Acoustical Design of a Multi-Purpose Hall for Natural and Amplified Sound

Transcription

1 Acoustical Design of a Multi-Purpose Hall for Natural and Amplified Sound Dirun Ergin Talayman Acoustics Ltd, Istanbul, Turkey. Zerhan Yüksel Can Yıldız Technical University, Istanbul, Turkey. Summary A new 726-seat multi-purpose hall at the Yıldız Technical University in Istanbul is being designed. The hall aims to serve classical music, opera, ballet and drama as well as conferences and various performances requiring sound amplification. The seating layout of the hall is based upon the diamond shape style. Reflection patterns of the wall and ceiling panels are analyzed to create uniform sound distribution throughout the hall. For natural sound, 3D modeling and acoustical simulations with Odeon software are done for two scenarios: one for opera and ballet performances and the other for classical music concerts, besides form-oriented studies. Drama and conference activities are evaluated together with Ease and Odeon software in a third scenario for amplified sound. The first scenario includes the flytower and the orchestra pit whereas in the second scenario the orchestra pit is closed and the stage is limited with the adjustable orchestra shell. Regardless of the stage configuration, the third scenario is designed for amplified sound sources within the hall where the total absorption is increased. The studies are performed together with the architects and the sound system engineers and all of the decisions are integrated regarding different requirements. PACS no Fw, Jz 1. Introduction Multi-purpose halls are supposed to accommodate a variety of events having different architectural and acoustical requirements. Design of multipurpose halls requires reconciliation between the needs of speech and music. Acoustical design of these hall types depends mostly on the definition of the program during the architectural design stage. The increase in the variety of performances (such as concert, opera, ballet, modern dance, drama, conference, etc) that will take place in the hall limits its acoustical success. Application of the variable acoustical design and equipping the hall with appropriate sound reinforcement systems are some of the possibilities to overcome this challenge. This paper covers the room acoustics and electroacoustical design process of the multi-purpose hall in the Culture and Congress Center at the main campus of Yıldız Technical University [1]. 2. Specifications of the hall A 726-seat multi-purpose hall at Yıldız Technical University in Istanbul is being designed. The hall aims to accommodate classical music concert, opera, ballet and drama performances as well as conferences. Sound Reinforcement System (SRS) design is also aimed especially for the functions related to speech. The architectural design prepared by the project team of the hall is shown in Figure 1. The hall has architectural characteristics that will meet the basic requirements of the program like flytower, orchestra pit and movable stage. However the limited land the building will take place forced the project team to exclude or minimize some of the important architectural spaces such as back and side stages. The room volume is 15000m 3, audience area is 546m 2, stage area is 450m 2 and the orchestra pit is 40m 2. Proscenium width and height are respectively 17m and 7.5m. Maximum source-receiver distance is 32m. The last two rows are under the technical rooms, the height in this area is 3.2m.

2 3.1. Reflection pattern analyses The study is started with the reflection pattern analyses for the first and the second scenarios. Wall and ceiling panels are rearranged in compromise with the architectural design team. Figure 1. Plan and section of the hall 3. Room acoustics design Room acoustics design of the hall is started after the basic architectural design of the hall was completed. After the initial examination of the acoustics of the original design, three scenarios based on concert, opera, ballet, musical, drama and conference are considered as shown in Table I and Figure 2. The sound reinforcement system is planned to be passive in the first and the second scenarios whereas it will be active on the third one. The flytower and the orchestra pit are open at the first scenario whereas they are closed in the second one with the orchestra shell as presented in Figure 2. Third scenario is examined for the functions that sound reinforcement systems will be used. Table I. Scenarios based on performance types and technical requirements Scen. No Perf. Type Sound Rein. Orch. Pit 1 Opera,Ballet Musical Passive Open 2 Concert Passive Closed 3 Drama, Conf., etc. Active Closed of the reflection pattern analyses for the first scenario are shown in Figure 3. Ceiling panels are designed to send vertical reflections towards the back rows in increasing number. Lateral reflections have prominent effects on determining the acoustical characteristics of the hall, especially for music. The fact that the width of the hall is quite wide was causing shortage of the lateral reflections for the audience especially in the middle of the hall. The first two convex wall panels are designed to provide lateral reflections covering the whole of the audience area. Figure 3. Horizontal and vertical reflection patterns for the 1 st scenario (opera,ballet,musical) A reflective wooden orchestra shell is designed for the second scenario which is examined for the concert function. Horizontal and vertical reflection patterns of the orchestra shell can be seen in the plan and the section at the Figure 4. In this scenario, the surfaces of the auditorium walls and ceiling are the same as those of the first scenario. The panels of the orchestra shell are convex to support the sound diffusion. Since the orchestra shell reflects the sound energy towards the stage as well as the hall, it strengthens also ease of ensemble and support parameters important for the performers Figure 2. Schemes of use based on the performance types

