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Multi-Functional Hall Acoustics

Building acoustic instructions of multi-purpose hall:

1. Construction overview and application requirements

The conference halls are mainly used for conferences and reports, the mini-show and film screening are also considered. The electro-acoustic form is the main form during application.

 

2. Building acoustic design related specifications:

GBJ118-88 Sound Insulation Design Code for Civil Buildings

GB/T50356-2005 Acoustical Design Code for Theater / Cinema and Multipurpose Halls

G57-2000 Theater Architectural design Code

GBJ16-37 Architectural Fire Protection Design Code

GBJ76-84 Hall Reverberation Time Measurement Code


3. Lecture Hall Architectural Acoustics Design Guidelines

The guiding principles of architectural acoustics design are as follows based on the acoustic requirements of the uses:

Reasonable interior reverberation time design;

Ensure that there is enough volume and proper voice articulation

Reasonable sound reflection diffusion design

Uniform sound field distribution and no sound quality defects that interfere with listening.

According to the above requirements, architectural acoustics design mainly includes lecture hall reverberation time control and elimination of sound defects.

 

4.Architectural Acoustics Design Indicators

According to the requirements of use, in order to ensure articulation and fullness of the voices at the conferences, based on the requirement of uses, design code requirements and the current form, the best reverberation time for this conference room is determined to be 1.0 ± 0.1 seconds (500Hz), low frequency allows 20% increase.

 

1. Existing state analysis

Sound absorption:

The wall surfaces of conference hall are treated by wooden perforated sound-absorbing panels and acoustic soft fabric covered acoustic panels, select the appropriate perforation and construction practices, the sound absorption requirements can be generally met. Based on past experience, although the wood perforated acoustic panels have better decorative effect, but the substrate is generally MDF, which releases larger formaldehyde. The taste is difficult to send out especially in some relatively closed environment, which will disturb the participants. In addition MDF are easily to deform in humid environments, and prone to corrosion in the presence of water. Thus, it is recommended to find some waterproof, environmentally friendly alternative materials. In addition, we should make the appropriate structural design according to the acoustic test report of the selected materials. The cloth covered is on the surface of fabric acoustic panels is recommended to do fire retardant treatment, the packing material should be sound-absorbing cotton wit a certain thickness and bulk density based on the acoustic requirements.

Diffusion:

The back wall of the conference hall suggests some diffuse materials, on one hand it can enhance reflected sound of the back row audience, on the other hand it can make the sound field of the entire venue more uniform to prevent interference by the back wall reflected sound on the front row audience.

Stage:

The side and back walls of the stage also undergo some sound absorption treatment. The ceiling is the acoustic ceiling to meet the needs of small size performances.

 

6.Indoor noise control

In order to create a quiet environment, noise must be controlled for the conference hall. Without of the consideration of outside noise, indoor noise level should be controlled below 35dB (A). Indoor noise comes mainly from the air conditioning vents, lighting apparatuses, seat turning noise and projector noise. Conference room air conditioning room is located at two sides on the back of the podium, Proper sound insulation measures are recommended for the air conditioner room. Use high sound insulation wall and sound insulation door, machine room equipment requires vibration damping treatment, so as not to affect the listening of the leader at the podium during normal meeting.

 

The level of background noise in the halls affects speech intelligibility and listening quality. Generally at the smallest sound level position in the hall, when the signal S / N is greater than 30dB, it will not have a significant impact on clarity; when the signal to noise ratio increases to 50dB, high-quality sound reproduction can be achieved. The average sound pressure level of the language electro-acoustic system in general halls is about 70 dB. The background noise is also the dynamic lower limit of the source component of electro-acoustic system, directly affecting the listening effect of the audience. According to the international standard noise evaluation NR curve, it is a parameter to evaluate noise annoyance and harm. The allowed noise value in various types of halls and specialized halls as well as indicators used in some halls in China according to the actual noise level and the design are mostly below NR40. To ensure adequate signal to noise ratio, on the condition that all the equipment generating noise in the conference halls are running, such as air conditioners, and controllable silicon dimming equipments, the background noise with an empty auditorium should meet the evaluation number less than or equal to NR35.

