Local Culture House in Utterslev Mose

Transcription

1 Technical University of Denmark Local Culture House in Utterslev Mose 2 ND semester project, DTU DTU Electrical Engineering Acoustic Technology spring 2008 Group B1 Troels Schmidt Lindgreen Kristoffer Ahrens Dickow Reynir Hilmisson

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3 Technical University of Denmark DTU Electrical Engineering Ørsteds Plads, Building Lyngby Denmark Telephone Title: Local Culture House in Utterslev Mose Course: Architectural Acoustics Project term: Spring semester 2008 Project group: B1 Participants: Troels Schmidt Lindgreen Kristoffer Ahrens Dickow Reynir Hilmisson Supervisors: Cheol-Ho Jeong & Jonas Brunskog Synopsis: In this project a simulation of a multi purpose hall was done using the room acoustical software Odeon. The work was done in collaboration with the Department of Building Engineering at DTU. The goal was to give advice on how to construct a multi purpose hall for music and speech. Aspects covered in this report are besides Odeon simulations sound insulation, subjective and objective acoustical parameters and the importance of room shape. Copies: Only distributed electronically Pages: 28 Appendices: 1 Date of completion: 26 th May 2008 No part of this report may be published in any form without the consent of the authors.

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5 Contents 1 Introduction Initial discussion Project description 3 3 Acoustic specifications Comment about noise from technical installations Starting point 7 5 Results of Odeon simulations Materials Ceiling reflector coverage Chamber music configuration EDT T C LF Strength Speech configuration STI EDT T C LF Strength Rock music configuration EDT T Sound insulation Demands by the Danish Building Legislation Recommended external noise limits by the Danish Environmental Agency Suggested solutions v

6 6.4 Sound insulation predictions made with Insul Multi Purpose Hall Smaller multi rooms Evaluation of the project Comments and conclusions Follow-up after completion of the building A Odeon procedure A1 A.1.1 From Music to Speech configuration A3 B Simulated receiver points A5 B.1 Chamber music configuration A5 B.2 Speech and rock configuration A5 C Theoretical aspects A7 C.1.1 Reverberance A8 C.1.2 Sound field energy A10 C.1.3 Strength A11 C.1.4 Clarity A11 C.1.5 Spaciousness A11 C.1.6 Timbre A12 C.1.7 From listener to performer A13 D Design of a loudspeaker system A15 E Layout of the building A17

7 May 2008 Chapter 1. Introduction Chapter 1 Introduction The aim of this project is to provide assistance to a group of 4th semester students from BYG-DTU, who are going to construct a local culture house, including a Multi Purpose Hall (MPH). Our role is to work as their consultants giving advice concerning the acoustics in this culture house. 1.1 Initial discussion Before going into detailed calculations and simulations, some discussions have to be carried out with the client. That is, how to design the hall with regards to its range of purposes. First of all, the shape and size of a music hall is of great concern. To avoid unwanted echoes, parallel walls should be discluded from the design as much as possible. Sound distribution, scattering and reflection paths are very important when designing a hall that has to offer a good sound experience. The acoustic challenge when designing a multi purpose hall is getting good sound for classical music, and at the same time making it possible to use the hall for lectures requiring a high speech intelligibility. In this project many of the geometrical aspects are predetermined by the client and thus we need to suggest (preferably minor) changes and design proper treatment for the acoustics. The client has decided the size of the hall along with most of the inside walls, seatings and balconies. Our working procedure is based on acoustic specifications, chosen on the basis of recommendations from experienced people working in the field of MPH-acoustics. The specifications are discussed with, and accepted by the client. Our goal is to get as close to these specifications as possible. The project will be lim- Page 1

8 Chapter 1. Introduction Technical University of Denmark ited by the deadline and by the ability of the client to supply AutoCAD drawings for us to work on in Odeon. Page Architectural Acoustics report

9 May 2008 Chapter 2. Project description Chapter 2 Project description The building will be used as a local culture house, and is located in Utterslev Mose, Kbh. NV. The building includes a multi purpose hall (MPH) which must be suited for persons. The size of the hall has been determined. Furthermore the building contains a foyer/bar area, three smaller multi rooms (to be used for IT, fitness, etc.) as well as a number of toilets, changing rooms, etc. The total area of the building is m 2. The client (BYG-DTU students) has asked for acoustic advice on the inside of the MPH only, and we should not be concerned with the acoustics of hall areas or smaller multi rooms. The client is not concerned with sound insulation either even though we have offered support on this area as well. In Chapter 6, a short desciption of this matter is shown. The MPH shall be used for both classical (chamber) and rhythmical music as well as for lectures, conferences and smaller theatrical performances. When being used for chamber music and some lectures/conferences (speech) the central part of the floor will be sloped seatings, whereas this will be removed and the floor will be flat during rock concerts and perhaps sometimes for conferences (speech, workshops,...). When the sloped seating part is removed the balconies are assumed not to be used. When being used for rock concerts or for weak speech, an amplification system will be needed. The client is aware of this, but does not consider the design of such to be part of the assignment. In Appendix D some general considerations regarding a loudspeaker system are given for the client to consider. In figure 2.1 and figure 2.2 an overview of the building site can be seen. Page 3

