For nearly half a century, the Royal Conservatory, Canada’s venerable music education institution, has occupied a distinctive late-19th-century masonry building at the northern edge of the University of Toronto campus on Bloor Street, one of the city’s major east-west thoroughfares. But in 1991, simultaneous with an administrative split from the university, the conservatory began an ambitious master-planning exercise, led by Toronto’s own Kuwabara Payne McKenna Blumberg Architects (KPMB), developing a scheme that included renovating McMaster Hall — its deteriorating 50,000-square-foot Victorian home — and expanding it to accommodate the school’s aspirations to both enhance its academic programs and play a greater role in the cultural life of the city.

For the centerpiece of its new complex, the client desired an approximately 1,100-seat concert hall that would serve the institution’s primary mission of training musicians. It wanted the space to have acoustics suitable for a wide variety of musical presentations, including vocal soloists, small ensembles, and full orchestras. But the conservatory also envisioned Koerner Hall, as it is now called, as a state-of-the-art venue that would attract international-caliber talent. And it appears that the room has more than met these aspirations. Since opening in late 2009, Koerner’s acoustics have been widely praised and it has featured such artists as mezzo-soprano Frederica von Stade, cellist Yo-Yo Ma, and jazz pianist Chick Corea.

Koerner, as well as other new facilities — practice studios, a library, rehearsal space, and classrooms — needed to fit into a hemmed-in parcel of land defined by the historically designated Victorian structure, a sports arena, and a picturesque pedestrian path known as Philosopher’s Walk that runs through the university campus. Without overpowering McMaster, which was originally built to house a Baptist college, the architects needed to squeeze 140,000 square feet of new construction into only 25,000 square feet of buildable area. Their solution involved layering functions and wrapping the expansion around two sides of the existing building. The programmatic elements are “essentially friction-fit,” says Marianne McKenna, a KPMB partner.

Although most of the new construction is tucked behind McMaster (recently renamed Ihnatowycz Hall), the configuration allowed KPMB to establish a public and modern presence on Bloor with a glazed main entry and box office and a slate-clad boxlike volume that houses a rehearsal room hovering above it.

For the part of the expanded conservatory that faces the pedestrian path, the architects reversed the arrangement of solid over transparent. Here they surrounded Koerner’s multitiered lobby with a glass curtain wall, pristinely detailed with glass fins, seemingly slipping it over a brick base containing practice rooms. And between the new construction and the historic building, they inserted an academic entrance that leads to a glass-topped atrium. The long and narrow space, trapezoidal in plan, is defined by McMaster’s highly textured and polychromatic masonry and a sleek new wall clad in black, smooth stone. The atrium has a café, open from the early morning to late at night, helping make it the school’s social hub. A slightly meandering route, via an overhanging walkway, leads performance-goers from the box office, through this dynamic space, to Koerner’s column-free main lobby floor. From here, or from either of two upper lobby levels suspended from above with steel hangers, guests are rewarded with views out over the footpath and the university campus.

Once inside Koerner, the audience finds an astonishingly sensual environment. Overhead is an undulant canopy, or what McKenna refers to as a “veil” of timber “strings.”

The ribbonlike elements of laminated oak strips twisted with jigs serve as the backdrop for the chorus at the first balcony level. The strings extend over the whole room, but above the stage and orchestra they support a walking surface for technical staff and conceal equipment and rigging, helping satisfy the client’s mandate for a visually uncluttered hall.

Although the basic geometry, modeled after famed shoebox halls such as Vienna’s Musikvereinssaal (1870), was chosen primarily for its ability to create immersive sound, the tall and compact volume associated with this type provided an added benefit, given the difficult site constraints. To take advantage of this height for seating while preserving the hall’s intimate feel, the perimeter walls and the outlines of balcony levels have been subtly sculpted. The room tapers toward the back, but then the balconies kick out in a slight reverse fan shape to provide a comfortable viewing position for people seated at the room’s sides, explains Anne Minors, principal of the eponymous London-based theater-planning firm.

Almost every surface in the room performs an acoustical function, helping deliver sound to the audience “like extensions of the instruments,” says Bob Essert, director of Sound Space Design. The firm, also based in London, acted as the project’s lead acoustician. Essert explains that the canopy’s walking surface reflects sound toward the seating area and also back to the stage, so that the musicians can hear themselves as they perform.

The sidewalls and the balcony fronts work in conjunction with the canopy. Chocolate-colored plaster tiles, 16 inches tall and 6.5 feet long, with a shallow radius in plan, are adhered directly to the perimeter walls’ foot-thick, poured-in-place concrete substrate, creating a basket-weave surface. The balconies, meanwhile, have oak-plank fronts and are slightly convex in section. These elements’ curved profiles make them ideal for scattering and blending mid-frequency sounds between 300 and 2,000 hertz, like those fundamental to notes played on a violin, says Essert. And to address higher frequencies, both the tiles and the oak cladding have been raked with a wire brush. The resulting small-scale texture provides warmth for classical music, but ensures that the environment is not too harsh for amplified performances. For such instances, the room also includes a system of retractable curtains that can be extended to fully or partially cover the perimeter walls and make the room “drier,” or less reverberant. A highly reverberant room — one where sound persists or lingers long after the source has stopped — is preferred for unamplified music, but is undesirable for performances that depend on amplification.

