Proceedings of the Institute of Acoustics

 

Improvement of stage-to-pit balance in a small multi-purpose hall with open style pit

 

SE Jeon Pusan National University, Busan, South Korea

YH Kim Youngsan University, Yangsan, South Korea

 

1 INTRODUCTION

 

The sound quality of a music venue has a major impact on both the performers and the audience¹. This is particularly important in opera houses or classical concert halls, where natural sound is used without the use of electrical sound, and the influence of architectural sound is important². When designing an opera house, there are design criteria such as 1.3 s to 1.8 s reverberation time³, 2.5 m depth of the proscenium⁴, and ensuring acoustic/visual intimacy². Another critical design factor is the balance of sound levels between the singers on stage and the orchestra in the pit⁵.

 

In an opera house, the singers on stage and the orchestra in the pit work together to create sound. However, because the sound power levels of the singers and the orchestra are very different, it is difficult to work together if one side is too loud. Therefore, studies have been conducted on stage-pit balance to control the volume of these sounds. In the previous studies, Barron considered the appropriate range of balance to be 0.9 dB to 4.5 dB⁶ and Sato et al. suggested a range of -2.0 dB to +2.3 dB⁷. In most cases, the sound of the orchestra in the pit is much louder than that of the singer⁸.

 

It is therefore essential to control the sound of the orchestra in the pit to control this balance. Since an ordinary opera house has the shape of a covered pit, the size of the opening of this pit controls the sound of the orchestra in the pit. However, there are some cases where a small or medium-sized multipurpose hall is not large enough to accommodate a covered pit. Therefore, in the case of such a concert hall, the performance is performed without an orchestra pit, and currently, the sound of the performer is so loud that the sound of the singer is often drowned out. Figure 1 shows an example of a small multipurpose hall with an open pit for opera performances. Therefore, further research is needed to control the sound of the orchestra with architectural acoustics.

 

This paper investigates architectural treatments to improve stage-to-pit balance using computer simulation in a medium-sized multipurpose hall without an orchestra pit. A 1,500-seat hall with a poor stage-to-pit balance of -2.6 dB due to its open-style environment was selected as shown in Figure 1, and the simulation model hall was reproduced by acoustic verification based on the field measurement results. To improve the stage-to-pit balance, architectural treatments such as changing the floor material, installing pit rails, and installing reflective panels on the ceiling were considered to find the optimum shapes to improve the stage-to-pit balance.

 

 

Figure 1: Example of a small multi-purpose hall with an open-style pit for opera performances

 

2 MATERIALS AND METHODS

 

2.1 A hall with an open-style pit for simulation modelling

 

A medium-sized multi-purpose hall with an open pit was selected for simulation evaluation. The target hall was approximately 1,500 seats, with a rectangular floor plan and a second-floor rear balcony. Figure 2 shows the interior views of the target hall. Field measurements of room acoustic performance were taken to build the computer simulation model in accordance with ISO 3382-1⁹. As the measurement results, it was found that the target hall had a reverberation time (RTmid-frequency) of 1.2 s, an early decay time (EDTmid-frequency) of 1.14s, a definition (D50,mid-frequency) of 54%, a clarity (C80,3B) of 3.3 dB, a lateral energy fraction (LFE4) of 0.18 from the stage sound source. Based on the measurement results, a simulation model was built as shown in Figure 3. Acoustic fitting of the computer simulation model was performed to ensure that the just noticeable difference⁹ (JND, relative 5%) of the reverberation time was within the range of the field measurements.

 

 

Figure 2: Interior views of the target hall

 

 

Figure 3: Computer simulation model with source and receiver position

 

2.2 Measures for the stage-to-pit balance

 

The previous studies^6,7 on the stage-to-pit balance have made subjective preference judgments for combinations of different source positions to investigate the relationship between acoustic parameters and subjective preferences. The stage-to-pit balance (B) can be defined as the G value on the stage minus the G value in the pit⁷. The balance was only assessed using the average G-value, but it is considered that the area that meets the minimum balance is also important. Since the volume in the orchestra pit is inherently louder than the singers' voices on stage, the balance value is prone to negative values. However, it is also not desirable to have too much volume on stage, so previous research has suggested a range of 0.9 dB to 4.5 dB⁶ or a range of -2 dB to 2.3 dB⁷. In this study, we set the recommended range suggested by Sato et al.⁷ as the target for balance improvement. The balance value measured on-site at the target space was -2.3 dB, indicating that the orchestra's loudness was largely transmitted to the audience due to the open environment with no pit rails installed. As a result, both singers and orchestra reported acoustic difficulties when performing small scale opera in this space.

 

2.3 Setting up an open-orchestra pit based on the performer size

 

In general, the area of the opening of the covered pit and the covered area are important, but the design criteria of the open pit are different. In a covered pit, the minimum floor area of the pit should be at least 1.5 m² per musician, but in an open pit, the minimum floor area of the pit should be 1.2 m² per musician⁹. The number of performers was defined within the maximum number defined by Gade⁵. Figure 4 shows the position of the loudspeaker in the pit and on the stage, divided by size according to the number of musicians. The loudspeaker settings were placed in the center according to the size of the musician.

