BS ISO 23591:2021 pdf download – Acoustic quality criteria for music rehearsal rooms and spaces
5 Criteria for rooms for music rehearsal 5.1 General Rehearsal rooms are divided by type of music (amplified, loud acoustic or quiet acoustic music) and type of ensemble (number of musicians). The division is made into individual practise rooms, small ensemble rooms, medium and large ensemble rooms. These room types are divided in accordance with different requirements as to room size (net volume, net area, net room height, room geometry), room acoustics (reverberation time, sound absorption, sound reflections) and other needs which distinguish the music types.
The division relates to whether the musicians play or sing alone (individual rehearsal or teaching), in small groups (either with the same instruments, voices or in ensemble of three to six persons) or in large groups (choir, marching band, big band, orchestra, etc.) Rehearsal uses of recital rooms are divided according to the music types; amplified, loud acoustic and quiet acoustic music.
Tables 1, 2, 3 and 4 define the criteria for properties of the different room types.
Acoustically, a music room is like an extension to the musical instrument that is being played in the room. This is particularly pronounced for singing and musical instruments without inherent reverberation, like wind instruments. Sound strength, G, and other acoustic properties of the room are crucial for the interdependence between the room and the musical instrument  . If the sound strength of the room is too low, the music will sound weak and the musician may try to compensate by forcing the playing, which may lead to harsh sound quality and decreased dynamic range of the music. On the other hand, if the sound strength is too high, the music will sound too loud and the musician may restrain their playing, which in turn will decrease the dynamic range of the music.
When acoustic response of the room works well with the instrument, good rehearsal conditions are achieved for the musician. It is important to consider sound strength, G, to reduce risk of hearing damage or hearing loss. Appropriate sound strength will assure the right quality of music rehearsal and recital as well. Informative Annex A describes the relationship between sound strength, reverberation time and net room volume. Together with sound strength, G, the main criterion used in this standard is reverberation time (see 5.7), which is a common and easily measurable parameter. However, when designing rooms for music, avoiding several other issues might be equally important; room resonances, colouration due to early reflections, flutter echoes, harshness due to playing directly towards a close, reflecting surface, positions of musicians etc. Such issues tend to be more important in small rooms.
Most of these issues can be analysed by inspection of the impulse responses, see ISO 18233  . In order to achieve a smooth frequency response in the bass range, it is desirable to have a favourable proportion between room dimensions, especially in rooms smaller than 300 m 3 . Ratios of 1:1 and 1:2 between room dimensions should be avoided. The ratio between width and length of the room should not exceed 1:1,6.
See B.2 for more guidance. Flutter echo and other echo and focusing effects (see 3.6 and 3.7) should be avoided. Within each main category of music rooms, variable acoustics may be needed. Some control of low frequency sound, either in the form of absorption, sound diffusion or scattering is necessary as well. For music rooms, the requirements to background noise given in the tables, apply. For other types of rooms and spaces whose primary purpose is not music rehearsal, requirements to background noise from service equipment stated for the different spaces or room types apply. In such rooms and spaces, every effort should be made to achieve equally good acoustic conditions as in music rooms.
NOTE 1 Flutter echo is often perceived in rooms where two parallel surfaces are reflective, with all other surfaces more absorbing. This often gives a high frequency tail of the sound decay, especially for impulsive sounds. For small distance between surfaces, this can be audible as a sound coloration. For large distance between reflective surfaces, a periodic series of echoes can be heard. The background noise from service equipment shall not exceed the tabled values for the different room types. Tonal sound of the noise, as defined in ISO/PAS 20065, shall be avoided because it is especially critical in music rooms. Background noise from other service equipment and from outside noise sources shall be subjected to special assessment. See 6.2 for requirements for background noise level. Good sound insulation between rooms is recommended, in addition to requirements for room acoustical conditions. The aim is to avoid disturbing noise from adjacent rooms and to ensure suitability and flexibility of the rooms for their desired purpose.BS ISO 23591 pdf download.