(Reaffiied 1996) ( Reaffirmed 2006) IS : 2526 1862 - Indian Standard CODE OF PRACTICE FOR ACOUSTICAL DESIGN OF AUDITORIUMS AND CONFERENCE HALLS Ninth Reprint DECEMBER 1998 ( Incorporating Amendment No. 1 ) UDC 534’84 : 699’844 : 725’83 0 CopWgh# 1975 BUREAU MANAK OF BHAVAN, INDIAN STANDARDS ZAFAR MARG 9 BAHADUR SHAH NEW DELHI Iloo Gr 5 December1963 IS : 2526 - 1963 Indian Standard CODE OF PRACTICE FOR ACOUSTICAL DESIGN OF AUDITORIUMS AND CONFERENCE HALLS Functional Requirements in Buildings Sectional Committee, BDC 12 Chairman LT-GEN H. WILLIAMS Representing Council of Scientific & Industrial Resesrch Members COLG. BENJAMIN Da. U. K. BOSE SERIN.K.D. Engineer-in-Chief’s SHRI R. S. MEHANDXI ( Alternate ) Branch, Army Headquarters ( Ministry of ( CSIR ), Directorate General of Observatories Transport & Communications ) Cent;iorfe;ilding Research CEOUDHUBY Institute SH~I B. C. RAYCEOUDHU~Y ( Afternate SRRI DALIP SIN~R DEPUTY DIRECTOR STANDARDS Railway ( ABCHITECTURE ) SHRI S. V. DESAI MRS. E. S. GRUXAN SIIRI J. M. BENJ~XIN SHRI R. B. GUPTA DR. K. HEINZ SHRI N. MAJIJXDER Sam N. S. MANKIXE~ SHRI S. R. BHISE ( Alternare ) DR. K; N. MATHUR SHRI K. C. SRIVASTAVA( ) Bombay Board Voltas Limited, ( Ministry of Railways ) Corporation Bombay Bombay Municipal ( Alternate ) Indian Institute Central Public of Architects, Works Department ( 32, Alipore Road, Delhi In personal capacity ) All India Institute of Hygiene ( Ministry of Health ) Ministry National Delhi of Labour Physical & Employment Laboratory & Public Health ( CSIR ), New Alternafe) SHRI C. B. PATEL SHRI J. L. SEH~AL ( APernate SHRI SAYED S. SHAJI SHRI D. P. SHARMA ( Alternate National Buildings Works, Housing Organization & Rehabilitation ( Ministry ) of ) ) Institute of Town Planners ( India ), New, Delhi f Continued on ppge 2 ) BUREAU MANAK OF INDIAN 9 BAHADUR STANDARDS SHAH ZAFAR MARC 110002 BHAVAN, NEW DELHI R. &RI Extra Assistant Director ( Bldg ). SINHA SHRI K. IS1 SARI L. New Delhi Voltas Limited. New Delhi SRRI 0. RAMACIXANDRARAO . NARASIMHAN ( Alternate ) SHRI P. RAMA RAO Assistant Director ( Bldg ).IS : 2526. C.1963 ( Continued from page 1) Members SHBI J. IS1 and Heat Insulation Subcommittee. TRIVEDI Directorate General of All India Radio ( Miuistry of Information & Broadcasting ) 2 . PURI SHRI N. New Delhi Institution of Engineers (India ). Cent~~or~eu_ildmg Research Bombay Institute Members SHRI J. SHASTRI SHRI S~AUKAT RAI SHRI H. BDC 12 : 5 ( Ministry Directorate General of All India Radio of Information & Broadcasting ) Indian Institute of Architects. D. D. P. ’ Acoustics Convener SHRI R. F. L. Deputy Director ( Bldg ) Representing Directorate General of Health Services (Ministry of Health ) Kanvinde & Rai. V. ANTIA ( Alrernate SRRI R. K. NARASIMHAN Directorate General of All India Radio f Ministrv* ’ of Information & Broadcasting ) DR M. PANCHOLY National Physical Laborstory ( CSIR ). Calcutta ) Directorate General of All India Radio of Information & Broadcasting ) Director. BENJAMIN SHRI N. R. K. P. DR. Sum DR H. IS1 ( Ex-officio Member ) ( Ministry Secretaries SRRI C. M. VIBVESVARAYA. L. CHOUDHURY ( CSIR ). . . .. . ....... ... . 9...... SCOPE . ... .. ... APPENDIX C ABSORPTIONCOEFFICIENTS INDIGENOUS OF Acous. . ADDITroNAL REQUIREMENTSFOR OPEN-AIR AUDITORIUMS . AND CONFERENCE HALLS . ... ... . . .2 Halls for Music . . . . SEATS REVERBERATION TIME DISTRIBUTION ACOUSTIC OF MATERIAL SOUNDABSORBING MATERIALS SOUNDAMPLIFICATION SYSTEM .... . . . . . . . . . .. . 7 7 8 8 8 8 11 12 14 14 15 4.. ... .. I. ... ... . . 15 10. .* APPENDIX B ABSORPTION COEFFICIENTS FOR BUILDING MATE.. .. . . Music . . ...5 General Purpose Halls Used for Both Speech and .. Open-Air Auditoriums and Conference Halls . .. . . ....... ..4 3. .. . RIALSAND FURNISHINGS .. . . . . 3. . . ... . 3. 8. .. ..2 Conference Halls . .2 5. . . .... . 3. 10...IS:2526- 1963 CONTENTS PAGE 0. TERMINOLOGY . . ... 2.. . . 6. .. . 18 19 3 . . 7. . . Cinemas ( Sound Picture Halls ) . . . TICALMATERIALS . . FOREWORD .. . 15 15 APPENDIX A SUMMARYOF COMMON ACOUSTICAL DEFECTS IN AUDITORIUMS & CONFERENCEHALLS AND RECOMMENDED ...1 Halls Used for Speech and/or Drama . . ... ....1 Open-Air Auditoriums 10.. . . ...3 3.... . GENERALPRINCIPLES DESIGN OF 4... .... .. ... . ... .. .. 