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Originally Posted by goneten  Although I am confused as to why 4" thick 96 kg/m3 material would start to reflect low frequencies. I assumed that it would absorb frequencies down low. |
Do not worry. If acoustics was simple, God would not have created aspirin.
As porous material gets thicker, it starts to reflect sound. You saw that in Bob's absorption data. It is not obvious, although it does sort of make sense. Keep filling the holes, or making the holes smaller in a porous amaterial, and the material becaomes less porous.
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The only reason why I mentioned prices was to give you an indication of what they go for in South Africa and to illustrate how ridiculous the pricing is of the various densities. Not sure if the pricing structure is the same overseas.
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Thanks for the information on South Africa prices. The price of mieral wool etc, all other things being equal, should vary directly with the density, as that is the actual material that is being bought. HOWEVER, different regions have different factories close by, and raw materials. Also depending on the market conditions, like a building boom or slump, mprices vary. In my part of the world, it also varies with the tyope of marleting. Whether it is a home construction supplier, or industrial dealer. The end effect is that the price varies according to no percievable logical manner. It is sort of like acoustics, oh, it is a part of acoustics.
Andre