A A A Volume : 44 Part : 2 Objective evaluation of multipurpose enclosures equipped with active acoustic enhancement systems - examples of halls based in Poland. Łukasz Błasiński 11 Department of Acoustics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, PolandABSTRACT From the acoustical point of view various events requires different acoustic conditions. Research on optimal acoustic parameter values that have been carried out for recent decades and the necessity to provide different acoustic solutions to events of a different type led to construction of rooms with variable acoustic conditions. In such rooms changes in parameters in multipurpose enclosures may be achieved by modifications of volume or a shape of a room as well as through the use of appropriate acoustic treatments. However, those modifications are limited and frequently insufficient due to the technical limitations. Therefore, active acoustic enhancement systems (AAES) based on signal processing and multisource redistribution of a modified signal in a room become more and more popular. Application of such systems allows adjustments of acoustic parameters required for particular performance. This paper presents results from measurements of objective parameters of multipurpose enclosures equipped with AAES. Investigated halls are located in Poland and were intentionally built or renovated as multipurpose rooms. All of those were equipped with Yamaha Active Field Control version 3 system. The measurements were performed according to ISO338-1/2 standards. In total 13 active acoustic system settings were analyzed to investigate their influence on room acoustics parameters. Keywords: room acoustics, concert hall, multipurpose hall, active acoustics system, reverberation 1. INTRODUCTIONFrom the acoustical point of view, various events require different acoustic conditions. Research on optimal acoustic parameter values have been carried out in recent decades. Optimal values of different room acoustics parameter can be found in many scientific publications [1-6]. The necessity to provide different acoustic solutions for events of a different type (e.g., symphonic concerts or speech), led to construction of rooms with variable acoustic conditions. In such rooms, changes in parameters in multipurpose enclosures may be achieved by modifications of the volume or shape of a room as well as through the use of the appropriate acoustic treatments. [7, 8]. However, one must bear in mind that those modifications are limited and frequently insufficient due to the technical constraints [9]. They also make the building costs much higher which is generally not accepted by the investors. Therefore, nowadays, active acoustic enhancement systems (AAESs) based on the signal processing and multisource redistribution of a modified signal in a room become more and more popular. Application of such systems allows for the adjustments of acoustic parameters required for particular performance [10].The earliest application of the AAES containing microphone-speaker loops which were merely to generate additional resonances and reflections were established in the 1960s [11, 12]. Enhancement of the acoustic behavior of the room can be achieved in two different ways: either by adding reflection based on the room’s natural reflection (regenerative approach) or by synthesizing reflection based on the direct sound (in-line approach). Regenerative systems use omnidirectional microphones placed over the critical distance from the sound source, regenerating natural reflections within the loops containing microphone, delay line, amplifier and speaker. In-line systems use cardioid microphones1 lukasz.blasinski@amu.edu.pl placed relatively close to the sound source and artificial reverberation engines in each system’s loop, adding artificial reverberation to original sound captured by the microphones [13, 14]. Over the years, several systems have been proposed by different manufacturers. Most recent AAES are hybrid regenerative systems with both - regenerative and in-line sections which provide a stable, natural sounding diffuse reverberation field [15].This paper is arranged as follows. Section 1 describes