1’7 REMEDIES FORTHE SAME . .. . ... ACOUSTICAL REQUIREMENTS 3.. . .. .1 4.. .. . . . .. ..... .. .. Site Selection and Planning Size and Shape . . .. cated cases expert acoustical advice should be sought at the planning stage itself in order to obviate excessive expenditure on corrective measures later on. acoustical experts and builders and has related the standard to the current practice followed in the country in this field. after the draft finalized by the Functional Requirements in Buildings Sectional Committee had been approved by the Building Division Council. observed or calculated. expressing the result of a test. cinemas. and conference halls as also recommendations for remedying the same are given in Appendix A for guidance.1963 Indian Standard CODE OF PRACTICE FOR ACOUSTICAL DESIGN OF AUDITORIUMS AND CONFERENCE HALLS 0. theatres and conference halls for general guidance of the architects It is.5 Metric system has been adopted in India and all the dimensions and quantities appearing in this standard have been given in this system. daylighting and orientation.6 For the purpose of deciding whether a particular requirement of this standard is complied with. ventilation. acoustics. such as heat and sound insulation. 0. 0. the final value. 0. Code covering sound insulation of nonindustrial buildings ( IS : 1950-1962 ) has already been published and This code is intended to cover others are in course of formulation. however.3 A summary of common acoustical defects usually noticed in auditoriums.1This FOREWORD Indian Standard was adopted by the Indian Standards Institution on 26 October 1963. 0. the basic principles of acoustical design of auditoriums. shall be rounded off in accordance with IS : 2-1960 Rules for Rounding Off Numerical Values 4 . 0.IS:2526.2 A series of codes are being prepared by the Functional Requirements in Buildings Sectional Committee to cover the functional aspects of buildings. 0. suggested that in all major and compliand builders. Due consideration has also been given to the practices and standards followed in different countries of the world.4 The Sectional Committee responsible for the preparation of this standard has taken into consideration the views of architects. This sound energy Unit - is expressed Product in sabins ( see 2. 1.3 Absorption of a Surface by its absorption coefficient. number and size of emergency exists. fire fighting. incident the purpose of this standard. 2. if any.7 This standard is intended chiefly to cover the technical provisions relating to the acoustical design of auditoriums and conference halls.The gangways left within and around walking into or out of a group of seats.0 For apply. toilets. and local regulations. where assemble for watching a performance given on the stage.4 Acoustical Treatment -Any or introduction therein of sound absorbing devices with the specific purpose of controlling the reverberation time of an enclosure. The should number of significant places retained in the rounded be the same as that of the specitied value in this 0. covered or open.1 This code does not give. is given a special shape for providing the ultimate background for scenic effects. of the sound following energy definitions absorbed to shall the 2.1.7 Back Stage Wall-The wall at the back of the stage facing the The back stage wall may also . 2. air-conditioning. wherever available.An enclosure.6 Auditorium . people 2. of the area of a surface multiplied 2. treatment of surfaces of an enclosure 2.5 Aisles . and design of various 1. 5 .24). such as lighting.be called Cyclorama when it audience.IS : 2526 . etc. off value standard.2 Absorption Coefficient-Ratio on a material. TERMINOLOGY 2. recommendations for ancillary facilities. SCOPE 1. and it does not cover all the necessary provisions of a contract.1 This standard covers acoustical types of auditoriums and conference requirements halls.1 Absorption 2. These shall be provided in accordance with relevant Indian Standards. the seating area for can 2.1963 ( Revised ). to be provided in auditoriums and conference halls. away from the stage. 6 . into which one or more rootis or small total opening between the stage ?nd the house 2.An auditorium where the performance is in the form of pictures projected on a screen with or without the accompaniment of scenic atmosphere.A distinct and clearly discernible at a point within the enclosure when any sound emanates from any part A quick succession of such echoes is called flutter or of that enclosure.12 Crush Hall -The addition to the foyer) outside the buying tickets. 2. etc.9 Balcony hall. for use by participants ( some2. amplifiers and loud-speakers) required to reinforce the sound emanating from a source in order to provide adequate loudness for comfortable hearing by the audience.Hall in front of the entrance wait before actually entering the house. 2.19 Public Address System ( PA System) -The complete chain of sound equipment (comprising essentially of microphones. waiting.10 Cinema .