Acoustics is an area of knowledge increasingly appreciated in contemporary design. The room size, shape, specific dimensions, textures of the walls, floor and ceiling influence the acoustics. Walls and ceilings reflect sound waves, causing them to overlap, resulting in reverberation and noise. When we talk about noise, we usually mean the loudest sounds that cause a headache, but we must remember buzz and hum can also be harmful. Long-term exposure to 60 dB sounds results in slower reaction, deterioration of concentration, mental and physical stress. Sound absorbing properties of building materials are characterized by so-called alpha reverberation coefficient of sound absorption. This coefficient takes values from 0 to 1. The sound absorption coefficient at a given frequency determines the ratio of the energy of the absorbed sound wave to the energy of the sound wave reaching a given surface. The value alpha = 1 means that the sound has been completely absorbed, while alpha = 0 means that the sound has been completely reflected. The alpha “w” index is calculated in accordance with EN ISO 11654, using the practical value of the alpha “p” absorption coefficient determined in octave bands and in standard frequency values. Sound absorption is the ability of the material to absorb acoustic energy or its part and convert it into thermal energy. This is the most important acoustic parameter because it lowers the pressure level, shortens the reverberation time and improves speech intelligibility.
|Table 1. Sound absorption classes respected by construction products in accordance with PN-EN ISO 11654|
|Class A||Class B||Class C||Class D|
Designers working over the appropriate acoustics of the concert hall, auditorium or conference room should design the interior acoustically so that some sounds could be controlled directionally, others reduced or eliminated. For example, sound absorption can be obtained by using perforated panels with round or oblong holes, in combination with properly selected mineral wool and air voids. When we want to reflect sound, we use smooth panels.