Warehouse weaves wonders in Princes Street.

Promoted by the Scottish Chamber Orchestra (SCO), the closing event of the Edinburgh Festival sees a performance by the orchestra emanating from the gardens beneath Princes Street, culminating in a spectacular fireworks display. The concert is broadcast through to several parts of the city, not least the length of Princes Street itself, where many thousands of revellers congregate. In terms of audio it has always been an ambitious finale and, as the event has grown in stature, this was SCO's 26th year, so the expectations placed upon the PA system provider have grown with them.

'We've always seen the need for a PA system to deliver to the crowds up on Princes Street,' said Cameron Crosby of Edinburgh-based Warehouse Sound Services Ltd, the company contracted to fulfil all audio requirements for the night. 'But the geographical layout means the solution is not obvious. From the gardens the orchestra faces uphill and across the street, rather than down it. To cover the audience in this area from the stage we would need to fly a PA at around 15m. Unfortunately due to weight restrictions we can't position cranes down there, so we fly off the main stage towers at 7.5m, and then place outfills throughout the gardens but maintain a zero time plane so that the listeners on Princes Street don't hear multiple time paths.'

The system specified was all d&b audiotechnik, comprising J-Series for the central area and Q1 loudspeakers for the distributed outfills. The Warehouse also installs a comparable system of Q1s a mile or so away in Inverleith Park, where a less boisterous, more family oriented atmosphere pervades. But it is the revellers down the length of Princes Street, stretching west and east from the central stage area, where Crosby and his company have found the biggest challenge. 'We've done a lot of work on this over the years and have always thought a distributed system along the length of the street the best way to address the crowds properly. But issues of crowd control, signal distribution, electrical power and amplifiers have always made this an unaffordable solution. That is until now.'

Crosby, it should be noted, is a persuasive purveyor of the argument for correct and proper usage of audio, and the SCO are very like-minded when it comes to issues of fidelity, but economic imperatives prevailed till this year. 'We did look at less complex ways of achieving coverage; tall towers with J-Series line arrays could cover the distance, but of course the street, relative to say a normal concert environment, is quite shallow front to back. What do you do with all that sound energy off to the sides? And of course everyone is facing south, towards the castle.' Crosby's solution was single Q7 loudspeakers, mounted on Manfrotto stands at 14m intervals all along the south side of the street. 'We'd calculated the distance, 14m between loudspeakers was ideal for coverage from the cabinet and, in terms of arrival time for the listener at the boundary between two adjacent loudspeakers, the variation was not really noticeable.' Needless to say, Crosby did real-world experimentation to confirm his calculations.

'The important thing and what had previously made this a difficult and expensive design was control. In our design, one D12 amplifier drove four Q7s. We placed a D12 amplifier at the midpoint with two loudspeakers each way, and linked all the amplifiers with d&b's Remote control network. This gave us control of individual level and time alignment to each loudspeaker from a central point. Time alignment was, of course, set earlier during fit-up, but the ability to control level down the street remains a necessity throughout the event.' With the last amplifier on the street almost 300m from central control point this distance is in excess of the stated remote CAN-Bus performance parameters but Crosby reported no problems. 'Naturally we tested this too, and through experimentation found an ideal CAT5 cable solution by using a combination of Ethernet to d&b R70s and CAN-Bus from there on. The mains was also pretty straightforward; there is a fair amount of locally placed mains available; we laid in 2.5mm² distro cable and didn't measure any appreciable voltage loss over the kind of distances we were running, but then the D12 is so efficient we were only pulling 8 amps to each one.'

The combination of stirring music and spectacular aerial displays will always wow the crowd, but did the client appreciate the efforts of the audio department? 'The orchestra were delighted with the result,' said Crosby. Will he repeat the system next year? 'Absolutely, and we're investigating running the R1 Remote control software across a Wi-Fi network. Our initial tests have been extremely positive.' If you think about the issues involved, Mr Crosby obviously enjoys the challenge; it might be clear air transmission for the Wi-Fi but the distances and the physical constraints they impose remain the same. Somehow you get the impression he'll overcome them.