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Performing spacesAcoustical renovation

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reinforced gypsum for sound diffusion in the major speech frequency range. Designed diffuser proles

deledce or ae hallesigners haviddle t

diffusion from lateral walls [4,5]. At that time, scattering propertiesof the diffuser proles were not veried due to the absence of thestandardized measurement methods of scattering and diffusioncoefcients [6]. Objective assessment of diffusion performance onthe surfaces of materials is now possible by measuring scatteringand diffusion coefcients [7,8]. In addition, systematic investiga-

vention space to a professional chamber music hall. For recital andchamber music performances, the reverberation time of the reno-vated hall with occupied seats was around 1.2 s. This RT target wasderived from a survey based on the acoustics of the recital halls inthe world with capacity of 400500 [10]. As shown in Fig. 1, thenew hall was designed with a reversed-fan type plan to provideabundant lateral reections to the rear part of seats.

The side walls which were made of Glass Fiber ReinforcedConcrete (GFRC) were tilted to give better spatial responsiveness

Corresponding author. Tel.: +82 2 2220 1795; fax: +82 2 2220 4794.

Applied Acoustics 73 (2012) 828835

Contents lists available at

A

l seE-mail address: kimyonghee@hanyang.ac.kr (Y.H. Kim).and suppressing acoustical aws such as utter echo, acousticglare, and tone coloration [13]. Therefore, appropriate designand application of diffusers is one of the important elements foracoustical renovation process.

However, it has been often applied highly diffusing surfaces toperforming spaces without any scientic investigation, such asstatues and decorations in the Grosser Musikvereinsaal, Viennaand ornate ceiling surfaces in the Beethovenhalle, Bonn [1]. Theuse of diffusers was introduced in large performing spaces suchas the Wellington Town Hall and the Christchurch Town Hall for

fusers were used for acoustical renovation, to investigate the acous-tical differences pre- and post-renovation and the process ofdesigning the diffusers, and to propose how sound quality can beimproved by acoustical renovation.

2. Acoustical renovation plans

2.1. Sejong Chamber Hall

The Sejong Chamber Hall (443 seats) was renovated from a con-1. Introduction

Performance halls are often remohave unsatisfactory sound performandifferent sound requirements than thers are used in architectural sound dacoustical quality [1]. Sound diffuscontributing to sound scattering at m0003-682X/$ - see front matter 2012 Published bydoi:10.1016/j.apacoust.2012.01.003were evaluated for both halls by measurements of scattering and diffusion coefcients of the 1:10 scalemodel diffusers. The effects of diffusers in both halls were also investigated by covering the lateral wallsclose to the stages with reective materials to control diffusive surfaces. As a result, spatial uniformityincreased with diffusive wall proles in both halls.

2012 Published by Elsevier Ltd.

when existing facilitiesre used for genres withs design allows. Diffus-in auditoria to improvee been recognized foro high frequency bands

tions have been conducted for determining the optimal diffuserswith hemispheric and cubic shapes [9]. However, studies of acous-tical renovations with sound diffusers have not been undertaken inreal halls. Therefore, more adequate diffuser design and evaluationprocesses are needed to promote the use of sound diffusers for ef-cient acoustical design.

This article aims to introduce the Chamber Hall and theM-Theater of the Sejong Performing Arts Center, Seoul, where dif-Scattering coefcientDiffusion coefcient

included more seats on the upper oors and additional spaces above ceiling reectors. The vertically-pat-terned diffuser prole with protruded cubic surfaces in the M-Theater was designed using glass-berTechnical Note

Wall diffuser designs for acoustical renov

Jin Yong Jeon, Choon Ki Seo, Yong Hee Kim , PyounDepartment of Architectural Engineering, Hanyang University, Seoul 133-791, Republic

a r t i c l e i n f o

Article history:Received 13 May 2011Received in revised form 20 December 2011Accepted 16 January 2012Available online 3 March 2012

