appreciated information; however, before I could reply back I lost the post. He made a reference to filling both the sealed portion with Dacron/BAF and the reflex/ported portion with foam. Some questions arose in my head in reference to the foam, and later as to if any generic polyfill could be substituted for the Dacron/BAF type material.

In reference to lining the reflex portion completely with foam, style of foam would be best? When I first thing of foam, the softer, black foam comes to mind. Then there is the hard, white styrofoam. I guess the difference is not only the material used to make the foam, but also the air content of each.

I had planned to filled the relfex portion with some type of polyfill material, most likely the stuff used for filling pillows that can be picked up at Wal-mart. This I would assume is near the same thing as a Dacron or BAF type filler?

However, I know there would be considerable problems with this material being ripped apart and blown out the ports, so foam makes a lot more sense.

When I think of sound insulators, I usually think of the black foam. I expect I could find this material where materials of that type are sold for eliminating echoing in large open rooms. The typical image of the hard, white styrofoam makes me think of macking material. Definately not something I want to try to cut, and I fear it would also be too dense. The other material I think of is the sheets of R rated foam you buy for a little extra insulation under vinyl siding and such.

Anyone have any thoughts on all of this?

Thanks!
Chris

 

[sreten]

Polyfill (polyester)/Dacron/BAF (bonded acetate fibre) are
all very similar as far as I know.

You cannot stuff the ported side as it would seriously impair
the Q of the ports resonance. You need to line it with soft
foam to prevent higher order resonances.

sreten.

 

[avatar307]

I found some soft black foam that I think will work great. I remembered I had this big packing crate in my garage that I brought home from work, and the inside is 50% full of soft black foam. (It was used to ship in a $200k digital projector from Australia.)

However, the foam is rather dense compared to most of the other soft black foam I have seen. It takes about 50 lbs to visably compress a 8" x 8" x 2" thick piece. It will hold it up to 50 lbs, and then suddenly compress 50%. At that point, pushing down on it with my weight does not really compress it much more.

I fear that lining the reflex portion of my 4th order with a material of this density will cause problems. So I guess my question is, how important is the density of the material? Is more density better or worse?

Thanks,
Chris

 

[avatar307]

Alright, I have determined that my black foam will just not work. For one, it is way too thick, for another I think it is so dense it will just absorb all the sound.

I would prefer lining my box with something with amplifying effects similar to Dacron/Polyfill... but that would involve the material moving, which would not be good in the relfex side of the box.

Thus, I have resolved the line the relfex portion with... well... that "egg carton" foam you put under your sheets to make a mattress more comfortable. This should be thin enough to not reduce the air volume in my reflex portion, thick enough to absorb any standing waves, and the irregular shape should do nothing but good.

Now... more questions. How should I glue it on? LOL As I tend to over do things and glue stuff with liquid nails when all it needs i rubber cement. My first instinct would be silicone, but I expect hot glue may work just as well.

Beyond that, the baffle for my speaker is set at an angle. So... do I even need to worry about lining it with foam, or will I not have a problem with high order frequencies because my speaker is not at a right-angle to any of the interior surfaces?

Don't worry all. I have enough stupid questions floating through my mind whenever I do anything to keep everyone amused with ideas to debate. Now if I could just figure out how I want to hook my amp up to my freaking GM battery. *growl*

-MC

 

[Volenti]

Contact cement, preferably spray applied, would be most suitable. (and easiest)

 

[sreten]

It shouldn't be difficult to arrange the foam to be entirely self
supporting, as all sides ideally need to be lined with the foam.

You have chosen the right sort of stuff.
It does not need to be glued to the walls.

sreten.