10 Chapter 2. Project description Technical University of Denmark Figure 2.1: Overview of the building site. From The size of the building is shown in red. Figure 2.2: Overview of the building site. Page Architectural Acoustics report

11 May 2008 Chapter 3. Acoustic specifications Chapter 3 Acoustic specifications The following parameters are defined as the specifications that must be fulfilled by the MPH. These parameters are explained in more detail in Appendix C. Reveberation time. From 1.3 seconds down to 1.0 seconds when using the sloped seatings. Preferably even lower when using the flat floor. Especially the low frequency range should be very dry for rock music and other amplified applications. Early Decay Time (EDT). From 0.9 to 1.3 seconds is recommended for a multi purpose hall this size. Clarity. For chamber music the clarity does not need to be very high and a recommended value is about 3 db. Since the room will also be used for speech, clarity needs to be high to improve speech intelligibility and is recommended to be about 10 db. Strength. Considering the hall size, the strenght should be sufficient for a wide range of purposes at values between 4 db and 10 db. Spaciousness. For chamber music a high spaciousness is good, but for theatre and speech we want to keep it a bit lower. There are two aspects of spaciousness. Apperent Source width (ASW). For Chamber music a high source width is desirable, while a low source width for speech is preferable. Listener envelopment (LEV). Also high for chamber music, but rather low for speech. Timbre. Should be medium (or changable) because the hall will be used for different purposes. Perhaps removable diffusers could be used to make the treble and bass Page 5

12 Chapter 3. Acoustic specifications Technical University of Denmark more dominant for chamber music, and bass absorbers could tone down the acoustical boost in the bass when playing amplified music like rock. Speech intelligibility. Speech should be clear and intelligible when the hall is used for conferences or lectures. Even sound distribution. The sound should be distributed evenly everywhere in the room. Stage support for musicians. The stage should support the musicians by distributing the sound from one side of the stage to the other. The stage need also support the musician by making the sound live to help creating tones Comment about noise from technical installations The client has not yet gained knowledge on how to design ventilation systems, and thus the demand of a ventilation system is removed from their assignment. In this report we will disregard any kind of noise from technical installations, since there are no such installations in the building. Page Architectural Acoustics report

13 May 2008 Chapter 4. Starting point Chapter 4 Starting point Computer simulations were made based on the client s wished regarding choice of geometry and material inside the hall. The tool used was Odeon 1 a room acoustic prediction tool. The objective was to obtain target values for the subjective parameters given by the acoustic specification. For a rock music configuration, amplification will be used and the sound will be equalized. Because of this most of the target values are not available, see table 4.1. Chamber music Speech Rock music Reverberation Time (T30) [s] Early Decay Time (EDT) [s] Clarity (C80) [db] 3 High N/A Lateral Energy Fraction (L80) 0.2 Low N/A Strength (G) [db] 10 N/A N/A Speech Transmission Index (STI) N/A 0.7 N/A Table 4.1: Target Values. There are more parameters that describe the acoustics, these are only the initial target parameters to get started on the design. Other parameters are discussed in Appendix C. Out of these target values the first thing that was looked at was the reverberance. The client s wishes was to have as much wood as possible in the interior. The floor a hard wood parquet floor was defined, but since it, during chamber music is covered by audience and sloped seats that are highly absorbant, supporting reflections has to come 1 The first problem encountered was importing the drawing supplied by the client into Odeon. The client was unable to make an importable drawing, so we ended up redrawing the model ourselves. This caused an unfortunate time delay Page 7

14 Chapter 4. Starting point Technical University of Denmark from the ceiling and the walls. The walls are defined as wood fibre with a considerable low absorption. As for the ceiling, the most satisfying material regarding absorption, is plaster board on battens. Page Architectural Acoustics report

15 May 2008 Chapter 5. Results of Odeon simulations Chapter 5 Results of Odeon simulations In this chapter, simulated results based on the specifications described in Chapter 3, are presented. The simulations are made in Odeon 9.10 using Precision setup to give the best possible simulation. Only relevant results are presented to give the best possible overview of the technical specifications of the multi purpose hall. All simulations have been calculated using receiver points to be able to present graphs with sound parameters as a function of frequency. According to the client, the balconies will only be used for chamber music. This is the reason why balconies are only simulated for the chamber music configuration. In Appendix B the simulated receiver points are shown for both configurations. The multi purpose room has a shoebox shape, and is close to symmetric with only the balconies being different in shape. This makes it easier to get a uniform distribution of sound and speech intelligibility in the room. This can be seen on figure 5.9 on page 14. Because the room has to be used for different purposes it needs to be configurable. This is done by having absorption hidden behind flipping panels which makes it possible to have different reverberation time depending on how many panels are flipped. The panels can be seen on figure 5.1. Page 9

