In the can

Not so long ago – during the early 1990s, to be precise – the British film industry lurched from one crisis to another. Award-winning director David Puttnam led a cast of thousands who pleaded in vain for extra Government cash to fund their projects. It wasn't forthcoming. US-produced blockbusters dominated our cinema screens and, bored with the same old scenes, audiences deserted in droves. Then along came The Full Monty and Lock, Stock and Two Smoking Barrels. The rest, as they say, is history.

Buoyed by a resurgence in ticket sales, the industry strived to build bigger and better cinemas, many of them out-of-town multiplexes. Sure enough these were well liked, but something a little bit different was needed to maintain peoples' interest. Cue Imax: a state-of-the-art film medium that is already redefining the cinematic experience¹.

Realising its potential, the British Film Institute (BFI) chose the Bullring roundabout near Waterloo Station as the site for the UK's largest Imax auditorium to date.

Financed jointly by the Arts Council of England Lottery Fund and the BFI and completed in just 18 months, the glass-encased £20 million landmark building was designed by Avery Associates Architects. The 'drum'-shaped, six-storey structure sits neatly on a giant 1·8 m-deep concrete raft. This is supported by a series of 60 giant springs to stop the building vibrating each time a Waterloo and City Line London Underground train passes just 4·5 m below the 5000-tonne drum. Imax auditoriums have to be a 'dead' space acoustically, of which more anon.

Inside the drum, the ground floor plays host to a ticket sales and reception area, in addition to a café-restaurant. Just prior to showtime, visitors are channelled up a flight of stairs to a holding area on the first floor. They are then able to enter the spacious and rather spectacular 482-seat auditorium. This hugely impressive deep-plan space houses the giant 20 m-high, 26 m-wide perforated vinyl projection screen, the surround-sound speaker system and the projection room itself.

"Imax Corporation design briefs are very strict when it comes to the environmental conditions in the auditorium and the projection room," said Alan Bacon, project director for m&e consultant TME Engineers. "They prefer to condition the space using a displacement ventilation system." Indoor air quality in the building is regulated by a ducted air system linked to air handlers in the third and sixth floor plantrooms. The sixth floor plantroom boasts four high-efficiency reversible heat pumps which feed into the chilled water or heating circuit to provide heating or cooling. Fresh air is routed down via a series of ducts and introduced to the auditorium through grilles located beneath the seats. These displacement diffusers are fed with 100% fresh air supplied through the floor void. The heat pumps in the sixth floor plantroom draw the air into the building via a series of louvres and exhaust return air via separate banks of louvres located at high level alongside the domed roof.

Twelve waterside fan coils provide heating and cooling for the projection room, rear-of-house offices and the café/restaurant at ground floor level.

Designing the acoustic systems

Stringent acoustic criteria laid down by the Imax Corporation meant the design team had to achieve NC25 in the auditorium. "Sound attenuation was a major concern," added Bacon. "The projection systems for Imax presentations are very noisy in themselves. They can generate up to 120 dB at 63 Hz". Not only that, but the high-fidelity, six-channel Sonics sound system delivers 11 600 W of audio power through 44 three-way bass speakers to the auditorium space. That's loud by any standards. To treat the space, acoustic engineer Peter Henson of the Bickerdike Allen Partnership asked for a baffled ceiling in the auditorium. The tiered secondary ceiling consists of curved and overlapping acoustic baffles. Each baffle is constructed from Melatech foam panels which are suspended from the structural soffit. Measured noise levels have been as low as NC20. Clearly, this design solution has worked well.

The cinema opened in June to rave reviews, showing the 3D and 2D adventures Into the Deep and Destiny in Space. The plaudits shouldn't be reserved solely for the Imax film medium, though. Thanks to the design team, commuters, residents and tourists can enjoy the Bullring in the way that Lambeth Council originally intended – as a lively cultural 'island'.