Why is sound absorption necessary?
Is sound absorption necessary?
Because when sound is reflected in a room without sound absorption, it can be heard by someone in a separate place as the sound overlaps, making the listener very uncomfortable.
On the other hand, in a room with too much sound absorption, it will be like talking on the prairie, and the speaker must make a very loud sound. For ceilings in spaces such as school classroom, office, conference room etc., it is important to have proper sound absorption effect to enable listeners to clearly listen to the speaker's voice, and enables the speaker to talk comfortably.
Sound absorption coefficient
In order to create a comfortable living space, not only sound insulation, we must not forget sound absorption.
Sound absorption is usually expressed by the term sound absorption coefficient.
In other words, it refers to the ratio between the sound produced towards the wall (incident sound) and the sound that does not bounce back (incident sound - reflected sound).
Therefore, no matter how the sound that does not bounce back is attenuated, it will not affect the sound absorption coefficient.
(In sound insulation, this attenuation is very important)
Sound absorbing material
Sound absorbing materials include porous type such as rock wool and resonant type such as perforated plate.
In the former, the material itself absorbs sound and it is characterized by being very soft. In the latter, sound absorption performance is imparted to what not to absorb sound by the material itself by providing innumerable holes on the surface of a hard board or the like.
Absorption principle of perforated sound absorbing board
A perforated sound absorbing material is one in which many holes with a diameter of about 5 to 15 mm are drilled in a board such as a gypsum board. When sound passes through this hole, friction occurs around the hole so sound is absorbed by thermal energy. Therefore, if there is no air layer behind the perforated plate, it will not absorb sound. Including the air layer behind it, these are called "perforated plate sound absorbing structure".
Because the hole is larger than porous sound absorbing material, it absorbs human voice with low to middle frequency range and long wavelength. Therefore, when this sound absorbing material is installed in the room, human voices become easy to hear.
