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Acoustic Application for Concert Hall

The concert hall is a building that offers musical performances. Professional concert hall was originally born in the 17th century in mainland Europe, forms the current colorful hall type after three hundred years of development and evolution. Playing and listening in the concert hall is a complex process, it is closely related to the style of the musical works, the performance level of the musician, and the space environment of the concert hall. It is this combination of the two factors of art and science that brings considerable particularity and design difficulty to the concert hall.

 

On acoustic characteristics of the concert hall, relationship between musical performance and concert hall is similar to the relationship between the musical instrument "stimulator" and "resonator". Music in the concert hall will experience the generation, propagation, mixing, reflection, absorption and other complex acoustic processes, and forms a wide range of sound effects. Therefore, another important factor for the musician's performance is the auditorium's own sound and acoustics in addition to the performance of their own skill. The acoustic design requirements of the concert hall are closely integrated with the architectural art. How to ingenious integrate music, acoustics, architectural art to create an atmosphere in which the user can perfectly enjoy the music,  a beautiful environment for listening to music is the problem must be solved in concert hall design.

 

The classification of concert hall:

Symphony hall, chamber music hall, chorus hall, solo recital hall, pipe organ concert hall.

 

Concert Hall Spatial Form Classification:

Traditional "shoebox" type concert hall, Non "shoebox" type concert hall

The traditional "shoe box" concert hall is the development and sublimation of the early music room. Its planar shape is rectangular, the proportion of space is close to 1:1:2(width: high: long), shallow balcony is provided along the side wall. Playing area and listening to music coexist in the same space, the interior decoration is elegant and gorgeous, and there are a large number of sculptures and large chandeliers.

 

The "shoe box" concert hall high and narrow space shape is also the product of the technical impact of the building structure at that time. Some well-known "shoe box" concert hall has good sound quality and beautiful architectural space, which is a good model in the history of music construction. Modern "non-shoebox" concert halls are generated in order to accommodate more listeners, create a more comfortable audio-visual environment and break through the traditional " audience" and "actor" isolated mode, and appeared in the form of circle, oval, fan, polygon and irregular and other hall forms, its design purpose is to inherit the good sound quality of the traditional "shoe box" concert hall, but also to meet the various needs of the modern concert hall.

 

Acoustic design of the concert hall

The architectural acoustics design of the concert hall is the core part of the stadium sound quality, it is also an important part of the concert hall architectural design. The sound quality formed after the complex acoustic processes of sound production, propagation, mixing, reflection and absorption are crucial for the use of music hall, and become the first factor to judge the success or failure of concert hall design. The concert hall has high sound quality standards, the main way of performing music is to play nature.  How to make full use of the limited natural sound energy, making the listener receive a loud enough, pure and beautiful sound is the ultimate goal of the acoustic design. Acoustic design of concert hall is a multidisciplinary integrated technology design. In concert hall engineering practice, the building acoustics design runs throughout the entire process from design to completion.

 

The concert hall body design

1.Make full use of the limited natural sound to make you hear loud enough.

2. To make the audience have a uniform distribution of sound intensity and good sound diffusion, avoid “dead corners”, and there is no echo, chatter echo, sound focus and room resonance and other sound quality defects.

3.The plane forms are used to facilitate the provision of auditorium strong and large coverage of early reflections

4.The plane form use the early reflections which are conducive to provide strong enough and large coverage to the auditorium as well as late reflections. The former can increase the direct sound intensity and the current sound source width, the latter is an important condition for the audience to obtain a sense of space.

5.The stage should have a good sound diffusion, and provide musicians instant access to each other.

 

Determination and control of reverberation time:

Reverberation time is an important acoustic indicator after the sound pressure level (volume). It is closely related to the volume of the hall. The larger the hall volume, the longer reverberation time, on the contrary, the reverberation time is shorter. Different works of music or similar music also has its own requirements for reverberation time (Table 1). Concert hall requires long reverb, and chamber music slightly lower, the chorus, solos and recitations further lower.

 

Table 1: the reverberation time requirements of different musical works 

reverberation time requirements of different musical works.png

In order that the concert hall achieves the design-expected best reverberation time, in addition to guaranteeing good reverberation frequency characteristics, we should also pay attention to the following questions:

1.Reasonably determine the volume of each concert hall: The volume of the concert hall is based on the type of music performance, generally controlled at 6-10m³/ seat is appropriate.

2.Reduce the audience and seat sound absorption: Sound absorption of the audience and seats in the concert hall accounts for about 80% of the total absorption of the hall. Therefore, do not neglect the choice of seat when designing reverberation time control.

3.Reflector and diffuser design: The reflection is to shorten the path difference between the reflected and the direct sound, diffusion is to make a uniform sound field and a good frequency response in the hall and eliminate sound quality defects.

 

Noise and vibration control

1.Sound insulation of enclosure structure: It mainly includes wall, floor, roof and windows and doors sound insulation treatment.

2.Air conditioning system noise elimination and vibration reduction: The silencing of air conditioning system mainly refers to reducing the noise of the ventilator brings to the concert hall through pipes and the noise of air flow at inlet and outlet.

