Acoustical considerations for designing a multipurpose venue

by sadia_badhon | December 10, 2020 9:24 am

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By Dylan Salazaar, P.Eng.

Historically, building design had a strong focus on one main purpose. While other uses were not intentionally excluded, the design typically centred on that primary function, such as a performing arts venue for a narrow range of performance types or an educational facility. Recently, there is a demand for venues serving more than one purpose. Much more is being required of these spaces, but with significantly fewer resources available—be it space, money, or the ability to change from one configuration to another. These demands will only increase as cities become more densely populated and land and construction become more expensive. Financially, it makes more sense to build one space serving multiple uses.

Multipurpose venues have the opportunity to be community hubs, serving a range of purposes and a significant number of people. Having a space that can be used for more than one kind of event also provides the potential for increased revenue generation. It is common for the rental calendar at such facilities to be booked solid with a range of activities. For example, a school group might hold a graduation ceremony, a performing arts troupe may perform a concert, and a faith congregation might use it for a worship service. With demand for multipurpose venues expected to increase, these spaces must be built to offer as much flexibility as possible to accommodate these different needs, now and in the future.

From an acoustics standpoint, designing multipurpose venues can pose some challenges. Acoustics impact the comfort and experience of users. The design must consider everything from the size and shape of the space to the materials used in the furniture, walls, and ceiling, as they all can change the overall sound quality. Moreover, the venue’s acoustics will differ depending on the activities taking place—an amplified musical performance will be different than a chamber ensemble or a Shakespearean play.

With all of these considerations, it is clear when an environment was not designed for a certain use, but just making do. For a movie night, one can set-up a screen in a room, but the seating or sight lines might not be ideal. Even with a sound system, it is possible the audience will suffer from lack of immersion if the system was designed for live performance instead of theatrical exhibition.

When designing multipurpose venues, building professionals need to consider all of these possibilities, as well as their potential benefits and risks. Considering different uses means balancing the overall experience for the widest range of users. While the goal is to optimize the space as much as possible, the fact is it would be very difficult and costly to accommodate 10 different uses in one space to the same excellent standard.

Managing competing needs without compromising acoustics

This was the reality when designing Lazaridis Hall at Laurier University in Waterloo, Ont. The $103-million building is home to the Lazaridis School of Business and Economics. It features a 1000-seat auditorium that also functions as a 400-seat lecture hall.

Since the space was intended to hold lectures, convocation ceremonies, and musical performances, it was critical to manage competing needs and expectations. To ensure optimal acoustics throughout the auditorium, detailed discussions were held with stakeholders about the requirements and expectations of the space. Over those conversations, the lectures and convocation ceremonies were deemed higher priorities than the musical performances, and the acoustical design reflected this.

Main purpose of the space

As mentioned earlier, programming greatly impacts acoustical needs. Is the space going to be used for sporting events, educational sessions, musical or theatrical acoustics, or multiple purposes? A multipurpose space requires greater acoustic flexibility. Since optimizing the space for one kind of event may be detrimental to another, priorities need to be determined before design begins. It is advisable to work with the relevant stakeholders to determine the areas of focus and develop a clear understanding of the needs and expectations of the space. In most cases, a space can be optimized for only one or two key uses, so determine the primary and secondary uses, followed by potential tertiary ones.

For example, the Aga Khan Museum in Toronto required great acoustic flexibility to accommodate music performances, lectures, film festivals, and school group visits. During the design process, the stakeholders decided the auditorium’s primary use would be to support natural acoustics of eastern instruments. Its secondary use was for amplified musical performances, and its tertiary use was for film screenings. This prioritization was important because, if the goal was to optimize for speech instead of music, the acoustic design would have been different.

For Lazaridis Hall, the priority was speech, so a noise criterion (NC) of 25 was selected. This number is used to rate indoor noise (such as the noise from an HVAC system) and represents the background noise in the frequency range of 31.5 Hz to 8 kHz. Typically, the lower the NC value, the quieter the room. For reference, in an office setting, an NC rating of 25 to 30 is typical of a quiet meeting room, whereas an open office space would have a higher NC rating of about 40. Had musical performances been the top priority for the space, a more restrictive and quieter NC rating would have been used. For example, world-class performance spaces can be as quiet as N1, which is the threshold of human hearing. Other high calibre performance venues can be NC 10 or 15.

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When a space is to be optimized for musical performances, additional variables need to be considered because different types of music require varied environments. One primary concern is the reverberation time (RT60) of the space, which is the time it will take for energy to decay in a room by 60 dB. The RT60 can be modified by changing the types or the location of finishes in the room, which introduces or removes acoustic absorption from the space. Physically changing the volume of the space is another possible intervention.

