Audience capacity
If the audience numbers in a room fluctuate, what impact does this have on acoustics? Often, when the seat count increases, rooms tend to go wider (as opposed to deeper) and take on a fan shape to maintain the stage size and sightlines. However, this shape is often disastrous for acoustic quality as the wider angles reflect sound toward the back of the room rather than the audience, or delay the reflect sound’s time of arrival. Direct sound goes from the performer to the listener in a straight line with no reflections. Sound reflections arrive after the initial sound, after bouncing off walls or reflectors, much like an echo in a cave. Geometrically, this occurs because reflections have to hit an initial surface, reflect off it, and then travel to the audience. The reflections have a greater distance to travel to reach the listener, and therefore, arrive later. However, reflections must arrive within a very short time frame of the initial sound to be construed as useful information to the human mind: within the first 50 milliseconds for speech (D50) and 80 milliseconds for music. Sound arriving after this period diminishes the intelligibility of speech or clarity of music. The goal is to optimize the amount of early reflections and diminish or eliminate the late ones.
This was a concern while designing Lazaridis Hall. A narrower design, rather than the wider fan shape, would have allowed for better distribution of reflections from the walls. However, this was challenged by the need for a larger seat count. To acoustically simulate a narrower or intimate room, fins were introduced along the walls to bring some of those reflections back toward the audience. The fins are located at a 90-degree angle to the stage so energy from the stage arriving at these strongly angled walls can be refocused back toward the audience, creating the same effect as if the room was more square or rectangular.
The hall needed to accommodate about 1000 seats for a musical or convocation events but as few as 300 for lectures—likely unamplified—and speaking events like TED Talks. This wide range made it critical to ensure the room does not seem cavernous and empty when the audience is smaller. To address this, a fixed stage was designed with three levels of seating: a lower level below stage height, a raised section above it, and a mezzanine or balcony level. Creating three distinct seating areas allows the venue to close off other areas for a smaller crowd or lecture, which ensures a more intimate environment for the speaker and audience. The main floor hosts seating for 600 people while the second floor area can accommodate about 400. At the upper height, the adjustable acoustic curtains used to control the RT serve a dual purpose, as they can be pulled in and out of the space to offer a more intimate setting.
It is important to remember the audience also introduces acoustic absorption into the space. This means the RT60 will decrease when a larger number of people are in the room.
The audience’s acoustical impact can be managed in two ways.
Absorptive or plush seating
When an audience member takes a seat, their body obstructs that surface. However, by obstructing one absorptive surface with another, the overall amount of acoustic absorption in the room remains relatively stable and the RT should not change materially (compared to the seat being empty).
Variable acoustics treatment
If the seats are hard and reflective, use variable acoustic treatment to introduce temporary absorption into the space when it is less occupied. Depending on the number of seats sold, or whether an event has seating only at a certain level, the amount of variable absorption can be used to tune the room for a desired RT60.
The practicality of changing configurations
Will there be dedicated staff on hand to change space configurations to accommodate different uses? How often and quickly will these changes need to be made? These two questions greatly impact design. If changeover time is limited, or staff is unavailable, the venue may require a simpler, less burdensome design that requires less moving.
Another option is to automate the transformation. For example:
- seats can fold into the ground or be installed on wagons that can slide under the stage;
- acoustic banners or curtains can be brought in and out of the room with the push of a button; and
- reflectors can be changed with an automated button.
However, these automations can increase project costs. If there is not an appetite to finely tune the room for each specific configuration, a simpler solution would be to create two or three broader configurations that will be appropriate for a range of uses. Designing broader configurations can help the venue reduce the number of theatre changes.
Getting a multipurpose venue right
Client design requests have evolved, and single-purpose venues are becoming rare. The economics of running a venue almost always demand multiple sources of revenue, which means multiple groups using the space in different ways. Although demand for multipurpose venues has grown, it is important these spaces are designed with care. Otherwise, the space will work well for one purpose only and may be compromised for others.
A successful design allows a space to be versatile and support other uses. Lazaridis Hall was originally intended for academic purposes, but it has become highly sought after and widely used to host a variety of Wilfrid Laurier University events and programs, such as musical performances, convocations, and fundraising galas in support of the music department. As a bonus, community groups are using it to host concerts, films, lectures, and special events. Its design is both beautiful and functional, making it a landmark in the city of Waterloo and the surrounding high-tech community.
Dylan Salazaar, P.Eng., is an associate with Aercoustics Engineering Ltd., one of Canada’s leading innovative firms specializing in acoustics, noise, and vibration control. Since joining Aercoustics in 2012, Salazaar has focused on various institutional architectural projects including Mackenzie Vaughan Healthcare, the Pan Am Sports Facilities in Toronto, Mosaic Stadium, and the McMaster University’s Peter George Centre for Living and Learning. He can be reached via e-mail at dylans@aercoustics.com.
