An incredible 1.9 million square feet development serving a catchment area of over 4 million people, the £1.8 billion Westfield Stratford City retail project is the largest urban shopping centre in Europe, featuring 250 shops, 70 eateries, three hotels, a casino, cinema complex and extensive office space. All of these elements make it one of the largest urban regeneration projects ever undertaken in the UK.
PEL Services designed and installed the complex PA and Voice Alarm (VA) system for this busy, high footfall visitor environment.
The sheer scale of this retail development is breathtaking and required those involved in its creation to use all their experience and talent in their separate fields to bring the project to fruition on time (just before the 2012 Olympics), to exacting standards and with a focus on enhancing the consumer experience by the use of technology.
The result is some very notable achievement, including one of the very best Public Address (PA) and Voice Evacuation (VA) systems to be found in a retail complex anywhere in the world.
An exaggerated statement to make? We don’t say this lightly: when you have manufacturers, consultants and architects who have all been in the business for 20, 30, 40 years or more making this same comment about the system at Westfield Stratford City, it’s time to take note.
The clarity and quality of the sound produced by the PA/VA system is exceptional, but what makes this all the more impressive are the challenges faced and overcome to reach that point, from the sheer size of the retail development through to the combined entertainment and security / safety requirements placed on the system. To pull this one out of the bag required a team effort by skilled partners.
PEL Services – a leading UK systems company that has been designing, supplying, installing, commissioning and maintaining sound, fire, security & communications systems for nearly 40 years – was awarded the PA/VA contract from M&E contractor Essex Services Group as a result of PEL’s extensive experience and because of its ability to take full design responsibility.
A development of this size and complexity requires detailed acoustic modelling before any thought of system design and equipment specification can be entertained. AMS Acoustics had undertaken the assignment at the previous Westfield project at White City and Essex Services Group felt that it would be appropriate to engage the services of this leading acoustic consultancy to work jointly on the Stratford City project, with AMS specifying the system performance requirement and PEL determining the constituents of the system and its configuration.
The first key stage of the process involved AMS taking the architectural plans detailing building materials, surface finishes etc. and, using proprietary and in-house development design software, undertaking acoustic modelling of the entire retail complex. Highly knowledgeable in their field, AMS was quickly able to identify six acoustic areas: two main areas (the Northern Mall and Central Arcade) and smaller ones such as lift lobbies and the welcome halls.
Loudspeakers were then entered into the software programme to allow the computer to predict speech intelligibility. This is performed by means of high resolution ray tracing that systematically probes each surface within the computer model which assimilates the raw data required to fine tune the system and acoustic properties in order to optimise the music and speech reproduction. This laborious yet vital exercise demands the enormous processing power of three 6 core computers, with each trace taking over two days to generate the resultant data.
From here AMS was able to specify the Sound Pressure Level (SPL) required and the speaker placement, allowing AMS to confirm the suitability of PEL’s loudspeaker selection and system architecture.
PEL is able to work with a number of PA/VA manufacturers but with a system of this size and complexity it was determined that only Bosch’s Praesideo digital system running across a dedicated fibre optic network was considered suitable for the task at hand.
Unlike traditional PA systems, Praesideo uses a network configuration rather than having all system elements connected to a central controller. This architecture gives real freedom in system design. The ‘daisy-chain’ network topology means system elements can be connected to virtually any point and any type of equipment to be located wherever most suitable in the building (e.g. power amplifiers closer to loudspeakers). What’s more, by connecting the network ends together, a ‘redundant’ loop is created so any break in the cable doesn’t affect operation – an important consideration in an emergency system.
The Praesideo system was specified by PEL to drive the top of the range Electro-Voice ZX1i full range cabinet speakers for the main mall, with ceiling speakers installed at the lower levels. Bosch modular ceiling loudspeakers were used in the smaller locations such as welcome halls and communal areas. Nearly 1500 loudspeakers were used in total, along with 45km of cable, 21 equipment rack locations, 25 equipment cabinets, each 36U (6’ high), and over 3 tonnes of batteries for back up!
PEL designed the system to be controlled from two independent fire command centres via a multi zone microphone console and GUI (Graphical User Interface). The system is interfaced with a number of ‘packages’, including the fire detection system, the centre’s own radio station and a special events package.
