Station announcements have long been the trigger for comedian’s jokes on stage, the impersonation of garbled messages always good for bringing a laugh. Writes Clive Kessell
Some of this implied criticism is valid but so many of the larger stations are acoustic horrors, the enclosed space with an overall roof being a fine echo chamber. Railway engineers have tried several theories and methods down the years to improve the quality of sound but never quite reached what could be called perfection.
Maybe the problem has no universal solution but in Scotland and in response to considerable public comment, Network Rail decided to engage some of the best brains in the acoustics industry to properly analyse the circumstances of Edinburgh Waverley prior to committing to hardware renewal. This has proved quite a challenge but the results are impressive.
Assessing the station
Edinburgh Waverley station is set in a hollow, so is relatively long with four through platforms and a number of bays at the east and west ends. Road access is from a ramp off the North Bridge that spans the hollow, leading to a central concourse area with taxis and other vehicles all descending to this level. Pedestrian steps and escalators from the north (Princes Street) and south (the Old City) lead to a footbridge across the complex with stairs down to platform level. The central part of the station is protected by an overall roof.
Much has been done in recent years to improve the fabric of the station and add more platforms but all work has needed to take account of the listed building status. Train services are about half diesel, half electric, so ambient noise levels vary considerably. As with most big stations, retail outlets abound and there is a ‘quiet’ central waiting area – passengers and staff in all of these need to hear important announcements.
Another factor entering the equation has been the need to improve the fire alarm and evacuation procedures from such a diverse site. Normal alarm bells do not trigger the public reaction that is required and most people just stand around wondering what all the noise is. A verbal message is much more effective and the VA (Voice Alarm) requirement became part of the project. Sounds straightforward enough but the impact is to make the resulting PA (Public Address) a safety system and this introduces significant requirements for reliability and availability.
Designing the system
The prime need has been to get clear and concise sound to every part of the station regardless of the ambient conditions. The novel element to achieve this is the use of intelligent loudspeakers. These are formed in long columns of individual speaker units, each of which has its own sound setting. The amplifier for the unit is contained within the loudspeaker column, thus each of these needs a power supply as well as a cable for the input sound signal.
Some 47 of these intelligent speakers are used in the central area where the overall roof (train shed) covers the station, there being three types – ’64’ very big; ‘48’ medium; ‘32’ small. The goal is to have a constant output volume whether standing close to the speaker or 50 metres from it. This suggests negating the laws of physics but amazingly it does work.![Edinburgh PA 'Big' Intelligent Speaker [online]](http://railengineer.uk/wp-content/uploads/Edinburgh-PA-Big-Intelligent-Speaker-online.jpg)
Each speaker has two audio feeds separated, wherever possible, in diverse routes to obtain maximum reliability and a data cable enabling each speaker to be separately monitored. All are set up individually and programmed in line with sound measurements taken on site.
The intelligent speakers are complemented by some 300 normal speakers mounted on lampposts and off canopies, in shops and customer locations, away from the train shed area. These latter operate from a conventional 100V line.
The system includes noise-sensing microphones so as to adjust sound levels if high background noise levels occur, typically a diesel train idling or starting away. Feedback from this is sent to the speaker amplifiers but once the announcement has started, the level will remain unchanged until completion.
New nodes
Distribution of sound from the central node unit located in the station basement to so many speakers was a challenge so ‘sub nodes’ have been provided in the north, west and east sections of the station. These are linked together by a fibre optic ring and enable a significant reduction in conventional cabling.
Getting the power distribution has been a major challenge. The main unit is sited next to the central node and comprises an Uninterruptable Power Supply (UPS) with associated battery. The battery supply has sufficient capacity to maintain the system in full operation for at least a half hour and an evacuation broadcast to all alarm zones for around another 30 minutes. However, this is considered insufficiently robust and so a standby generator will kick in after a three minute in-built delay if the mains power fails.
The importance of resilient power arrangements has resulted in some very large cables to connect the five nodes. Finding cable routes with a sufficient bending radius tested the initiative of the installation team.
The PA in operation
Almost all train announcements are automatically generated and triggered. The pre-recording was done by the ATOS operation in Nottingham but using a person with a Scottish accent to ensure familiarity with the local populace.