Keywords:Diffuser

a b s t r a c t

This paper investigates theperforming spaces. Consideof two performing halls: thforming Arts Center, Seoul.vious shape of a rectangulaHall was designed usingM-Theater was renovated

Applied

journal homepage: www.eElsevier Ltd.tion of small performing spaces

ik Leerea

terial characteristics of diffusers for acoustical renovation of existing smallion is given to acoustical effects on sound elds through the practical caseshamber Hall (450 seats) and the M-Theater (630 seats) in the Sejong Per-e Chamber Hall was completely refurbished into a recital hall from its pre-nference space. The saw-tooth shaped wall diffuser prole in the Chamberass-ber reinforced concrete for mid-frequency sound diffusion. Thea live and intimate space for dramatic performances with a design that

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J.Y. Jeon et al. / Applied Acoustics 73 (2012) 828835 829and clarity by creating strong lateral reections over the audienceseats. The angles of the inclined lateral walls were determined bycomputer simulations [11]: they were varied and the lateral en-ergy fractions (LF) of the audience seats were compared accord-ingly. The results showed that sufcient LF (above 0.20) wasobtained when the top of the wall proles had been vertically in-clined toward audience area (the angle between the inclined walland the oor was 84). In order to provide late reverberance inthe hall, an open-type ceiling structure was applied as shownin Fig. 2. Wooden louvers were used for the ceiling with acousti-cally transparent functions. According the previous study [12],the designed open-type ceiling can be classied as a lightlyabsorptive open ceiling structure which shows low absorptioncoefcients of 0.26 or under by frequency bands. A detailed de-sign for diffusers on the side walls will be discussed in the fol-lowing section.

2.2. Sejong M-Theater

Another venue of the Sejong Performing Atrs Center, the Sejong

Fig. 1. Floorplan ofM-Theater (630-seats) was renovated from a small multi-purposehall of 447-seats to a drama and musical theater for better acousticperformance. Before the renovation, the space in unoccupiedconcert mode was too dry (RT was 0.92) and little supports byabsorptive lateral walls in both aspects of sound strength (G was1.8 dB) and spatial impression (1-IACC was 0.51). The renovationincluded an increase in seating capacity. A basic proscenium-typestage was maintained to accommodate composite arts. Variableacoustic elements, such as an orchestra pit and shell, could beadded so that acoustical conditions could be changed for differentgenres. For plays or musicals, the occupied reverberation time atmiddle frequencies was designed to be around 1.0 s.

Fig. 2. Section of the new ChamberThe new oor-plans and section are as shown in Figs. 3 and 4,respectively. The orchestra pit was installed. It can be part of an ex-tended-stage or an extended-audience area depending on the pro-duction requirements. In order to secure a better view from theauditorium, the rake of the oor was increased and a staggeredseat formation was introduced. Ceiling reectors were added to en-large the reective sound energy at the rear of audience seats. Theceiling reectors consisted of three parts. The rst reector coversthe whole auditorium. The second reector covers the rear part ofthe rst oor and the second oor. The third reector covers therear parts of the second oor. Glass-ber reinforced gypsum(GFRG) boards were used as materials for the ceiling reectors tosecure the sound strength and reverberation time.

3. Design of diffuser proles

Acoustic performance of diffuser proles can be evaluatedthrough measuring scattering and diffusion characteristics [9,13].Physically, scattering coefcient indicates ratio of scattered soundsexcept for specular reection, and diffusion coefcient indicates

new Chamber Hall.how reections are evenly distributed at the materials surfaces.In this study, the diffuser shape and size were designed to be suit-able for the halls main purpose. The scattering and diffusion coef-cients of 1:10 scale model diffusers were measured for objectiveassessment of the performance of the designed diffusers. All thedimensions used in the scale model diffusers are in actual size.