16 Chapter 5. Results of Odeon simulations Technical University of Denmark Figure 5.1: View from stage when absorbend panels are flipped. 5.1 Materials The client would like wood on as many surfaces as possible. Because of this, different kind of wood are used in the multi purpose hall. The materials chosen are all available in Odeon The seats are simulated using lightly upholstered seats. The chosen materials can be seen in table 5.1. Part Odeon no. Material Floor 2021 Wood parket floor on concrete Stage 2020 Wooden floors Seats 909 Have the same absorption coefficient with and without people sitting, like Balconies mm wood on 40 mm studs Ceiling 2294 Plasterboards on battens with large air-space above Walls mm fibre board on laths with a cavity above 100 mm deep Doors 2466 Solid woodpanel doors Absorber mm thick mineralwood against ceiling Absorber Natural wood veneer finish with special acoustical absorption, from Table 5.1: Chosen materials for the multi purpose halls. 5.2 Ceiling reflector coverage The ceiling is used as main reflection surface. Several source positions are used in the simulation to ensure a sufficient sound distribution to every guest of the audience and anywhere on the stage no matter where the performer might stand. The final coverage is simulated and shown on figures 5.2, 5.3 and 5.4. Page Architectural Acoustics report

17 May 2008 Chapter 5. Results of Odeon simulations Figure 5.2: Refection from center of the stage. Figure 5.3: Refection from front side of the stage. Figure 5.4: Refection from back side of the stage. 5.3 Chamber music configuration For simulation of the configuration for chamber music, three sources where used to simulate several musicians. The audience is simulated sitting down with a general ear height of 1.2 m above the floor EDT As seen on figure 5.5, EDT is lower than desired. Yet it is acceptable within the margin of acceptance, as it is a multi purpose hall and some compromises must be accepted. Page 11

18 Chapter 5. Results of Odeon simulations Technical University of Denmark Figure 5.5: EDT for chamber music T30 As seen on figure 5.6, the simulated results for T30 with configuration for chamber music is around 1.3 seconds. The reverberation time is lower for high frequencies, but this is due to the absorption from the air, and is considered acceptable. Figure 5.6: T30 for chamber music C80 As seen on figure 5.7 the clarity is a bit too high. The specification describes 3 db, but the average simulated results are between 4 db and 5 db for C80. A way of lowering the Page Architectural Acoustics report

19 May 2008 Chapter 5. Results of Odeon simulations clarity is to make the reverberation time higher, but this is not possible given the volume of the multi purpose hall combined with the materials desired by the client. Figure 5.7: C80 for chamber music LF80 As seen on figure 5.8 the average simulated result for LF80 is 0.22 for all frequencies. The result is achieved by a combination of geometrics. Figure 5.8: LF80 for chamber music. Page 13

20 Chapter 5. Results of Odeon simulations Technical University of Denmark Strength For the chamber music configuration, the multi purpose hall has a strength of 7,1 db. This is close to the 10 db desired in the specification, and the result are acceptable. 5.4 Speech configuration For simulation of the configuration for speech, only one source was used to simulate a single speaker. The audience is simulated standing up with a general ear height of 1.8 m above the floor. Absorption panels are flipped to lower reverberation time, as seen on figure STI When flipping the panels to be absorping, simulations predict speech intelligibility expressed by means og STI as shown on figure 5.9. Every point is above 0.60 which means the speech intelligibility is classified as good. Figure 5.9: STI for speech configuration. The marked places with very high STI is due to limitations in the model of the multi purpose hall. There are no seats is the places as they are inside the balconies EDT As seen on figure 5.10, EDT is lower than desired. These results show a configuration between full absorption and no absorption. This means EDT can be changed by flipping fewer panels, hiding absorption. Page Architectural Acoustics report

21 May 2008 Chapter 5. Results of Odeon simulations Figure 5.10: EDT for speech configuration T30 As seen on figure 5.11, T30 for the speech configuration is under 1 s. This is good as there is will be less reflections, resulting in a higher clarity, and better STI. Figure 5.11: T30 for speech configuration C80 As seen on figure 5.12, clarity is around 6.5 db. This could be improved by lowering the reverberation time, but this will change other results. The clarity is a compromises, and the values are accepted. Page 15

22 Chapter 5. Results of Odeon simulations Technical University of Denmark Figure 5.12: C80 for speech configuration LF80 To improve speech intelligibility, late reflection must be kept to a minimum. As seen on figure 5.13 the values are near 0.23 which is fine. Figure 5.13: LF80 for speech configuration Strength Strength for the speech configuration is 4.4 db. This is low and could result in a need for an amplification system, depending on the speaker. The strength could be improved by using a reflector near the speaker to add early reflections. Page Architectural Acoustics report

23 May 2008 Chapter 5. Results of Odeon simulations 5.5 Rock music configuration For simulation of the configuration for rock music, three sources where used to simulate a band. The audience are simulated standing up with a general ear height of 1.8 m above the floor. Absorption panels are flipped to lower reverberation time as for the speech configuration, but there are also flipped panels on the rear part of the stage. This is to prevent sound from being reflected, and thus making it possible to control the music entirely by speakers EDT As seen on figure 5.14, EDT for the rock music configuration is very low. This is good in an amplified environment, and is further explained in Appendix D. Figure 5.14: EDT for rock music configuration T30 As seen in figure 5.15 T30 is around 0.7. This is in agreement with the specifications. Page 17

