UNIT 2Design of Auditorium

Size, shape, sitting arrangement design criteria for speech and music, acoustical defectsin an auditorium, sound foci and dead spots, acoustical correction design andmodification techniques.

Auditorium

KEY POINTS:• Most auditoria are designed to fulfil a number of purposes• The object is to ensure a near 100% of usage • Every member of the audience should he able to see and hear the whole performance

Contents• 1 Introduction• 2 Seating• 3 Auditorium design• 4 Theatres• 5 Studio theatres• 6 Concert halls• 7 Conference halls• 8 Cinemas• 9 Multi-purpose auditoria• 10 Support facilities• 11 Legislation

Auditorium

1. Introduction

Visual and aural limitations:(a) Plan: for a performer at centre stage B there is an arc Y beyond which visual and auralperceptions are impaired. However, for performers nearer the sides of the stageat A and Cproduce more restrictive curves X.(b) Section:Similarly, visual and aural limits in section also set an arc centred on the performer

2. Seating

Auditorium seating: definitions of terms and dimensional information (a) Plan.(b) Section

2.1 Design of Auditorium Seat

2.2 Working Dimensions Auditorium Seat

2.3 Supports

2.4 Other factorsa) Acousticsb) Ventilation and Heatingc) Upholstery

3. Design of Auditorium

It determines the maximum distance from platform or stage at which the audience is able toappreciate the performance and for the performers or speaker to command anaudience. Thisdistance varies according to function type and the scale of the performance:• For drama it is essential to discernfacial expression, and the maximum distance shouldbe20 m measured from the setting line of a proscenium stage or geometric centre of an openstage.• For opera and musicalsdiscerning facial expressions is less critical and the distance canbe30 m.• For dance the audienceneeds to appreciate the whole body of dancers and facialexpression: the distance should not exceed20 m.• For full symphonic concerts acoustic conditions predominate.• For chamber concertsacoustic conditions also predominate but visual definition assistsachieving an intimate setting.• For conference speakerand lecturer there are two scales: discerning facial expression,restricted by20 m; larger scale where facial expression is not regarded as critical.• For slide, video, television and overhead projectionvisual limitations are determined bytheir respective technologies.

3.1 Audience Requirement

3.2 Visual Limitations

• This refers to the distances across which speech, singing and music can be clearly heardwithout the need foramplification , and beyond which they cannot.

• For drama, opera and classical music amplification is deprecated; but itis acceptable forvariety and essential for rock music.

• For amplified sound the auditorium requires adead acousticwith no reflected sound fromthe platform or stage and limited or no reverberation; loudspeakers are positioned toprovide full and even coverage of the audience.

• The volume and quality of the unamplified sound is dependent on thevolume, shape, sizeand internal finishes of the auditorium, and on itsresultant reverberation time.

• It is therefore not possible to lay down limits as for visual appreciation.Even experts inacoustics find that their predictions are not always borne out in practice, althoughtheyshould be consulted and their advice followed wherever possible.

3.3 Aural limitations

• With a single levelonly, the pitch of the rake requires particular attention to achieve asense of enclosure.

• The Greek amphitheatre is the example.• Seating capacitywithin aural and visual limitations can be increased by the addition of

one or more balconieswithin the overall permissible volume of the auditorium. Similarly,boxes, side galleries and loges can be added to the side walls, especially in the case of theproscenium format.

3.4 Levels in the auditorium

• With traditional seating the maximum number is22 if there are gangways at both ends ofthe row, and11 for gangway at one end.

• Thus in all but the smallest auditorium the gangways divide the seating into blocks.• Rows with more than22 seats are permitted if the audience is not therebyimperilled .• The term ‘continental seating’ is used for rows of seats with an increased back-to-back

dimension extending the width of the auditorium with exits at both ends.• This arrangement is only appropriate toproscenium stages.

3.5 Number of seats in a row

• Spacing is controlled by the clearway between the leading edge of the seat (in an uprightposition, if tippable) and the rear of the back of the seat in front.