 

Sound and vibration isolation measures

Effective sound insulation and vibration isolation measures should be taken in the conference hall. The vibration isolation indicators shall be in accordance with GB3096-82 Urban Area Environmental Noise Standard: 50dBA in the daytime, 40dBA at night time, with good control on sound insulation, local noise, sound resonance, acoustic focus, sound scattering, sound diffusion and standing waves.

 

Building acoustic requirements for conference halls:

1.The sound quality in auditoriums, lecture halls and multi-purpose halls should mainly ensure he requirement of articulation. An appropriate intensity factor and uniformity are preferred throughout the halls. There should be no echo, multiple echo, chatter echo, sound focus and resonance anywhere in the audience halls, and there shall be no disturbance from equipment noise, projector room noise and environmental noise.

2.If the auditorium volume is more than 1000m³, a sound amplification system is preferred to be used, and the position of the loud speaker should be taken as the main sound source.

 

Form Design of Audience Halls:

1.When the sound source is natural sound, the plane and sectional design of the audience halls should make the early reflected sound field distribute uniformly. The delay of the early reflected sound reaching the auditorium relative to the direct sound should be less than or equal to 50ms (equivalent to 17m).

2.The volume of each seat in the audience hall is preferred to be 3.5 ~ 5.0m³/ seat. (Note: for the audience halls with proscenium mirror frame type stage, the volume shall be calculated according to the stage of the curtain line as the boundary.)

3.For the audience halls with balconies, the overhanging depth D of the gazebo should not be greater than 1.5 times 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 should be determined as per the sight difference "C", which should be equal to 120mm or above.

 

Reverberation time for audience halls:

The options of the reverberation time for the fully occupied audience halls should meet the following requirements:

1.When the frequency is within the range of 500 ~ 1000Hz, the appropriate volume of different reverberation time range showed in Figure 2 is preferred.

2.Reverberation time ratio subject to the 500 ~ 1000Hz are preferred to in accordance with Table 2.

3.The reverberation time should be estimated subject to the frequencies of 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz. The estimate values shall be two-digit valid values.

reverberation time .jpg


Reverberation time impact on the 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 is conducive to achieve sound fullness, but too long reverberation time will reduce the articulation of the sound, that is, the speech intelligibility. It is generally that the halls mainly used for language programs, the reverberation time is preferred to be shorter to improve intelligibility; for the halls used for music performance, the reverberation time may be longer as appropriate to improve the sound fullness. It is critical to have a proper length of reverberation time. For conference halls, it is generally recommended that the best reference reverberation time is 0.8 to 1.0 seconds.

 

Matters to be noted in acoustic decoration for conference halls:

There is a big difference between indoor acoustics and outdoor acoustics. As we all know, indoor sound quality is not the same as the outdoor sound effect. First, the same sound source in the room is louder than the outside, this is because the reflections produced by the interior walls act as a superposition. Secondly, indoor and outdoor sound field are different. In the open air, the farther away from the sound source, the smaller the sound is. 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 the indoor acoustics theory, the sound in the room 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, the early reflected sound within 50ms, and reverberation sound formed after various reflections of the sound waves beyond 50ms on the indoor interfaces.

1.The walls around the room are recommended to be corrugated sound absorption walls. At the same time, try to avoid all wall surfaces being at the same height, try to increase the unevenness of the overall wall surface to maximize the sound absorption. The specific method include provision of decoration patterns on the wall or carpet and other accessories on the walls.

2.Thicker and breathable carpets are recommended for the ground of the rooms. This design has a good sound absorption effect on the high frequency audio signals, so as to prevent sound feedback.

3.Prevent the top surfaces of the room from being at the same as much as possible, try to increase the unevenness of the overall roof surface. At the same time, sound-absorbing panel is preferred to be used as the main decoration materials.

4.Use thick cloth similar to velvet as the curtains, try to keep a distance of more than 15 cm away from the window to create a cavity that absorbs low frequency sound signals efficiently.

5.Choose the cloth or suede material chairs in the room. In addition, the conference table itself is a large easily overlooked sound reflector, and at present there is no good, effective solution but to minimize the surface area of the conference table, for example, to make the table round or arc shaped.

6.All sound-absorbing materials can not be the same kind. Otherwise, there might be excessive absorption sound signals in the room, leading to defect in the overall signal defects.

7.The doors and windows need to 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, as closely as possible. Use thick door with hollow filler (sound-absorbing cotton) in the construction as far as possible to prevent the sound leakage. 


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