According to classic acoustics theory there are five requirements which, when met, result in good acoustics:
- Appropriate reverberation time depends on the size of the room. W. Furrer’s recommendations can be used in rooms which are between 200 and 20,000 cubic metres. Unless it concerns a concert hall for classical music, the reverberation time must in so as far as possible be the same throughout the entire frequency range.
- Uniform sound distribution is important in large rooms and halls, where the sound must be able to be heard equally well everywhere. It is important to take sound distribution into account in the architecture. A variation of max. ±5 dB anywhere in the room is an appropriate requirement.
- Appropriate sound level for normal conversation is 60-65 dB, and in a busy street 70-85 dB. In large gatherings, a public address system in a dampened room can be used to ensure an appropriate sound level.
- Appropriate, low background noise is one of the most important acoustic criteria – especially in concert halls and theatres. In a room, the background noise may come from technical installations or ventilation systems.
- No echo or flutter echoes must occur for the acoustics to be good. It is easy to prevent echo by installing a little sound-absorbing material on the wall.
In addition, ensuring that the sound field in the room is diffuse is another fundamental rule. This can be achieved by distributing the sound absorbers on several non-parallel surfaces, by avoiding spherical, cuboid or cylinder shapes in for the room and by using as many sound-spreading elements as possible. In addition, it must be ensured that control rooms, listening rooms and cinemas in particular are built up symmetrically around a vertical plane bisecting the central space.