Porous Absorber

A porous absorber is any material containing interconnected air-filled pores through which sound energy is converted to heat by viscous friction and thermal exchange. Common examples include mineral wool, glass wool, acoustic foam, fabric-wrapped panels, and acoustic plaster. Porous absorbers are most effective at mid and high frequencies, with absorption increasing with thickness and with distance from the mounting surface (air gap). A general rule is that a porous absorber is effective at frequencies whose quarter-wavelength is less than the absorber thickness plus any air gap. Flow resistivity, measured per ISO 9053, is the key parameter governing performance: optimal values are typically 5,000–50,000 Pa·s/m². Porous absorbers are the most widely used type in building acoustics and form the basis of most ceiling tile, wall panel, and duct lining products.