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An acoustic and service sidewall in an auditorium

A programme of radical improvements has revitalised the 825-seat repertory theatre, built in 1971. The seating has been replaced and re- aligned to improve sight-lines and eliminate central aisles; this gave the opportunity to provide a new underfloor fresh-air supply system and to design side-walls which screen new air-supply ducts, improve the acoustics and incorporate speakers, lighting and signage.

The original 1971 structure - a concrete frame infilled with masonry, with a concrete 'bowl' forming the underbelly of the auditorium - has been retained. New rows of seating are fixed to a plywood deck set onto a steel frame made of simple angles and channels. Slotted bolt connections allowed adjustment to suit the complex curved geometry; they were removed once the frame had been correctly welded into position.

Fresh air passes down dropper ducts concealed in the side walls into a primary plenum box built into the wall construction; from here it flows via sound attenuators into the floor void. Each row overlaps the one below, creating a slot which discharges fresh air at low velocity and without the use of grilles ensuring adherence to strict noise-control criteria.

The service side-walls are curved in plan and formed of Gyproc metal wall lining system which, to give acoustic mass, supports a double layer of plasterboard backed with 22mm mdf, pre-slotted to allow it to be curved. The wall incorporates acoustic diffusers, articulated to help distribute sound.

Throughout the design process, emphasis was placed on ease of construction and use of simple prefabricated components.

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