-4 hall intended times with non-participating audience) in a discussion or deliberation on a topic in the form of speech or conversation made by one person at a time seated anywhere in the hall. hall main ( sometimes provided hall for purposes such in as reflected sound received 2.13 Echo .The gradual rise in the level of seats in successive rows.11 Conference Hall .20 Raking of Seats .15 Lounge 2.14 Foyer . first entrance 2.IS : 2526 . Soffit The area of under surface over part of the house or may not project beyond of the balcony within the 2.8 Balcony FloorExtra floor constructed for seating additional audience which may the rear wall.16 Lobby open.18 Proscenium Overhang -The It includes the still visible to the audience when the curtain is lowered.1963 2.21 Rear Wall -The wall facing the stage at the end of the hall. curtain and the arch or the frame work that holds it. 2. 2. front area of the proscenium that is 2. flutter echo. 2. ante-room. Sitting Passage room in which the audience may or place for relaxation. so as to ensure unobstructed view of the stage performance to the audience. 2.17 Proscenium -The through wliich the audience witness a performance on the stage. of echo. beyond the proscewherepitch 2. This equal to sound absorption of one square metre of’ open window ‘.2. 2. or time taken by the reverberant sound to 2.Unit of sound absorption in metric system.Portion nium into the house.27 Staggering of Seats . etc. sound. 3.An arrangement of seats in a manner by seats are displaced (relative to each row) by half-seat in every successive row.Adequate reverberation is important proper biending and fullness of music. . window. a) correct b) absence c) correct reverberation d) low background 3. roof. the reverberation time requi-ed in this case is lower than that required for 3. 2.28 TheatreAn auditorium where the performance is essentially given by ‘live ’ characters with or without the accompaniment of 3.In view of the fact that a certain amount of reverberation is already present in the recorded sound.25 Sound Insulation of Building Components-The ievel of sound when it passes through a building floor. Purpose time Halls should Used be for Both in-between Speech that and Music -The for in 3.1 provided 3. of stage which extends. loudness level at all parts noise.22 Reverberation completely enclosed - Persistance of sound in an enclosure ( partially ) after the source of sound has stopped.1 Halls Used for Speech and/or Drama -The in this case.IS : 2526 . of the hall.3 General reverberation and 3. and to lend time is clarity clarity of speech depends on: is most 3.1963 2. 2.Such staggering ensures a clear view from each row with relatively less raking than is necessary if seats are exactly one behind the other in successive mws. 2. is reduction in the component like wall.23 Reverberation Time -The decay to one-millionth of the sound intensity level existing at the time the source of the sound is stopped. The reverberation required to be higher than for halls meant for speech only. NOTE .3.4 Cinemas ( Sound Picture Halls) .26 Stage Apron . door.24 Sabin ( m2) .2 Halls for Music . ACOUSTICAL important REQUIREMENTS Optimum time. 9 m2 per person.5 to 5. When air-conditioning is provided special care should be taken to attenuate the plant noise 2nd the grill noise.000 2 dynes/cm2 ) on a logarithmic scale. NOTE 2 Decibel ( dB ) is a unit of sound intenaity level and expresses the ratio of a given sound level to the minimum perceptible level ( quantitatively 0.2. which arise are dealt with in 10 OF DESIGN 4. 4. Suitable volumes for different types of .1 The size should be fixed in relation to the number of audience required to be seated. orientation.The choice of site for an auditorium is governed by several factors which may be mutually conflicting.1 Depending on thelsambient noise level of the site. but a compromise has to be struck between the various considerations involved.gangways ( excluding the stage ) should be calculated on the basis of 0.5 Open-Air acoustical additional Auditoriums requirements requirements and Conference Halls-While the general are similar to those specified for halls (see 3. A noise survey of the site should be made in advance so that nois) locatio s are avoided where! possible. as otherwise elaborate and expensi e e construction may be required to provide requisite sounl insulation.particularly necessary to keep the level of extraneous noise low by proper orientation and site selection in caies where no air-conditioning is provided and doors and windows. height may vary from 6 m for small halls 4. For this purpose plant should be suitably isolated and ducts as well as the plenum should be so designed that raise gets adequately