Acoustic Design of Concert Hall of Hebei Art Center of China

Summary

The Hebei Art Center was built in Shijiazhuang City, Hebei Province, covering an area of 2.4 hm2 with a total construction area of 32 000 m2, including 2,780 Acrobatic Show Halls and 980 concert halls, as well as related supporting rooms and service facilities. The concert hall is mainly for playing symphony and chamber music, and is also used for many other functions. It accommodates 980 listeners (535 stalls and 445 balconies) with an effective volume of 8500 m3, each with a volume of 8.7 m3 and a total surface area of 3368 m2. In order to adapt to the multi-functional use requirements, and each function has a good reverberation time, the concert hall adopts a adjustable sound absorption device with a combination of a cylindrical swivel and a curtain, and is distributed computer control.

The acoustic design of the concert hall begins with the physical design of the project stage, which runs through the entire process of design, construction and completion of the project to ensure the sound quality of the hall. The Art Center was built in October 1999 and opened in November 2000 after commissioning. The 7th International Acrobatic Art Festival was held here. After performing in various dramas, the concert hall generally gave high praise to the sound quality and adaptability in the hall. Figure 1 shows the exterior of the Art Center.

Acoustic design of the concert hall

The acoustic design of the concert hall includes the determination of design indicators, body shape analysis, control of reverberation time, noise control, testing and debugging of subjective and objective acoustic indicators, etc., which are described as follows:

1. Determination of acoustic design indicators

 Acoustic design indicators are determined on the basis of reference to foreign materials, combined with national conditions, listening to the opinions of relevant departments and obtaining the approval of the owners. The various acoustic design control indicators determined by the concert hall are shown in Table 1:

2. The shape design of the concert hall

The shape design is related to a series of acoustic problems such as sound diffusion, sound field distribution, frequency response, intensity and distribution of early reflection sound, loudness of the back seat and elimination of sound quality defects. Therefore, the acoustic design must enter the role at the program stage.

The plane of the Art Center Concert Hall is hexagonal, which is much more advantageous than the traditional shoe box style, which is shown in the following aspects:

① The audience is in an inverted fan-shaped plane, and the listeners in the front and middle areas have more early tendency to reflect sound than the shoe box type in the corresponding seat.

② Eliminates the echo caused by parallel walls, which is a very advantageous facility in the modern Baroque-style concert hall.

③ All the audience seats are within the projection angle of the sound source, which has good directionality and frequency response. The front half of the gallery on both sides of the traditional shoe-box concert hall is poorly oriented.

④ In the case of the same number of listeners, the distance from the back seat to the mouth is shortened. The distance from the back of the art center concert hall to the stage is only 23m, and the number of listeners in the back can be reduced.

⑤ The stage is horn-shaped, which saves area compared to the shoe box-style rectangular band, and facilitates the mutual hearing of the musicians and the spread of the harmonious music to the audience.

Through the above analysis and comparison, in the case of small capacity, the Art Center Concert Hall still does not use the traditional shoe box type, but adopts a hexagonal plane.

The cross-section design of the concert hall lowers the ceiling of the performance stage to shorten the delay gap of the early reflection of the audience in the front area. Similarly, the ball-section diffuser is suspended under the short ceiling, which makes the musicians better. The mutual hearing condition; the cone-shaped reflector in front of the mouth is mainly used to strengthen the sound level of the rear seat; in order to enhance the sound diffusion, the side wall of the hall is provided with a semi-cylindrical body and an adjustable cylindrical swivel when the reflecting surface is exposed. Also a cylinder. The flat, cross-section and interior of the concert hall are shown in Figures 2 and 4, respectively.

3. Adjustable reverberation time design [1]

A modern concert hall, whether professional or for versatile use, must be equipped with an adjustable reverberation device. The reason is very simple: First of all, different music works require their own reverberation time, in order to make each work have good reverberation time, it requires adjustable devices; secondly, in order to give full play to the efficiency of the concert hall, improve the economy. And social benefits, it is appropriate to expand the scope of its use, which is a practical issue that must be considered in the design of modern halls.For this reason, the concert hall has set up reverberation device controlled by computer.

To ensure adjustable reverberation effectiveness, follow these design guidelines:

①The adjustment structure must have sufficient variable sound absorption (sufficient adjustable area and strong sound absorption structure), and there is a similar variable sound absorption in the coverage frequency range of 125hz~4000hz;

② Variable sound absorption structure, when the reflective surface is exposed, it should have lower sound absorption for low frequency and can play the role of sound diffusion;

③Variable sound absorption structure should have easy operation, reliable performance and advanced adjustment means.

According to the above criteria, 40 rotating cylinders (800mm in diameter, semi-cylindrical sound absorption, and other semi-cylindrical reflection) and 6 variable sound absorption device combined with adjustable curtains are used in the concert hall.

4. Materials for each interface in the hall

The design of each interface material in the hall is mainly to control the reverberation, obtain good sound and eliminate the sound quality defects; the inner wall of the hall adopts the structure of the multi-layer board and the plywood; the reflective surface of the adjustable cylinder is 20mm thick pine enterprise. The plywood is attached with a plywood; the rear wall of the building is an adjustable curtain inside the wooden grille; the back wall of the pool is a sound-absorbing structure of wood, a wooden floor and an overhead wooden board, and a gypsum board ceiling.