3. Soundproofing and vibration isolation of other engineering equipment: Such as elevators, generator room, as well as stage lighting machinery noise control and vibration control.

 

Theater sound design and concert hall design guidelines are the same, the difference is that the theater has a huge stage, and a orchestra pit in front. Acoustic support for actors on stage depends on the stage setting. In addition, the acoustic power of singing is far less than that of a large orchestra. So the sound quality design is more focused on the direct sound intensity and volume of the audience in terms of forms. The reason why traditional form of horseshoe-shaped multi-storey box has great vitality is just because it shortens the distance between the back seat audience and the stage, thus provides sufficient volume to the audience, which is simpler than the concert hall in the control of reverberation time and sound quality defects. This is because the theater requires a wider range of best reverberation time. It can be deemed as the best so long as it is within the range of 1.1-1.6s at fully occupied condition at medium frequency (500Hz). Therefore, it is more flexible in the choice of materials and measures for the parts negative for the sound reflection (e.g. to provide diffusers or sound absorption materials). The desired reverberation time value will not be affected by setting the sound-absorbing material or structure.

 

As there are different optimal values for the auditorium's reverberation time due to the variety of operas, and some of the current theaters are also used for musical performance, the auditorium is required to set adjustable reverberation. For example, the America Audley Theater in United States is set with lifting sound absorber and adjustable curtain device, which enlarges the scope of application of the theater. In the plane design of auditorium, the design guidelines for concert hall design are fully applicable. But in the auditorium section and stage design, we must focus on the following aspects:

 

1.The ground rise of audience hall

In the theater with natural sound performance, the height of the singing actor as a sound source on the stage is about 1.6~2.7m. The stage is usually 0.9~10m higher than the front row, the total height of about 2.5 ~ 2.7m. The rising ground slope should be determined based on the height of the sound source and the distance from the auditorium, as well as reducing the acoustic absorption (acoustic interference) of the front audiences. From the perspective of increasing the direct sound intensity, the ground rise should be much larger than the sight line design requirement ( C value), and try to shorten the distance between the sound source and the last row seats as much as possible. The theater of Beijing National Palace Museum has the highest ground rise in Beijing, thus it has better vision and strong direct sound intensity. But the rise of must also consider the convenience of passage, ceiling height and safety of seats (or balconies). A higher ground slope rise can also reduce the amount of attenuation in the pool when the sound is diffracted across the guardrail, so as to improve the density of accompany. The figure shows the comparison between the sound attenuation amounts subject to two ground slopes.

2. Ceiling design for audience halls

Theater auditorium ceiling design should solve the following problems in acoustics:

The incline of the ceilings and side walls in front of the platform provides early reflected sound to the audience in the middle of the seat area and the musicians in the orchestra pit to improve the penetrating power of singing, and evenly reflect the accompany to the entire halls and enhance the sound level at the backseats.

 

3.Back wall of audience halls

If not handled properly, the auditorium's back wall is easy to produce echo to the front of the seat area and the stage. Especially when the plane of the back wall is curved and its curvature center is in the front seat or stage, it will cause the sound aggregation and strengthen the echo. So acoustic treatment must be taken, there are three measures, that is sound absorption, diffusion and strengthen the sound level of the rear seat (through the rear inclined surface).As the reverberation time of the theater audience hall  is shorter than the concert hall, the above three measures can be selected according to decoration requirements. But if the hall uses adjustable mixing device when it is used for music performance, sound absorption measures should not be used, because it will reduce the adjustable reverberation time. In the theater, the singers on stage hope to get feedback of the sound, that is to hear the sound of the stage reflected from the rear wall, the breast board of the balconies, but the sound required to return is not an echo. Nakamura (1991) and other people consider based on a large number of experiments when the delay time is 140ms, and the first reflected sound is 25 ~ 30dB lower than the direct sound (measured by the microphone at 1.0m before the singer), sound feedback without echo can be realized. Okano (1994) conducted a similar experiment with a group of soprano singers, ask them to judge how much the sound level is allowed to reflect on the wall. For delay times of 120, 170 and 220ms (respectively equivalent to 20.5m, 28.5 and 37m away from the rear partial reflection surface), the most sensitive singer thinks the level is allowed to be below the direct sound, which are respectively 36, 38 and 42dB (measured at 1.0m before the singer). In order that the singer can get the sound feedback from the back wall the breast board of balconies, these surfaces can not be made into diffusion structure, neither can the backseat be enhanced. Only sound absorption treatment can be conducted. However, the reliable way to judge sound absorbing material (or structure) sound performance is to conduct reduced scale compensation model test.


Orchestra pit and balcony gazebo in theaters

The acoustics of the theater is to clearly distribute the music into the hall without distortion, better balance and harmony, no sound distortion. To realize good coordination between singers and the musicians, the signers must be able to hear a clear and balanced band sound, so that they can properly adjust their voice. Musicians in the orchestra pit should hear the rest of the band, not delayed by the length of the orchestra pit, musicians can also hear singing to maintain good harmony. As for visual requirements, singers and musicians can easily see the command. More importantly, musicians and singers can hear each other, open type orchestra pit has such advantages.


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