24 Chapter 5. Results of Odeon simulations Technical University of Denmark Figure 5.15: T30 for rock music configuration. Page Architectural Acoustics report

25 May 2008 Chapter 6. Sound insulation Chapter 6 Sound insulation In this chapter we consider general guidelines and recomendations concerning the sound insulation of the building. Our client is not concerned with this matter and since we have no information regarding the dimensions and materials of the building (except for the MPH of course) we will only be able to present general guidelines based on assumptions. 6.1 Demands by the Danish Building Legislation There are no specific demands by the Danish Building Legislation regarding the sound insulation in public culture houses. However, if some of the rooms are to be used for education, like teaching night-school, music or drama, there are certain limits to the sound insulation that must be fulfilled. As of February 2008 the limits are as seen in the following link: (in Danish) stk. 1 says: (Translated from Danish) Buildings and their technical installations must be designed in such a way, that sound from adjacent rooms, the technical installations of the building, or from nearby roads and railways, is limited. This must be done to an extend suitable to the planned use of the buildings, and such that those who are inside the buildings are not bothered by the sound. Reasonable demands to the acoustic environment could be as listed below. Foyer/bar area Reverberation time T s. Noise level (A-weighted) from outside, 33 db Page 19

26 Chapter 6. Sound insulation Technical University of Denmark Noise level (A-weighted) from technical installations, 30 db Absorption area, 1.2 the floor area. The suggested limits are based on on similar demands from the Danish Building Legislation regarding the acoustics in open areas in teaching environments. It can be argued that a higher reveberation time and a lower absorption area, would be acceptable for a café/bar area especially if the ceiling height is high compared to the floor area. Knowing the exact dimensions and geometrical shape of the foyer would make it possible to set up more suitable demands. Smaller multi rooms Reverberation time T s. Sound reduction index, R W 65 db (50 Hz - 5 khz). Noise level (A-weighted) from outside, 33 db Noise level (A-weighted) from technical installations, 30 db The suggested demands to the smaller multi rooms are based on similar demands from the Danish Building Legislation regarding the acoustic environment in rooms used for teaching. If the rooms are to be used for non-amplified music, like choir pratice, a higher reveberation time would be preferable. Turnable panels with absorbtion on one side and diffusion on the other could in this case be build into cupboards to make the acoustic environment changable. Multi purpose hall Based on the assumption that the sound pressure inside the MPH (during concerts) can reach levels up to 130 db, it is reasonable to demand that the weighted sound reduction index of the walls is at least 100 db and preferably even higher. Regarding the acoustic enviromment inside the MPH, demands are set and covered earlier in this report. 6.2 Recommended external noise limits by the Danish Environmental Agency As this project is a public building, there are no limitations given in the recommendations by the Danish Environmental Agency ( - in Danish). However if we should set limits to how much noise is allowed outside the building, Page Architectural Acoustics report

27 May 2008 Chapter 6. Sound insulation we could compare it to the recommended limits for industrial buildings in public recreational areas. The recommended limits are L AEq =40 db during weekdays (Monday to Friday, 7am to 6pm, and Saturday, 7am to 2pm). The rest of the week the recommended limit is maximum L AEq =35 db anywhere outside the building. Note that if tones or impulses are part of the noise, 5 db should be added to the measurements when determining the noise level. Music is not covered by this punishment. 6.3 Suggested solutions The MPH is placed inside a glass building. The surrounding area is Utterslev Mose, Kbh NV. The exact geografical placement of the building is sufficiently far from nearby roads, such that external noise from road traffic can be assumed neglectable, when considering rooms located inside the building (MPH and smaller multi rooms). Measurements carried out and presented to us by another project group, in the course 31240, Architectural Acoustics, showed that the background noise level is less than 55 db(a). The layout of the building can be seen in figure E.1, Appendix E. The geografical placement of the building site is seen in figures 2.1 and 2.2 in Chapter 2. There are no nearby neighbours, so sound emitted to nearby residential areas will not cause problems either. However if the environmental demand of 35 db outside the building must be satisfied, an acoustician should be consulted with the purpose of designing the glass facades that constitute the outer walls. It is important that the usage of the foyer is known before designing the outer walls. If the foyer will be used for smaller musical performances during nighttime (e.g. jazz-nights) the sound reduction of the glass facades must be sufficient to ensure that the limits can be kept and that people using the surrounding recreational areas are not disturbed. As mentioned earlier, we assume that there is no noise from technical installations to be considered. Foyer/bar area As suggested above, an acoustic engineer should be consulted regarding calculations concerning the glass facades. Such calculations can not be carried out without knowing more about the geometrical size and shape of the facades, and thus we shall make no attempt to do so. Treating the room with absorption can be done either by using an absorbent ceiling or by Page 21