Adjustable acoustic elements can change the sound in a room to better serve different uses. For example, retractable absorptive surfaces, such as curtains or banners, can reduce or increase the RT60 of a space to help with intelligibility, musical clarity and, in some cases, envelopment.

At Lazaridis Hall, curtains on the second floor can be pulled into the room to reduce the RT60. Conversely, removing the curtains allows an increased RT in the room, which may create a more complimentary range if a certain music type is being played. With the curtains present, the lowest RT60 measured in the audience is 1.1 seconds. With the curtains removed, the highest RT60 measured is 1.3 seconds.

Aside from RT, another metric used is distinctness (or: D50), which is the amount of energy arriving at a given position within the first 50 milliseconds of the direct sound compared to the overall sound energy. The design target for Lazaridis Hall was 50 per cent, which represents good intelligibility and effective communication. Speech intelligibility can be optimized in a room by ensuring a low RT60, a quiet background noise level, and increasing early sound reflections from nearby surfaces. In this design, speech intelligibility can be improved in the space by bringing in the curtains to reduce the reverberation time. For types of music thriving on longer reverberation time (when speech intelligibility is not the priority), the curtains can be withdrawn to improve the musical experience, at the expense of natural speech intelligibility.

A number of fixed reflectors were designed and placed in the hall to optimize the D50 and maximize the amount of energy sent to the audience. These reflectors include some of the walls, suspended ceiling reflectors and the front of the balcony facia, which was specifically curved to improve the coverage of useful reflections. The ceiling reflectors are painted black, and hide above the slat ceiling below. The slat ceiling was designed to be acoustically transparent, allowing sound to pass through and be reflected off these hidden reflectors.

The combination of the reflectors and the drapery provides the right balance for the Lazaridis Hall audience. The reflectors provide early reflections of sound to the audience while the curtains absorb and minimize late energy reflections. This, combined with a low background sound level, optimizes the overall speech intelligibility in the space.

An analysis tool was used to design reflection patterns from surfaces such as the ceiling and balcony facia. The tool integrates directly into 3D modelling software and enables quick evaluation and adjustment of reflection patterns based on complex shapes and curves to send as much useful acoustic energy across the audience plane as possible.

Natural acoustics

For music, an acoustically ‘pure’ experience is one where unamplified instruments and voice create an excellent experience with clarity and envelopment. Think opera or drama—at their best, these experiences offer the highest level of engagement and intimacy when the audience knows they are hearing the performer directly. Hearing the actors or performers take deep breaths, or hearing their footfalls on the floor, creates an immersive experience. Large opera houses provide this sense of intimacy even in the back row, whether there are three people in attendance or 4000.

Spaces can almost always be designed to function with a sound system, but depending on the programming and environment, natural acoustics may be an option. For example, lecturers at Lazaridis Hall may not always use a microphone, so the room’s natural acoustics were factored into the design. The main auditorium can use natural acoustics for all of its intended uses: lectures, convocations, and musical performances.

However, natural acoustics might not always work if there are other competing needs for the venue. As desirable as natural acoustics can be, there are venues where the required use cases are so varied they need a completely electronic solution. Similarly, there are venues where natural acoustics may not be desired by users—think a rock music venue or a lecture space for faculty that only wants to communicate through microphones and speakers.

Once the acoustic priorities are determined—including whether natural acoustics are even needed, review the most stringent acoustical requirements first and then work from there. Designing for natural acoustics means limiting the background noise, carefully placing reflectors, and strictly controlling reverberation time, all of which place pressure on budget and co-ordination.

Audience location

Acoustics are greatly impacted when the performer-to-audience relationship changes. Consider a thrust stage, which extends out into the audience. This provides an immersive experience for the audience, but it poses significant acoustical challenges as performers are facing away from parts of the audience. In an audience in the round configuration, the audience surrounds the performer, and we cannot rely on the performer to remain in one location or to project in one direction. In the worst case, certain areas in the audience may receive none of the performer’s direct energy. Acoustic reflector locations and shapes must be designed to encourage useful reflections, depending on a range of performer positions and facings.

Introducing complex curves to the reflectors can increase the exposure the reflectors get to different performer locations, and can also optimize the audience coverage from a single reflector. Another option is to have different reflector configurations—locations, heights, and angles—depending on the audience-to-stage configuration. Also, good acoustic design utilizes reflectors to reflect sound back onto the stage for the benefit of the performers.

Experienced performers will be able to adjust their performance style to cover as much of the audience as possible, for the greatest amount of time. Acoustic designers must determine if the acoustic geometry is optimized even as the location of the performer or audience changes.

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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.

[4]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.

Source URL: https://www.constructioncanada.net/acoustical-considerations-for-designing-a-multipurpose-venue/

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