3.1. Determination of diffuser proles

3.1.1. Saw-tooth diffuserIn the Chamber Hall, the target frequencies from the scattering

surfaces are relatively low for chamber music performances. When

Hall. (a) 1st Floor (b) 2nd oor.

cous830 J.Y. Jeon et al. / Applied Adesigning the diffuser, two major factors were considered: (1)strengthening the envelopment using scattered reections and(2) spreading out even sound strength by scattered early lateralreections throughout the auditorium.

The stage-facing diffuser parts on the reverse fan-shaped wallswere curvilinear saw-tooth in shape, as shown in Fig. 5, to achievethe even level condition and to prevent acoustic glare and tonecoloration. The diffuser proles consisted of small (width 0.6 m height 0.3 m) and large (width 1.2 m height 0.3 m) modules.Glass-ber reinforced concrete (GFRC) was selected for the diffusermaterial due to the diffuser length (3.54 m).

3.1.2. Vertically-patterned diffuserIn the M-Theater, sound diffusers made of GFRG were installed

on the auditorium walls and balcony fronts in the same manner asin the Chamber Hall. Fig. 6 explains the proles of the diffuserswith a plan and sections. Combinations of different sized boxeswere designed to scatter the sound rays at mid-to-high frequency

Fig. 4. Section of the

Fig. 3. Floorplan of thtics 73 (2012) 828835ranges for vocal sounds in drama and musical performances. Theupper protruded wall proles were determined to deliver evenreections to the audience in order to create a diffuse sound eld.The convex prole in a set of diffuser modules was targeted formiddle frequency diffusion and the vertically-patterned proleson the surface were for additional horizontal diffusion at highfrequencies.

new M-Theater.

e new M-Theater.

Fig. 5. Prole of saw-tooth diffuser (unit: mm).

cousFig. 6. Prole of vertically-patterned diffuser for the M-Theater. Upper gureindicates horizontal section (unit: mm) (a) saw-tooth diffuser (b) vertically-patterned diffuser.

J.Y. Jeon et al. / Applied A3.2. Scattering and diffusion coefcients of diffusers

In order to measure scattering and diffusion coefcients of thedesigned diffusers, a diffuser specimen was reproduced at a 1:10scale as shown in Fig. 7. Fig. 7a and b indicate the diffuser prolesof the Chamber Hall and the M-Theater, respectively. The diffuserspecimen was formed as a circular plate according to both ISO17497-1 [7] and AES-4id-2001 [8].

Measurements of scattering coefcients were carried out in a1:10 reverberation chamber made of 20-mm thick acryl plates(poly-methyl methacrylate, PMMA). The ceiling and three wallsof the chamber were skewed to control utter echo or structuralmodes. Small tweeter units for high audio frequencies were usedas the sound source, and a 1/8 in. microphone (B&K) was usedfor the sound receiver. Two source position and three receiver posi-tions were considered. Each measurement was done in four cong-urations according to presence of specimen and rotation ofturntable. In a measurement of rotating-plate condition, 72 im-pulse responses measured within a rotation cycle were averagedsynchronously. Meanwhile, measurement of diffusion coefcientswas carried out using a 1:10 scaled 3D goniometer in a test cham-ber with less than 0.2 s of RT. Two sound sources that were 0.5 mfrom the middle of the specimen were considered for normal (90)and oblique (55) orientations, and 55 receivers were located withequal interval in a half circle of 1.0 m-radius. In all combination ofsource and receiver positions, the rst reections in the measuredimpulse responses were derived using signal processing tech-niques by comparisons to a without-specimen condition. Bothscattering and diffusion coefcients were analyzed in 1/3 octavebands. In all measurements of scattering and diffusion coefcients,the edge of the specimen was covered with a 2-mm thick and 25-mm high acryl border.

