Bosch upgrades communications in Mersey Tunnel

  • November 30, 2022
  • Steve Rogerson

The Mersey Tunnel in Liverpool has seen its IP-based public address and voice alarm system upgraded using Bosch’s Praesensa technology.

Connecting the city of Liverpool with the Wirral under the River Mersey, the Mersey Tunnel complex had an aging and faulty emergency public address system that needed replacing to keep users in the road tunnels safe.

PAS Sound Engineering won the tender to deliver the project, quoting Praesensa by Bosch as the appropriate technology due to the locations of the racks and the fibre connectivity in the tunnels.

The Mersey Tunnel complex consists of two separate road tunnels – Queensway and Kingsway. Both start in central Liverpool, with the Queensway Tunnel running to Birkenhead and the Kingsway Tunnel running to Wallasey. Both also have their own independent control rooms.

The tunnel authority had previously struggled with various equipment faults on its largely unsupported system and required a flexible, networkable option. The flexibility of Praesensa gave it the ability to interface with the existing fibre network and loudspeaker circuits. As such, taking the Bosch technology allowed a reliable and resilient replacement to be provided at a much lower cost and in a shorter timeframe than an entirely new installation.

The project required the update of the failing distributed public address technology while maintaining the operation of as much of the older equipment as possible. The existing loudspeakers were tested, inspected and refurbished where necessary, avoiding an expensive replacement programme.

The IP-based Praesensa was able to connect directly with the existing fibre network and immediately accommodate changes. All devices are IP-connected, facilitating both centralised and decentralised set-up as well as easy interconnectivity with other systems. PAS installed 29 Praesensa eight-channel amplifiers, each with a capacity of 600W, two Praesensa controllers, four desktop LCD call stations with the same number of call station extensions, and 144 Praesensa end-of-line devices.

The system is proven for the distributed audio over IP requirement, is flexible to adapt to the operational requirements, and has sufficient power with integrated channel options to allow for a compact form factor in the various equipment racks.

The reduced size of the equipment now allows for tidier and more compact rack layouts, while the installation offers more options for zone grouping across multiple amplifiers at different equipment locations in both tunnels. When adding or defining new audio zones or groups, the system updates the changes effortlessly. Following the upgrade, the 16 equipment outstations can provide real-time monitoring and fault reporting to maintenance and operations staff remotely over the IT network. Delays from the eight-channel amplifiers proved suitable to time-align the sound emanating from the existing loudspeaker locations.

The two control rooms are able to communicate anywhere on the 8km of tunnels with pre-recorded or live information broadcasts. Controllers at each location allow for redundancy in the event of a major failure, bypassing a faulty device to maintain full functionality always. Praesensa’s no-single-point-of-failure concept with built-in redundancy includes all devices and network connections, critical signal paths, and functions, which can all be constantly supervised.

This is now in full operation and functions without any issues. The user interfaces at call stations provide confidence to the operators who find the selection of pre-recorded messages and ease of broadcast routing a benefit to their monitoring of tunnel operations.