OVERVIEWThe redevelopment of St Pancras was the architectural restoration and extension of a unique London landmark. First opened in 1868, William Barlow’s train shed held the world record for the largest enclosed space for many years. A 100 ft high roof with a span of 243 ft and a length of 689 ft makes the Barlow shed a very impressive space. The restoration works included completely re-glazing the roof and taking the paintwork back to its original pale sky blue. The deck extension, originally created by Sir Norman Foster, is designed to house the extra long Eurostar trains in their new home from Waterloo. Not just a train station St Pancras features top quality retail stores including Europe’s longest champagne bar.
AMS REMITThe CTRL construction and redevelopment work began in 2001. AMS were brought onboard in 2003 by Emcore Rail to design a Voice Alarm system (also to be used as a public address system) to operate in the public areas of the station including platforms, concourses, ticket offices, car park and escape routes. The Barlow shed was a particular challenge with its high reverberation time and architectural constraints. The visual aesthetic was naturally very important to the architects and the aural aesthetic was important to us.
DESIGN TARGETSAt platform level, the system specification asked for a sound pressure level of 95dBA + 5dBA headroom. An STI (Speech Transmission Index) of 0.45 minimum was to be achieved. Ground floor levels (concourse areas) required a slightly lower sound pressure level target of 90dBA + 5dBA headroom. An ambient noise sensing system is utilised to reduce these high system levels during periods of low occupancy and noise. The Voice Alarm system would need to meet all relevant standards including BS 5838 and BS 60849.
COMMISSIONING RESULTSTo date, only the Barlow shed areas, deck extension and Midland main line ticket office and concourse have been measured. The voice alarm system achieves the sound pressure level targets with speech signals. The STI target could not be achieved in the concourse areas of the Barlow shed and Midland main line due to the excessively high reverberation times (in excess of 5 seconds at mid frequencies) and restricted loudspeaker mounting positions.
SUBJECTIVE RESULTSThe speech intelligibility on the platforms is fair in the Barlow shed area to very good in the deck extension. Given the reverberation times and restricted loudspeaker mounting options, the speech intelligibility in the concourse areas is the best that can be achieved.