Study on the Optimal Strategy of Campus Concert Hall——Take the

Concert Hall of Sun Yat-sen University as an Example

Chenxi Yang 1 School of Architecture, South China University of Technology, State Key Laboratory of Subtropical Building Science No. 381, Wushan Road, Guangzhou, Guangdong, 510640, China Wang Hongwei 2 South China University of Technology School of Architecture, South China University of Technology, State Key Laboratory of Subtropical Building Science No. 381, Wushan Road, Guangzhou, Guangdong, 510640, China Yang Zhang 3 South China University of Technology School of Architecture, South China University of Technology, State Key Laboratory of Subtropical Building Science No. 381, Wushan Road, Guangzhou, Guangdong, 510640, China

ABSTRACT With the increasing functional demand of universities, the construction of campus concert halls is become more common. In addition to being a venue for bands to perform, university concert halls are often used as conference halls, in particular. They not only require good music sound effects, but also have certain requirements for speech intelligibility. Using the ODEON software to simulate the design plan of the concert hall of the Zhuhai campus of Sun Yat-Sen University, it is found that the acoustic parameters in the balcony area are unsatisfactory such as uneven sound pressure level, low bass ratio and so on. In response to the shortcomings, the body shape was changed by adjusting the ceiling and adding floating cloud reflectors, so as to vary the distribution of sound field. This strategy can make the above-mentioned acoustic parameter values more evenly distributed in the concert hall and keep the speech intelligibility in the auditorium at a medium level. The above design methods can effectively guide the sound quality design of university concert halls.

1. INTRODUCTION

From the overall trend of development [1], after thousands of years of evolution, concert hall architecture mainly has two kinds of development tendencies: one is the tendency of specialization,

1 15169153358@163.com

2 wanghw@scut.edu.cn

3 z 8970667@gmail.com

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its function points to specific performance types, and has strict requirements on design quality, visual and acoustic technology, but its adaptability is not strong; The other is the tendency of multi-function. Through various means, the same viewing space can adapt to multi-function use, so as to improve the space utilization rate and save the cost. A large part of the construction demand of the latter comes from the campus, especially the university campus. According to the data of the National Statistical Bulletin on the Development of Education [2], in the past decade, the number of full-time higher edu- cation students in China has soared from about 15 million in 2002 to 31.67 million in 2011, and the number of colleges and universities has increased from 2003 to 2762, and the construction of new campuses has sprung up. As people from all walks of life pay more attention to art education, the construction of campus concert hall will be more and more.

The computer acoustic simulation of the concert hall is carried out, and a series of acoustic in- dexes as the band performance place are analyzed, so as to clarify its sound field characteristics and put forward acoustic measures, which has a high reference value for the acoustic design of modern concert hall buildings. Odeon software is based on geometric acoustics. It combines virtual sound source method and sound line tracking method to simulate the computer sound field [3], and has audible function. It has been widely used in the fields of engineering design and scientific research. Now, most studies focus on some parameters closely related to music sound quality, such as T 60 , L f , C 80 and so on. For example, Nitidara [4] studies Gamelan Bali to explore how long reverberation time is most suitable for the musical sound performance of that concert hall; Giménez [5] explored the relationship between subjective and objective parameters by issuing questionnaires to the audience at the live concert and collecting data through measurement; Kravchun [6] designed the sound quality of the concert hall according to the acoustic requirements of the pipe organ; Arau [7] briefly describes the design of a concert hall in Barcelona, focusing on the listening feelings of musicians on the stage; Gade [8] summarizes major contributions to Stage Acoustics for symphonic orchestras; Shiyuan C. et al. [9] Analyzed a concert hall with adjustable reverberation time; Jiqing W. [10] summarized some progress in the sound quality design of concert hall in recent years, such as the determination of perceived loudness, clarity and bass index of concert hall.

Given all of these, the previous studies have paid little attention to the speech intelligibility in the concert hall. The main purpose of this paper is to study how to improve the speech intelligibility of the auditorium as much as possible and make its acoustic characteristics adapt to multi-functional use by means of adjusting the body shape without damaging the effect of musical sound performance.

2. METHOD

2.1. Research Site

The Concert Hall of Zhuhai Campus of Sun Yat-sen University is mainly used as a large-scale symphony performance venue, which also has the functions of music education and conference report. The plane adopts the form of "mountain vineyard" [11], and many gradually rising low walls are formed by using auditorium with different heights to provide more lateral reflections for the audito- rium. The indoor volume is large, and the ground slope is steep. Each audience seat has a good line of sight and a high sense of space enclosure. This plane form is the product of closely combining architectural art with sound quality design, and it is also an innovation of the plane form of concert

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hall. It not only improves the capacity, but also produces a unique artistic effect in space. Final plan finalized 412 orchestra seats and 757 balcony seats. The internal volume of the hall is about 12976m³, and the volume of each seat is 10.95 m³. The first floor of the concert hall is 27.2m in its widest point, 31.2m in its longitudinal length (Figure 1(a)), and in the second floor they are 38.8m and 48.2m (Figure 1(b)). The stage is a central performance platform with a width of 23.4m, a depth of 12m and a height of 0.9m. The reverberation time of each octave in the hall [12] is shown in Table 1. In order to reduce the consumption of natural sound energy, the interior is decorated with GRG. A high degree of agreement bet ween architectural acoustics and inte rior design in form and spirit has be en achieved.

