PA application in airports and train stations – why is it so difficult?
What we can learn from special acoustic challenges
Surprisingly, the acoustics of public transport hubs are often neglected. Train stations and airports are planned with a focus on walking paths and supply routes – and with noise protection to the outside. In the indoor areas, however, they are places with a high density of sound sources – trains or aircraft, people, music, speaker announcements and acoustic signals. This complexity, combined with the large open spaces, high ceilings and hard materials, creates acoustic chaos. The resulting volume of sound makes it difficult to identify and understand individual sounds or announcements. On the one hand, this means stress and, on the other hand, it limits accessibility enormously. We consider: could it be done differently?
Many different sources of noise encounter a lack of acoustic measures
Poor acoustics in train stations are particularly problematic for the hearing impaired. Because they are all the more dependent on announcements about departure times and arriving trains. The combination of excessive noise levels and heavy reverberation makes it difficult to distinguish between the many competing sounds. But the announcements in train stations and airports are often incomprehensible even for people with average hearing. This leads the actual task of PA technology in public places ad absurdum: information transmission. Missing a flight because the PA system is drowned out in the noise chaos is perhaps the biggest concern for travellers at an airport.
Technically speaking, airports and train stations generate a large amount of acoustic energy that planners have to cope with.
The challenge is not purely acoustic
In the world of PA technology, one of the most interesting challenges is sound in large, open and highly frequented spaces such as train stations and airports. Typically, only the mandatory voice alarm system is given consideration. Newcomers to the industry are often surprised that public transport hubs do not yet sound any better. There is however another factor here: the PA technology and the architecture have to perform a balancing act between aesthetics and pragmatism. Knowing how sound behaves in particularly large spaces can help architects and planners to create rooms with higher experience quality, if they see the priority.
High ceilings, many smooth surfaces made of glass or concrete, minimalist metal furniture: the pragmatic acoustics combat modern architecture.
Acoustic measures
Sound reflections depend on the materials used, surfaces, and the size and shape of the room. These sound reflections must be tamed. Materials such as fabrics or soft furniture can improve sound quality. This is because they theoretically absorb a large part of the noise that arises from conversations, rolling suitcases and echoing footsteps. However, fabrics quickly become soiled in highly frequented public places. Therefore, when textile materials are used, it must be out of the physical reach of the public. Train stations and airports can use classic acoustic panels on walls or ceilings to decrease reverberation time. Ceiling sails are a modern solution here.
The most important frequencies in this scenario are between 250 and 2000 Hz
These are the frequencies of human speech. Given the volume of the rooms, the best average reverberation time (RT) is between 0.6 and 0.8 seconds, tending to be slightly longer at approx. 0.75 seconds. In the catastrophic acoustic conditions of train stations and airports, the reverberation time at 250 – 2000 Hz can be up to 3 - 5 seconds. This is a condition that isn't just "uncomfortable", it can actually negatively impact the psyche – the opposite of experience quality.
Large flag panels for the ceiling can enormously decrease the reverberation time. This works particularly well because free-hanging panels can absorb sound on all sides and not just on a single surface.
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Combining acoustics with aesthetics
Acoustic elements for the ceiling can also discreetly cover the building services inside airports. Many textile acoustic solutions can even guide the gaze and ensure a pleasant ambience over a large area. Here, planners must only ensure that building-service elements that require regular maintenance are not covered.
Employees also benefit from good acoustics – not just the travellers
This not only benefits the passengers. The employees who work there every day are also relieved. This is an aspect that is rarely considered when planning large transport hubs: how heavy is the stress on the employees from continuous sound exposure? Train stations and airports can be improved not only through subsequent or additional acoustic measures – a good technical concept is often lacking from the start.
Speech intelligibility Bild © AdobeStock/Sunny studio
Additional visual measures: not everything has to be said
Other solutions at train stations and airports are more visual information; on the one hand with classic signs, and on the other hand on display boards. This sounds trivial and obvious. But a concept combining visual and auditory information policy makes sense above all if it helps to reduce auditory overstimulation.
