1 – INTRODUCTION
Qingdao Movie Metropolis Grand Theatre (the Grand Theatre) is located within the 400-acre Qingdao Movie Metropolis in Qingdao, the world’s largest movie and television production hub.
The Grand Theatre was purposely designed as the main venue for the proposed Qingdao International Film Festival. It is the largest movie theatre in Asia, and the only theatre in the world installed with both Dolby Atmos, and an electronic room enhancement system.
The total floor area is 24,000 m2. The auditorium seats an audience of 1970, including 1298 seats in the stalls and 672 seats in a single balcony. The auditorium is horse-shoe shape, 41m wide at the widest point, 40m long from the rear wall to the proscenium, and has an average ceiling height of 14m. The volume of the auditorium is 19990m3, which gives 10m2 per seat. The main stage is 20m x 37m and both side stages are 16m x 11.5m. The proscenium is 24m wide by 13m high to accommodate a large movie projection screen if needed.
Design and construction started in 2014, and the theatre officially opened in April 2018. Figures 1 and 2 show the interior view of the auditorium and the external view of the building.
The project is currently owned by Sunac, and was owned by Dalian Wanda Group before its completion, the former employer of the both authors. The acoustic consultant was Marshall Day Acoustics, the previous employer of the first author. The authors’ positions provide a wide and comprehensive perspective on the project.
With an emphasis on how key design decisions were made, this paper describes the solutions for key room acoustic design issues, which were:
• How to achieve variable acoustics, best for the different uses required by the Qingdao Film Festival Organisers (QDFFO)
• What the appropriate natural reverberation time should be
• How the interior was best designed to realise the required natural reverberation time
2 – KEY DECISION-MAKING PROCESSES
The design of the Grand Theatre project was heavily controlled by the project owner, which provided a full technical team, including architectural acousticians, electronic acousticians, theatre engineers, interior designers, and architects.
During the key decision-making processes, the project owner’s technical team and the acoustic consultant guided and challenged each other before reaching any conclusion that satisfied both sides. When controversies were unresolved, an expert panel was brought in. After the issue was fully discussed and investigated, the project owner’s technical team made final decisions.
The final product was thus a fusion of the efforts of both the acoustic consulting team and the project owner’s technical team.
3 – THE USES OF THE THEATRE, DEMANDED BY THE QINGDAO FILM FESTIVAL ORGANISERS
The Grand Theatre was required to host a variety of events during the festival. During the design stage, the Qingdao Film Festival Organiser (QDFFO) defined some priorities uses, and each had different acoustic requirement. The three defined priorities and their acoustic requirements were as follows:
• Cinema projection, using Dolby ATMOS, which would constitute 80% of the performances to be held in the Grand Theatre. This use required the auditorium to have a very short reverberation time producing minimum room effect, thus recorded sound can be reproduced with high fidelity
• Award ceremony, which requires a medium level of reverberation time so that high-speech intelligibility can be achieved while stimulating a participative audience
• Live orchestra performance, which requires a much longer reverberation time to give fullness of the sound, while achieving satisfying clarity, envelopment and loudness. It also required good communication across the stage
Despite the acoustic requirements for each priority being large, the QDFFO required that the Auditorium had to achieve top quality results, for all the prioritised uses.
4 – HOW TO ACHIEVE VARIABLE ACOUSTICS, BEST FOR THE PRIORITIESED USES REQUIRED BY THE QDFFO
4.1 The Architectural Method vs. the Electronic Method
Two types of methods exist to achieve variable acoustics: architectural and electronic.
The architectural method is conventional. This is to achieve variable acoustics by varying volumes within a room, such as through movable walls or ceilings, or by varying quantities of absorption within a room, such as installing retractable absorptive curtains. Two examples are the Hall one of the Sage Gateshead in the UK, and the Concert Hall of Theatres on the Bay in Singapore.
The electronic method uses an electronic room enhancement system. Its mechanism is collecting sound on stage and ambience sound in the audience, and then these components are integrated into the system processing. The processed signals are output to dozens of loudspeakers spread around the audience, and on stage, to create an acoustic field close to a natural acoustic field.
Although electronic room enhancement systems are not commonly used, they have been developed over the past 50 years by at least 14 companies, and have been installed in over 800 halls all over the world.
