July 18, 2017
By Steve Titus, B.A.Sc., P.Eng., and Kiyoshi Kuroiwa, B.A.Sc., P.Eng.
The Toronto Centre for the Arts (TCA) was originally built to offer a mix of smaller theatres, a recital hall, and one main stage for various performing arts presentations. This array allowed both the production companies and community groups to offer a range of shows to patrons. In the beginning, the main stage hosted major performing productions under the management of Livent Corporation, which filled the theatre on a regular basis.
After Livent ceased operating in 1998, the centre became the home of Dancap Productions, with successful runs of shows like My Fair Lady and Jersey Boys in the facility’s largest theatre. When the curtain fell on Dancap, the larger main stage sat mostly vacant while change in the surrounding community increased the demand for smaller theatre space.
Rather than allow the larger space to sit vacant, the decision was made to split the main stage into two smaller theatres. The two new theatres would better serve the community and be easier to fill. Led by architecture firm Diamond Schmitt Architects, renovations began in 2014 to divide the 1800-seat main stage into two: the Greenwin Theatre (with seating for 296) and the Lyric Theatre (with seating for 576).
The project team was given one major limitation: the Toronto Centre for the Arts wanted to keep the original shell intact so the theatre could be returned to its original form if change was demanded again and a larger theatre was needed. Creating the two theatres at TCA within the existing shell of the original main stage was a first for all parties involved, and would require innovative thinking on a tight budget. From a design standpoint, this was no small feat—particularly when it came to acoustics.
In a performing arts centre, acoustics are integral. Placing two theatres within the confines of the main stage without being able to physically split the building posed numerous acoustical challenges. Not physically separating the theatres means there is always a path for noise and sound to transfer from one to another. A similar project was completed at the Queen Elizabeth Theatre in Vancouver in 2006—however, the two theatres in that building were structurally separated during the renovation process. This allowed for a simpler acoustical solution in providing adequate separation between the venues, but the structural challenges and expense involved in physically separating the existing venue were not viable within TCA’s budget constraints.
For plays and performances in the space, optimizing speech intelligibility was a key goal. To accomplish this, the team focused on the following design parameters and set targets accordingly.
A technical indicator of speech intelligibility, distinctness (D50) is defined by 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 is > 50 per cent. Speech intelligibility can be optimized in a room by ensuring low background noise and increasing the D50 (ensuring more early energy arrives at the listener position).
2. Acoustic strength
Used to quantify the total acoustic energy arriving at a given listener location, acoustic strength (G) is a technical indicator of how loud a space naturally sounds, and it provides another parameter for designers to use to better optimize the space.
3. Reverberation time
Reverberation time (RT) relates to the period it takes for energy to decay in a room by 60 dB. While this is the most well-known acoustic parameter, RT does not provide a complete assessment of the acoustical environment in the space.
4. Early decay time
Early decay time (EDT) is similar to RT, but focuses on the decay of the early sound. EDT is a technical parameter more representative of how humans perceive the reverberance of a given space. For many spaces, EDT and RT are very similar; however, in extremely large volumes, a difference may be observed between the two. While RT is the measure of the reverberance in the space, EDT will provide a better indication of how audiences perceive that reverberance. For example, in a large volume, the RT will be high, but if enough absorption is located in close proximity to the listener, the EDT may be lower. In this case, although the RT is high, the perception of the listener is the space may not be ‘lively’ or reverberant because the EDT is lower.
5. Noise criteria
Noise criteria (NC) is used to rate indoor noise, such as the hum from air-conditioning equipment. For this theatre, the target was to maintain the existing quiet ambient noise levels. With much of the existing equipment being reused, it was critical to ensure all mechanical equipment, including the HVAC system and the new ductwork for the Greenwin Theatre, remained quiet enough to maintain the background noise levels.
6. Sound transmission class
Sound transmission class (STC) is a single-number descriptor indicating how much sound is attenuated across a given partition. The STC rating system was developed as a way to classify various wall, floor, or ceiling assemblies based on how well they performed at minimizing speech transfer. Generally, a higher STC value indicates a partition will provide more attenuation than one with a lower value. However, because STC was developed for speech, it is important to consider the source of the noise being evaluated—especially if it is not speech-based—when developing the appropriate demising partition construction.