reduced so as to be within the permissible limits.5 m for large halls.1 Site Selection and Planning .1 The average to 7. so that the background noise level of not more than 40 to 45 dB (as measured on ‘A’ scale of sound level meter ) is achieved within the hall.1). It is . In fact. are normally kept open during the performance. The height of the hall is determined by such considerations as ventilation. the quietest possible condition should be provided SO that intelligibility of speech does not suffer and even soft passages of music are heard.IS : 2526 .1. presence ( or absence ) of balcony and the type of performance. The problem of noise is an important consideration. The floor area of the hall including . The volume per person required to be provided should normally range between 3.1.1963 3.2 Size and Shape 4. Ceiling may be flat but it is preferable to provide a slight increase in the height near the centre of hall.6 to 0. GENERAL PRINCIPLES 4. 4. layout and structural design should be arranged to provide necessary noise reduction.2.5 ms. IS : 2526 . The proscenium may bear any suitable ratio with the height of the hall to suit stage requirements and considerations of visibility.. 5. likely to cause a delayed echo or flutter echo should be appropriately treated with a sound absorbing material.The performance the hall is to cater for. mended that the distance of the ‘farthest seat from the curtain line should not normally exceed 23 met es. The side walls should be arranged to have an angle of not more than 100 degrees with the curtain line.5 m from the proscenium end. Also. It would be large for theatres. Difference between the direct path and the path reflected from side walls shall not exceed 15 m.2.2 Floor plans of various shapes are used. In the case of talking pictures synchronisation of sound with-lip movement is most essential. architecturally finished in any manner required.2. in the case of theatres a person with normal vision should be able to discern facial expressions In order to satisfy these conditions.5 side Wall -Where the side walls are non-parallel as in the case the walls may remain reflective and may be of a fan-shaped hall. li. size of the stage depends upon the type of 4.0 halls 4. engineering or 9 to a roof economic . the upper limit is suitable for musical performantes while the lower limit may be chosen in the case of small general purpose auditoriums.0 . it cannot be avoided. any of the surfaces.2. but the one which is considered to give satisfactory results without introducing complications in the acoustical treatment of the hall is the fan-shaped plan. Where the side walls are parallel they may be left untreated to a length of about 7. In addition. if sound absorbing material is not required from other considerations. it is recomof the performers.6 Roof are mainly and Ceiling -The governed by requirements pertaining architectural. 4. auditorium rear wall(s) should be either flat 4.0 .3 Stage .4 Rear Wall -The This should not be concave in shape.2. while it would be comparatively small for cinema halls which again depends on the size of the screen. 4. 5’5 In the case of(c)..1963 auditoriums are given below but it is recommended adopted only in special cases: that higher values be Cubic Metres per Person a) Public lecture halls b) Cinemas or theatres cl Musical halls or concert 3. the acoustical design shall indicate either the surface to be splayed or convex corrugations given in order to avoid any tendency for the sound to focus into the hall. but where or convex in shape. 4.2.5 to 45 4. 1 Noise from aircrafts . Concave shaped ceilings (in the form of dome or barrel ) should be avoided. + h - rf H--h. and nth rows behind the row which is at a distyce S from the source.For good visibility as also for good listening conditions. the difference last s= = horizontal distance from the source to the F+r) ( row which does not require elevation.6. . . are elevations of the fir/et. 4. the trusses. ho.-i 7.Wherever this problem arises due to frequent and heavy showers the same method should be followed as suggested for noise from aircrafts ( see 4. . second.. . e hn_.Where more accurate values are considered floor may be calculated by the following formula: necessary. ‘ head clearance ’ in relation to the sound source. in height between one row of people and the next. . the slope of the h.1 ). if the seats are staggered ( see 2. It is possible to reduce this to 8 cm. 4. . r = back to back distance h= between rows of seats.1963 In large halls a false ceiling is usually provided below considerations.. .IS : 2526.2.) -St-( . A suitable soundproof false ceiling should be provided below the roof under such circumstances. The rear portion of the ceiling may be treated with sound absorbing material partly for control of reverberation and partly to prevent build-up of audience noise.2.2. and h. the successive rows of seats have to be raised over the preceding ones with the result that the floor level rises towards the rear.2..1 Floor . and hi.27 ). 