Foam, thicker foam or Open Cell

[qguy]

Hi My current subwoofer in a sealed enclosure uses yellow foam (looks/ feels similar to foam used in beds) I need to put the driver in a smaller enclosure will changing the foam to a denser type of foam virtually increase the volume of the cabinet ? will open cell fibre do the same ?

[pjpoes]

Thicker foam will just be reflective and do little to increase the percieved volume of the box. You want something like Acoustafill. I find that a mixture of industrial felt, or opencell polyurathane foam, and acoustafill works best. However I will say, the magnitude of the effect is debated, so you may still not get the results you want.

[SY]

Here's an easy test: if you compress the foam and it takes a while to recover, it's closed cell and unsuitable. If it pops right back, it's open cell and suitable. Look for a highish density (8pcf is a good number to shoot for), or even better, a foam loaded with filler.

(8pcf ~ 125kg/m3)

[Cal Weldon]

Closed cell won't absorb much water and open cell is a sponge.

Consider using basalt based insulation often referred to as rock wool. I think for adding virtual volume, this would be a good choice.

The test I like to use is to hold up a tweeter or midrange on the far side and try and listen through it. Rock wool seems to do an excellent job. The better it works at high frequencies, the better it will likely do at lower, IMHO.

At some point, it has no effect.

[planet10]

Rock Wool is making a comeback... i have only taken it out of old Dynacos, not used it. My suggestion for maximizing the aparent enclosure size is fibergalls insulation + an aperiodic enclosure.

dave