3 Figure 4. Horizontal and vertical reflection patterns for 2 nd Scenario (concert) 3.2. of room acoustics parameters EDT acceptable interval is found in between 1.22 and 1.44 seconds. for C80 and LEF80 are similar to the first scenario Calculations Hall is modeled in Odeon Room Acoustics Software Version 10. The results of the main acoustic parameters and the subjective perception defined in ISO :2009 [6] are assessed following the simulation of the acoustic models. All parameters are spectrally averaged following ISO :2009 [6]. Source and receiver locations used in the simulation are shown at Figure 5. Reverberation time (RT), early decay time (EDT), clarity (C80), and lateral energy fraction (LF80) are evaluated in the process of acoustic design for musical functions. Reverberation time (T30), early decay time (EDT), definition (D50) and speech transmission index (STI) are evaluated for speech functions. The acceptable interval is of high importance for the multi-purpose halls. For that reason function, volume and the usage of sound reinforcement systems are examined. The acceptable of the room acoustics parameters are determined according to hall volumes which are 8400 m 3 for the first and the third scenarios and 5100 m 3 for the second one. For the first scenario (opera, ballet, musical) the acceptable interval for RT is decided in between 1.08 and 1.35 seconds [2,3,4]. EDT acceptable interval is found in between 0.97 and 1.22 seconds. for C80 are determined between -2dB and +4dB according to different literature [2, 5]. 0,20-0,25 range is accepted for LF80 [5]. STI is also taken into consideration for this first scenario, especially for opera performances and it should be over 60% for good intelligibility [5]. For the second scenario (concert) the acceptable interval for RT is decided in between 1.35 and 1.60 seconds [2,3,4]. Figure 5. Source (S) and receiver (R) locations used in the simulations Wooden panels having high reflectivity are used at the front part of the lateral wall surfaces and the ceiling as well as at the area around the stage, depending on the reflectivity pattern analyses given in Section 3.1. Two types of perforated wooden panels are used to reach the required absorption; the one with a high quality of absorbency in low frequencies (used in the lateral back walls) and the other having a broadband absorbency (in sloping and plane back wall surface and around the technical room panes) in order to prevent the reflection from the back wall. Perforated wooden panels having high low frequency absorbency are chosen for the surface under the technical space. The materials used in the acoustic simulation studies are shown in Figure 6. The hall is accepted as totally occupied with the audience.