28 Chapter 6. Sound insulation Technical University of Denmark using absorbents on the walls. Depending on the room, a combination of these two could be the best solution. Absorbents for the walls could for instance be designed as artistic paintings, such as those distributed by the Danish company AkuArt, Smaller multi rooms We advice the client to use double construction walls and 35 db DS (Danish Standard) certified doors as a minimum. If some of the multi rooms are to be used for music or other loud activities, a two-door construction should be considered. Suggestions to walls satisfying the demands set in 6.1 above, are made using the software prediction tool Insul. The results are shown in section below. In the case of ventilation ducts running through several rooms, special care should be taken in order to avoid the distribution of sound from one room to the other. It is also recommended to use seperated constructions in order to reduce the risk of flanking transmission of unwanted sound. Finally we strongly recommend that an acoustician is consulted regarding the acoustic environment inside the multi rooms, in order to make sure the rooms are suited to their uses (this should be done early in the design process to keep expenses at a minimum). Concerning the reveberation time in the smaller multi rooms, it would be possible to use either an absorbing ceiling or to use absorbant material on the walls depending on the volume and the purposes of the rooms. Changable absorbants could be built into cabinets, such that the room could be more or less reveberant depending on its use. This should only be considered in the case of using the rooms for choir practice or other non-amplified music. In most other cases it would be possible to find a suitable acoustic design without the use of changable settings. Multi purpose hall To avoid flanking transmissions we recommend that the MPH is built on a seperate foundation, and that the walls are double constructions. Furthermore the walls should have sufficient mass to provide good sound reduction in the lower frequency range, since the MPH will occationally be used for bass-heavy amplified music. Suggestions to wall constructions, based on Insul predictions are presented in section below. The entrances to the MPH should be double constructed as well. Page Architectural Acoustics report

29 May 2008 Chapter 6. Sound insulation 6.4 Sound insulation predictions made with Insul The following results have been calculated using the software tool Insul (version 6.1). The margin of error on the weighted sound reduction index R W, is ±3 db according to the software. Note that this software predicts the weighted sound reduction index, and that our demands are in terms of the apparent sound reduction index R W. The apparent sound reduction index is expected to be lower than it s non-apparent counterpart, and thus there should be a good margin from the Insul calculations down to the demands to R W. R W is calculated by the method described in ISO Predictions are made for the frequency range from 50 Hz to 5 khz, even though the reference curve used to determine the single number R W is only based on the values from 100 Hz to 3.15 khz. The broader frequency range is considered, because it is likely that the rooms will be used for music, where this frequency range gives a better description of the expected spectral content of interest. In the case of amplified music with heavy bass the lower frequencies are of great importance Multi Purpose Hall The Insul predictions regarding the walls between the foyer and the MPH are based on 300 mm concrete at both outer and inner sides of the walls. Between the concrete layers is 400 mm airspace with 300 mm mineral wool. Double steel studs at placed at every 600 mm. The construction is double to avoid sound bridges and the concrete is chosen to ensure good sound insulation at low frequencies. The result is shown in figure 6.1. The predicted sound reduction index is R W = 129 db and good sound insulation even at low frequencies is seen. Page 23

30 Chapter 6. Sound insulation Technical University of Denmark Figure 6.1: Weighted sound reduction index for the suggested MPH walls. The blue line is the predicted sound reduction index made with Insul. The red line is the reference curve used to determine the single number R W Smaller multi rooms For the smaller multi rooms two different suggestions are made. One is made using three layers of 12.5 mm gypsum board on each side of the wall. Between them is 250 mm airspace with 200 mm mineral wool. Double steel studs (no contact) are placed at every 600 mm. Again the double construction avoids sound bridges from one side of the wall to the other. The result is shown in figure 6.2. The predicted sound reduction index is R W = 77 db, but it can be seen that the sound insulation is not very high towards the lower frequencies. In figure 6.4 a drawing is shown to illustrate the construction. If better sound insulation at low frequencies is required some mass needs to be added to the construction. Therefore an alternative suggestion is considered. This construction uses three layers of 12.5 mm gypsum board on one side and 150 mm of concrete on the other. Again the two sides are seperated by 250 mm airspace with 200 mm mineral wool. Double steel studs are placed at every 600 mm. The result is shown in figure 6.3. The predicted sound reduction index in this case is R W = 89 db and better sound insulation at low frequencies is seen. Page Architectural Acoustics report

31 May 2008 Chapter 6. Sound insulation Figure 6.2: Weighted sound reduction index for the suggested walls for the smaller multi rooms. The blue line is the predicted sound reduction index made with Insul. The red line is the reference curve used to determine the single number R W. Figure 6.3: Weighted sound reduction index for the alternative suggestion regarding walls for the smaller multi rooms. The blue line is the predicted sound reduction index made with Insul. The red line is the reference curve used to determine the single number R W. Page 25

