BFLS’s demountable stage shell is shaped by precise acoustic engineering, writes Felix Mara. Photography by David Grand
More from: Roger Stephenson Architects goes under
Most of us are prone to take good or, at least, audible acoustics for granted, being accustomed to spending time indoors listening to amplified sound. It’s when we’re outside that we become more aware that satisfactory sound transfer isn’t something that just happens as a matter of course.
The problems are particularly acute when high-quality unamplified sound is a priority. Accepting this challenge, Soundforms, billed as the world’s first ever mobile acoustic performance shell, has been developed to bring indoor quality and acoustics to outdoor venues.
Originally conceived by BFLS director Jason Flanagan with conductor and music producer Mark Stephenson, who formed a consortium specifically for this project with BFLS associate director Paul Bavister, Arup Acoustics associate Ian Knowles and Olly Watts of ES Global, its prototype was completed in March this year and Soundforms, which made an appearance at the London 2012 Olympic Park, hit the headlines in July (AJ 12.07.12) when a version of it won Littlehampton Council’s Stage by the Sea competition for a £40,000 shelter and performance space.
Rival contestants were incensed that the resources they had invested in working up site-specific submissions were wasted when what one described as ‘a modified version of a standard product’ won.
The 18-month Soundforms design and fabrication programme benefited from £500,000 of Enterprise Investment Scheme funding, which helped the consortium to pursue its target of a format for visually striking venues, capable of being installed in three days and demounted in one, with enhanced broadcast quality and, with a range of three sizes, suitable for festival audiences of up to 40,000 or able to provide exceptional acoustic sound quality for audiences of 500-750.
‘The shell aims to create the on-stage acoustic of a concert hall, and is radically different to the acoustic performance of a typical open-air concert fabric enclosure,’ says Flanagan. ‘Musicians will be able to hear each other with much greater clarity, thereby ensuring higher standards of performance.’ Optimised acoustic reflectors installed onto the fixed overhead and vertical side stage wing trusses create an inner surface delivering a dynamic on-stage acoustic, enhancing the degree of ensemble between different sections of a band or orchestra. The strength and clarity of the acoustics at Soundforms’ launch concert in March was so good it was almost impossible to believe the music was unamplified. To increase the sound levels projected towards the audience, a ‘peak’ projects overhead, beyond the conductor, reflecting as much sound as possible down towards the audience.
‘Our starting point was the model of an indoor concert hall, similar to the one at the Royal Welsh College of Music and Drama, which I worked on with Jason,’ says Knowles. ‘We avoided directing too much energy back at the performers and bounced it towards the audience using geometry and a mixture of visible 18mm plywood reflecting panels, painted white, and acoustically transparent lycra screens with additional plywood panels behind. Grasshopper software, used as a parametric plug-in to Rhino, helped to optimise the form of the peak and Arup used Odeon acoustic software to fine-tune the acoustic design. But, despite the use of software as a form-finding tool, Soundforms is a dead ringer for a gaping shark.
‘The Inflated fabric skin is supported on a lightweight aluminium frame, which rotates into position around an articulated pin joint, locked to a steel stage grid and weighed down with 26 tonnes of ballast to resist wind load,’ says Bavister. ‘The trusses are rotated and simultaneously pull the external fabric into position, rather like a pram lid, and the skin is then inflated and the acoustic panels flown into position.’ Alternatives to ballast, with enhanced wind uplift resistance are also available.
The skin comprises eight white PVC-coated polyester cushions inflated to various depths by hoses connected to a low-noise AHU, which are attached to the frame with belts and buckles before being connected together with waterproof, airtight zips. The outer skin was designed and manufactured by Architen Landrell and Tensys who worked on Snell Associates’ demountable Garsington Opera pavilion and have been involved in the NASA space programme.
To return to the Littlehampton saga, the apologia for Soundforms might argue that BFLS’s submission was, after all, a modified version of the product, which is marketed as being customisable; that the council had a strong case for choosing a submission with such exceptional acoustic credentials; and that it is unlikely it would have invested its own resources in the competition if it had all but pre-selected the winner. Would the reaction have been the same if the winner had been a practice which time after time makes almost identical proposals for very different sites?
There is also a long-standing debate around whether architects should work on buildings which are products or prototypes for mass production. The case for would argue that these benefit from architectural input and generous levels of design time, whereas the case against might say it undermines the demand for architects and the supply of buildings which are sensitive to the genius loci. Regarding the case for, it would certainly be hard to deny the positive contribution of BFLS’s architectural expertise to the Soundforms enterprise.
AJ Buildings Library
See images and drawings of Soundforms by BFLS
Soundforms: Peak performance