4 nd Scenario (concert) 3D acoustic simulation image obtained from Odeon software is seen in the Figure 8. Figure 6. The materials used in the acoustic simulation (A:reflective wooden panel, B:low frequency absorber perforated wooden panel, C:broadband absorber perforated wooden panel) 3.4. Simulation results st Scenario (opera, ballet, musical) 3D acoustic simulation image obtained from Odeon software, showing above mentioned materials, is seen in the Figure 7. Figure 8. View from the orchestra shell (2 nd Scenario) In this scenario orchestra pit is closed, orchestra shell is placed and SRS is passive. Room acoustics parameters acceptable and the averaged of the results from the simulation are shown in Table III for the second scenario. All of the for T30, EDT, C80 and LF80 are within the acceptable intervals. Table III. Room acoustics parameters acceptable and the averaged obtained from the simulation (2 nd Scenario) Figure 7. View from the stage (1 st Scenario) Room acoustics parameters acceptable and the averaged of the results from the simulation are shown in Table II for the first scenario. for T30, EDT, D50 and LF80 are within the acceptable interval whereas clarity is a little bit above the limit. STI value is at the limit of acceptable value for the intelligibility. This means that for drama productions the support of the sound reinforcement system will be unavoidable. Table II. Room acoustics parameters acceptable and the averaged obtained from the simulation (1 st Scenario) T30 ( Hz) 1,08 1,35 1,13 EDT ( Hz) 0,97 1,22 1,03 C80(3) ( Hz) ,4 D50(3) ( Hz) >%50 0,59 LF80(4) ( Hz) 0,20 0,25 0,21 STI >%60 0,62 T30 ( Hz) 1,35 1,60 1,49 EDT ( Hz) 1,22 1,44 1,41 C80(3) ( Hz) ,6 LF80(4) ( Hz) 0,20 0,25 0,23 When compared to the first scenario, it is seen that RT is longer, EDT is closer to RT, C80 value is decreased, and LF80 is increased. Thus a better result is obtained for classical music performances. 4. Electro-acoustic design The third scenario of the study covers the functions (drama, conference, etc) that will be performed with sound reinforcement system. In this scenario, at first a shorter reverberation time is obtained through variable acoustic design approach. The studies for the selection and placement of loudspeakers are conducted in order to get a homogenous sound level and intelligibility of speech in all of the audience area. JBL Line Array Calculator II software is used for the selection of the loudspeakers. The selected loudspeakers are placed in the hall via Ease v4.3 software and the acoustic simulation of the hall is obtained.

5 4.1. Design approaches and targets For the third scenario (drama, conference, etc) the acceptable interval for RT is decided in between 0,88 and 1,08 seconds [2,3,4]. Motorized acoustic banners are placed on the reflective surfaces to diminish the reverberation time and prevent the negative effects of lateral reflections. The effect of the banners on the reverberation time is examined in the simulation through Odeon 10 software. The acceptable and the averaged of the results for T30 from the simulation are shown in Table IV for the third scenario. Table IV. and the averaged for T30 obtained from the simulation (3 rd Scenario) T30 ( Hz) 0,88 1,08 1,03 In the third scenario, within the scope of the electro-acoustic modeling, Direct Sound Pressure Level (SPL), Total Sound Pressure Level (Total SPL), Clarity (C50), Definition (D50) and Speech Transmission Index parameters are evaluated. During the design process, it is aimed to reach a direct SPL value of 90 db that is necessary for drama productions [2]. The difference range for Direct and Total Sound Pressure Level should be maximum 6dB (±3) throughout the audience area [7]. The Clarity value for speech should be positive, the Definition value should be over 50% and STI should be over 75% for very good intelligibility [5] The placement and selection of the loudspeakers While placing the loudspeakers in the hall, the wide geometry of audience area and the performance types are taken into consideration. It is presupposed that the best result will be obtained by the placement of the loudspeakers around the stage area. Left (L), center (C) and right (R) line array loudspeakers are placed over proscenium and fill loudspeakers are placed on the stage floor in order to achieve homogeneous sound level coverage and quality for the whole audience area. The locations and the aiming of the loudspeakers are shown in Figure 9. Figure 9. The locations and the aiming of the loudspeakers The designed line array loudspeaker consists of 8 components. Although it was targeted to achieve uniform sound level coverage throughout the audience area, levels were relatively lower on first to rows. In order to prevent the outcome of this case, 6 fill loudspeakers covering the whole of the audience area are located on the stage floor (Figure 9). The relationship between the line array loudspeaker layout, the audience area, the coverage areas and sound pressure levels for four octave bands is illustrated in Figure 10. It is seen that the sound pressure levels of different octave bands are close to each other except the increase in 500Hz and 1000Hz. The loudspeakers frequency response at various points of audience area is also shown at the graphic in Figure 10. It is seen that at 500 Hz and higher frequencies, the variation between different spots located in the audience line are within 5dB range. However the variation below 500 Hz between the spots increases to 10dB range. Figure 10. Line array loudspeaker design: the coverage areas for four octave bands and the frequency response at various points of audience area