 

Figure 4: Orchestra pit's usage setting considering the size of the performers

 

2.4 Orchestra pit design factors

 

In this study, three architectural treatments were considered to improve the stage-to-pit balance: Add sound absorption within the orchestra area, increase pit rail height, and install a ceiling reflector with one-side sound absorption.

1. Add sound absorption - As shown in Figure 5, the sound absorption area was designated for each orchestra size, which is expected to improve balance by absorbing some of the sound of the pit.
2. Pit rail - The pit rail increases the height of the pit rail at intervals of 0.4m from 0m to 2m, and then absorbs the pit rail. This is expected to improve balance by further reducing the sound of the pit by increasing the area of the sound absorption by absorbing the floor beyond the sound absorption treatment to the wall.
3. Ceiling reflector - The ceiling reflector is thought to be sound absorbing on one side and reflecting on the other side, and it is simulated by angle, size, and position to absorb the sound of the pit and reflect the sound of the stage's vocalist to find the best condition to deliver smoothly to the auditorium, which improves the stage-to-pit balance.

 

2.5 Simulation configurations

 

Table 1 shows the simulation configurations considered in this study. For the simulation, the influencing factors were first identified by changing the floor material and pit rail height to the basis. After that, in order to further improve balance, a ceiling reflector on the upper part of the pit was installed on the 1.2 m-high pit rail that does not cover the visible line.

 

Table 1: Simulation configurations by cases (*: Visually transparent material)

 

3 RESULTS

 

3.1 Effects of pit rail height and flooring material

 

Figure 5 shows the simulation results of the pit rail height and reverberation time according to the floor finishing material by classifying them according to the size of the performer. The result expressed as hollow dots is a case where the floor inside the pit is finished with a reflective material, and the result expressed as solid dots is a case where the floor inside the pit is modified with a sound absorbing material. In the absence of pit rails, the reverberation time in the auditorium according to the stage sound source changed to about 1.2 s, and the reverberation time in the auditorium according to the pit sound source changed to 1.07 s to 1.11 s, depending on the size of the performer, and the difference was expected to be up to 0.15 s. On the other hand, the reverberation time of the case finished with a sound-absorbing material was reduced by up to 1.3 s compared to the reflective finish. 3 s compared to the case with the reflective finish, and in particular, the difference in reverberation time between the stage and the pit sound source was expected to be within 0.05 s. For the sound-absorbing finish, the effect of changes in the height of the pit rail was examined, and as the height of the pit rail increased, the reverberation time of the pit source tended to increase, especially for small player arrangements, up to 0.18 s. However, the reverberation time of the auditorium to the stage sound source did not show a significant correlation with the change in the height of the pit rail.

 

 

Figure 5: Simulated results of RT values in accordance with pit rail height and flooring material

 

Figure 6 shows the simulation results of the pit rail height and reverberation time according to the floor finishing material by classifying them according to the size of the performer. The result expressed as hollow dots is a case where the floor inside the pit is finished with a reflective material, and the result expressed as solid dots is a case where the floor inside the pit is modified with a sound absorbing material. Looking at the case finished with reflective material in the current situation, the clarity in the auditorium according to the stage sound source was changed to about 3.27 dB to 3.41 dB, and the clarity in the auditorium according to the pit sound source was predicted to be 3.33 dB depending on the size of the performer, and the difference was up to 0.08 dB. On the other hand, the enclosure finished with a reflective material reduced clarity by up to 0.9 dB compared to the enclosure with a sound-absorbing finish, and in particular, the difference in clarity between the stage and the pit source was predicted to be within 0.47 dB. For the sound-absorbing finish, the effect of changes in the height of the pit rail was examined and the Clarity of the pit source tended to increase as the height of the pit rail increased, especially for small players, up to 0.34 dB. However, the clarity of the auditorium at the stage source did not show a significant correlation with the change in the height of the pit rail.

 

 

Figure 6: Simulated results of C80 values in accordance with pit rail height and flooring material

 

Figure 7 shows the simulation results of the G-value according to the height of the pit rail and the floor finishing material by classifying them according to the size of the musician. The result expressed as hollow dots is a case where the floor inside the pit is finished with a reflective material, and the result expressed as solid dots is a case where the floor inside the pit is modified with a sound absorbing material. In the current situation where there is no pit rail, G in the auditorium according to the stage sound source is expected to be about 6.49 dB, G in the auditorium according to the pit sound source is up to 8.80 dB to 8.82 dB, and the difference is up to 0.02 dB. On the other hand, the sound absorbing enclosure reduced G by up to 2.13 dB compared to the reflective enclosure. For the sound absorbing finish, the effect of changes in the height of the pit rail was examined, and as the height ofthe pit rail increased, the G corresponding to the pit sound source tended to decrease, especially for small players, by up to 1.94 dB. However, the reverberation time of the auditorium to the stage source also decreases by 0.8 dB as the height of the pit rail changes.