the aim of the research; section 2 - rooms’ acoustic parameters as well as measurement procedure. Section 3 contains the results obtained in the performed measurements. In section 4 obtained results are discussed. Section 5 presents conclusions.2. AIM OF RESEARCHThe main goal of the study was to investigate how the use of the active acoustic system affects the standard objective room acoustic parameters values. As a consequence, it would answer the question whether the use of the system can provide optimal acoustic conditions in terms of the type of performance. Four multipurpose enclosures based in: Łańcut, Wieluń, Mińsk Mazowiecki and Puławy were measured. All halls are equipped with the Acoustic Field Control version 3 system produced by Yamaha.3. METHODOLOGY OF RESEARCH3.1. Objective room acoustics parameters There are many different parameters that can be measured in a room. However, in this paper we focused on ISO standards [16, 17], thus the most common room acoustic objective parameters were chosen to analyze their values in the investigated halls as Reverberation Time (RT), Early Decay Time (EDT), Clarity (C80, C50), Definition (D50), Initial Time Delay Gap (ITDG), Center Time (Ts), Interaural Cross Correlation (IACC) and Speech Transmission Index (STI) [4, 18, 19-22].3.2. Measurement procedure According to the standard mentioned above, an omnidirectional Neotek Dodecahedron DO12-PLUS sound source with dedicated amplifier and iSEMCom EMX7150 omnidirectional microphones were used. Both the measurements and their analysis were performed using the EASERA (AFMG Technologies GmbH) software with Roland Octa Capture UA1010 interface. IACC parameter value was measured with a Neumann KU100 dummy head.In each room measurements were carried out in 4 different sound source’s positions on the stage and with one positioned directly in front of the stage. 6 measuring microphones positions were used in each room, except the room in Puławy. In Puławy separate measurements were performed for the microphones located on the ground floor and on the balcony. In total 30 sound source - microphone combinations were used to calculate the average values of the acoustic parameters for halls based in Wieluń, Mińsk Mazowiecki and Łańcut and 60 combinations of sound source – microphone were used to calculate average values of room acoustic parameters in Puławy. Exemplary map of the measurement points in Łańcut are depicted in Figure 1. Red squares represent sound source placements, while blue squares - microphone measurement points. In the other rooms similar arrangement of sources and microphones were used. During the measurements, all AAES presets were measured. Additionally, in the hall in Mińsk Mazowiecki the influence of the curtains was examined. Figure 1: Measurement points in Łańcut3.3. Measured enclosures and acoustic enhancement systems Four multipurpose halls with AFC3 system installed were examined. The halls are located in Poland in the following cities: Łańcut, Mińsk Mazowiecki, Puławy and Wieluń. Examined halls have auditoriums on a rectangular plan and the audiences are slightly inclined towards the stage. In Wieluń there is a balcony with 50 seats placed in two rows. Balcony in Puławy has a bigger surface than the audience ground floor, there are 83 seats more on the balcony than at the ground floor. All enclosures are used as multi-functional rooms, except Wieluń which is mainly a cinema. Acoustic Field Control version 3 (AFC3) by Yamaha with several presets are installed in each measured hall. Independent Early Reflection (ER) setup is also provided and may be turned off or on regardless of enhancement part of AFC3 system. In these three halls system operators cannot change the value of Reverberation Time (RT), only the prepared presets can be recalled. All the measurements were performed for each of prepared AFC3 settings with the ER module turned on. In Łańcut ready-made presets have not been prepared. The operator has two encoders at his disposal. One is for ER level control and the second is for setting RT length. Three system settings were measured in Łańcut. Respectively for 1/3, 2/3 and 3/3 of maximum values of encoders