Fig. 8 shows the measurement results of scattering coef-cients. The averaged scattering coefcients at all 1/3 octave bandfrequencies were similar (prole for the Chamber Hall: 0.42, pro-le for the M-Theater: 0.47). For comparisons with the previousstudy [6], the averaged scattering coefcients at 5003150 Hz

Fig. 7. Diffuser specimen at 1:10 scale.tics 73 (2012) 828835 831were 0.52 for the Chamber Hall and 0.75 for the M-Theater,respectively. Because the highest scattering coefcient of thehemisphere diffuser was 0.7 at a structural height of around at0.25 m with 70% of surface density, the designed diffuser proleensured providing signicant scattering during performances.The frequency characteristics of the designed diffusers seemedto be suitable for the main purposes of the halls: the saw-toothdiffuser was aimed to scatter low- to high-frequency reectionsfor the orchestra music source, and the vertically-patterned dif-fuser was aimed to scatter higher frequency bands for vocalsources. Comparing the two different diffuser proles, the saw-tooth shaped diffuser showed higher scattering characteristics at100400 Hz, but the vertically-patterned diffuser showed higherscattering characteristics at 10003150 Hz. In case of vertically-patterned diffuser, scattering coefcients around 1600 Hz wereover 1.0 due to edge effects of the cubes with different heightsas shown in Fig. 7b.

Fig. 9 shows the measurement results of diffusion coefcients.The averaged diffusion coefcients at all frequency bands were0.36 for the Chamber Hall and 0.20 for the M-Theater. Diffusersfor the Chamber Hall showed much higher diffusion coefcientthan for the M-Theater. This was most likely caused by the differ-ent diffuser proles. However, for the vertically-patterned diffuser,diffusion coefcients at 8002000 Hz, which correspond to the fre-quency bands of vocal sources, were emphasized.

4. Diffuse characteristics in halls

Based on the designed diffusers, acoustical renovations of thehalls were completed as shown in Fig. 10. After completion, theeffects of diffusers on the sound elds of both halls wereinvestigated.

cous832 J.Y. Jeon et al. / Applied A4.1. Measurement conditions and set-up

To achieve with- and without-diffuser conditions, 5-mm thickplastic boards were installed over the major diffusive surfaces onthe lateral walls in both halls. The edge of each hanging plasticboard was fastened as much as possible using ropes. The averagedabsorption coefcient of the 5-mm thick plastic board was 0.08. Itdid not exceed 0.2 at any frequency bands in the 1/3 octave. Table1 shows the pictures of the measurements with and without dif-fusers. The surface areas of the plastic boards used in the ChamberHall and the M-Theater were 77 and 55 m2, respectively. As for thein situ experimental condition, an additional absorption from pa-nel vibration might be caused by the gap between diffusers andboards due to various structural heights of diffusers.

Acoustical measurements were made according to ISO 3382-1[14]. Fig. 11 shows the measurement position in both halls. Adodecahedron loudspeaker was located on the stage as a soundsource. Receivers were located over the audience area (12 positionsin the Chamber Hall, and 11 positions in the M-Theater). All mea-surements were performed while the halls were empty. Four

Fig. 8. Scattering coefcients of the saw-tooth diffuse

Fig. 9. Diffusion coefcients of the saw-tooth diffuser (CH) and the vetics 73 (2012) 828835acoustical parameters were derived: reverberation time (RT, T20),early decay time (EDT), clarity (C80) and interaural cross-correla-tion (IACC). Mid-frequency bands (5001 k Hz) were consideredfor averaging RTm and EDTm, and 3-bands (5002 k Hz) were con-sidered for averaging C803B and 1-IACCE3.