The project was split into two phases. The Greenwin Theatre was to be completed within three months to avoid bringing other productions to a complete halt during construction, and the Lyric Theatre followed soon after and was completed in November 2016.
The Greenwin Theatre
The Greenwin is the smaller of the two newly created theatres. Its foundation is based on the stage and backstage areas within the existing fly tower of the main stage. Although the Greenwin is a more-intimate venue, there is nothing small about its physical presence. As a result of being constructed in the fly tower, the Greenwin is extremely tall and occupies a large volume. This significant physical volume is uncommon for a drama theatre and results in a very high reverberation level, which posed significant acoustical challenges and needed to be tightly controlled, since the theatre is designed primarily for drama. The 25-m (80-ft) tall fly tower is prominently featured as part of the design, but acoustic absorption was incorporated to optimize the acoustics in the space.
The acoustic challenge with this theatre was the volume of the space. The desire was to have a level of intimacy, but this is hard to accomplish when its large, open nature can mean the reverberation is relatively high. The simplest acoustic solution would have been to put a drop ceiling in to decrease the space’s height. However, the client wanted to maintain the dramatic effect of being able to see the fly tower and rigging.
With respect to the ambient background noise, the goal was to maintain the background sound level previously present, which was NC 25 (Figure 1). While the RT in the Greenwin Theatre is higher than this type of space is normally designed for, the goal was to keep EDT—the subjective impression of reverberance—low, and increase D50 to improve speech intelligibility.
Once the targets were set, the team used computer modelling to determine where to place material to help with noise, reverberation, and acoustics. For example, curved ceiling reflectors were added to the design to provide the necessary angle to get the sound energy from the stage into the audience and ensure it did not dissipate into the fly tower. The reflectors were strategically designed and located to optimize the D50 and maximize the energy that could be sent to the audience within the first 50 milliseconds.
A significant amount of absorption was incorporated, with drapery and curtains used in the tower and along the walls. The use of drapery yielded the benefit of being able to ‘tune’ the sound in the venue, increasing or decreasing reverberation by moving, opening, and closing curtains to expose some walls over others. Ultimately, the design allowed the reflectors to provide useful early acoustic reflections to the audience, while drapery absorbed and minimized late acoustic energy reflections. Coupling this with a low background sound level allowed the overall speech intelligibility in the space to be optimized.
The design objectives were successfully achieved in the Greenwin, but more importantly, the vision of converting the old fly tower into its own unique venue was fully realized. The experience in this venue is unlike any other drama theatre. Guests entering it are immediately exposed to the dramatic effect of seeing the rigging and the high ceiling, yet the acoustic experience is still intimate.
Building the wall
Given the two theatres had to be built within the existing space and could not be physically separated into isolated structures, the challenge was to create a divide between them to limit sound transfer. Typically, with sensitive performance venues, the levels of separation and isolation are designed to ensure noise intrusions do not affect the experience under simultaneous amplified use. This often results in designs requiring STC 70 or higher.
The level of separation or isolation required to achieve this is substantial, and typically would require a ‘room-within-a-room’ construction. With this style of construction, the performance hall would quite literally have been constructed as an independent room within an existing room, supported by vibration isolation rubber or springs. Essentially, the inner room is ‘floating,’ and there are no rigid contact points between it and the outer room. This is done to ensure there are no conduits for noise to pass from the outer structure to the floating one, and anything that crosses this boundary (i.e. ductwork, sprinklers, and other building services) must be acoustically detailed. Given the constraints of this project, it was not feasible to provide this level of separation.
The solution was to create a double-wall system between the theatres by incorporating a single masonry wall with a separate drywall assembly on the Lyric Theatre side. To ensure solid isolation, the designers used two layers of 16-mm (5/8-in.) drywall for the metal-stud wall and filled it with 100-mm (4-in.) fibreglass acoustic batt insulation. The access corridor between the two theatres was used to create an additional acoustic buffer.
