The walls of large theaters, concert halls, and recording studios usually use sound-absorbing board materials to reduce sound reverberation. The most effective high-frequency and intermediate frequency indoor acoustic material is glass fiber, so the walls are usually filled with glass fiber cotton.

The selection of sound absorbing materials in the listening room is extremely important, greatly affecting the sound quality.

For all sound absorbing materials, the general rule is that the thicker the material, the better the low-frequency sound absorption effect. Therefore, a 1-inch thick glass fiber layer can absorb frequencies up to 500 Hz. If 2 inches thick, they can absorb frequencies up to 250Hz.

Indoor tests have also shown that high-density sound-absorbing cotton can actually form a certain degree of acoustic reflection, indicating a decrease in sound absorption effect. Therefore, when selecting materials or looking for DIY, people should refer to the product's density specifications for proper installation.