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Figure 1: Plane of Concert Hall in Zhuhai Campus of Sun Yat-sen University. (a)Orchestra floor.

(b)Balcony floor. Table 1: Recommended reverberation time design index.

Frequency/Hz 125 250 500 1000 2000 4000

Recommended Rever- beration Time Design Index T 60 /s

1.90~1.68 1.90~2.19 1.90 1.90 1.71~1.90 1.12~1.90

2.2. Structure Analysis

The indoor performance effect of the concert hall with pure natural sound performance is closely related to the reflected sound from each interface [13]. In order to reasonably organize the reflected sound, it is necessary to analyze the shape rationality of the original building scheme. In the original architectural scheme, there are arc-shaped reflection plates with a height of 7m above the stage. The angle of each plate is fixed, at the same time, the ceiling shape of the concert hall is unreasonable (Figure 2(a)), so the sound energy cannot be reflected to the auditorium area.

Figure 2: Schematic diagram of reflected sound energy of ceiling. (a) Before. (b) After. According to the above analysis, the key to improving speech intelligibility in concert hall is to increase the ratio of reflected sound energy in direct 50ms. Therefore, the shape of the ceiling in the

concert hall was reconsidered, and the fixed circular arc reflector was changed to a separate reflector [14] (Figure 2(b)). The inclination angle of each plate was designed according to the demand to di- rectionally project sound energy to the auditorium. In view of the above changes, two simulation results are obtained by using Odeon software for comparison.

2.3. Model Establishment

In order to achieve better artistic effect, the wall and ceiling of the concert hall decided to use GRG (Glass Fiber Rein forced Gypsum), a new type of inorganic composite gypsum board material added with glass fiber. The floor of the auditorium is Solid wood flooring. The floor of the perfor- mance platform is a wood floor with a cavity. According to the above materials, the corresponding sound absorption coefficient and diffusion coefficient are selected in the simulation, and the audito- rium is set to a full-field state (Table 2).

Table 2: Sound absorption coefficient of each interface.

No. Materials Octave Center Frequency (Hz) Diffusion Coefficient 125 250 500 1000 2000 4000 1 Auditorium(m 2 ) 0.39 0.51 0.72 0.72 0.61 0.58 0.65 2 Roof plasterboard 0.12 0.09 0.06 0.05 0.05 0.04 0.25 3 floating cloud reflectors 0.10 0.09 0.06 0.05 0.05 0.04 0.20 4 Stage wall 0.10 0.09 0.06 0.05 0.05 0.04 0.40 5 First floor side wall 0.10 0.09 0.06 0.05 0.05 0.04 0.30 6 First floor back wall 0.10 0.09 0.06 0.05 0.05 0.04 0.20 7 Second floor side wall 0.10 0.09 0.06 0.05 0.05 0.04 0.20 8 Second floor back wall 0.10 0.09 0.06 0.05 0.05 0.04 0.20 9 Guardrail board 0.10 0.09 0.06 0.05 0.05 0.04 0.20 10 Stage wood flooring 0.12 0.08 0.05 0.05 0.04 0.04 0.05 11 Auditorium wood flooring 0.08 0.06 0.04 0.05 0.05 0.04 0.05 12 Door 0.11 0.07 0.05 0.05 0.04 0.04 0.02 13 Window 0.20 0.10 0.06 0.03 0.03 0.02 0.02 A total of 21,756 sound rays are set in the model, and NR-20 standard is adopted for background noise. The grid is divided by 0.8 m × 0.8 m on the plane 1.20 m from the ground in the audience area., so as to simulate the distribution and change of each acoustic parameter value represented by different color blocks in the whole audience area. The architectural acoustic effect is closely related to the sound producing position, so the sound source position is selected at where the first violin performs at [15]. 3. RESULTS

3.1. Reverberation Time (T 30 ), Bass Ratio (BR) and Sound Pressure Level (SPL)

According to the computer simulation results and data of indoor sound quality, the average re- verberation time of intermediate frequency (500~1000Hz) in the concert hall of the current design is about 1.87s, which can meet the requirements of natural sound performance. As Figure 3 shown, the reverberation time is slightly reduced compared with the original design, but both of them are within the recommended range. It can be seen that the reverberation time distribution in the whole hall is

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uniform. The reverberation time in some corner areas is slightly longer, which is a normal phenome- non.

Figure 3: T 30 simulation results under full field condition . Bass ratio (BR) is subjectively related to warmth. From the simulation results shown in Table 3, it can be seen that the average bass ratio of the concert hall is 1.0, slightly lower than the recom- mended value (1.1~1.25), while it is greatly improved compared with the original design (0.8). The reason is that the reduction of reverberation time in intermediate frequency is greater than that in low frequency.

