Transforming the former locomotive shed into an interactive art space, London’s Roundhouse recently hosted the Arboreal Lightning sound and light installation commissioned by singer-songwriter and composer, Imogen Heap. 

The work combined interactive visuals and Ambisonic sound, that supported artist performances and the audiences’ own experience. 

As the centrepiece for her Reverb mini-festival, Arboreal Lightning was a large-scale interactive installation, designed by Alex Haw at his atmos studio, which transformed sound and gesture into an immersive environment. Built at the side of the Roundhouse stage, the tree’s LED strip ‘branches’ spread throughout the venue’s structure, reacting to the sounds produced by both performers and audiences. The Ambisonic installation used a system of K-array loudspeakers to deliver the sound.

‘Imogen asked us to build an audio component into the tree, and we worked closely with sound designer/composer Robert Thomas on the Ambisonics system, says Louis Mustill, director of production company Artists & Engineers. ‘We’ve done a lot of work in the past with surround-sound and it was really good opportunity to do an immersive audio project in the Roundhouse, which is an amazing space.’

A long-term collaborator with Sennheiser UK, Heap introduced Mustill and Thomas to the company. After they had discussed the project with Sennheiser UK’s Dave Wooster, he agreed to supply the K-array system: ‘We chose an Ambisonics set-up because we wanted people to hear sounds literally coming towards and going past them,’ he says. ‘The idea was to include a 3D soundscape which, as the tree’s “branches” spread throughout the main space of the Roundhouse, had to cover the whole area as well. We ended up with a huge soundscape.’

The K-array set-up comprised a KR402 system mounted in a single line behind the ‘trunk’ of the tree, providing a strong sound source from the tree itself, with six KH15s mounted around the perimeter of the Roundhouse’s main space, plus two more overhead to give the all-important sense of height to the Ambisonic system. Two KO20 subs were stacked beneath the stage.

‘The sound had to be fully immersive and what I found amazing was the volume and audio quality from such compact speakers, says Mustill. It’s a really great system for doing surround projects because it’s so small, yet it’s powerful and sounds so good.’

Thomas designed four sequential ‘moods’ that the tree could be in – fire, a thunderstorm, a storm and a dream section. As the tree reacted visually, the Ambisonic system provided a suitable soundtrack.

‘The first mood had crackling fire-like sounds filling the space, this built up to a crescendo of lightning, thunder and electrical static sounds during the storm,’ he says. ‘The storm section had sounds like rain falling while, in the dream section, we remixed Imogen’s songs ‘One Time’ and ‘Propeller Seeds’ into a kind of dreamscape.’

This section was complemented by recorded messages left by members of the public from the ‘listening chair’ – an interactive exhibit that the artist had installed at the Roundhouse in the weeks leading up to the Reverb festival, as well as throughout the event.

‘Imogen invited everyone to engage with the festival by recording a message from the chair,’ says Thomas. ‘All the messages were processed in real time - distorting, effecting and panning them to float around in the three-dimensional soundscape while the tree was in dream mode.’

Despite considerable technical challenges, the Arboreal Lightning installation succeeded in capturing the imagination of audiences who enjoyed the Reverb festival, as well as non-ticketholders who were given the opportunity to experience it for a limited time. ‘There was a lot of work involved, but it was very easy to use the K-array system in a way that created a really good quality soundscape,’ Thomas reports. ‘What made the speakers particularly appropriate for this project is their excellent directional response. We had to set them back quite a way in the space, but they could still focus the sound in a particular area, which meant we could create a convincing 3D soundscape.

‘They are relatively small and quite discreet, but still have the power we needed to project the sound. On top of that, the subs were the best ones I’ve ever worked with, they were so powerful.

‘We were very happy with the finished result, thanks in no small part to the K-array loudspeakers, says Louis. We’re talking to Dave and Sennheiser about other projects that we can work on together again in the future, which is very exciting.’