4.2. Results and discussion

Table 2 shows the measurement results of acoustical parame-ters. For RT and EDT, the coefcient of variation (CV, standarddeviation divided by its mean) was calculated as a relative stan-dard deviation to evaluate spatial distributions of acousticalparameters. For C80 and IACC, the standard deviation was calcu-lated for evaluation of regional distribution properties instead ofCV due to the limitations on the denitions of those parameters.From these results, the M-Theater had a shorter reverberation time(0.96 s) due to drama performance, and the Chamber Hall had areverberation time of 1.18 s. By controlling the diffusive surfaceusing at plastic boards, the measured acoustical parameters werechanged. In the M-Theater, RT and EDT were slightly decreased

r (CH) and the vertically-patterned diffuser (MT).

rtically-patterned diffuser (MT) (a) Chamber Hall (b) M-Theater.

after the installation of plastic boards. CV of RT was not changedby diffuser treatment, but CV of EDT was signicantly changedand almost doubled. This seems to be caused by the hard reective

The reason for the difference between the Chamber Hall and theM-Theater in terms of CV of EDT and standard deviation of 1-IACCE3 could be found from the different design targets for the hallacoustics: The Chamber Hall for recital use and the M-Theater fordrama use. The Chamber Hall is reverberant space with higherEDT, and the spatial distribution of EDT was good enough withoutdiffusers. Thus, diffusive walls did not improve spatial distributionof EDT. However, the M-Theater is a little more dry space with anopen stage house. Thus, the early reections from the at surfaceson the lateral walls were not scattered enough compared to thediffuse surfaces.

The results for C80 showed opposite tendencies from the RT orEDT. In the M-Theater, C80 with diffusers was lower than withoutdiffusers, but C80 in the Chamber Hall was not very different withor without diffusers. However, C80 was commonly decreased bydiffusers in both halls. This is because additional at materialmay provide some absorption at low frequencies due to the thinplate structure having air gap between the surface and the diffus-ers behind.

As for binaural dissimilarity, 1-IACC with diffusers was higherthan the without-diffuser condition in the M-Theater. In theChamber hall, 1-IACCE3 was 0.64 both with and without diffusers.This result might reect the fact that the hall, due to its originalplan-shape, already had the highest sound diffusion even withoutdiffusers on the lateral walls. However, diffuser proles in bothhalls signicantly affected the spatial distribution of 1-IACCE3. Inparticular, 1-IACCE3 was signicantly improved by diffuser wallsonly in the Chamber Hall. The saw-tooth diffuser in the Chamber

Fig. 10. Perspective of the renovated halls. (a) Chamber Hall (1F) (b) M-Theater (2F/1F).

J.Y. Jeon et al. / Applied Acoustics 73 (2012) 828835 833surfaces near sound sources. In particular, Fig. 12, which presentsthe frequency characteristics of CV of EDT in the M-Theater, indi-cates that the diffuser prole contributes to higher frequency dif-fusion at over 500 Hz. This indicates that the current diffuserprole contributes to even distributions of early reections. How-ever, in the Chamber Hall, neither RT nor EDT was changed by dif-fuser treatment.

Table 1

Measurement scheme with and without diffusers in both halls. Bold lines on the right ind

With-diffusers (current condition)

Chamber Hall

M-TheaterHall mainly affected middle frequency bands of the IACC as shownin Fig. 13. However, in the M-Theater, size of the diffuser proleswas relatively smaller than the Chamber Hall case. From the re-sults on the standard deviation of 1-IACCE3, it was found thatthe larger diffuser prole of the saw-tooth shape in the ChamberHall contributed to the more uniform distribution of binauraldissimilarity.

icate the boundaries of the installed plastic boards.

Without diffusers (plastic board)

coustics 73 (2012) 828835834 J.Y. Jeon et al. / Applied A5. Summary

In this paper, the surface characteristics of diffuser proles andthe effects of diffusers on sound elds in small performing spaceswere investigated through practical design cases for the SejongChamber Hall and the M-Theater.

Diffusers were the major features used to acoustically revive thecurrent spaces. The diffuser proles were designed according to thevenue properties: vertically-patterned diffusers reinforced highfrequency sound diffusion for the M-Theater and saw-tooth typediffusers reinforced middle to high frequency sound diffusion forthe Chamber Hall. The acoustical properties of the diffuser proleswere tested by measuring scattering and diffusion coefcients andthe frequency characteristics of the diffuser proles for the twohalls were applied for the design targets.