Three examples of a particularly successful combination of acoustics and architecture
1. King's Cross railway station in London
The refurbishment of this station (completed in 2012) included an impressive new booking hall with a striking steel roof. Steel and glass were used – which is actually acoustically disadvantageous. However, a special acoustic plaster was applied to the walls and ceilings to absorb the sound and create a pleasant acoustic experience.
1. King's Cross railway station in London
The refurbishment of this station (completed in 2012) included an impressive new booking hall with a striking steel roof. Steel and glass were used – which is actually acoustically disadvantageous. However, a special acoustic plaster was applied to the walls and ceilings to absorb the sound and create a pleasant acoustic experience.
2. Suvarnabhumi Airport in Bangkok
This airport is known for its ultra-modern design with large areas of glass and an impressive corrugated steel roof. Despite these materials, the airport has good acoustics, thanks to special ceiling panels that absorb sound and an intelligent room layout that minimises sound propagation.
2. Suvarnabhumi Airport in Bangkok
This airport is known for its ultra-modern design with large areas of glass and an impressive corrugated steel roof. Despite these materials, the airport has good acoustics, thanks to special ceiling panels that absorb sound and an intelligent room layout that minimises sound propagation.
3. Arnhem Central Station in the Netherlands
This architectural masterpiece uses an organic, flowing shape and lots of glass. However, acoustics have been carefully considered, using absorbing materials and a sophisticated room layout to minimise unwanted reverberation and create a pleasant sound environment.
3. Arnhem Central Station in the Netherlands
This architectural masterpiece uses an organic, flowing shape and lots of glass. However, acoustics have been carefully considered, using absorbing materials and a sophisticated room layout to minimise unwanted reverberation and create a pleasant sound environment.
Technical measures
Even in a building where glass surfaces and bare concrete predominate, good speech intelligibility can be achieved through accompanying technical measures.
Create targeted PA zones: set up special zones with high-quality PA application in highly frequented areas. Use speakers that are specialised in clear speech reproduction. Very sophisticated amplifier systems are also available for targeted multi-zone PA application.
Use directional speakers: use (combined with point 1) loudspeakers that direct the sound specifically into certain areas. This reduces background noise in less frequented areas and improves the signal-to-noise ratio. One example would be column speakers, which radiate 120° horizontally and 40° vertically.
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3. Use active noise suppression: incorporate active noise suppression technologies in your PA systems. These help to minimize background noise and increase speech intelligibility. Active noise cancelling creates a signal that is the exact opposite of the background noise to effectively "delete" disruptive noise.
4. Adjust volume dynamically: change the volume of the announcements depending on the current noise level. The volume should be higher when there is a high level of ambient noise and lower when there is little noise.
5. Use digital signal processing: equip your speakers with digital signal processors. These filter out background noise for the speaking person, thereby increasing speech clarity.
6. Optimise the announcements: use clear, simple and short wording for your announcements. Avoid unnecessary information and ensure clear pronunciation.
7. Select the right technology: consider which speaker types best suit the acoustic conditions. Whether ball speakers, wall-mounted speakers or built-in speakers – careful planning and coordination of the PA system is decisive.
8. Perform regular maintenance and tests: check the speaker systems regularly and carry out necessary maintenance work. In this way, you ensure that your systems always function optimally and that you can identify and rectify any problems at an early stage.
The signal-to-noise ratio (SNR) is a fundamental concept in PA technology that plays a decisive role in speech intelligibility. It describes the ratio of signal strength (in this case voice communication) to background noise. A high SNR means that the signal (speech) is significantly stronger than the noise, resulting in improved speech intelligibility.
Ultimately, better acoustics can result in a quieter environment, especially in busy places. Curious to learn more about PA technology, PA application and DIY projects? Visit our Magazine.
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