4.2 Rain noise . where H = height of sound source above normal head level. The remaining portion of this ceiling is constructed to take acoustical treatment. . As an empirical rule the angle of elevation of the inclined floor in an auditorium should not be less than 8 degrees.6. 10 . The elevation is based on the principle that each listener shall be elevated with respect to the person immediately in front of him so that the listener’s head is about 12 cm above the path of sound which would pass over the head of the person in front of him. The portion of the false ceiling near the proscenium is constructed of reflective material ( usually plaster of Paris ) and is suitably inclined to help reflections from the stage to reach the rear seats of the hall.6.If the auditorium is so located that aircraft noise causes a serious disturbance (that is when noise level created inside the hall is more than 50 dB ) special precautions should be taken to make the ceiling soundproof.-. NOTE . 2. 4. adjacent to the audltprium shotild be isolated from the main hall by suitable ( well fitting ) doors so that the acoustics of the hall are not influenced by these rooms.9 Line of Sight . etc.The elevation of the balcony seats should be such that line of sight is not inclined more than 30 degrees to the horizontal. number and size of entrances also depend At least 20 percent on the size and seating capacity of the auditorium.2. Incidentally. etc. these spaces should be acoustically treated so that the noises originating there do not cause any disturbance in the main hall. the distance ofthe front row works to about 3. at the same time.10 Foyers.3 Further. SEATS 5. its projection into the hall should not be more than twice the free height of the opening of the balcony recess.3 The width of a seat should be between 45 cm and 56 cm.Where a balcony is provided. verandahs.2. such as foyers.10. Crush Halls. this will also reduce air-borne noises coming from outside.2. 4.10. 1%3 4. In the case of existing doors and windows where leakage of sound is observed.2 The angle subtended with the horizontal at the front-most observer by the highest object should not exceed 30 degrees. provide draught strip rubber or felt on the rebates. 11 .s ( curtain line ) distance from the auditorium rear wall.Is : 2526 -.11 Doors and Windows -Where properly fitted doors and windows should be provided. the external noise level is high. it would be necessary to improve the fitting of the shutters and. lounges.1 The seats should be arranged in concentric arcs of circles with the centre located as much behind the centre of the curtain it. Attached Rooms .6 m for drama and it should be 4. Their rebates should preferably be lined with draught strip rubber or felt.2 For lobby and lounge. 4. heavy curt\a. drawn line as 5.8 Balcony . Minimum distance of front seats should be determined by the highest point required to be seen on the stage w@ich is usually raised by about 75 cm or more. 4. 4.5 m or more for cinema purposes.10. 4. of the seating area of the hall 1s recommended for foyer. On this basis.ns may be used to aid absorption of external noise from foyers. 5. flanking verandahs.1 The foyer area.2. areas at least corresponding to 10 percent of the seating area in the hall are recommended.2. 5.2.All the enclosed spaces. . These values are for a frequency of 500 cycles. REVERBERATION TIME 6. For it is enough to consider only one frequency .. wherever possible. = total in m3. units 6. indicated in Fig. = absorption and S. in seconds. higher 85 cm and 106 cm. may be provided which shall vary between in successive rows is required.. A. not appreciably affected by This is particularly important for fluctuating audience occupancy.16 lrequired according V to give the desired to Sabine’s formula S.4 The reverberation purpose of this code. 5.6 Upholstered seats shall be provided. required. = A 6.1963 5. 6.2 The number of absorption reverberation time may be calculated which is as follows: A = where A = %. furnishings and two-thirds of the audience. the as time varies at different frequencies. value coefficient tiea in to each 6.5 Seats should be staggered sideways in relation to those in front so that a listener in any row is not looking directly over the head of the person in front of him. Y -G volume T = reverberation a. of seats spacing 5.4 The back to back distance of chairs If extra comfort shall be at least 85 cm. 1 depending on the function of the hall. This may be deducted from the total absorption A indicated by the formula given below: A. provided by various surfaces. 