 

 

Figure 7: Simulated results of G values in accordance with pit rail height and flooring material

 

Figure 8 shows the simulation results of the balance according to the height of the pit rail and the floor finishing material by classifying them according to the size of the musician. The result expressed as hollow dots is the case where the pit floor is finished with reflective material and the result expressed as solid dots is the case where the pit floor is modified with a sound-absorbing material. In the absence of a pit rail, as at present, the balance value in the case finished with reflective material is -2.3 dB. When modified with a sound-absorbing material, it can be seen that the balance value is improved to -2.1 dB to -1.9 dB. Looking at the effect of changing the height of the pit rail, it can be seen that as the height of the pit rail increases, the balance value tends to increase to 0.2 dB, especially for small player arrangements.

 

 

Figure 8: Simulated results of stage-to-pit balance in accordance with pit rail height and flooring material

 

3.2 Additional ceiling reflectors

 

After installing the pit rail up to 1.2 m so as not to disturb the visible line, an additional ceiling reflector was installed in the orchestra pit. Simulations were then carried out using height, angle, and area to find the optimum shape and position of the reflector to improve balance.

 

Figure 9 (a) shows the balance values obtained by simulating the height of the ceiling reflector. When the height of the ceiling reflector is installed closest to the pit, the value of the balance is approximately -1.4 dB, when installed at a medium height it is -1.8 dB and when installed closest to the ceiling it is -1.6 dB. This result shows that the height of the ceiling reflector has no significant correlation with the value of the balance. Figure 9 (b) shows the balance values obtained by simulating the angle of the ceiling reflector. When the angle of the ceiling reflector is 0 degrees, the balance value is -1.4 dB, when the angle is 30 degrees it is -1.6 dB, when it is 60 degrees it is -2.0 dB. It can be seen that when the angle of the ceiling reflector is flat, the balance value improves.

 

For the combination effect of the ceiling reflector, the angle was fixed at 0 degrees and the side closest to the stage was defined as zone A, the centre as zone B and the far side as zone C. As shown in Figure 10, the result is that the further away from the stage the ceiling reflector is installed, the better the balance, and especially when installed in the B+C area, the balance value increases to -0.9 dB.

 

 

Figure 9: Simulation results of the balance effect by reflector height and angle

 

Figure 10: Balance effect of reflector combination

 

Contour maps were drawn to test whether the design presented not only improved the average balance but also affected the range of areas that met the minimum balance. Figure 11 shows the contour map corresponding to each case. Case (a) is a contour map of the current state where no situation has been established. It can be seen that the area within -2.0 dB, the minimum balance standard, is very limited to the centre of the stage. Case (b) is a contour map when the pit rail is installed at 1.2m, which is the height of the visible line. It can be seen that the area belonging to -2.0 dB, the minimum standard of balance, has expanded a lot compared to case (a), but it seems that the optimum balance has not yet been achieved in the part close to the stage. Case (c) is a contour map where a ceiling reflector is installed in a B+C area where a pit rail is installed. It can be seen that the part that meets the minimum balance standard of -2.0 dB has become so wide that it occupies most of the seats.

 

 

Figure 11: Spatial distribution of the simulated balance values in contour maps by cases

 

4 CONCLUDING REMARKS

 

This study was carried out to investigate how balance could be improved in open pits. The results showed that adding absorbent materials to the floor and pit rails, and installing pit rails, improved balance while reducing the sound of the orchestra pit. In addition, when ceiling reflectors were installed in the orchestra pit, it was found that placing them in the centre and rear of the orchestra pit was the most effective in improving balance. In addition, a contour map was drawn to see if these situations were effective in increasing the area that met the appropriate balance value, and when ceiling reflectors were installed at the centre and rear of the orchestra, most of the seats met the appropriate standards.

 

5 ACKNOWLEDGMENTS

 

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2022R1F1A1072690).

 

6 REFERENCES

 

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2. L. Beranek, Concert Halls and Opera Houses, Springer-Verlag, New York, 536-537 (2004).
3. M. Barron, The Current State of Acoustic Design of Concert Halls and Opera Houses, Acustica (2000).
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5. A. Gade, Acoustical Problems in Orchestra Pits; Causes and Possible Solutions (2001).
6. M. Barron, Auditorium acoustics and architectural design, E & FN Spon, London, 333 (1993).
7. S. Sato, N. Prodi, On the Subjective Evaluation of the Perceived Balance Between a Singer and a Piano Inside Different Theatres (2009).
8. Robin K. Mackenzie, The Acoustic Design of Partially Enclosed Orchestra Pits (1988).
9. ISO 3382-1, Acoustics — Measurement of room acoustic parameters — Part 1: Performance spaces (2009).
10. A James, Extremes, flexibility and authenticity in orchestra pit acoustics, Proc. Inst. of Acoust. 19, 137-144 (1997).