Audio Engineering Society UK

Title: Lord’s Cricket Ground: Voice Alarm
Location: Royal Academy of Engineering, London
Description: Lecture by Roland Hemming of RH Consulting
Start Time: 18:30 for 19:00
Date: Thursday 14th October 2010

A recording of the lecture is available here (13MB mp3)

Lecture Report

With an portfolio encompassing the Millennium Dome, Ascot Racecourse, Twickenham, and St. Pancras International station, Roland Hemming most recently turned his sound system design and project management expertise to Lord’s Cricket Ground, which is currently undergoing a multi-year renovation project.

Three interrelated aspects of the new system were covered in Roland’s talk. The first of these concerned the correct approach to standards compliance. The second covered the more general technical challenges involved in fitting out a large and complex sports venue, where the public address system is used routinely to entertain as well as inform. Thus the system must at once be versatile enough to cope with any conceivable situation, simple enough for a novice to use, and robust enough to withstand partial failures and still carry on working in an emergency. The third aspect is the diplomatic side of the work, and the importance of communication and commercial skills in managing a large installation project.

Voice alarm systems for public address are covered by a number of standards. These specify such things as the speech intelligibility of the system and the need for distributed redundancy of circuits and amplification to avoid any single point of failure. They also stipulate requirements for fire resistance, remote fault monitoring, and operability in the event of a power failure. Many of these needs are specified fairly loosely, providing scope for interpretation. Consequently, much of the skill in working with voice alarm systems is in knowing how much redundancy and fireproofing to build into the system, and where to put it. The latest of these standards is EN54, which will be enforced from 2011, and introduces product testing to the mix. Further to this, there are other standards that cover specific installations, including BS7827, which concerns sound systems for sports venues.

The best practice for voice alarm installation often diverges from that found in professional audio engineering, as the emphasis is on failsafe design that entrusts dynamic control of loudspeaker amplification and routing to pre-programmed paths that are self-regulating, without the need for human intervention. Redundancy is harder to achieve over data networks: unlike audio, Ethernet must be singly-connected and wired point-to-point, and cannot normally be run in loops, but this can be done in stadia using spanning tree technology.

Certain special cases are exempt from EN54, including self-powered loudspeakers and loudspeakers for ‘special’ applications (those, for example, with particular directivity characteristics). Also exempt are ‘kit systems’, made from individual elements of non-Voice Alarm equipment that together comprise the system: the discretion is then left to the project manager to justify the safety of the resulting system, and the local safety authority to approve it.

The Lord’s system comprises eight distributed digital rack rooms. This distribution not only assists redundancy, but also keeps down the length of cable runs. The system is designed to be truly expandable, which can mean anything from moving the walls around in a hospitality box to razing and rebuilding an entire stand. Four control stations provide the opportunity for live announcements, controlled by a touch-screen user interface that allows these to be directed appropriately. Although the venue will eventually divide into 165 sound zones, this is greatly simplified for normal operation so that the system can be employed by an announcer with just a few minutes of training. Hybrid transformers allow audio to be injected into individual areas to provide localised input where this is required. The system features Dante audio networking technology providing audio over IP, ASL Vipedia audio processors, Lab.gruppen amplifiers, and DAS loudspeakers. A local analogue loop provides emergency backup in each rack room, and the use of many small speakers allows every spectator to be reached without disturbing the neighbours.

One of the most difficult elements of any installation, not least one concerning such a historic venue in such an exclusive neighbourhood, is the balancing of the many vested interests. The local council, residents, the various committees, the operators themselves, and the safety team must all be satisfied with the system’s specifications and performance. Discussions prior to installation take years, and can continue after the major part of the installation is complete. The installation itself, being by far the most expensive stage of the operation, is often over in a matter of weeks and must therefore be planned with precision. The potential for catastrophe makes these large projects an exercise in risk management. Without satisfaction, there can be no compliance; without compliance, there can be no venue; without a venue, there can be no business.

Report by Ben Supper

For those who wish to know more about voice alarm, Roland has co-written a book on the subject that is available from avitas-global.com.