1. = individua1 of CC. it is necessary to calculate the quantity of existing absorption A. sound time absorption. halls where the audience provides the major part of the required sound absorption.IS : 2526 .1 The optimum reverberation time for a hall of particular volume may be chosen from the curves given in Fig.3 In order to estimate the quantity of absorption A. so that the acoustic charcteristics of the hall are. 0. of the corresponding m2 corresponding surface(s). . 1 The following materials generally categories: material used may be broadly classified into the Acoustic a> plaster ( a plaster with cement ).1963 7. (b) the balcony parapet. glass wool tiles. This is relatively more in the high frequency range than in the It. cl Wood particle board. most of the absorption is provided by the audience. and (e) such other areas as will contribute to indirect sound arriving at any point in the hall later than 50 milliseconds after the direct sound. becomes desirable middle or in the low frequency range. _i) Special 8. asbestos board or metal sheet ) backed by mineral or glass wool quilt or slab. 8. teak ply. e) Mineral/glass wool quilts and mats. and backed absorbers by air. These areas are (a) the rear wall. 14 . Those areas which cause objectionable sound reflection and need to be treated with sound absorbents should be earmarked for treatment with sound absorbing material. granulated unperforated insulation and per- b) Compressed forated. 4 Compressed wood wool. cane or wood which includes fibreboard. (c) any areas which may reflect sound back to the stage.2 In an average hall.IS : 2526 . SOUND ABSORBING MATERIALS 8. The rest of the sound absorbing material required to be introduced in the room should be distributed over the various remaining surfaces.1 Reflecting surfaces shall be so designed as to aid distribution of sound. to introduce special low frequency absorbers ( such as wooden panelling used as wainscot or otherwise ) on ceilings and walls which will provide the requisite amount of absorption so as to achieve optimum reverberaThe amount of tion time over as wide a frequency range as possible. constructed of hardboard. (d) concave areas which have a tendency to focus sound in certain places. therefore. backed by perforated h) Composite units of perforated board (hardboard. DISTRIBUTION OF ACOUSTIC MATERIAL 7. etc. f-1 Mineral/compressed 9) Composite units of perforated hardboard fibreboard. the absorptive materials required should be calculated on the basis of the absorption values at one or more frequencies in each of the low. it is necessary to treat back stage wall acoustically.3 If direction should be so located the stage. of wind generally remains the same. 10. if into convex surfaces cm width.IS : 2526 .2 Conference Halls . Overall shape should be flat it is desired to be concave.1963 middle and high frequency regions namely 125.1.1 and 4.1.While the general considerations given in 4. particular care should be taken in the case of open-air auditoriums as these are not enclosed.1 Open-Air Auditoriums . The loudspeaker system should be so designed that it is capable of providing an average level up to 80 dB over the entire listening area. 10. like theatres and cinema halls.1 Back stage wall should be made reflective vex shaped surfaces. where it exceeds 6 m. sound amplification should be resorted to in case the number of audience exceeds 600 or back ground noise is more than 45 to 50 dB. The absorption coefficients for various materials are given in Appendices B and C.1 would apply to open-air auditoriums also. 9. ADDITIONAL REQUIREMENTS FOR OPEN-AIR AUDITORIUMS AND CONFERENCE HALLS 10. lies in the possibility of 15 . 500 and 2 000 c/s. SOUND AMPLIFICATION SYSTEM 9.4 Even if reflectors are provided as recommended in 10. Prevailing noise conditions should not exceed 45 dB on ‘A’ scale. Where background noise is high or the hall is large. A ceiling reflector should be provided for directing the sound to the rear seats. it should be broken which in either case should be of at least 90 to 180 and broken into conin plan.2. Wind velocities naturally experienced at site should not exceed 16 km/h.1. 