Fig. 11. Measurement positions in both halls.

Table 2Average values of the measured acoustical parameters in both halls.

Chamber Hall M-Theater

Diffuse Reect Diffuse Reect

RTm [s] 1.18 1.18 0.96 0.94CVRT 0.02 0.02 0.03 0.03EDTm [s] 1.11 1.12 0.79 0.76CVEDT 0.05 0.05 0.11

a 0.20a

C803B [dB] 2.9 3.0 6.6 7.1St. Dev.C80 0.48 0.47 0.21 0.211-IACCE3 0.64 0.64 0.55 0.53St. Dev.1-IACCE3 0.35

a 0.43a 0.46 0.49

a Signicant difference by T-test between two groups with a condence intervalof 95%.

with the wall diffuser prole in relation to the measured scatteringcoefcient characteristics. In the M-Theater, COV of EDT was re-duced by 0.09 with the wall diffuser prole in relation to the mea-sured diffusion coefcient characteristics. Different tendencies ofspatial distribution of IACC and EDT were found due to differentbasic acoustical conditions according to the hall design. In sum,the acoustical effects of wall diffuser proles were shown to befunctions of the spatial distribution of IACC in the Chamber Hallin relation to diffusion coefcients, and the relative standard devi-ation of EDT in the M-Theater. These results suggest that use ofwall diffusers for acoustical renovation improves spatial distribu-tion of the sound energy.

As summarized in this paper, the design and evaluation pro-cesses of wall diffusers will suggest some useful clues for more de-tailed acoustical designs of other small performing spaces. In thefuture, a method for the in situ investigation of diffuse sound eld

J.Y. Jeon et al. / Applied Acoustics 73 (2012) 828835 835Fig. 12. Frequency characteristics of COV of EDT in the M-Theater.The effects of wall diffuser proles on the sound elds of thehalls were investigated by covering diffusive surfaces with reec-tive boards after the completion of the venues. As a result, the stan-dard deviation of 1-IACCE3 in the Chamber Hall decreased by 0.08

diffusion coefcients. Appl Acoust 2011;72(11):899905.[14] ISO 3382. Acoustics measurement of room acoustic parameters. Part 1:

Fig. 13. Frequency characteristics of standard deviation of 1-IACCE in the ChamberHall.Performance spaces, Geneve; 2009.may be needed for more efcient design of diffuser locations or tocreate proles based on hall shape or size.

References

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[6] DAntonio P, Cox T. Two decades of sound diffusor design and development.Part 1: Applications and design. J Audio Eng Soc 1998;46(11):95576.

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[8] AES-4id-2001(r2007). AES information document for room acoustics andsound reinforcement systems characterization and measurement of surfacescattering uniformity. J Audio Eng Soc 2001;49:14965.

[9] Jeon JY, Lee SC, Vorlnder M. Development of scattering surfaces for concerthalls. Appl Acoust 2004;65:34155.

[10] Hidaka T, Nishihara N. Objective evaluation of chamber-music halls in Europeand Japan. J Acoust Soc Am 2004;116(1):35772.

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[12] Kim YH, Lee HM, Seo CK, Jeon JY. Investigating the absorption characteristics ofopen ceilings in multi-purpose halls using a 1:25 scale model. Appl Acoust2010;71(5):4738.

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Wall diffuser designs for acoustical renovation of small performing spaces1 Introduction2 Acoustical renovation plans2.1 Sejong Chamber Hall2.2 Sejong M-Theater

3 Design of diffuser profiles3.1 Determination of diffuser profiles3.1.1 Saw-tooth diffuser3.1.2 Vertically-patterned diffuser

3.2 Scattering and diffusion coefficients of diffusers

4 Diffuse characteristics in halls4.1 Measurement conditions and set-up4.2 Results and discussion

5 SummaryReferences