Once specified, PEL produced system schematics and calculated the amplifier (50935 watts in total) and battery power required to maintain the system in the event of mains failure. To replicate operating conditions and thoroughly trial its performance the entire system was then set up within an empty warehouse rented by PEL for the exercise. It was then witness tested by the client and the professional team before handing over the detailed specification to Essex Services Group for them to install the loudspeakers.
But that was far from the end of the story. Once installed PEL carried out the commissioning of the system and provided operator training.
A basic system was up and ready by February 2011 as required and then developed as the centre was fitted out.
Challenges Faced & Overcome
We have already seen the incredible scale of the PA/VA system at Westfield Stratford City which brings challenges in itself; but what about the other aspects that have proved to be demanding? What about the acoustically hostile environment a shopping centre poses? And how do you get a system to perform to satisfy two separate requirements that are almost mutually exclusive?
All PA/VA systems in a retail environment are used partly for ‘performance’ (music, messages etc.) but with the emphasis understandably given to life safety, i.e. voice evacuation. Invariably the ‘performance’, in respect of clear, intelligible annunciation of the safety messages, is compromised by the desire for good bass response to satisfy the ‘entertainment’ quality. Clearly Westfield Stratford City did not want safety compromised under any circumstances but it did want the performance aspect to play a far more eminent role than is usual which PEL and AMS combined to achieve very effectively.
The trick is to carefully balance the two. Whilst it is exceptionally difficult to achieve, in the case of Westfield Stratford City, the team effort between AMS, PEL and Bosch, as well as the architects, won the day!
If, at the early acoustic modelling stage, an equipment based solution to audio intelligibility could not be found AMS worked closely with the architects to solve the problem, even advising on changing building materials and to the extent of adapting the building design where necessary.
AMS Acoustics refers to this aspect of a building’s design as ‘Aural Aesthetics’. Modern architectural design often focuses on open spaces and bringing light into the building, using materials such as metals, glass, and marble. However, these can cause rampant acoustics – the sound literally bounces off the surfaces and reverberates, making it difficult to communicate and in the worst case making the space an unpleasant place to be. AMS strives to work with architects to harmonise the sensory elements and to make them aware of the importance of aural aesthetics and its impact.
At Westfield Stratford City a very good working relationship was established with the architects who were very receptive to AMS’s advice. In the top Northern Mall, for example, the plan was to put the speakers behind the ‘ribs’ in the ceiling, which compromised the system performance, so discreet insertions were made in the ribs for the speakers, which overcame the problem. Additionally in the Central Mall acoustic absorption material was added to the ceiling to good effect without adversely affecting the overall visual element.
The main malls also proved challenging given their height and the number of levels encountered. The danger posed here was incoherent sound merging from these different levels, but PEL and AMS overcame this with the clever use of delays. AMS calculated the signal delay required and PEL set the individual delays and EQ of each amplifier.
The success of this expertise and attention to detail speaks for itself: the system proved so good that Nicole Scherzinger’s performance at the official launch opening ceremony was fed through the centre’s PA system in preference to the dedicated performance system hired specifically for her, as it was considered superior. A remarkable achievement! Of course this had the added benefit of allowing the singer to be heard not only by the assembled dignitaries within a localised area but to everyone throughout the centre.
The other main acoustic challenge faced at Westfield Stratford City came from the exceptionally noisy giant extractor fans that are used to remove smoke and fumes in the event of a fire; a case of one life safety device negatively affecting another, in this case the VA system. With the higher than anticipated sound output of the extractor fans it was evident that they would drown out the VA system. The generally accepted maximum SPL for noisy public areas is 90 dBA. But to overcome the output generated by the fans, 93 dBA was a critical requirement and hence the solution was to go bigger and louder, with PEL using twice as many amplifiers.
The PA/VA system at Westfield Stratford City is a testament to the quality of the equipment used and to the expertise of those involved in the system design, specification and installation. From the acoustic modelling and speaker placement, to the equipment specification and calculations and on through the testing, commissioning and even the logistics involved in such a large system, every part of the system design has been pre planned and scrutinised to provide Westfield with a PA/VA system to be genuinely proud of.
If employing the skills and experience of industry leading experts reflects the Westfield Group’s focus on enhancing the customer experience then the technical excellence of the PA/VA system can stand as a proud testament to their wisdom.
Vic Swain, Engineering Director, PEL Services Ltd.