6 4.3. Simulation results The selected loudspeakers are placed in the hall and the acoustic simulation of the hall is obtained through Ease v4.3 software. 3-Dimensional acoustic simulation image obtained from Ease software is illustrated in Figure 11. Figure 11. 3D image obtained from the electro-acoustic modeling (3 rd Scenario) Room acoustics parameters acceptable and the averaged obtained from the simulation are shown in Table V for the third scenario. All of the for Direct SPL, Total SPL, C50, D50 and STI are within the acceptable interval. The usage of motorized acoustic banners is prevented the possible negative impacts of reverberation on the sound reinforcement system. Table V. Room acoustics parameters acceptable and the averaged obtained from the simulation (3 rd Scenario) SPL ( Hz) difference T SPL ( Hz) difference C50(3) ( Hz) >0 7 D50(3) ( Hz) >%50 %83 STI 0,75-1,00 0,78 5. Conclusion In the study the acoustical design of a multipurpose hall is realized with respect to both room acoustics and electro-acoustic design approaches. Studies are started by the definition of the activities that will be performed in the hall. Three scenarios; the first being for opera, ballet and musical, the second for concert, and the third for drama and conference are considered on the acoustical design. The sound reinforcement system is planned to be passive in the first and the second scenarios whereas active on the third one. Appropriate formation of ceiling and wall panels are put forward via reflection pattern analyses for the first and second scenarios. Surface materials allowing acceptable of the room acoustics parameters are found with the acoustical simulations using the Odeon software. JBL Line Array Calculator II software is used for the line array loudspeaker design. After the selection of loudspeakers, their locations are determined and the acoustic simulation of the hall is obtained through Ease v4.3 software. In the design process adjustable acoustic design approaches are taken into consideration. Evaluation of the room acoustics parameters obtained from the simulations showed that in general targeted are reached for all of the scenarios. The best result is obtained for the second scenario, whereas clarity is high and low frequency RT is long for the first one. Acoustical design of the multi-functional halls is always accepted as the most challenging one. In addition to this fact, starting the acoustical design after the architectural design was completed caused extra difficulties to overcome the defects due to the geometry of the hall. Although acceptable are reached in all scenarios through the facilities of integrated design approach and variable acoustic design, this study showed once more the importance of the synchronization of architectural and acoustics design processes. References [1] D. Ergin, Z. Yüksel Can: Room Acoustics Design for Multi-purpose Hall to the Culture and Congress Center at the Main Campus of YTU. 10th National Acoustics Congress, TAKDER (2013) [2] M. Long: Architectural Acoustics. Elsevier Academic Press, Boston, [3] Z. Maekawa, J. Rindel, P. Lord: Environmental and Architectural Acoustics, Spon Press, Oxon, 2011 [4] DIN 18041: : Acoustic quality in small to medium-sized rooms. DIN, Germany, [5] M. Barron: Auditorium Acoustics and Architectural Design. Second Edition. Spon Press, Oxon, [6] ISO :2009 (E): Acoustics Measurement of room acoustic parameters Part 1: Performance spaces. ISO, Switzerland, [7] D. Templeton: Acoustics in the Built Environment Advice for the Design Team. Architectural Press, Oxford, 1997.