32 Chapter 6. Sound insulation Technical University of Denmark Figure 6.4: Construction drawing for suggestion no. 1 regarding the walls of the smaller multi rooms. The drawing is made ny Insul. Page Architectural Acoustics report

33 May 2008 Chapter 7. Evaluation of the project Chapter 7 Evaluation of the project In this chapter conluding thoughts on the project will be disussed. The follow-up procedure, that will be used after completion of the building will be described. 7.1 Comments and conclusions Further simulations in Odeon could be carried out in order to optimize the system of variable absorption, regarding size, shape, material and distribution, etc. It would also be advantageous to look more closely into simulations with different setups and levels of audience occupation in between the extremes. Fine tuning of different parameters in a multi purpose hall is very time consuming, and takes a lot of simulation study, and thus the results of this report are limited by the deadline. Delayed and unsufficient documentation/autocad models from the client, has been unfortunate for the time schedule of this project. In spite of these obstacles, the cooperation has been interesting and profitable for both acousticians and building engineers. 7.2 Follow-up after completion of the building In order to document the acoustics of the Multi Purpose Hall, and to ensure that the goals set in the acoustic specification are fulfilled, measurements must be carried out upon the completion of the building. Measurements must also be carried out to document that the specifications agreed upon for the other rooms are realized. If the measurements show unexpected behavior at certain frequencies, the acoustics of the MPH can be fine tuned using diffusors or absorbants. The following international standard procedures will be used: Page 27

34 Chapter 7. Evaluation of the project Technical University of Denmark ISO 3382:2000. Measurement of the reverberation time of rooms with reference to other acoustical parameters. ISO 140-4:1998. Measurement of sound insulation in buildings and of building elements. Field measurements of airborne sound insulation between rooms. ISO 717-1:1997. Rating of sound insulation in buildings and of building elements. Airborne sound insulation. Measuring the MPH using ISO-3382 methods serves two main purposes: 1. Documenting that the acoustic specifications are fulfilled. 2. Fine tuning the room, e.g. by adding diffusors and/or Helmholtz resonators. Finally it is important that the end-user is given sufficient instructions on proper use of the room and its changable acoustic configurations. Page Architectural Acoustics report

35 Project group B2 May 2008 Appendix A Odeon procedure Odeon is a good and effective tool to simulate acoustics in a concert hall. It points out obvious problems in short time, making it possible to deal with initial design flaws in an equally short time. It is possible to place yourself (visually) inside the structure, giving a better overview of the design and the possible problems that have to be solved. The initial problems of concern in this structure after importing the first model were: The view from the balconies towards the stage is bad and there are no balcony rails. The ceiling was not distributing sound well enough. The sloped floor was not optimized. The reverberation time was too low. There were no doors in the building. The design of the ceiling was not distributing the sound well enough. Reflections was solved by changing the slope and size of the ceiling panels. Starting above the stage to ensure that the musicians get a sufficient sound distribution, then moving out from the stage, adjusting the different parts of the ceiling to cover the whole area. The balconies suffered a lack of direct visual sight, and they had no rails making them very uncomfortable to use for the audience. The front balconies covered up to 1/3 of the view to the stage from the back balconies and had very little slope, resulting in no view to the stage if the seat in front of you is occupied by a person. The client was consulted and the problem was solved by making the balconies closest to the stage smaller, and raising the back end of the balconies, while providing rails on all balconies too. The front end of the balconies was lowered to almost floor level to make all balconies have a slope of around 5 degrees. This was preferred by the client, instead Page A1

36 Appendix A. Odeon procedure APPENDIKS Figure A.1: Design of ceiling reflectors of the initial design with very limited view of the stage,due to the slope of the balconies. This also removed problems with getting early reflections under the balconies considering the small room dimensions and the balconies being so close to the stage. At the same time, doors where places in agreement with the client. Note that no part of the audience is placed directly under the balconies at any time. Changes were made on the sloped floor. It was made shorter and lower giving us both advantages and disadvantages. The disadvantage making it shorter is that more rows are on the floor, and not on the sloped floor making it more difficult to see the stage. By making the sloped floor smaller in volume, the total volume inside the hall increased, improving the reverberation time. Material was changed to improve reverberation time, but the client s wished were still fulfilled as the change was done by using different kinds of wood. After finding the best wood materials, the reveberation was still to low however. The only option to get higher reverberation time was to create at larger volume by raising the ceiling by 2 meters. Only the ceiling near the stage remained in place to get early reflections to the stage and audience. Since it is a dramatic change from the original plan, the client was consulted and the suggestion was approved without problems. By raising the ceiling, the target value for the reverberation time of approximate 1.4 seconds was achieved according to Odeons global reverberation time tools, which uses Sabines formula modified with weighting using ray tracing. Page A Architectural Acoustics report

37 Project group B2 May 2008 A.1.1 From Music to Speech configuration In speech configuration, the sloped floor is removed and thus increasing the volume of the hall. This is a potential problem in sense of getting the reverberance down since the volume get higher and the seats located on the floor have are high absorbing which are no longer present. We discussed with the client how it is feasible to vary the reverberation time and reflections for a more dry configuration suitable for speech and rhythmic music. An easy and efficient way of doing this is to design turnable panels and thus changing the absorption area. Turnable panels were added on the walls and the ceiling, reducing the reflections, see figure 5.1 on page 10. This gave good results regarding the reverberation time, as can be seen in section 5.4. Page A3