controlling both ER and RT parts of AFC3 system. There are two curtains in the hall in Mińsk Mazowiecki. One curtain can cover the back wall of the stage, the other can cover the whole space of the stage. Unfolding the curtains provides additional acoustic absorption in the room - therefore RT values of different curtain settings were also measured. The table 1 shows the number of seats and AFC3 presets in each measured enclosure. Table 1: Number of seats and AFC3 presets at the measured hallsTotalSeats in the amphitheaterSeats on the balconyAFC3 presets Łańcut 325 325 0 3seatsMińsk Mazowiecki 408 382 26 3Puławy 497 207 290 3Wieluń 320 269 51 4 4. RESULTSThis part contains the results of the measurement performed in each of the examined halls.4.1. Multipurpose venue in Łańcut Figures 1, 2 and 3 present EDT, RT20 and RT30 values obtained in Łańcut. Table 2 shows the mean values of the parameters measured in Łańcut.EDTRT202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency [Hz]AFC Off AFC v1 AFC v2 AFC v3AFC Off AFC v1 AFC v2 AFC v3Figure 1: EDT with different AFC3 setups inFigure 2: RT20 with different AFC3 setups inŁańcutŁańcutRT302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]AFC Off AFC v1 AFC v2 AFC v3Figure 3: RT30 with different AFC3 setups in Łańcut Table 2: Room acoustic parameters - ŁańcutŁańcut EDTRT20RT30C50 [dB]C80 [dB]D [dB]ITDGTs [ms] IAAC STI[s][s][s][ms]AFC3 off 0,73 0,88 0,89 4,30 7,50 0,72 6,52 42,05 0,75 0,69 AFC3 v1 0,85 1,12 1,15 3,80 6,70 0,70 47,63 0,60 0,67 AFC3 v2 0,92 1,22 1,24 3,50 6,40 0,69 50,93 0,69 0,66 AFC3 v3 0,99 1,31 1,34 3,40 6,00 0,68 54,11 0,69 0,65 4.2. Multipurpose venue in Mińsk Mazowiecki Figures 4, 5 and 6 present EDT, RT20 and RT30 values obtained in Mińsk Mazowiecki for the folded and unfolded curtains within the stage. Figures 7, 8 and 9 present EDT, RT20 and RT30 values for three different presets of AFC3 and with both curtains open. Figures 10, 11 and 12 present EDT, RT20 and RT30 values for all possible setups. Table 3 shows the mean values of the parameters measured in Mińsk Mazowiecki.EDTRT202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency [Hz]Open curtains One curtain closed Two curtains closedOpen curtains One curtain closed Two curtains closedFigure 4: EDT with different curtainsFigure 5: RT20 with different curtainspositions in Mińsk Mazowieckipositions in Mińsk MazowieckiRT302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Open curtains One curtain closed Two curtains closedFigure 6: RT30 with different curtains positions in Mińsk Mazowiecki EDTRT202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency [Hz]Open curtains ACF v3 AFC v2 AFC v1Open curtains ACF v3 AFC v2 AFCv1Figure 7:EDT with different AFC3 setups inFigure 8: RT20 with different AFC3 setups inMińsk MazowieckiMińsk MazowieckiRT302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Open curtains ACF v3 AFC v2 AFC v1Figure 9: RT30 with different AFC3 setups in Mińsk MazowieckiEDTRT202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency [Hz]Open curtains One curtain closed Two curtains closedOpen curtains One curtain closed Two curtains closedACF v3 AFC v2 AFC v1ACF v3 AFC v2 AFCv1Figure 10: EDT - all possible setups in MińskFigure 11: EDT - all possible setups in MińskMazowieckiMazowiecki RT302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Open curtains One curtain closed Two curtains closedFigure 12: RT30 - all possible setups in Mińsk MazowieckiACF v3 AFC v2 AFC v1Table 3: Room acoustic parameters - Mińsk MazowieckiMińsk Maz. EDTRT20RT30C50 [dB]C80 [dB]D [dB]ITDGTs [ms] IAAC STI[s][s][s][ms]AFC3 off,curt. open 0,83 0,91 0,90 1,50 4,80 0,58 17,98 58,86 0,71 0,64AFC 3 off, onecurt. closed 0,82 0,88 0,87 1,80 5,00 0,60 56,32 0,70 0,64AFC 3 off, twocurt. closed 0,73 0,81 0,80 3,00 6,20 0,66 48,79 0,73 0,67AFC3 v1 0,98 1,24 1,27 0,80 3,80 0,54 68,44 0,66 0,61 AFC3 v2 1,29 1,27 1,29 0,80 3,80 0,54 69,66 0,63 0,60 AFC3 v3 1,24 1,61 1,60 0,10 3,00 0,51 80,36 0,60 0,574.3. Multipurpose venue in Puławy Figures 13, 14 and 15 and Table 4 present EDT, RT20 and RT30 values obtained at the hall based in Puławy.EDTRT 202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency [Hz]AFC v3 