What Is Mass Law?

- Oct 16, 2018-

There is a general rule for the sound insulation of partition walls, that is, the heavier the material (the density of the surface, or the greater the mass per unit area), the better the sound insulation effect. For a single-layer dense-density wall, the surface density increases by a factor of 6 dB, and this law is the law of mass. For double-layer gypsum board walls, the mass law plays an important role, that is, increasing the number of layers or thickness of the board can improve the sound insulation. Since the form of audible vibration of the keel double-wall system is very complicated, the embodiment of the mass law is more complicated than a simple single-wall. The sound insulation effect of the single-layer gypsum board is very poor. For example, the standard weighted sound insulation of the gypsum board of 12 mm thick and the surface density of about 10 kg/m2 is Rw=29 dB. Even if four layers of such gypsum board are stacked and the sound insulation amount is theoretically Rw can only reach 41dB. Lightweight homogeneous walls, such as gypsum blocks, aerated concrete slabs, expanded perlite slabs, lightweight perforated plates, etc., the surface density is mostly 60-100kg/m2, which is limited by the mass law, and the sound insulation quantity Rw=35- 40dB. For single-layer heavy wall, the areal density is more than 250kg/m2, such as 120 brick wall, 90 thick hollow concrete block, 100 thick concrete wall board, etc., the sound insulation Rw can reach about 45dB, and the surface density exceeds 500kg/m2. The sound insulation of 200 thick concrete walls can reach 50-55dB.

 

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