The acoustic consulting team and the project owner’s technical team had different preferences between the architectural and the electronic method. An expert panel forming by five prominent professionals was brought in. Among the five, four supported the electronic method, and one the architectural method.
The pros and cons of the architectural method and the electronic method given by the design teams and the expert panel are summarised in Table 1 below.
Those preferring the architectural method generally did not believe that the acoustic field generated by electronic room enhancement systems could compare with natural reverberant field. Their typical proposal was to design natural acoustics for award ceremonies that achieves 1.4s-1.6s at middle frequencies, then reducing the reverberation time for cinema projection by using a retractable curtain, and increasing the reverberation time for live orchestra performances by using a physical or electrical orchestra shell.
This strategy could not provide adequate early lateral reflections to the audience in the middle of the hall during live orchestra performances as the auditorium had to be 41m wide. This resulted from requirements for TV facilities, broadcast camera positions and the general requirements previously imposed by the theatre consultant and the client’s theatre technical team during the initial phases of the project. The sound clarity, loudness and envelopment required for orchestral performances cannot be achieved, even if the reverberation time is suitable. In addition, it would require installation of a large quantity of retractable curtains to cover the walls and ceilings for cinema projections which would be in use for 80% of time. The use of drapes and curtains would significantly affect the interior design.
The electronic method can address these problems. These were the main reasons that other professionals supported the electronic method.
4.2 Decision on Variable Acoustic Method
After a thorough investigation of the pros and cons of the two methods, the following conclusions were reached: the architectural acoustic design should suit best quality of movie projections; while an electronic room enhancement system should be used to adjust the reverberation and other acoustic parameters to suit the other two types of events.
The project owner’s technical team identified three systems which have most successful projects in recent years: Vivace by Salzbrenner Stagetec Mediagroup and BBM; Constellation by Meyer Sound; and E-coustic by LARES Associates. Through a bidding competition, Vivace won the contract.
5 – WHAT SHOULD BE THE APPROPRIATE NATURAL REVERBERATION TIME FOR SUCH A GIANT CINEMA ROOM?
5.1 Defining the Suitable Reverberation Time Criteria
For movie projection, the prime requirement is to reproduce recorded sound tracks accurately. Within reason, the reverberation characteristic of a movie theatre should be as short as practical. Excessive reverberation, results in reduced intelligibility of the dialog.
Dolby’s guidelines for Dolby stereo theatres and well recognised THX standards recommend reverberation time at 500Hz octave band for a cinema room as a function of room volume, which are reproduced in Figure 31,2. Based on the recommended curve, the suitable reverberation time for this Auditorium with a volume of 19990 m3, is approximately between 0.95s and 1.3s.
Existing venues for film festivals and ‘grand’ movie premieres exist over the world. The most famous include the 3,332-seat Dolby Theatre in Los Angeles, the 2,300-seat Grand Théâtre Lumière in Cannes, the 1,754-seat Stage Theatre am Potsdamer Platz in Berlin. Current reverberation times in these venues are not publicly available.
According to the acoustic consultant for the Dolby Theatre, it was understood the reverberation time of the Dolby Theatre was 1.1s on average across the audience. The reverberation times of many others are unknown. Some are known for not providing adequate acoustic conditions, and acoustic refurbishments have been discussed for several years.
The electronic room enhancement system suppliers also recommended that an reverberation time of 1-1.2 seconds at middle frequencies be desirable, for a 2000-seat auditorium. Therefore, the reverberation time design target was set at 1-1.2 seconds.
Dolby also recommend reverberation times at other octave bands, as a factor of reverberation time at 500Hz, that is reproduced in Figure 41. It was used as a reference to define reverberation time criteria at other frequencies.
Figure 3 – Dolby and THX recommended reverberation time at 500Hz octave band versus room volume1,2
5.2 Design Criteria
The natural room acoustic design criteria are summarised in Table 2, and the acoustic criteria for the other two types of events – when using the electronic room enhancement system – are summarised in Table 2.
6 – HOW THE INTERIOR WAS BEST DESIGNED TO REALISE THE REQUIRED NATURAL REVERBERATION TIME
6.1 The Proposed Interior Design Scheme
The aesthetic effect of the interior design scheme was determined, as shown in Figure 5, before the priorities of the uses of the auditorium were clarified. It can be seen that the design had hard-looking surfaces. To achieve a reverberation time as low as 1.0s-1.2s for such a large auditorium, a vast amount of absorptive material need to be installed. The choice of such a design imposed further constrains on the interior finishes.
