Keeping mum for auntie

"on BBC one now it's EASTENDERS, and Kat has a sexy surprise for Alfie..." From next month the familiar words of BBC announcers will come from a setting where soundproofing has had to work overtime. Rather than locking away its continuity announcers and sound engineers in windowless basements, the BBC has put them at the heart of the hubbub in its new Broadcast Centre in London.

To stop sound bouncing around the open plan offices and multiple atriums and create a hear-the-pin-drop zone for the announcers and engineers was the job of Buro Happold's Zé Nunes. His acoustics career began when his rock star dreams ended. "I couldn't play guitar," he says, "so I ended up as the soundman."

The Broadcast Centre was his biggest challenge yet. His task was to insulate the eight first-floor play-out rooms from the atriums, the offices above, and the constant roar of the A40 outside. Atriums, filled with glazing, flood the Broadcast Centre with light. But glass is a poor acoustic insulator compared with dense blockwork or stud partitions, and Nunes needed something in the atriums to soak up the reverberations.

The solution came in two parts. The first was to install acoustic boards on the soffits underneath each level's balustrade, with perforations leading to a large internal cavity where sound is dissipated. The second was to come up with a way of increasing the surface area within the atriums. So he designed the striking rows of 350-odd perforated timber fins stuffed with mineral wool insulation that hang off the atrium walls. "They're a nice way to put in a very ugly product," says Nunes.

Noises off
The big challenge was insulating the play-outs from the atriums. To keep atrium noise out, Nunes built glass corridors to separate the atriums from the play-outs. For the glazed screens that wall the play-outs themselves, the specification was astonishingly difficult. They had to pass every single one of 22 tests conducted at different frequencies – a much easier to achieve average is the norm for office partitions.

"I've been in the acoustics industry for 25 years," says Steve Gardner, acoustics consultant for Optima Architectural Glass, which made and installed the glass screens, "and it's the most stringent spec in glazing I've ever come across. You get higher for solid walls, but it's very unusual in glass."

The answer? Double-glazing with a twist. The mullions and panes are separated to create an unbroken floor-to-ceiling airgap.

The play-outs are kitted out with acoustic ceiling tiles and wall panels, but the holy of holies are the booths they contain for the continuity announcers. Each booth is entirely separate structurally from the play-out, with independent walls and windows butting up against those of its host.

Engineering silence is a relatively recent discipline. But look down from the BBC's blastproof, triple-glazed first-floor facade, and you'll see but not hear the never-ending traffic flow in and out of London.