The Lyric Theatre
Once the Greenwin Theatre was completed, the focus turned to the Lyric, which was a more-elaborate project. With the fly tower of the main stage now behind a concrete wall, the stage of the Lyric Theatre was built within the existing audience chamber of the main stage, over the original orchestra pit and first 10 rows of seating.
With respect to the reverberation time and background noise levels, the targets are listed as 1.4 seconds and NC 25, respectively (Figure 2). These were essentially the conditions present in the original hall—the desire was to maintain these levels for the new theatre.
The challenge with the Lyric Theatre, like the Greenwin, was to find a way to make a more-intimate venue within the much-larger original space and create an excellent acoustic experience similar to the original hall. As the original hall already had a design strategy incorporating sufficient acoustic absorption for amplified performances, the approach here was to see whether the new space could rely on the design of the original. The new theatre was built using an interior shell with strategically located panels to achieve the acoustical goals.
The new shell (i.e. walls) of the Lyric Theatre was constructed from a unique system made up of individual interlocking chevron boxes, which were essentially steel boxes constructed in a chevron pattern, imagined like a Lego block system. The chevrons were located and angled using computer software and modelling programs to ensure they would be able to get the sound energy to the audience at the right time and place.
Each of these chevron boxes was designed to be acoustically different. Some were intended to be acoustically transparent, allowing acoustic energy to escape and reach the absorption on the walls. Others were designed to be acoustically reflective, keeping useful early acoustic energy within the new shell. In addition to being a part of the acoustic design, the chevrons are also used as a lighting feature. The boxes are covered with translucent material and feature light-emitting diode (LED) backlit acoustic panels that can change colour to create different moods depending on theatrical needs.
For the Lyric Theatre, the team reused as many existing materials as possible. For example, the acoustical engineers determined some of the old balconies and upholstered chairs should stay, because they would help create a better acoustic environment even if they could not be seen. This reduced the amount of additional acoustic absorption that needed to be added, and by keeping the old seating intact but hidden from view, the theatre could be returned to its original setting if desired.
For all performance venues, the key measure of success is to see how well-used the space is. Early indications of space usage at the new TCA are promising, and the reception has been positive. The ability to take advantage of the original hall and create a customizable shell utilized for acoustics, lighting, and the overall esthetic in the Lyric was an exciting challenge that pushed the envelope of design and functionality. In the Greenwin, the ability to create a dramatic space while maintaining a sense of acoustic intimacy allows people to consider alternative approaches to the traditional ‘black box’ theatre.
Despite the project constraints, the design and construction of these theatres proved to be successful, and will pave the way for more projects of this kind. As many other performing arts venues struggle with under-utilization, The Toronto Centre for the Arts redesign may serve as a promising case study for many others.
Steve Titus, B.A.Sc., P.Eng., brings more than a decade of experience to being president/ CEO of Aercoustics Engineering Limited, a privately held firm specializing in fostering innovation in acoustics, vibration, and noise control. Over his career, he has been responsible for the acoustical design and delivery of several high-profile projects such as the Sick Kids Research Tower, Corus Quay, Thunder Bay Courthouse, and St. Lawrence Market North redevelopment. Titus is co-chair for Canstruction Toronto, and he sits on the Finance and Audit Committee of the Consulting Engineers of Ontario (CEO). He can be reached via e-mail at firstname.lastname@example.org.
Kiyoshi Kuroiwa, B.A.Sc., P.Eng, created and leads Aercoustics’ contract administration department. He is responsible for the acoustic design and contract administration of architectural projects such as the Aga Khan Museum and Ismaili Centre in Toronto, Simon Fraser University School for the Contemporary Arts in Vancouver, and Mount Allison University Purdy Crawford Teaching Centre in Sackville, N.B. Kuroiwa has applied his experience playing piano and percussion in orchestras to the acoustical design of projects. He can be reached at email@example.com.
Source URL: https://www.constructioncanada.net/when-one-theatre-becomes-two-combining-the-old-and-the-new-to-deliver-exceptional-acoustics/
Copyright ©2021 Construction Canada unless otherwise noted.