Sprawling, noisy transportation facilities such as airports, bus and train terminals present difficult public address challenges for sound system designers. With long hallways, large echo-ridden rooms and many reflective surfaces, it takes a good understanding of acoustics, sonic energy flow and current technology to deploy an effective and intelligible sound system.
The purpose of any public address system is to communicate a message. Speech clarity is especially important in transportation situations where passengers rely on the system to hear arrival and departure notices, paging announcements and emergency and safety information. An email with half the words missing would not be an acceptable form of communication, and you certainly shouldn’t accept a similar effect from a poor public address system.
The biggest challenge facing sound system designers in this type of application is to devise a system that has a high direct-to-reverberant sound ratio. This means that systems need to focus sound directly to the listeners’ ear, while moving sound energy away from walls, ceilings and other acoustically reflective surfaces. The solution seems straight forward, but in practice, it is very difficult to execute with conventional loudspeakers.
To achieve this, sonic beam steering control technology allows speakers like JBL’s Intellivox digitally controlled speaker system to focus sonic energy exactly where it is needed—at the listener. Think of the Intellivox’s sonic beam like a spotlight as opposed to a floodlight. Beam steering products have a very narrow vertical coverage angle and a very wide horizontal coverage angle. A process involving precise manipulation of the output level and phase relationship between adjacent components of the overall loudspeaker can easily be controlled via software, allowing the sound designer to adjust the vertical directivity and focus. This allows these vertical column speakers to be mounted parallel to the wall, but still aim sound directly at the listeners’ ear level and away from walls, floors and other surfaces.
Traditional beam steering products have limitations, however. A balance has to found between how narrow the sonic beam is, how high the speaker is physically mounted and how much of the audience can therefore be kept within the coverage area. As the height of the speaker is raised and the steering angle increased, the vertical coverage will also have to be increased in order to cover the same audience area. The larger the vertical coverage becomes, the more sonic energy will come in contact with reflective surfaces in the room and the overall direct-to-reverberant field will decrease.
“Beam Shaping” technology, pioneered by JBL, combats this issue by allowing the sound designer to create a complex asymmetrical vertical sonic beam. By altering the shape of the sound dispersion, the vertically-mounted speakers can better cover all listeners with direct sound (see the image to the right). With this leading technology—developed by the same team who first brought beam steering to market over 20 years ago—much finer, more precise control is possible. Now a speaker can be programmed to evenly cover the nearfield audience while maintaining consistent SPL and frequency response out to the furthest listener.
Related technology is employed in HARMAN’s AXYS Tunnel solution. Here is a video with real-world examples of how the technology improves intelligibility in even the most challenging of installations:
This advanced technology gives far more flexibility in the speaker’s physical mounting position, making it easier to find a compromise between the architect’s vision and the ideal speaker placement. These tall, narrow units have been recessed into walls, placed inside custom-built enclosures and housed within customer information displays.
When faced with the challenge of sound system design for large, noisy areas with reflective surfaces, advanced sonic beam steering is an essential solution. How do you bring clarity to public address systems without sacrificing the aesthetics? Let us know in the comments.