unusual damping materials

R

RickH

Junior Audioholic
Recently I went to purchase some good quality polyfill for some small bookshelf speakers i was building. I stopped at Good will as they sometimes have bags of it for sale. I happened to pass a bunch of used sleeping bags and noticed there was a large weight difference in identical sized bags.
Upon closer inspection I discovered that the better "bags" used a much more dense material. Same stuff basicly,just more dense. I paid $4 for a single bag containing 6 pounds of "800 hollowfill". Thats a lot of weight for a small sleeping bag. Tell me I'm crazy,("you wont be the first!) ,but I noticed a marked difference in the damping ability of this material over normal poly fill.
I guess my point is that I feel this may be a way to buy some seriously superior damping material for a fraction of the cheap stuff. You might want to
steam it however....cant imagine how I would explain to someone how I got bed bugs in my speakers!!!
 
annunaki

annunaki

Moderator
Regular poly fill does little to actually 'dampen' or tame internal reflections in an enclosure. It's primary function is usually to allow the enclosure to seem slightly larger with sealed applications.

To properly dampen reflections lining the walls of an enclosure with mineral wool sheets (thicker for lower frequency absorption) or a similar material of like density works best. Typical density of this material is 8/lbsft^3. Getting materials that match this density work very well. You will want to wrap this in grill cloth to prevent the fibers from moving around, though it is minimal.

McMaster-Carr sells this, simply do a search for mineral wool and scroll to the bottom to find sheets.

Owens Corning 705 pressed fiberglass sheets also work well as a viable alternative to mineral wool.
 

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