I.Building Acoustic Requirement for Conference Halls
1. The sound quality in the audience halls of the conference halls, lecture halls and multi-functional halls shall mainly meet the requirement of articulation. An adequate intensity factor and uniformity are preferred at all the places in the halls. There shall not be any defects like echo, multiple echo, flutter echo, sound focusing and resonance at any positions in the audience halls, and there shall no be any disturbance from the equipment noise, projector room noise and environmental noise.
2. If the volume of an audience hall is more than 1000m³, a sound amplification system is preferred to be used, and the positions of the loudspeaker shall be taken as the main points of sound source.
II.Form Design of Audience Halls
1. In case of natural sound as the sound source, the plan and sectional design of the audience halls shall make the early reflected sound field distribute uniformly. The delay time of early reflected sound reaching the audience halls, compared to that of direct sound, is preferred to be 50ms(equivalent to 17m) or below.
2. The volume of each seat in the audience halls if preferred to be 3.5-5.0m³/seat. (Note: for the audience halls with proscenium mirror frame type stages, the volume shall be calculated, taking the curtain line of the stage as the boundary.)
3. For the audience halls with balconies, the overhanging depth”D” of the gazebos is preferred to be not more than 1.5times the net height “H” of the lower opening of the balconies.
4. For the audience halls with mainly natural sound, the rise of each row of seats shall be determined as per the vision rise difference “C”, which is preferred to be 120mm or above.
III. Reverberation Time for Audience Halls
1. The selection of the reverberation time for the fully occupied audience halls shall meet the following requirement;
2. When the frequency is within the range of 500-1000Hz, the proper ranges of reverberation time subject to different volumes shown in Figure 1 are preferred;
3. The reverberation time ratios subject to 500-1000Hz are preferred to be in accordance with Table 1;
4. The reverberation time shall be estimated subject to the frequencies of 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz. The estimated values shall be two-digit effective values.

Figure 1

IIII. Influence of Reverberation Time on indoor Sound Quality a short reverberation time indicates a situation dominated by direct sound and early reflected sound, which can improve the voice articulation. But if the reverberation time is too short, the sound will become dry and the volume will be weakened. A long reverberation time helps to achieve fullness of the sound, but too long a reverberation time will reduce the articulation of the sound, i, e, the speech intelligibility. It is generally considered that for the halls mainly used for language programs, the reverberation time is preferred to be short as appropriate to improve the intelligibility: for the halls used for musical performances ,the reverberation time can be longer as appropriate to improve the sound fullness.It is critical to have a proper length of reverberation time. For the conference halls, the generally recommended best reverberation time for reference is 0.8-1.0s.
V. Matters to be Noted during Acoustic Decoration for Conference Halls.
        There are large differences between indoor acoustics and outdoor acoustics. As we all know, the indoor sound quality effect is no the same as the outdoor sound effect. First, with the same sound source, it is louder in an indoor environment than outdoor due to superpositon of sound as r result of reflection on the indoor wall surfaces. Secondly, the indoor sound field is different from the outdoor sound field. In the open air, the farther from the sound source, the smaller the sound will be, while in an indoor environment, there is not much difference within a certain area, because of less sound absorption and less sound energy loss as a result of reflection on the wall surfaces.
        According to indoor acoustic theories, the indoor sound is divided into direct sound, early reflected sound and reverberation sound. The sequence of these types of sound reaching the ears is as follows: direct sound first, and then early reflected sound within 50ms, and reverberation sound formed after various reflections of the sound wave beyond 50ms on the indoor interfaces.
1. The surrounding walls of the rooms are recommended to be corrugated sound absorption walls. In the meantime, prevent the wall surfaces from being at the same height ad much ad possible, and try to increase the unevenness of the overall wall surfaces to maximize the sound absorption. The specific methods include provision of decoration patterns or carpets and other accessories on the walls.
2. Thick and permeable carpets are recommended for the grounds of the rooms. Such a design has good sound absorption effect to the high frequency sound signals so as to prevent sound feedback.
3. Prevent the top surfaces of the rooms from being at the same height as much as possible, and try to increase the unevenness of the overall roof surfaces. Besides, sound absorption absorption board is preferred to be used as the main decoration material.
4. Use thick cloth similar to velvet as the curtains, and try to keep a distance of more than 15cm from the windows to create an empty space to effectively absorb the low frequency sound signals.
5. Select chairs with cloth or suede materials in the rooms. Besides, the conference table itself is a large reflector that is easily ignored. Till now, there is no effective solution but to reduce the surface area of the table, for example, to make the table to be round or circular shaped.
6. The sound absorption materials cannot be just one type. Otherwise there may be excessive absorption to one frequency sound signals in the rooms, leading to defect in the overall sound signal.
7. The doors and windows shall be thickened, as they are most possible for sound leakage. Try to use double-layer ones if possible. The doors that are often used for entry and exit shall be closed tight, better sealed. And in terms of structure, try to use the doors with packing (sound absorption cotton) to prevent sound leakage.