• For traditional seating the minimum clearway for people to pass along the row is 300 mmand this dimension increases with the number of seats in a row. Forcontinental seatingthe clearway isnot less than 400 mmandnot more than 500 mm.

• Legislation also dictates the minimum row-to-row dimension at760 mm: this is usuallynot adequate and the minimum should be850 mm for traditional seating.

3.6 Row to Row Spacing

(a) Row to row dimension and clearway with fixed seating.(b) Row to row dimension and clearway with tipped-up seating

• As gangways are essentialescape routes, their widths are determined by the number ofseats served.

• The minimum is1100 mm.• They can beramped up to 10%, but only 8.5% if likely to be usedby people in

wheelchairs.• If the seating rake is steeper, gangways must have steps extending the full width and these

must have consistenttreads and risers in each run.• This means that therow-to-row spacing and row rise should be compatible with a

convenient gangway tread and riser; and this in turn means that theshallow curveproducedby sightline calculationsshould be adjusted to astraight line.

3.7 Gangways

3.7 Seating Geometry

3.8 Sightlines for a seated audience

P Lowest and nearest point of sight on the platform or stage for the audience to see clearly.HD Horizontal distance between the eyes of the seated members of the audience, which relates to the rowspacing and can vary from 760 mm to 1150 mm and more.EH Average eye height at 1200 mm above the theoretical floor level: the actual eye point will depend on seatdimensions.E Distance from the centre of the eye to the top of the head, taken as100 mm as a minimum dimension forthe calculations of sightlines. For assurance that there is a clear viewover the heads of those in the row infront this dimension should be a least 125 mm.D Front row of seats: the distance from point P to the edge of the average memberof the audience in the frontrow.

Sightlines at transverse gangway; the angle of the rake line is constant

The angle of horizontal vision for a stationary head is 40°

The maximum comfortable amount the head can

be turned from the seat centreline is 30°.

Horizontal sightlines of the

performer

4 Means of escape

• The maximum travel distance from seat to exit within the auditorium is determined by theneed to evacuate from each level of the auditorium within2½ minutes.

• For traditional seating the maximum travel distance is18 m measured from the gangway, forcontinental seating15 m from any seat.

Travel distance

Exits

• From each level of the auditoriumtwo separate exitsmust be provided for thefirst 500 seatswith an additional exit foreach further 250 seats. Below table gives the minimum total ofexit widths required by legislation. Each exit from the auditorium must lead directly to a placeof safety.

• Wheelchair users should be provided with flat or ramped escape routes which may beseparatefrom other routes. Ramps should not be longer than 4.5 m or steeper than 8.5%.

Exit routes

• The route must be a consistent width the same as the exit. There must be no bottlenecks andall doors within the route must open in the direction of escape.

• Routes within the building should have fire-resistant enclosures. There are specialrequirements for all doors opening onto fire escape routes.

Stairs

• Staircase flights should have at least two risers and not more than 16. All treads should be 275mm and risers 180 mm.

Ramps

5 THEATRE

Relationship diagrams for buildings for

opera, musicals, dance and drama. If for

drama only, the orchestra pit and

musicians spaces may not be required:

Where the building serves only touring

companies or with a resident company

whose production facilities are elsewhere.

Where production facilities are needed

5.1 proscenium stage

Vertical sightlines for proscenium stage. Vertical sightlines for open stage

Auditorium formats for drama on open stages:

a End stage.

b Fan shape, 90° arc with or without rear

balcony.

c Thrust stage, 180° + arc, with or without rear

balcony.

d Theatre-in-the-round.

e Transverse: audience on sides of stage

6 Factors to be considered in the acoustical design of an auditorium

1. Area and Volume

Area= 0.60 Sq. M to 0.90 Sq. M

Volume

Cinemas or theatres = 4.0 Cu. M. to 5.0 Cu. M.