38 Appendix A. Odeon procedure APPENDIKS Page A Architectural Acoustics report

39 Project group B2 May 2008 Appendix B Simulated receiver points B.1 Chamber music configuration Figure B.1: Simulated receiver points for chamber music configuration. B.2 Speech and rock configuration Figure B.2: Simulated receiver points for speech and rock configuration. Page A5

40 Appendix B. Simulated receiver points APPENDIKS Page A Architectural Acoustics report

41 Project group B2 May 2008 Appendix C Theoretical aspects After the first meeting with the client we got a better view of the project regarding subjective and objective aspects of the acoustics of the hall. This led us to sound field discussions. This chapter can be regarded as background information. A sound field in a hall is basically the direct sound and the reverberant sound (reflections). Reflections are then divided into the early reflections and late reflections. The combination of how these early and late reflections interact play a huge role in the acoustics of the hall. Indirect sound is also a part of the sound field which has to be considered. This is echo and flutter echo. Echo is sound that has been reflected with sufficient time delay, and is of a sufficiently high level to be heard as distinct from the original sound. Flutter Echo is a rapid but repetitative succession of sounds from a sound source, usually occurring as a result of multiple reflections in a space with hard, flat and parallel walls. When considering reflector design to ensure strength and spaciousness in the music performance, one has to be carefull not to design the reflecting path to long. Theory says that if the first reflected wave is stronger than the direct wave, it will be perceived at echo much easier compared to when it is weaker then the direct wave. This means that it is not wise to place a reflector too close to the audience. Another thing that is stated, is that if the reflection path is to long it also can be perceived as echo. A good combination of this reflection path is to ensure that there is no one distinct reflection but more a scattered, distributed reflections that will be equally spred in time and space. The energy of sound events arriving within 50 ms, is perceived as a single-louder-event. If this energy of sound events is separated with more than 50 ms, then it can be perceived as echo (depending on the reverberation time in the room). Clarity by definition is the ratio Page A7

42 Appendix C. Theoretical aspects APPENDIKS between the early reflected sound reaching the listener within ms of the arrival of the direct sound, integrated with the direct sound. If this sound energy within this ms is large in relation to the later arriving sound, the discreet notes in a piece of music stand apart from one another, giving music a sensation of clarity. A Short EDT provides high clarity (good for speech and rythmic music), while long reverberation time provides liveliness to music. Therefore, for a multi purpose hall as this one, the objective will be to vary the reverberation time by reducing reflections in order to get satisfying acoustical conditions for different purposes. When constructing a multi purpose hall, a carefull consideration has to be taken regarding the sound field and all the reflections. Predictions can be made with the room acoustic software Odeon. Designing good acoustics in a room involves several parameters, subjective as objective. These parameters are recognized as relevant descriptors of major aspects of the acoustics of the room. Many of these aspects are now described in an ISO standard, which involves standardization of measurement methods and many of the objective parameters. In this chapter a description of the energy parameters concerning the acoustics will be provided. Subjective Objective Description Reverberance T30, EDT Dead / Live Clarity Clarity C Muddy / clear Intelligibility Speech:STI Clear/unclear Loudness Strength G Quit / Loud Spaciousness Lateral Energy Fraction (LEF) Expansive Apperent Source Width < 100 ms: ASW Expansive Listeners Envelopement > 100 ms: LEV Constricted Timbre/Tone color Bass Ratio/ Treble Ratio Weak/loud Table C.1: Subjective and Objective Room Acoustic Parameters C.1.1 Reverberance The best known subjective room acoustic aspect is the reverberance. The objective measurement of this quantity is the reverberation time, T, which was first described hundred years ago by W. C. Sabine. By definition, it is the time it takes the sound field to decrease by 60 db in the room, after a continuous sound source has been turned off. In practice this time is often difficult to evaluate, since the background noise can be heard before the sound source has dropped 60 db. Because of this, a smaller interval of the decay curve has been introduced. A decay curve from -5 to -35 db (or -5 to -25 db) below the initial value. The Reverberation time T30 is calculated from the slope of the backwards-integrated octave Page A Architectural Acoustics report

43 Project group B2 May 2008 band curves. The slope of the decay curve is determined from the slope of the best-fit linear regression line between -5 and -35 db, obtained from the backwards-integrated decay curve. T = 2 (t 35 t 5 ) (C.1) In this equation t x denotes the time when the decay curve has decreased ti X db below the initial value,or if we let R(t) represent the squared value of the decaying sound pressure and shut off the sound source at time t = 0:. 10 log ( ) R(t x ) = XdB (C.2) R(0) An alternative measure of the reverberation time, which has turned out to be better correlated with the reverberance perceived during running speech and music, is the early decay time (EDT). This is the time it takes the decay curve to decrease from 0 to -10 db. Early Decay Time (EDT) is obtained from the initial 10 db of the backwards-integrated decay curve. EDT = 6 (t 10 ) (C.3) Figure C.1: Figure is taken from lecture notes in course Though EDT describes the reverberance better than the parameter T, T is still regarded the basic objective parameter due to its general relationship with many of the other room acoustic parameters. This relationship is mainly based on diffuse field theory, which pre- Page A9