10. This level can be obtained in an acoustically well designed hall provided the volume does not exceed 1 400 m3 and the maximum distance from the speaker to listener is of the order of 23 m.2 Depth of stage should be arranged to suit individual requirements.1 A loudness of speech level of about 60 to 70 dB is required for comfortable listening and good intelligibility provided the ambient noise level is within the acceptable values given in 4.1. 10. the auditorium that wind direction is towards the audience from 10.1.Basic difference between conference halls and auditoriums. a sound amplification system becomes necessary. however. 10.1.1. This reflector may be a hard reflecting surface slanting at a suitable angle towards the audience and fixed over the main sound originating area of the stage.1. because of size or other requirements. Conference halls may have any shape to suit architectural In designing conference haJJs partior any other special requirements. 10. 10. be given to the requirements.2. more area of ceiling would need to be treated.2 Optimum reverberation time should be chosen from Fig. But where necessitated.ng should be confined to peripheral regions only. low level loudspeakers or head p. In a conference hall a table or cluster of tables is generally placed in the centre of the hall. 10. 16 .2.hones should be provided for individual or a group of seats. and persons who are listeners as well as speakers sit around the table.4 surfaces Absorbent material of the hall. 10.5 Ceiling should not be domed and should not be ‘higher than 6 metres.2.1 Acoustics of the halls should be so designed as to ensure proper conditions for listening. should be distributed evenly over the wall 10. assuming that a person may speak or listen from anywhere in the hall. In the case of larger halls with considerable heights. 1 ( speech ). following cular consideration should.IS : 2526.2.1963 sound originating. therefore. Acoustical treatment on the ceili. It may be noted that too long a reverberation time muffles and confuses the speech intelligibility while too short a time prevents build-up of proper Ievel for good listening.2. in the former case from any part of the hall.3 Use of sound amplification system should be avoided as far as possible. provide proper fitting doors and windows with requisite sound insulation. badly fitting doors and windows or noisy air .conditioning system 17 . Excessive 1 absorption (Selective 1 absorption Avoid unsuitable shapes Make offending surface bent Avoid curvilinear interiors Provide fusion even difof sound 3 Sound Alter shape or use absorbents on focussing areas Introduce suitable diffusers surfaces about 4 Dead spots 5 Insufficient Bound volume Dispose hard reflecting the source of sound Adjust absorption reverberation to give optimum 6 Colouring of sound quality Use combination of absorbents to obtain uniform absorption coefficient over the required frequency range Uso wood panel absorbents which resonate over a wide frequency range and fix these on battens provided at irregular intervals. Adopt rigid corn+ truction with studs.IS : 2526 .3 ) A SUMMARY OF COMMON ACOUSTICAL DEFECTS IN AUDITORlUMS AND CONFERENCE HALLS AND RECOMMENDED SL No. etc Select construction with requisite sound insulation. etc Uncontrollea 1 resonance 7 back. Remote reflecting 1 surfaces foci Concave reflecting interior surfaces Irregular distribution of sound [Lack of reflections close to Source of sound i. Reduce noise from air-conditioning equipment by isolating the machine and/or treatment of plant room. DEFECT REMEDIES FOR THE SAME RECOMMENDATIONFOR -_-h______~ Design Existing Buildings (4) (51 absorbents highly absor- CAUSES r-New (‘1 1 (2) Excessive verberation Echoes re- (3) Insuflicient sorption Unsuitable abshape Add 2 i . High ground noise Poor sound insulation.1963 APPENDIX ( Clause 0. 02 @Ol on 75 mm air space Wood veneer 10 mm thick on 50x75 wood studs at 40 cm centre to centre Glass agclinst solid surface Marble Audience.20 0.09 0.40 0.23 0.04 0. Chairs.04 005 0’10 0.04 0’09 0.12 0.03 0.07 0.12 0. 475 g/m2 draped to half its ABSORPTION COEFFICXEKT AT ~-_----__--__ 2 000 c/a 125 c/s 500 c/s 0.03 0’01 0.16 ( per 0.46 0.03 0.66 0.16 0.10 0.25 Masonry and Building Material 10 11 12 13 14 15 16 Brick wall 40 cm thick Plaster in wall plaster of Paris suspended Ceiling.15 Draperies.IS : 2526 .50 0. Floor.14 o-19 0’26 0.11 0.05 0.05 0.05 0.03 0.13 0.2 ABSORPTION COEFFICIENTS ) B FOR BUILDING MATERIALS AND FURNISHINGS SL MITERIAL NO.40 0’26 0.02 0. velours 610 g/m” as above draped to half their area or concrete floor Stage curtain wood on solid wood boards on timber frame 0’02 0. Draperies.49 0’35 0’55 0.18 0.1963 APPENDIX ( Clause 8. Hangings and Floorings 1 2 3 Carpet. Linoleum Floor.3s 0.01 0. upholstered Seats ( unoccupied seat ) in fully upholstered seats 0.44 seat with spring ) fully upholstered 18 . 