Musical Halls and Concert halls = 4.0 Cu. M. to 5.5 Cu. M

Public Lecture halls = 3.5 Cu. M. to 4.5 Cu. M

2. Shape

3. Sound Absorption

4. Site Selection

5 Seats and Seating Arrangement

• Arrangement

• Back to back distance

• Balcony

• Balcony Seats

• Covering of Seats

• Front Most Row

• Raising of Seats

• Width of Seats

7 Constructional and planning measures for good acoustical design of auditorium

• Seeing and hearinghave to be satisfied.

• Sight lines from every seating position to the entire stage will show whether the seats areproperly located or not.

• Proper elevation of rowsof seats and their staggering will ensuregood visibility.

• To appreciatefacial expressionsbeyond 20m is difficult.

• About0.6 to 0.8 sq. m/ seatand4 to 5 cum / personwould be reasonable.

• Fan-shape or rectangular shapeare common.

• A reflection reflective canopy over the stage, to direct sounds to rear areas is a must.

• Changingslopes of ceilingalso help in the passage of sound to distinct areas.

• Avoid parallel walls.

• Use ofSplayed sound reflective surfaces behind the sound sources.

• Note the purpose, number of seats (assuming 80% occupancy) location ofstage, sidecorridors, positions of doors and windows.

• Rear portions be treated with absorbents to avoid‘echoes’at the height of about2.5mso thataudience may not be tempted to disturb it.

8 Defects in an auditorium and their Remedies

9 Do’s and Don’t for good acoustical design of auditorium

Take care of

1. ‘Dead-Spots’when the sound level is low.

2. ‘Echoes’from concave surfaces.

3. ‘Whisper’ when sound source is close to a long curved surface and sound goes tangential

along the wall.

4. ‘Flutter’ when sound-source and listeners, both are between a pair of hard surfaces.

5. In ‘Auditoria’, surfaces required todisperse sound reflectionof 50cm. This is to avoid

echoes and provide diffuse reverberation.

6. Flutter echo can also occur betweentwo non-parallel surfaces if the sound source, S is

located between them.

7. Noises bothinternal and external likely to be created are to be considered at the design

stage itself.

8. Sound recorded on films should not be modified in the hall. For this theRT be kept ˂1 sec.

by properabsorbent treatment.

9. Traffic side be located bythick plantation and absorbent corridors.

10. Rehearsal rooms and mechanical equipmentrooms should not be under the stage.

Occupancyabove the auditorium should beavoided. Avoid sliding doors. Use gasket doors.

Corridors and Lobbies be treated with sufficient absorbents.

11. If the auditorium is expected to bemultipurpose, as for lectures, dramas, orchestras, get-

together, marriage partiesetc. full frequency response sound systemis to be employed.

12. Upholstered and elevated seats with good sight lines be arranged to minimizethe distance

from the performance area.

13. Central 80% areaof the ceiling be kept reflective and remaining20% along the perimeter

are kept absorptive.

14. Side wallsbe kept reflective and diffusive with many irregularities. Rear wall shouldhave

deep absorptive finish. Floor (In front of the stage) be carpeted to control‘Foot Fall Noise’.

15. Fabric seats (not leather)with perforated seat pans provide stable RT when auditorium is

partially occupied.

16. Avoid Vaults and Domes. Back ground noise be controlled by proper masking. Mechanical

systems noise by absorbent covers and duct born noise by internal duct lining absorbents.

17. Sound reinforcing systemis needed when the number of seats ismore than 200. In that

case, a central system, just above and in front of the stage opening with line of sight of all

seats are preferred .

18. In large auditorium and larger occupancy, shallow balcony (depth less than twice the opening

height) with its front face treated with absorbents is desirable.

19. Electrical control-room, if needed, should be at the rear and the operator should be able to

see the happenings on the stage, hear the control sound.

20. Provision forhanging reflectors and absorbentsis needed to provide variable RT for films,

dances, speeches, etc. Flat floor is necessary for variable occupancy, games, parties,

exhibitions etc.

Partha Sarathi MishraAsst. Professor

School of ArchitectureGITAM University

parthaconcept@gmail.com

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