6.2 Absorptive Finishes
6.2.1 Absorptive Constructions
Commonly used hard-looking absorptive constructions are perforated panels with absorption behind. The thinner the panel is, the higher the perforation rate, and thus the higher the absorption.
Perforated metals can be made very thin, with a high perforation rate, so they were preferred. However, it is difficult to form curvatures in both longitudinal and cross directions, which were proposed for the ceilings.
Glass Reinforced Gypsum (GRG) can be molded freely. Therefore, perforated GRG were used for the ceilings. GRG was also used for some side walls to form a continuous esthetic effect. Limited by the required structural strength, the thickness of GRG panels was 16mm, and the perforated rate was 19%. A chamfered pattern was integrated in the perforation (as shown in Figure 6) to maximise absorption and provide additional diffusion at high frequencies. The perforated GRG was backed with 100mm thick fibreglass at 48kg/m3 in a cavity no less than 200mm deep (side walls) or in a large ceiling plenum. Framing of panel should be at 600mm centres.
The proposed rear walls had curvature only in one direction, and perforated metal panels were used. The perforated metal is 3mm thick with perforation at 3mm diameter at 28% open area against 100mm thick fibreglass at 48kg/m3 in a cavity no less 200mm deep. Framing of panels should be at 400mm centres.
The distribution of the two types of surfaces are marked in Figure 6.
6.2.2 Absorption Coefficients of Absorptive Constructions
Absorption coefficients of the proposed absorptive constructions were first predicted using proprietary software Zorba during the design stage when test results were unavailable. The absorptive constructions were tested in a laboratory at a later stage. Figure 7 shows the testing setup in the laboratory, and the predicted and test results.
It can be seen from Figure 7 that for perforated GRG constructions, the absorption coefficients dropped rapidly above 1000Hz. Considering higher absorption provided by air and seat at high frequencies, the reduced absorption provided by perforated GRG panels above 1000Hz could be balanced.
6.3 Reflective finishes
To generate an even distributed sound field and avoid late reflections, it is important that unabsorbed sound energy is scattered. This is especially important in a highly absorptive environment.
Perforated GRG can still reflect large amounts of energy above 1000Hz, and needed to be treated. Other reflective surfaces in the Auditorium were identified as the balcony front and control room windows in the rear walls. Detailed analysis of the reflections from these surfaces were conducted assuming sound sources were located at typical locations: 1.5m above the stage in the middle of proscenium line, the centre of the projection screen, the stage-right sound system position, the centre of the stage sound system position. This resulted in recommendations to eliminate late reflections and echoes.
6.3.1 Perforated GRG ceiling
The ceiling was designed with convex curvature at both longitudinal and cross directions, which could scatter sound well, as shown in Figure 8.
6.3.2 Balcony front
The balcony front facing the stage is a concaved curve in a plan view. To avoid late reflections and focus generated by these surfaces, the profile of a double curvature in a section view was recommended as shown in Figure 9 to defuse reflections. To provide effective diffusion above middle frequencies, the curvature height of the convex curve was required to be no less than 10% of the curvature length.
6.3.3 Control room windows
Several windows were designed along a concave rear wall, which may have created echoes and focus. The windows in question were:
• The sound control room window
• The lighting control room window
• The interpreter booth windows
• The projection windows
Their locations are marked in Figure 10.
The sound control room window should open and shut. When fully open, no detrimental reflections should be created. When closed, curtains were recommended as covers.
The lighting control room has a window that will be fixed and closed. Its design does not allow curtains, due to its functions. An echo analysis (Figure 11a) showed the window needs to be tilted forwards at least 20 degrees to avoid echoes in the audience and the stage, when the sources at both left and right line array.
The Interpreter booths windows were fixed and closed and did not have curtains provided. The windows could create echoes and focus at the audience. Analysis (Figure 11b) showed the three windows on each side needed to tilt forward at least 15 degrees, and rotate vertically by 7 degrees, 5 degrees and 10 degrees respectively.
