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BACKGROUND The original Wembley Stadium, in London's north-western suburbs, was without doubt the world's most famous football (as in soccer) ground. With a capacity of nearly 100,000, it is one of the largest sports stadia in Europe as well as being one of the UK's most instantly recognisable landmarks. It was with some pride, therefore, that specialist UK systems company Nebula Audio were appointed to update the stadium's sound system in 1999. The brief was to replace the existing single fibre distribution system (installed in 1989) with a dual-redundant network, incorporating multiple fault detection in each zone, and to replace the many hardware equalisers and limiters in each zone with venue-wide digital domain processing. At the same time, a more sophisticated touchscreen-based paging control system was to be introduced. MAXIMUM REDUNDANCY Nebula chose to implement the new distribution system using CobraNet technology. A total of 14 racks - 2 main and 12 subs - are installed around the stadium. In addition to containing the power amplifiers for the immediate area, the subracks each contain a Peavey Miniframe 108, and the two main racks a Miniframe 208. These are all networked together via Ethernet for control purposes, and all are fitted with CobraNet interface DSP cards. This network of 14 MediaMatrix units provides totally decentralised processing for the system, providing a very high degree of redundancy in that half of them can fail simultaneously and the system still function normally. At the time this installation was the largest MediaMatrix system outside the USA. COBRANET THROUGHOUT Two dual runs of fibre cable were laid around the entire stadium, forming two double, concentric, interwoven rings, starting and finishing at the Main Control Room (situated between Wembley's famous twin towers). The subracks’ connections to the fibre rings was alternated, such that Ring Pair A served the odd-numbered racks and Ring Pair B the even, for maximum redundancy. Furthermore, as each pair used primary and secondary fibres, even greater failsafe protection was afforded. CONTINUOUS FAULT MONITORING Continuous monitoring of every CobraNet unit is carried out by Ikon AVS proprietary SID units, which are interconnected via two concentric CAT5 rings using the same alternate-connection method as the fibre rings. The SID units’ primary function is to monitor the 20KHz low-level trace tone (superimposed on the audio within the MediaMatrix system) at the amplifier outputs, thus detecting the failure of a single channel of amplification. CUSTOM CONTROL SYSTEM A unique aspect of the system is that the entire MediaMatrix system is controlled via the Ethernet network from a main network server PC. This system uses Peak Audio’s RATC (Remote Access Terminal Control) system, which permits full control of every parameter of the system with standard TCP/IP protocol. It also means that the user interface can be designed to be absolutely specific to the installation, thus requiring no knowledge whatever of the MediaMatrix system itself on the part of the operators. This is an area of system design in which Nebula Audio have become specialists, and for Wembley provided a set of custom paging stations with large LCD touchscreens for the main control desks. These display a very clear, colour-coded plan of the stadium, enabling an operator to immediately select a single area, multiple areas or the entire stadium for paging. Fault conditions and non-availability of an area are also displayed on the plan. The paging stations themselves consist of a dedicated life-safety-compliant CPU
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