Legislation dictates the minimum number of atten-dants to be present during a performance. Each atten-dant requires a scat in the auditorium.


In multi-purpose auditoria where different formats or uses are combined then all or part of the raked seating will require to be movable. This can be achieved by forming a structure off a flat floor, and include: Bleacher seating: Telescopic structure with tippable upholstered seating with backs, able to be retracted Into the depth of a single and highest row. The rows are straight and the extended structure is a simple rectangular block, which places a discipline on the seating layout.

Temporary seating with raked floor, (a) Retractable, or telescopic seating system as proprietary systems each row retracts into ow behind until the stored unit IS one rear row deep. The sealing – continuous bench, fixed Individual seats with lip-up seats fwith or without arms) – is hinged to lie flat in a stored position. Unit widths are restricted to 6 M and the number of rows LIP to 3C M. The stepped f oor and seating can be pulled out and retracted electrically. by towing bracket or manually according to size. Fot seating with arms and tip-up seats, the minimum riser height is 250 mm, The seats can be loose, with a secure fixing to the riser when in use, on the stepped floor which can be retracted only: the addition of loose seats will take time to set up. but the seats can be used in other situations when the bleachers are retracted. (b) Rostra: a set of metal/timber units able to be built up to form a stepped floor on a flat floor, wi h loose seating secured onto floor or riser, or fixed seating on upper units. Each rostra unit can be collapsed by hinged legs or sides to reduce storage requirements. (c) Sealing units: large units on braked casters or air cushion with either loose seating secured onto floor or riser, or fixed seating, Large sto age area required to accommodate the units when not in use, (d) Demountable kit of parts: proprietary system to form stepped floor or scaffolding built up to form stepped floor- Trolleys are available to mova kit ot parts to and from storage areas, (a) Hyd aulic method: sections ot a flat floor capable ot being raised to varying heights to form a stepped floor; loose seating can then be secured onto the risers.

raked seats 2

Rostra: Complete raked units with cither permanent or removab e seats, on wheels or air pallets for ease of movement into storage areas when not in use.

Sectional rostra: A set of boxes able to be built up to form raked units with removable seats. The storage requirements are less than complete rostra.

Kit of parts: Scaffolding or equivalent set of componcnts able to form raked levels to receive seating. This is the most flexible system, it has efficient storage requirements, but is labour intensive. I-Iydraulic lifls: Mechanical method of raising sections of the flat floor to form a rake floor to receive seating. Loose seats, secured in position when required for performances, can bc used with functions requiring a flat floor.

Specific Studies

Average cyc height at 1120 mm above the theoretical floor level: the actual eye point will depend on seat dimensions.

Distance from the centre of the eye to the top of the head, taken as 100 mm as a mmimum dimension for the calculations of sightlines.

For assurance that there is a clear view over the heads of those in the row in front, this dimension should be at least 125 mm. Front row of seats: the distance from point to the edge of the average member of the audience in the front row. The closer the first row to the platform/stage, the steeper will be the rake. For orchestral and choral musicy the area immediately in front of the platform may hc required to he clear for acoustic reasons. For rock concerts a rail and space may be required for security reasons between audience and stage.

Sightlines: seated audience

For the whole of the audience to have an unmter- rupted view of the performance and its setting over the heads in front and clear of overhangs, the section and plan of the auditorium needs to conform to certain limitations set by vertical and horizontal sightlines.

Vertical sightlines

Vertical sightlines may be calculated by establishing: Lowest and nearest point of sight on the plat- form/stage for the audience to see clearly The platform/stage height, when raised, can range from 600 to 1100 mm above the lowest level of the auditorium and point P can be the leading edge, or setting line for the performance, at or above the platform/stage level. If a forestage is part of the proscenium or end stage formats then pomt P needs to relatc to the forestage. If an orchestra pit is included between stage and seating then point P may be regarded as the conductor’s head. With a symphony orchestra in a concert hall, the ability to see each musician at the front of the stage {who partially masks the other musicians) may not be critical and point P may be taken as over 600 mm abovc the platform lcvcl at the front edge. For dance the audience requires to see the feet of the dancers so the point P needs to be taken from at least the setting line at stage level.

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For opera, musicals and drama, The longitudinal section is a parabolic stepped floor as the theoretical rake produced by the sightline calculation. This gives every member of the audience similar viewing conditions. This may be rcduccd to a single angle or series of angles. When applied as described the rake will also be steep. This is satisfactory for a single tier of seating with no balconies and is especially appropriate for open stage formats. If a balcony or balconies are introduced, as with proscenium formats, the rake of the lower bank of scats can be reduced, assuming vision to be every other row allowing for point being seen between heads in the row in front. The vertical distance between a point from the eye to the top of the head for calculation purposes can be reduced to 65 mm. If the scats are staggered then the situation can be marginally improved. This is particularly applicable with the design of a large auditorium where, within the visual and aural limitations, the aim is to maximize the seating capacity. This implies a balance between sightlines, height of the auditorium and seating capacity: a reduction in the accumulative height of the lower level of seating allows more height for balconies, With the smaller auditorium, especially with the audience partially or wholly surrounding the stage and a limited number of rows of telescopic seat, an Increased height of the rake to the seating encourages a sense of enclosure of the stage, while providing good sight.