Announcements in airport terminals are often hard to decipher. It is a dynamic, fast-paced environment, and passengers can find it challenging to understand announcements due to background noise and/or poor system design.
All too often, the concept and design phase get diverted by the glamour of the latest video innovation, and we forget to deliver intelligible sound to match. This is partly because human beings tend to focus more on what the eyes see than what the ears hear, which results in many great looking terminals sounding terrible.
Practically all airport passengers’ journeys rely on the public address (PA) system through where information is provided by way of real-time announcements accessible to all. This critical information is important and time-sensitive, but easy to miss or misunderstand.
For many organizations – and the airport industry is no exception – the high cost of ineffective communication is often not recognized until the damage has been done. Perhaps it would be different if there were a “communication costs” line item in the budget.
However, when senior managers are asked to take 10 minutes to think about the costs of communication issues in their business, they can quickly identify millions of dollars lost to poor communication.
An airport is a unique space where the combination of areas includes gate areas, concourses, departures, ticketing, baggage claims, curbside areas, retail, and more. These areas all have varying ambient noise levels, multiple languages, multiple operators, and security concerns that set out a challenging environment.
Many hone their sound design skills in small, acoustically friendly rooms with relatively low noise floors. This does not prepare one to work in larger spaces. You can get away with a lot regarding loudspeaker selection and placement in a small room. The different choices generally produce different tonal colorations. This is not even remotely true in a large space such as an airport terminal. Here, if you make the wrong choices, the listener will not understand the words. And all the equalizers and DSP in the world will not fix it. Intelligibility should not be confused with high fidelity. A system can sound good and be unintelligible, and a system can be intelligible and not sound good. The goal, of course, is to have positive outcomes in both intelligibility and fidelity.
Many airports seek professional design services for new projects and extensive renovation projects; the importance of parameters such as room volume and shape, surface finishes, and noise control is not always clear during the design process. PA systems are sometimes updated or replaced without awareness that room acoustics and ambient noise conditions are vital to the success of an intelligible PA system. An expert in the field of acoustics and system design should be engaged for satisfactory PA system deployment and how a PA system can be optimized for best performance, given actual acoustical conditions.
The most widely accepted quantitative measure of intelligibility is the Speech Transmission Index (STIpa), a measure of speech transmission quality. The absolute measurement of speech intelligibility is a complex science. The STI measures some physical characteristics of a transmission channel (a room, electro-acoustic equipment, etc.), and expresses the ability of the channel to carry across the characteristics of a speech signal. STIpa is a well-established objective measurement predictor of how the characteristics of the transmission channel affect speech intelligibility.
There are many types of loudspeakers found in airports; normally, the type of loudspeaker is selected for a particular space and application. At very close distances, say less than 10 feet, the direct sound dominates, and speech intelligibility becomes good. Intelligibility may be close to 100 percent, even though the space has a long reverberation time. For example, it is important not to install ceiling speakers in extremely high ceilings. This article explains the benefits of digitally steered loudspeakers and how they mitigate such challenges of intelligibility vs. fidelity.
Self-powered, beam steerable speakers are a proven solution for delivering significant communication improvements in the most challenging acoustic spaces. These loudspeakers are regarded as the cutting-edge solution for clarity and intelligibility. When it comes to placing sound, digitally steerable solutions may be the only answer. Intelligible messages are critical; the message must be clearly understood the first time for instructional and emergency scenarios in public buildings and transportation hubs.
The biggest challenge is designing a system that will have a high direct to reverberant sound ratio. In other words, we need to maximize the sound that arrives directly to the listener’s ear whilst at the same time reducing the sound energy that bounces off walls, ceilings, and other acoustically reflective surfaces. Practically, it is challenging to achieve this with conventional loudspeakers. The sound wave that is emitted by a conventional loudspeaker expands as a sphere. By the time the sound has reached its intended participant it has expanded by a massive amount. Only a tiny fraction of the sound that comes from the loudspeaker (direct sound) reaches the listener's ear, typically 1 percent in a large reverberant space. The remaining 99 percent of the sound is called the indirect sound. It is the indirect sound that contributes to unintelligible sound if it is neglected. Treating a venue with absorptive or diffuse surfaces can be prohibitively expensive; so, in fact, while the piece-part cost of a digitally steerable column might seem high, you are likely spending much less to achieve the desired result.
Another beneficial application for beam steering technology is when architectural constraints limit the preferred positioning of conventional loudspeakers. Generally, you need fewer columns to cover much larger areas, so installs are less invasive. This equates to lower installation costs compared to distributed constant voltage systems. In some cases, we have seen digitally steerable columns in airport applications cover distances of up to 230ft (70m) with a single loudspeaker.
A unique and intuitive GUI is used to generate the steering algorithm. The beam can be asymmetric in shape and vary in intensity allowing the same SPL distribution from the front to the back of a space. In many cases, we can also specify quiet areas between beams. From the defined listening area input by the user, they determine target SPLs over the coverage area. Multiple audience areas can be specified if required. The steering algorithm is then loaded to the loudspeaker. This sequence of steps can be carried out in a matter of minutes.
The requirement for speech intelligibility is becoming law and being written into legislation. We must provide the features required to meet worldwide standards. Examples of these standards and codes of practice: EN54, NFPA, BS5839, and EN50849.
Sound reinforcement systems in public spaces must meet a minimum STIpa score for public safety reasons. There are several features that self-powered, beam steerable loudspeakers can offer, allowing these loudspeakers to be used as the main PA in voice alarm system or mass notification system. As part of a PA/VA system in critical applications, the beam steerable loudspeaker also needs to guarantee complete system integrity.
We need to now consider communications applications as we look toward a travel environment that will be affected long-term by the global pandemic. How can the correct audio system help meet these new needs?
A major event can transform the air travel experience for years to come. Two decades ago, TSA did not exist, and you did not need to be flying to get airside. At that time, an airport was open to the public. Today we have spacious check-in areas, and then security areas, that are very densely populated. It took the average passenger several years to get used to the notion of security screening. Today, the COVID-19 pandemic presents the air travel industry with a similar challenge in that travelers will feel more comfortable if they are allowed to space farther apart.
Will we resize airport terminals? If so, there will be a need to cover these areas with announcements and mass evacuation messages. Most airport terminals are configured in the shape of an hourglass; check-in areas are generally quite spacious, then we have security and another large space airside.
Will passengers be accepting of the extensive lines at security that create a choke point? Will security checkpoints be less onerous and more of a spread out ‘walk-through’ experience as better technology is developed? Perhaps we will start to spread that load out and in different places throughout the terminal, allowing more flow as people can use all the space available more efficiently.
Invariably this will mean deploying, reconfiguring, and upgrading the PA/VA system to cover larger areas more effectively with improved intelligibility. In turn, this will create more efficient operations, safer passenger throughput, and a generally enhanced passenger experience.
Graham Hendry is Vice President of Strategic Development at Renkus-Heinz, where he leads the creative vision and execution of product and market development for the company. Hendry’s background encompasses engineering, product management and customer facing roles – a unique blend that allows him to take on the responsibility for both developing product lines and bringing them to market.
