Off the Wall: Controlling Sound Reflection

  |  August 23, 2017

Every facility has a unique set of audio and video challenges. Some are simple, others more complex. Venues with tall, reflective wall surfaces can fall into the latter category. Put that venue outside, surround it with features such as terrain, buildings, and flora and facility operators lose a lot of control over how their programming sounds. They often call on AV designers to work around these inconsistencies—often using new, innovative sound techniques to provide a delightful and consistent sound experience.

We recently faced a unique situation at Longwood Gardens in Kennett Square, Pennsylvania, where we used “reflection masking” to mitigate sound reflections off tall surfaces that were disrupting the listening experience.

Longwood Gardens has a long history of providing a beautiful environment with fountains, gardens, and a serene natural setting in which to spend an afternoon. A short-form fountain show is presented multiple times per day, as well as a larger long-form fountain show with fireworks periodically throughout the year.

A new immersive audio environment was needed to match the visual experience of the renovated and enhanced fountains and gardens. Part of this involved placing loudspeakers in front of the audience so that the sound could come from the same direction as the fountain location; similar to mounting loudspeakers behind the screen in a movie theater. The old design had ALL the sound coming from behind the audience. The challenge to this was that at the rear of the audience areas there were tall surfaces of the existing historic buildings creating reflections that would disrupt the listening experience. There was no acoustic treatment that could solve the outdoor space’s issue; we had to solve the problem another way.

Reflection Masking to Build an Immersive Audio Experience

A system of loudspeakers was developed behind the listeners to create additional energy, coined “reflection masking.” Rather than hear a single strong reflection in the sound, these loudspeakers are carefully delayed and voiced to create additional reverberant energy to subtly distract the listener’s ears into subconsciously suppressing the perception of the reflection off the rear wall. It is still there, but with the additional information that the audience is hearing, it’s not perceived as a distracting reflection but instead as a part of an immersive audio experience that is happening all around them.

This is not the same as “sound masking,” which is a well-established means of creating noise in office buildings and other public spaces to suppress other sounds happening around them. This is often done to minimize distractions in a work environment or increase voice privacy in a medical waiting room or secured facility, for example. With Longwood’s system of reflection masking, the time arrival of a signal is manipulated at the audience’s ear to mask a potentially distracting sound, rather than creating a steady-state signal to block out all sounds.

Sound field energy was modeled during the design.

Building Confidence in Design Decisions

In order prove these concepts to project stakeholders and garner confidence in design decisions, our team set up a full system mockup before the renovation started. The concepts shown during the mockup were approved and the final design and construction effort moved forward.

Mockup tower speakers on historic wall.

Maintaining a Consistent Audio Experience

Steerable loudspeakers were used in the masking system in order to create an area of even sound pressure across a very wide listening area. This was important to keep the listening experience consistent across a broad seating area. Digital signal processing feeds the loudspeakers and allows for multiple configurations to be stored and easily recalled when needed. For example, if there is a smaller audience in attendance on a given day, parts of the system can be selectively shut off to minimize distractions in other parts of the property.

Creating an immersive audio environment isn’t always easy. Throw in an outdoor location and a tall, reflective surface like a big wall and you will need to get creative to establish a consistent audio experience. Armed with a better understanding of sound reflection and reflection masking, you can seek out the help you need to define your problem and find the right solution for your space.

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