AFC v2 AFC v1 AFC OffAFC v3 AFC v2 AFC v1 AFC OffFigure 13: EDT with different AFC3 setups inFigure 14: RT20 with different AFC3 setupsPuławyin Puławy RT 302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]AFC v3 AFC v2 AFC v1 AFC OffFigure 15: RT30 with different AFC3 setups in Puławy Table 4: Room acoustic parameters - PuławyPuławy EDTRT20RT30C50 [dB]C80 [dB]D [dB]ITDGTs [ms] IAAC STI[s][s][s][ms]AFC3 off 0,66 0,75 0,74 5,10 8,70 0,76 32,71 35,70 0,53 0,69 AFC3 v1 0,76 0,94 0,95 4,10 7,40 0,72 42,77 0,54 0,65 AFC3 v2 0,80 1,08 1,12 4,00 7,10 0,71 45,55 0,43 0,65 AFC3 v3 0,87 1,43 1,52 3,80 6,80 0,70 48,92 0,46 0,644.4. Multipurpose venue in Wieluń Figures 16, 17 and 18 and Table 5 present EDT, RT20 and RT30 values obtained in Wieluń.EDTRT202,502,502,002,001,501,50RT [s]RT [s]1,001,000,500,500,000,00125 250 500 1 000 2 000 4 000 8 000125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]Frequency {Hz]AFC Off AFC v1 AFC v2 AFC v3 AFC v4AFC Off AFC v1 AFC v2 AFC v3 AFC v4Figure 16: EDT with different AFC3 setups inFigure 17: RT20 with different AFC3 setupsin WieluńWieluń RT302,502,001,50RT [s]1,000,500,00125 250 500 1 000 2 000 4 000 8 000Frequency [Hz]AFC Off AFC v1 AFC v2 AFC v3 AFC v4Figure 18: RT30 with different AFC3 setups in Wieluń Table 5: Room acoustic parameters - WieluńWieluń EDTRT20RT30C50 [dB]C80 [dB]D [dB]ITDGTs [ms] IAAC STI[s][s][s][ms]AFC3 off 0,43 0,42 0,43 8,50 13,90 0,87 11,49 20,81 0,83 0,80 AFC3 v1 0,63 1,08 1,16 5,20 8,70 0,76 39,36 0,87 0,72 AFC3 v2 0,48 0,96 1,30 7,50 11,60 0,84 27,31 0,84 0,77 AFC3 v3 0,54 1,16 1,44 7,00 10,60 0,83 30,37 0,88 0,75 AFC3 v4 0,60 1,26 1,48 6,40 9,80 0,81 35,05 0,76 0,745. DISCUSSIONSuggested values of the room acoustics parameters are well described in literature [3, 6, 24, 25]. The maximum RT value obtained as a result of the operation of the AFC3 system is usually twice as high as the RT value of the room itself. Therefore, it is possible to change the RT value in a wide range and adapt the enclosures to the events of a different types. Similar results of the AFC3 performance, providing different acoustic conditions were obtained in previous studies [26]. The widest range of the RT values were obtained in Wieluń, where the primary function of the measured hall is the cinema. The highest RT value is three time as high as the RT for the hall without AFC3 system. RT30 values in Łańcut vary from 0,89 to 1,34 s; EDT - from 0,73 to 0,99 s. EDT values do not change as much as RT values, which suggests that all reverberation decays have a dual-slope decay shape. The analysis of the STI values obtained from calculations have similar values for rooms with and without AFC3 system which leads to the conclusion that the high speech intelligibility is achieved regardless of the way the AFC3 works. C50, C80, D50 and other parameters measured in this study are in the range of expected values, proportionally to the obtained RT values. The comparison between RT values obtained for two different curtain settings and for the AAES system shows that the use of the latter gives a broader range of RT values. Additionally, changing the AFC3 presets can be very quick and does not change the interior design of the hall. 6. CONCLUSIONSThe analysis of the results gathered revealed that using the AAES system it is possible to obtain various acoustic conditions appropriate for the different kind of performances. The analyzed enclosures meet the required objective acoustic criteria of the following type shows: conference room, drama theater, amplified pop music hall, chamber hall, choir hall and opera hall according to the values of parameters known from literature. Modern AAES provide the enhancement of the acoustic parameters at a high-quality level and with wider variability compared to passive solutions (e.g., sound-absorbing curtains). However, obtaining the proper conditions is possible only when the room is properly designed. The use of halls equipped with the AES allows to carry out performances with the appropriate acoustic conditions at the significantly lower cost compared to the cost of building independent halls for each purpose separately.As this study contains only objective acoustic parameters of the room equipped with an AAES, further research is needed including subjective assessment of the quality of this type of enclosures. 