Improving acoustic comfort aboard our trains
Whether you’re reading, watching a video, working, or simply relaxing, one reason you enjoy your train journey is the peaceful environment. That’s why we measure the quality of our onboard acoustics—so we can adapt them to your travel activities and make your journey even more comfortable.
Our “Onboard Noise Level Acceptability” project introduces innovations to make your train journeys even more comfortable. After two years of research, we now have tools that measure how passengers experience noise, based on their specific needs, and regardless of which train space they’re in (coach, bar car, etc.). Guillaume Lemaitre, Project Manager with SNCF’s Technology, Innovation and Group Projects Division, explains the project.
How we ensure peace and quiet on your train
How did this research project come about?
Guillaume Lemaitre: One of the advantages of travelling by train, compared with other transport modes, is that the time spent onboard can be put to good use. Passengers can work, rest, read... as long as noise levels allow it. That’s why SNCF Voyageurs and the Centre for Rolling Stock Engineering commissioned studies to better understand how onboard noise levels affect passengers’ activities. Based on these findings, we’ve been able to define optimum noise levels for carrying out these activities.
What exactly does the term “acoustic quality” refer to on a train?
G.L.: That question was central to our project. Typically, we would’ve addressed this issue by simply asking passengers to listen to a sound and tell us if they found it bothersome. But, the question is: do we really know exactly when a noise starts to bother us? We took a different approach. We started with the premise that a noise becomes bothersome when it prevents a passenger from accomplishing activities like reading, phoning, working, or watching a video. That’s why we assessed when a noise level starts to disturb our customers’ activities.
How did you do that?
G.L.: We built a life-size model of a TGV INOUI passenger carriage and asked volunteers to sit inside while we created different sound environments and noise levels. We asked them to perform various activities they would typically do when travelling by train, such as reading a text or watching a video. Then, we objectively assessed their ability to carry out these activities under different conditions. This experiment allowed us to establish precise noise thresholds for different onboard passenger spaces (like the coach seating area, bar car, etc.) and various activities, all reflecting the different services and experiences we offer our passengers.
Can you tell us more about these noise thresholds?
G.L.: We now know at which noise levels people can comfortably watch a video or read a text, and at what point noise starts to affect their ability to understand and work effectively. We also better understand how decibels impact a person’s ability to hold a telephone conversation in the vestibule, or conduct a conversation in their seat. Now, it will be easier to set noise thresholds for our various train spaces and work with our train manufacturers to design optimal onboard environments. All in all, it’s about enhancing customer satisfaction aboard our trains.
Was it impossible to measure any of this until now?
G.L.: We had acoustic measurements, but lacked this kind of detail and analysis. Previously, we simply adhered to thresholds set by the International Union of Railways1 (UIC). Basically, we reasoned that, based on experience, decibels shouldn’t exceed a certain level. But we lacked concrete evidence from customers to make manufacturers understand the importance of respecting these thresholds.
Now, we can explain: “In this space, the noise level should be kept to this number of decibels so passengers can read a book. If it goes up by 3 decibels, they won’t be able to read anymore.” And if a manufacturer suggests exceeding a certain threshold, now we will be able to base our decision on what we know is best for our passengers. Plus, there’s the project’s groundbreaking feature...
Which feature is that?
G.L.: It’s the introduction of precise acceptance thresholds based on our passengers’ activities. Using our newly created database, we can now specify which noise levels are comfortable for various activities and train spaces.
How can this tool be used?
G.L.: The project contributes new data and opens up new opportunities. In practice, by establishing precise thresholds that shouldn’t be exceeded, and identifying technical solutions (new materials, etc.) to help us respect those thresholds, these findings are already allowing us to explore new service offerings such as workspaces, phoning areas, and more. So, having this tool is a real—and timely—advantage since the market is opening up to competition.
Is your device only for TGVs?
G.L.: No, it can be used for all rolling stock: Transilien, Intercités and TER trains. In fact, the Centre for Rolling Stock Engineering2 (CIM) is already using it to improve acoustics in Regio2N and high-capacity trains. It could also be applied to other modes of transport—and maybe even to assess noise levels in your open-plan workspace. I don’t see why not!
Typically, how do you reduce onboard noise levels?
We reduce the sound sources and prevent noise from spreading with “passive” solutions, for example, by adding insulating materials. Mind you, this makes our rolling stock heavier, which in turn increases energy consumption and costs. The good news is that innovative solutions are emerging that address these issues.
Which innovative solutions?
Solutions like metamaterials3, which offer a better weight-to-acoustic quality ratio, and “active” solutions, which we’re also exploring. Active noise control, for example, uses loudspeakers to cancel out disturbing noise by creating counter noise.