50 mm from trusses Plyboard 0’02 0. Cotton area line& unlined fabric. Carpets.15 0. etc 17 18 19 Audience seated ( per person ) Chair.08 0.51 0071 0.03 0.10 0’08 0.30 mm 0. 65 o.52 0’36 0.40 0.61 0.1 25 Compressed fibre board: a) Unperforated b) Perforated uniformly over part depth ( rigid backing ) c) Perforated randomly over part depth ( rigid backing ) 3 Compressed wood particle board a) Perforated b) Perforated ( rigid backing ) ( rigid backing ) painted painted O.4 0.38 0’4 0.50 0.60 0.44 and c) Perforated ( rigid backing ) d) Perforated and ( rigid backing ) 4 a) Wood wool board b) Wood wool board from wall) 5 6 7 Mineral mats glass wool (50 quilts mm and 25 25 50 Bonded & compressed mineral/ glass wool tiles Composite units of perforated hardboard backed by perforated fibre oard with wool a) Mineral/glass scrim mat ( rigid backing ) with b) Mineral/glass wool scrim mat ( rigid backing ) 25 25 50 0.37 0’34 ‘0.42 19 .61 0.12 500 4s 0. AT mm 1 2 Fibrous ( acoustic g/cm3 0’1 0.10 0’09 0.08 0.20 0’99 0.06 0%) 0’49 0.7 19.05 0.85 0.24 O.55 0.2G 2 000 c/s 0.50 0.7 19.35 0.76 4000’ c/s 0.82 0.08 0.62 0’20 0.95 0.OG 0.5 0.57 0.96 0.40 0.99 0.74 0.29 0.69 0’8 ) plaster 20 12 12.04 123 cl* 0.--A.25 0.1963 APPENDIX ( Clause 8.1 12.17 0.s4 0.31 with wool d) Mineral/glass scrim mat faced with perforated ( 10% open area) hardboard ( rrgid backing ) 50 0’08 0.2 ) C ABSORPTION COEFFICIENTS OF INDIGENOUS ACOUSTICAL MATERIALS SL MATERIAL No.98 OGI 8 c) Mineral/glass with wool scrim mat faced with perforated ( lOolo open area) hardboard ( rrgid backing ) 25 0’08 jlO.iS 0.24 O.2 0.04 0.IS : 2526 .3 0’55 0.‘iG 0.99 0.05 0.3 0’3 0.4 O.67 0.OG 0’15 0.59 0.1 12. THICKNESS DENSITY ABSORPTION COEFFICIENT '--------.91 0.30 0.7 12.35 0. 35 0. Roorkee.35 c) Composite panel 5 mm perforated plywood 50 mm mineral wool and 22 mm cement asbestos (suspended from trusses ) d) Composite panel 5 mm pcrforated plywood 50 mm mineral wool and 22 mm hardboard ( suspended from trusses ) - - 0.09 - NOTE-The absorption coefficients of materials given in items 2 b). MATERIAL THICKNESS DENSITY ABSORPTION COEFFICIENT AT r-----h_--_ mm 9 Miscellaneous: a) Strawboard b) Strawboard from wall spaced 50 mm 13 13 glom3 125 ois 500 ols 2000 4000 ’ da 0.30 0.36 0.67 - - - 0.20 0.1963 SL No. 2(c).24 0.IS : 2526.47 0.95 0.24 - 0.30 4s - 0. 20 . 3(a) td 3(d) and 8(a) to 8(d) are based on tests made at the Central Buil h mg Research Institute. NEW DELHI 110002 Telephones: 323 0131. PO.BUREAU OF INDIAN STANDARDS Headquarters: Manak Bhavan. Behind Leela Cinema.I. C-Scheme. 670 Avinashi Road. E9.T. 43. Second Floor. T. Sahibabad Industrial Area. HYDERABAD 500001 E-52. BHOPAL 462003 Plot No. Delhi . Campus. Khanpur. Sector 34-A.91 11 3239399. 2nd Floor. Bhadbhada Road.I. THIRUVANANTHAPURAM *Sales Office is at 5 Chowringhee Approach. Ganga Nagar. LUCKNOW 226001 NIT Building. Sarvodaya Nagar. 29. Chitaranjan Marg. AHMEDABAD 380001 * Peenya Industrial Area. COIMBATORE 641037 Plot No.G. PUNE 411005 T. 5th By-lane.N. Andheri (East). 9 Bahadur Shah Zafar Marg. Road. GUWAHATI 781003 5-8-56C. Nurmohamed Shaikh Marg. MUMBAI 400007 $Sales Offtce is at ‘F’ Block. Sahibabad 201010 Regiqnal Central Offices: : Manak Bhavan. Site IV. Road. MUMBAI 400093 Branch Offices: “Pushpak’.323 3375. CALCUTTA 700072 tSales Office is at Novelty Chambers. V. Princep Street.O. CALCUTTA 700054 Northern : SC0 335-336.T. R. IV Cross Road. Nampally Station Road.89 23 52 51 71 26 23 05 32 36 35 621 17 271085 309 -65 28 222 39 71 695034 atSimco Printing Press. BANGALORE 560058 Gangotri Complex. 5th Floor. NEW DELHI 110002 *Eastern : l/14 CIT S’chemeVII M. Maniktola. Mathura Road. University P. Grant Road. JAIPUR 302001 117/418 B. Nagar. No. 140421. 116 G. Narashimaraja Square. Unit VI. NAGPUR 440010 Patliputra Industrial Estate. Behind Marol Telephone Exchange.91 11 3239382 Telegrams : Manaksanstha (Common to all Offices) Telephone 8-77 00 32 Central Laboratory: Plot No.T. Gokulpat Market. 9 Bahadur Shah Zafar Marg. 1st Stage. 20/9. L. BANGALORE 560002 Printed 550 13 48 839 49 55 55 40 21 40 36 27 21 01 41 8-28 88 01 8-71 19 96 54 11 37 20 10 83 37 29 25 21 68 76 23. GHAZIABAD 201001 53/5 Ward No. Barua Road. Gupta Marg. 62-63. Unity Building. Palayam.C. 323 9402 Fax : 91 11 3234062.P. Bangalore-Tumkur Road. CHENNAI 600113 twestern : Manakalaya. PATNA 800013 Institution of Engineers (India) Building 1332 Shivaji Nagar. FARIDAB‘#D 121001 Savitri Complex. KANPUR 208005 Seth Bhawan. Sector 16 A. BHUBANESHWAR 751001 Kalaikathir Buildings. CHANDIGARH 160022 Southern 32376 17 337 86 62 60 38 43 235 23 15 832 92 95 : C. Naval Kishore Road.