Just as critical as the techniques intended to distribute music throughout a room are the measures taken to keep potentially disruptive sounds, like the hum of the ventilation system and the buzz of lighting, or the din of traffic, to a minimum. To that end, the client wanted what is referred to as an “N1” performance space — one where background noise is kept at or below the threshold of human hearing.

The strategies for eliminating sources from within the building were fairly straightforward. For the mechanical system, for example, designers located rooms containing air-handling units, chillers, and other noise-producing equipment in locations remote from the hall. They also specified attenuation in ducts, and carefully detailed them so they wouldn’t act as bridges, carrying sound from adjacent spaces into Koerner. In addition, the team briefly considered displacement ventilation. This type of system ­— which is increasingly common in performance spaces where background noise, and also energy conservation, are concerns — distributes cool air through diffusers in the floor, allowing it to slowly and silently rise as it warms. However, when cost estimators deemed the necessary underfloor plenum too expensive, mechanical designers opted for a more traditional approach, creating a scheme with large-diameter supply ducts that introduce air into Koerner from the ceiling above the veil. Return grilles are located in the floor in and around the lowest rows of seating. Because the ducts are large, the system operates at a very low velocity, and is therefore extremely quiet, explains Joseph Merber, president of Toronto-based Merber Corporation, the project’s mechanical consultant. “It creates a gentle ‘rainfall’ of air,” he says.

Controlling the intrusion of sound from outside the conservatory building presented the project team with a bigger challenge — one complicated by a subway running under Bloor Street and by outdated ice-making equipment housed inside the sports arena and less than 20 feet from where the design team planned to place the stage.

To better understand how much of a problem these sources posed, early in the design process acousticians placed accelerometers around the site to measure the ground’s vibration. Since this survey was performed before excavation had begun, it provided an estimate, rather than a precise assessment, of structure-borne sound that would travel from the soil to the building’s foundation and ultimately to the hall’s interior, explains Marc Bracken, a principal at Aercoustics, the project’s local acoustician. Nevertheless, the study’s results indicated that without mitigation, the vibrations would be perceptible inside the performance space. Then, through an acoustical simulation process called auralization, which allows project teams and clients to listen to the sound of an unbuilt room, acousticians demonstrated that the hall should be designed as its own concrete box, structurally independent from adjacent steel-framed portions of the expansion. They recommended that 12-inch-thick rubber isolators be inserted at the tops of columns supporting the level just below the hall. The resilient pads, which deflect about 3⁄4 inch under the hall’s weight, allow the portion of the building below the isolators to move in response to ground’s vibrations, but prevent their transmission to the superstructure above.

Acousticians devised a similar system for the rehearsal hall. Here acoustic isolation was considered necessary because the room hovers over the main entry on the part of the site closest to the subway line, and also because the space, which can seat up to 200 people, doubles as a venue for small-scale performances, along with a 230-seat hall in the historic building.

For the new 900-square-foot, 33-foot-tall practice and performance space, the project team created a “box within a box” with a shell of steel and concrete surrounding an interior steel-framed structure sitting on isolation pads. Designers provided a connection to the urban environment with a generous double-walled corner window, elegantly framed in mahogany. A 2-foot gap between the interior and exterior insulated glazing units prevents the intrusion of unwanted sounds.

Vibrations were less of a concern for the two floors of small practice studios stacked under Koerner’s lobby. Instead, the worry was that rehearsing musicians would disturb each other. So to address transmission between horizontally or vertically adjacent studios, designers incorporated such elements as ceilings suspended with isolation hangers, and carefully detailed the ceilings to keep them separate from sound-isolating walls between studios. They also worked with the mechanical engineers to ensure that the ventilation system wouldn’t act as a conduit for sound from one room to the other.

The measures do not prevent sound from traveling into the corridors, since such transmission was not considered disruptive. This feature could even be considered a bonus, since it allows anyone walking through the hallway (including visiting journalists) to hear what the musicians are playing. And in mild weather, when the windows of the practice studios are likely to be open, sounds of an instrumentalist rehearsing a technical passage or of a singer vocalizing drift out onto Philosopher’s Walk, creating an acoustical connection to the surrounding environment. Along with KPMB’s thoughtful and elegant architecture, these sounds help broadcast the conservatory’s cultural and educational mission.

Completion Date: September 2009

Gross square footage: 190,000

Total construction cost: $110.0 million