44 Appendix C. Theoretical aspects APPENDIKS dicts the decay to be purely exponential, i.e., the distribution of the impulse response energy in time should follow an exponential function: ( ) 13, 8 h 2 (t) = A exp t T Where the constant -13.8/T is determined by the requirement that: for t=t. (C.4) ( ) 13, 8 10 log t = 60dB (C.5) T C.1.2 Sound field energy An impulse response of a room is a very powerful information. It can tell you everything no need to know about the acoustical response of the room. It contains the energy description of the sound field between two positions. Figure C.2: Figure is taken from lecture notes in course Sound Pressure Level, Clarity, Deutlichkeit and Spaciousness, which are LEF, ST early, ST late and ST total. The energy of each reflection is added to the appropriate terms in the formulas for all the energy parameters, according to its time and direction of arrival. After the response calculation, Clarity, Deutlichkeit, Centre Time, Sound Pressure Level, Lateral Energy Fraction, ST early, ST late and ST total is derived. The information achieved in the impulse response provides time of arrival and level of reflections. It tells you also how direct sound is combined with the early and late reflections. If these combinations are poorly designed, the acoustics of the room can be terrible. Page A Architectural Acoustics report

45 Project group B2 May 2008 C.1.3 Strength The sound pressure level, or the strength, describes how well the hall reinforces the sound. If the hall is to damped, then the hall is to dry and music will not sound good. G = 10 log 0 tdir 0 h 2 (t)dt h 2 10m (t)dt [db] (C.6) C.1.4 Clarity A further description of the room is the concept of clarity, i.e. the early to late arriving sound energy ratio. This describes the degree to which every detail of the performance can be perceived as opposed to everything being blurred together by late arriving, reverberant sound components. This parameter is correlated to the early-to-total sound energy ratio (Deutlichkeit,D80). D 80 = 80ms 0 0 h 2 (t)dt h 2 (t)dt (C.7) Which than gives the clarity: ( ) D 80 C 80 = 10 log [db] 1 D 80 (C.8) Clarity is a measurement of the ratio in db between the energy in the impulse response arriving before and after 80 ms. The higher the ratio, the more the early sound dominates, and the clearer the sound. Early reflections which arrive within about milliseconds are not heard as separate from the direct sounds. Rather, they tend to reinforce the direct sound. For rapidly varying sound, such as speech, the limit is around 50 ms while for slowly varying music, the limit is closer to 80 ms C.1.5 Spaciousness A subjective parameter which describes the feeling of sound arriving from many different directions,controlled by the Lateral Energy Fraction. There are two aspects of spaciousness. Apperent Source width (ASW). An impression that gives the listener a wider experience of the sound. Listener envelopment (LEV). An impression of being inside the sound. Page A11

46 Appendix C. Theoretical aspects APPENDIKS Again, these two aspects are controlled by reflections. That is, direction of incidence from the impulse response reflections. When a larger portion of the early reflections (up to 80 ms) is detected from the lateral directions, ASW increases. LEF = 80ms 5ms 80ms 0 h 2 l (t)dt h 2 (t)dt (C.9) Where h 2 l (t) is the impulse response from a figure 8 microphone, picking up the energy only from the lateral reflections, and h 2 (t) is the impulse response from an omnidirectional microphone picking up the energy from the direct sound. It is mainly the energy at low and mid frequencies that contribute to spaciousness. Consequently, LEF is normally averaged over the four octaves Hz. The higher the value of LEF, the wider the ASW. When the level of the late, lateral reflections is high, LEV gets higher. Listener envelopment seems to be determined mainly by the spatial distribution and the level of the late reflections (arriving after 80 ms). A parameter called Late Lateral Strength relating the late lateral energy to the direct sound at 10 m distance from the source has been proposed for measurement of this quality. LG = 80ms h2 l (t)dt tdir 0 h 2 10m (t)dt (C.10) A high degree of listener envelopment is produced when the sound is diffuse. One tactic to increase intimacy in a large hall is to cantilever balconies into the hall from the side wall to increase diffusion and provide lateral reflections. C.1.6 Timbre Timbre is the bass/treble ratio. This ratio determines how warm or bright the hall is. Timbre describes the degree to which the room influences the frequency balance between high, middle and low frequencies, i.e. whether the sound is harsh, bright, hollow, warm or whatever other adjective one would use to describe tonal color. BR = T 125Hz + T 250Hz T 500Hz + T 1000Hz (C.11) TR = T 2000Hz + T 4000Hz T 500Hz + T 1000Hz (C.12) Page A Architectural Acoustics report