Wembley Stadium, London

Wembley Stadium in London, England

Note: The following article pertains to the original Wembly Stadium. The stadium has since been torn down and is being rebuilt. However, the CobraNet installation worked so well and the technology so clearly demonstrated its value that CobraNet has been specified and is being installed in the new Wembley stadium.

BACKGROUND

Wembley Stadium, in London's north-western suburbs, is 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 M+D Design were appointed to update the stadium's sound system in 1999. One of M+D's specialisation’s is Life Safety techniques, and they have developed their own product line of fault reporting and custom control systems for large venues. 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

M+D 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. This installation is believed to be 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.

Each amplifier subrack included a two-channel fibre hub, with automatic changeover to the secondary ring in the event of failure of the primary. The hub converts the incoming bitstream to a number of CAT5 outputs; one to each of the 8 channel CobraNet output units in the particular subrack; one connects to the CobraNet port on the local Miniframe 108; one provides the Ethernet link to the Miniframe. Thus audio and control data are multiplexed within the same bitstream.

CONTINUOUS FAULT MONITORING

Continuous monitoring of every CobraNet unit is carried out by M+D’s 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. The CAT5 fault detect ring is monitored by the main server in the Control Room.

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 [now Cirrus Logic'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 a an area of system design in which M+D Design 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 separately networked to the main server.

The RATC system is impressively fast; when an emergency status is actioned, levels and delays for every amplifier feed in the stadium are altered - over 800 parameters; and their new settings confirmed back the server by the local miniframes, all within half a second.