7. ACKNOWLEDGEMENTSProfessor Jędrzej Kociński for scientific supervision. Hall directors for providing the halls for the measurements. Michał Siek and Maciej Hadyk from MOstrowski company based in Wrocław for renting the measurement equipment.8. REFERENCES1. Beranek L. Concert Halls and Opera Houses: music, acoustics and architecture, Second Edition,Springer-Verlag INC. New York (2004) 2. Ando Y. Architectural Acoustics, AIP Press Springer (1998) 3. Barron M. Auditorium Acoustics and Architectural Design, E. and F. N. Spon , London (1993) 4. Meyer E., Thiele R. Room acoustical investigations in numerous concert halls and broadcastingstudios using more recent measurement techniques, Acustica 1956; 6; 25 5. Kuhl W. Experiments on the optimum reverberation time of large music studios, Acustica 1954;4: 618 6. Schroeder M. R., Gottlob D. and Siebrasse K. F. Comparative study of European concert halls:correlation of subjective preference with geometric and acoustic parameters, Acoust. Soc. Am . 56 (4), pp 1195–1201, (1974) 7. Arni P. Rooms with reverberation time adjustable over a wide frequency band, J. Acoust. Soc.,Am . 22 (3), pp 353–354 (1950) 8. Ward W. C. Elko G. W. Kubli R. A. and McDougald W. C. The new varechoic chamber at AT&TBell Labs, Wallace Clement Sabine centennial symposium, Cambridge, Massachusetts, USA 5– 7 June, (1994) 9. Adelman-Larsen N. W., Thompson E. R. and Gade A. C. Suitable reverberation times for hallsfor rock and pop music, J. Acoust. Soc. Am. 127 (1), pp 247–255, January 2010 10. Watanabe T. Ikeda M. Various Applications of Active Field Control, Audio Engineering Society ,Convention Paper 8859, Presented at the 134 th Convention, 2013 May 4-7 Rome, Italy 11. Olson H. F. Acoustoelectronic auditorium, J. Acoust. Soc. Am . 31 (7), pp 872–879 (1959) 12. Dutton G. F. Reverberation reinforcement by delayed electro-acoustic feedback – Ambiophony,Audio Eng. Soc 31st Conv., New York, October 1966, Preprint 485 (1966) 13. Poletti M. A. Active Acoustic Systems for the Control of Room Acoustics, Proceedings of theInternational Symposium on Room Acoustics , ISRA, 29-31 August, Melbourne, Australia (2010) 14. Bakker R. Gillian S. The history of Active Acoustic Enhancement Systems, Proceedings of theInstitute of Acoustics Vol. 36. Pt. 2. 2014 15. Bakker R. Design and tuning of active acoustic enhancement system, Proceedings of the Instituteof Acoustics Vol. 36. Pt. 2. (2014) 16. PN-EN-ISO3382-1 Acoustics – Measurement of room acoustic parameters – Part 1: Performancespaces (2010), 17. PN-EN-ISO3382-2 Acoustics – Measurement of room acoustic parameters – Part 2:Reverberation time in ordinary rooms (2010), 18. Sabine W. C. Collected papers on Acoustics, Dover, New York, 1964, First published 1922 19. Kuerer R. Isolation of single number criteria from impulse measurements in room acoustics,Acustica 1969; 21: 370 20. Damaske P. Ando Y. Interaural cross-correlation for the multichannel loudspeaker reproduction,Acustica 1972; 27:232 21. Houtgast T. Steeneken H.J.M. The modulation transfer function in room acoustics as a predictorof speech intelligibility, Acta Acustica United with Acustica , 28, 66–73. (1973) 22. Reichardt W. Abdel Alim O. Schmidt W. Dependence of the limit between useful and uselesstransparency of the kind of music, f the reverberation time and the onset time of sound decay, Applied Acoustic 1974; 7: 243 23. Marshall L.G. An acoustic measurement program for evaluating auditoriums based on theearly/late sound energy ratio, Journal of Acoustical Society of America , 96, 4, 2251–2261, 1994 24. Beranek L. Concert and Opera Hall, How They Sound, Published for the Acoustical Society ofAmerica by the American Institute of Physics (1996) 25. Bruckmayer F. Schaltechnik in Hochbau, Franz Deutklicke Verlag . Wien (1962) 26. Watanabe T. Miyazaki H. Sawara S. Ikeda M. Bakker R. Active Field Control in the Teatr Wielki– Opera Narodowa, Audio Engineering Society , Convention Paper 9330, Presented at the 138 th Convention 2015 May 7-10 Warsaw, Poland Previous Paper 794 of 808 Next