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Table 3: Simulation results of bass ratio (BR). Before After BR （ SPL ） , minimum （ dB ） 0.0 0.1 BR （ SPL ） , maximum （ dB ） 1.7 2.1 BR （ SPL ） , average （ dB ） 0.8 1.0 It can be seen from the distribution chart of sound pressure level that the sound pressure level in the orchestra is higher, while that in the balcony is lower. Through the comparison, it can be found that the maximum sound pressure level of the auditorium is obviously reduced (Table 4), and the distribution of sound pressure level is more uniform, especially in the balcony, which is the result of shape optimization.

Table 4: Auditorium sound pressure level (SPL) simulation results Before After SPL （ A ） , minimum （ dB ） 9.5 9.5 SPL （ A ） , maximum （ dB ） 24.4 18.1 SPL （ A ） , average （ dB ） 13.5 12.5

3.2. Language Articulation (D 50 ) and Speech Transmission Index (STI)

According to the simulation results of D 50 shown in Figure 4, the average values of audience area clarity are 0.43 (500Hz) and 0.44 (1000Hz). Compared with the original design, the simulation value of D 50 in auditorium area has been improved at all frequencies, which indicates that more re- flected acoustic energy will arrive within 50ms after direct sound, especially in the balcony, which is the result of shape optimization. Especially in the frequency band with relatively concentrated speech

+00 ater on 7 on Frequency (Hz)

sound [16], the value of D50 has been greatly improved, which is helpful to improve speech intelli- gibility.

Figure 4: (a) Language articulation (D 50 ) simulation results. There is a good correspondence between speech transmission index (STI) and language intelli- gibility or language clarity. Especially in educational buildings, STI is an important standard to eval- uate their sound quality [17-18]. According to the simulation results shown in Table 5, the STI of the concert hall is in the range of 0.40~0.64, with an average of 0.54. The corresponding language intel- ligibility level is medium (0.45~0.6). Compared with the results of the original design, the optimized structure makes the language intelligibility rise slightly. The numerical distribution range is more concentrated, indicating that the language intelligibility in the hall is closer, and it is not easy to have acoustic defects.

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Table 5: Simulation results of speech transmission index (STI) Before After STI, minimum 0.43 0.47 STI, maximum 0.79 0.62 STI, average 0.51 0.54 4. CONCLUSIONS

This paper simulates the concert hall of Zhuhai Campus of Sun Yat-sen University, focusing on reverberation time (T 30 ), speech articulation (D 50 ), speech transmission index (STI) and other param- eters. The simulation results show that, the hall acoustics can be optimized without changing the material by changing the form of ceiling and reflectors. The acoustic characteristics of the concert hall are that the overall reverberation time is relatively flat, the low frequency part is slightly pro- longed, and the high frequency part is slightly shortened, which conform to the general law of the concert hall reverberation time. The sound pressure level distribution of the audience reception sur- face is more uniform, indicating that the sound energy in the auditorium diffuses well. The sound pressure level is slightly lower than before, because more of the sound is reflected into the auditorium, where the absorption coefficient is higher, and the sound energy density in the hall naturally decreases. The bass ratio is higher, and the music sounds warm.

* . . oe * faa Frequency (Hz)

STI and D50 is closely related to language intelligibility, and they are important index to evaluate whether the hall is suitable for language communication The ceiling is changed so that the balcony could receive more primary reflected sound energy and the sound energy increases within 50ms after the arrival of direct sound which leads to the improvement of the language articulation in the main frequency band (300~3400) of speech sound, just as the D 50 simulation value shows. Part of the low- frequency D 50 value is less improved might because GRG ceiling has a higher low-frequency sound absorption coefficient. STI has a more complex calculation method. Its value is used to describe the difference between the original signal and the received signal. Simulation results show that STI value is in the middle range (0.45-0.6). Too long reverberation time will damage the language intelligibility. From the reverberation time curve, the shortening of reverberation time in each frequency band is also an important factor to improve the language intelligibility, so that the initial consonants and finals heard by the audience become clearer and the language intelligibility is higher.

At present, most of the research methods of campus concert halls in China are still based on the traditional concert hall sound quality design. In order to obtain better sound quality, improve the warmth of music and so on, it tends to take longer reverberation time. In the traditional sound quality design of concert halls, the index of language clarity is usually not taken into consideration. Language clarity determines whether teachers or speakers can clearly convey their ideas for places like campus concert halls that need to undertake the functions of music education and conference report. In the past, the most common way to improve language intelligibility was to control reverberation time by arranging sound absorbing materials in the hall, which was a waste of sound energy and greatly dam- aged the musical sound performance in the concert hall. This paper proposes to change the sound field distribution in the hall by optimizing the body shape, and seek a balance between language sound and music sound. The method proposed in this paper can guide the construction of a more economical and applicable campus concert hall.

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