The seats in the concert hall are the most influential sound absorbers in the concert hall. In order to reduce the sound absorption and to be as close as possible to the audiences'own sound absorption, hardwood board chairs are adopted, with only cushions and cushions as fabric.

5.Noise control

The noise control of Concert Hall includes two parts: sound insulation of enclosure structure (wall, ceiling, door and window), noise elimination and vibration reduction design of air conditioning system. The former calculates and tests the sound insulation of components to ensure that each component has the required weighted sound insulation; the latter designs the noise attenuation, vibration reduction (foundation and pipeline) and airflow restriction to ensure that the noise in the hall meets the design targets.

Acoustic measurement of the concert hall

Acoustic measurements after the completion of the concert hall, including reverberation time, sound field heterogeneity, early reflections, clarity and noise levels. It is described as follows:

1. Reverberation time (rt) determination [2]

The reverberation time is measured according to the adjustable sound absorption structure in the hall under three different sound absorption states. The results are shown in Table 2:

2.warmth (bass ratio) br

Warmth is the improvement of bass. It represents the fullness of music. It is the ratio of low-frequency reverberation to mid-frequency reverberation time, that is (empty field), the full field is 1.04.

2. The sound field unevenness is characterized by the difference between the maximum sound pressure level pmax measured in the hall and the minimum sound pressure level pmin, that is, δ lp = pmax - pmin (db), and the measurement results are shown in Table 3

4. Early reflection sound sequence determination

An important indicator of the sound quality of the concert hall In addition to the reverberation time, another indicator is the intensity and coverage of the early reflected sound, as well as the delay gap. An early reflected sound sequence within 100 ms was determined for this. The sound source uses an electric spark sounder, and the measuring point configuration is shown in Figure. 5. The reflected sound sequence is shown in Figure 7 (12 points were measured, and only 8 points are listed in order to reduce space).

Characterizing the superior and inferior condition of the reflected sound, usually using the clarity (sound energy ratio) c value, that is, the decibel value of the ratio of the early acoustic energy to the late sound field, and the time boundary of 80ms (music) and 50ms (language), namely:

When calculating, the late sound energy takes 1000ms, and the average value of c50(3)db obtained at the position of 8 measuring points is;

C80(3)=-1.26db, c50(3)= 1.41db

C80(3) is the average of 500hz, 1 000hz and 2 000hzc80 values, and c50(3) is similar.

5. Early reflection sound delay gap ti

The early reflected sound delay gap ti represents the time delay between the primary reflected sound and the direct sound. When ti is less than 20ms, the primary reflected sound has the effect of enhancing the direct sound intensity and improving the intimacy. Since the ti values of the measuring points in the hall are different, the current value of the ti in the pool is representative, and the ti value can be obtained in the range of 7 to 20 ms according to the 10 rows of reflected sound sequence diagram.

6. Rear seat loudness l

The loudness of the rear seat in the hall is only 23m from the rear seat (upstairs) to the performance stage, and the stalls is less than 20m. Therefore, the sound pressure level is greater than 80dba (peak value) when the symphony is played naturally.

7. Hall noise level n

The measured background noise in the hall is 27dba, and the air conditioner is 29.7dba.

Regarding whether there is a sound quality defect in the hall, analysis by impulse response test and sound attenuation curve shows that there is no sound quality defect in the hall. The above is the 8 items of the concert hall acoustic test.

Analysis, Evaluation and Adjustment of Acoustic Measurement Results

The measurement results of the above acoustic parameters correspond to the design indicators (see Table 1), and it can be confirmed that the design has reached the expected index. Through trials, musicians, and listeners generally believe that music has good sound quality, in which the sound is pure, the syllables are clear, the sound is round, and the bass has a good fullness. In particular, the reverberation time device is controlled by a computer, which satisfies the requirements of reverberation time for different musical works and categories (symphony, chamber music, chorus music, etc.) and gives a high evaluation. However, there are also a few music lovers and musicians who think that the middle seats in the 5th to 8th rows of the stalls are still lacking in early reflection. In this regard, the adjustment of the inclination of the suspension reflector on the stage is improved (see Figure 8).

In addition, some musicians (mainly the Hebei Symphony Orchestra) believe that if the upper limit of the adjustable reverberation in the concert hall is 1.6s (according to the experience of the Guangdong Xinghai Concert Hall: the concert hall was designed according to the requirements, The reverberation time in the hall reached 1.82s, which generally reflected that the reverberation was too long, and then adjusted to 1.65s, which was recognized. It can be upgraded to 1.7s, which will have a better effect on the symphony performance. In this regard, an improvement scheme ④ has also been made, that is, the original sound absorption structure of the back wall of the stalls is changed into a convex arc-shaped diffuser (36 m2) of 23 mm thick wood board and a carpet (80 m2) which cancels the lateral walkway of the stalls, according to calculation, The maximum reverberation time in the hall can reach 1.73s. However, the program still has different opinions (some people think that for national music, the reverberation should not be too long. In addition, Chinese musicians are not accustomed to playing in the halls with long reverberation, tending to be clear), so Not implemented yet. The design scheme is shown in Figure 9.

The Concert Hall of Hebei Art Center was completed and opened in January 2000 at the turn of the century. It has been used for more than a year and the performance of various musicals and other functions have shown that the hall has good sound quality and has very good Great adaptability. Its completion not only for Shijiazhuang City, but also for the North China , and even the country has added an elegant temple to appreciate elegant art.