[Ethan Winer]

Originally Posted by Nosound

I already know about Ethan's link but no mention of Rockwool only rigid fiber board.

Not so. The following is from my Acoustics FAQ.

--Ethan

Now that you know what rigid fiberglass is, where the heck do you buy it? You probably won't find it at your local hardware store or lumber yard, but many insulation suppliers stock it or can order it. Start by looking in your telephone directory under Insulation and also Heating / Air Conditioning Suppliers. You can find the name of an Owens-Corning dealer near you by calling 800-GET-PINK (800-438-7465) or from the Locator page on the Owens-Corning web site. Other companies, such as Knauf, Armstrong, and Delta, make similar products, and they often cost less than fiberglass from Owens-Corning. You can contact them directly to find a distributor near you. In the interest of completeness, here are some other manufacturers that make similar products: Johns-Manville, CertainTeed, Roxul, Ottawa Fibre, and Fibrex.

When assessing rigid fiberglass, it is important to know its density so you can compare equivalent products. Owens-Corning 703 has a density of about three pounds per cubic foot (45 kilograms per cubic meter), and 705 is about six pounds per cubic foot (90 kilograms per cubic meter). Therefore, products from other companies that have a similar density will have similar absorption characteristics at the same frequencies. Note that some companies call their products mineral wool, mineral fiber, or rock wool, but acoustically they are equivalent to fiberglass.