Management of announcements is controlled from Nottingham and transmitted to Edinburgh via a router in Birmingham. Triggering of messages uses a combination of timetable and train running databases. Such is the advancement of message construction from individual words and phrases that it is not obvious to the untrained ear that it is computer derived.
Currently, only a single message is made for each train service, this being broadcast five minutes before departure giving platform number, departure time and calling points. Arrival information is only announced for trains not terminating at Edinburgh.
Additional messages are broadcast if disruption occurs. Although a zoning facility does exist, currently every announcement is heard everywhere. Microphones for live messages are located in the station reception office and the signalling control centre, needed mostly for ‘person alert’ communication but also if serious out-of-course situations occur.
Retail units, the ticket office and all other public areas can be programmed whether or not to have train announcements depending on the disturbance likely to result, but must receive any voice alarm messages.
Voice Alarm operation
Any fire alarm activation from a call point or smoke detector will initiate an alert to the station reception and triggers a ‘call to inspector’ voice message. That person then has six minutes to go to the alarm site and check whether the situation is indeed a real problem or, more likely, an equipment fault or minor incident such as the toast being burnt. If no further action is needed, a call to the station reception will lead to the alert being re-set.
Failure to resolve the alarm trigger within six minutes will result in a voice evacuation message being broadcast. Should a second alarm be generated during the six-minute timescale, the evacuation message will immediately result.
![Edinburgh PA Tannoy Cntrl for Intelligent Spkrs [online]](http://railengineer.uk/wp-content/uploads/Edinburgh-PA-Tannoy-Cntrl-for-Intelligent-Spkrs-online.jpg)
Controlling an evacuation is itself a challenge and with the arrival of fire engines and personnel, additional information will be broadcast from one of five Fire Microphones that are positioned around the station (pictured above). From these, the public will be told the routes to be followed and any other relevant data.
This procedure may sound draconian but so far no unintended evacuations have taken place. Any VA message will have priority over any train announcement.
Providing the System
With such a complex system, no single supplier was capable of providing all the elements. Network Rail competitively tendered for a management contract and system integrator, which was awarded to Babcock International. From this a number of sub contracts were let, the most significant being:
- T G Baker based in Clydebank near Glasgow for acoustic design and programming of speakers, also the construction of the main and sub node racks;
- ASL Ltd of Lewes for their Vipedia product that routes the audio signals to the speakers;
- Tannoy of Coatbridge who supplied the intelligent speakers;
- Ogilvie of Stirling for cable running, power provision and overall installation;
- Lanarkshire Welding for design, fabrication and installation of speaker bracketry.
To satisfy the listed building requirements, photo montages of the speaker installation had to be produced so that the visual aspect could be agreed in advance. Testing had to be carefully managed so as not to interfere with the day-to-day running of the station but also not to disturb nearby residents at night. Complaints from some home owners, hotels and art galleries did arise and led to a consultative process being put in place from which the operating volume of the system has been constrained.
Testing and commissioning
To test each intelligent loudspeaker, firstly a known frequency is injected and used to set the loudspeaker’s maximum level which is between 85 and 88dB. The loudspeaker is then equalised and balanced using ‘pink noise’ (a range of frequencies with a corrected balance to match the response of the human ear) to achieve roughly the same level of around 85dB. Following this, a repetitive drum click is broadcast to each platform at 80dB to confirm and adjust the loudspeakers’ audio delays. This ensures the announcements heard from each speaker will arrive at the human ear at the same time.
When all loudspeakers have had gain, equalisation and delays set-up, the system is tested from the audio inputs (microphones, recorded announcements and evacuate/alert messages), these being broadcast to each zone from which volume levels are set. Lastly, sound intensity measurements are made to confirm the system’s intelligibility.
Authorised in 2012, installation work commenced in September 2013 and the system was commissioned on 28 February 2014. Getting it right was never going to be cheap but the overall project cost of £2.5 million is considered well worth it for the significant gains that have been made.
So is the new system a success? Most people will not even notice the new speaker columns so improvement can only be measured by the lack of complaints on audibility from the public. Certainly, announcements are much clearer than before and thus, to date, the team are confident that success has been achieved.
A nice touch has been the re-use of the old equipment, the speakers going to a University Student who wants to see his study of ambionics put into practice and the amplifiers being acquired by the Strathspey heritage railway.