The projection windows cannot be lilted. Absorptive curtains were recommended to cover the surfaces when not in use.
(a) The lighting control room window titled forward by 20 degrees. Estimated delay time is
(b) The interpreter booth room windows titled forward by 15 degrees and rotated vertically by 7, 5 and 10 degrees. Estimated delay time is 49ms
7 – ODEON SIMULATION
Four typical source positions were used in the ODEON simulation: 1.5m above the stage in the middle of proscenium line, at the centre of the projection screen, at the stage-right sound system position, and at the centre sound system position.
The receiver positions were distributed over a grid of 1.0m x 1.0m over the theatre’s entire audience area. This meant the acoustic performances of the design were assessed for approximately every second seat in the theatre.
The predicted and measured acoustic properties of the perforated absorbers as given in Figure 7 have been used in the simulation. The predicted average values of the parameter are provided in Table 4.
The differences between occupied and unoccupied values are small – approximately 0.05s at each octave band – because audience absorption is only a moderate part of the room’s total absorption.
These small differences did not appear explicitly due to rounding to the first decimal place.
The simulation results showed little difference in the averaged values of reverberation time among the four source positions. The predicted differences between 10th and 90th percentile is within 0.1s across the frequency range.
Distribution of the Early Decay Time (EDT) at 1000Hz with source position located at the projection screen centre is provided in Figure 12 as an example. This parameter relates to the subjective perceived reverberation during running music or speech. It can be seen that the distribution of the reverberation in the Auditorium is generally homogeneous for its dimensions.
The ODEON simulation indicates that the design targets could be achieved using the proposed interior design.
8 – COMMISIONING TESTING
Commissioning testing was carried out in the Grand Theatre with the fire curtain up, in general accordance with international standard ISO 3382-1:2009 Acoustics – Measurement of room acoustic parameters – Part 1: Performance spaces. Impulse responses were recorded using a 30-second swept sine signal, played through a dodecahedral loudspeaker placed 1.5m above the stage floor. Recordings were made using a Core 4 channel Tetramic placed, at 18 positions in the stalls and 9 positions in the balcony.
The measured results are presented in Figure 13, and show the Grand Theatre meets all room acoustic design criteria.
The decay ranges of the impulse responses from 125Hz octave band were found to be satisfactory, above 45dB at all measurement positions. The decay range of the impulse responses at 63Hz octave band were 36-48dB in the stalls, and 36–38dB in balconies. The last 10dB decay at 63Hz were contaminated by the background noise level. Thus, it was expected the reverberation time at 63Hz would be shorter than the measured results, which is desirable, if a source could generate satisfactory sound level at 63Hz.
The measured reverberation times at low frequencies were lower than the predicted results by the Odeon simulation. It is probably because the assumed absorption coefficients of the seats used in the Odeon model was conservative at low frequencies.
9 – SUBJECTIVE EVALUATION
During commissioning, a survey was conducted on stage using hand-clap, and no echoes or late reflections were found. A similar survey was conducted in the audience area at stalls level. Again, no echoes or late reflections were found. The natural acoustics of the theatre sounded dry and suitable for the intended uses.
More than 20 acousticians, sound engineers and musicians were invited for a subjective evaluation. The programme included a Dolby Atmos demo, singing and a live string concert using VIVACE, and a speech and recorded music using the PA system. Some photos taken during the evaluation are shown in Figure 14.
The evaluation comments are summarised below:
• Generally, the evaluators regarded the sound quality produced by all the sound systems as excellent
• When Dolby Atmos was used, the locations of sound images were accurate, dialogues were clear, with excellent envelopment and space effect
• When VIVACE was used, the sound of both live music and singing was natural. It was convenient to switch to other modes, and performers reported good support
In summary, the auditorium provided good room acoustic environment for all the sound systems, and its design targets were achieved.
10 – ACKNOWLEDGEMENTS
The contents of this paper have been distilled from a 4-year dedicated effort by the professionals from Marshall Day Acoustics, and Dalian Wanda Group’s technical team, which the authors greatly appreciate.
11 – REFERENCES
1. Dolby laboratories Inc., Technical guidelines for Dolby stereo theatres. USA (1994).
2. Theatre Operations of Lucasfilm Ltd, THX sound system program instruction manual, architect’s and engineer’s edition. California, USA (1994).