Telus Centre, Royal Conservatory of Music, Toronto
With aspirations that their new facilities be at least as good as their world renowned music education programmes, the RCM set out to create the best possible facilities on a tight budget. Together with the faculty and administration, Sound Space Design set very high standards for the acoustics of the Koerner Concert Hall and the new teaching studios.
The RCM realised that their need for an excellent performance and rehearsal venue for their orchestras and choirs was compatible with the greater music community’s need for an excellent chamber music hall of about 1000 seats in central Toronto. So we created acoustics that would be excellent for student symphony orchestra as well as for top rank professional chamber music and chamber orchestras. SSD Director Robert Essert brought to the project his experience of leading the acoustics design of some of the best halls of the past 30 years: Lucerne KKL (Switzerland), Sage Gateshead (UK), Chan Centre (UBC, Vancouver) and the Four Seasons Centre in Toronto.
The Koerner Hall acoustics are adjustable, and the staging flexible, to serve the wide range of orchestral, chamber and choral music, traditional music, the evolution of (global) music, electronics and concert-going habits in the coming decades. Recording sessions, multi-media, electronic events and popular music will all find a home in this hall. This breadth of quality is achieved without compromising the mandate for excellent orchestral and chamber music acoustics. Within all of this flexibility, the "signature sound" of the hall remains identifiable and key to the success.
the SSD acoustics team
Sound Space Design, lead acoustics consultant
with Toronto collaborators Aercoustics Engineering (acoustics, building isolation) and
Engineering Harmonics (sound system design)
Anne Minors Performance Consultants was auditorium and technical systems design consultants.
the venue
Acoustics are designed with the tools of scale, form and detail
This concert hall is a compact room geometry, and acoustics binds together the performers and audience. There is no proscenium wall to act as a visual or acoustical barrier. This may sound obvious, but it is key that the design team could focus on music and music acoustics. A fundamental difference between a theatre and a concert hall, this idea of a single room is essential for the musicians to get a direct feel for the space and how their sound is perceived by the audience, and for the audience to feel embraced and involved in the music.
By locating 10% of the audience seats behind and to the sides of the performance platform we use the presence of the sound absorbing audience and benches in this area, carefully choosing the distance between orchestra and walls to achieve appropriate balance between sections in the orchestra and a transparent, unconstricted sound quality. This hall will have none of the “boxy” sound occurring in halls with a tight, enclosed concert shell around the performers.
We have optimised the room shape for classical music – professional chamber music, soloists and RCM ensembles, including symphony orchestra. The auditorium is tall and narrow. The stage is wide enough for a full symphony orchestra, yet the room is narrow enough to create a strong, immersive sound to support soloists and chamber ensembles. We used a narrow width and tall height to build up and maintain the density and smoothness of sound. We incorporated two side balconies and a 3rd technical ledge at the top to reflect just the right amount of sound energy back to the lower part of the room, where it adds up to produce clarity and immediacy on the main floor and on stage.
Acoustics on stage
Another of the key goals on this project has been to give the performers on stage the best possible advantage to hear each other and to feel supported by the room. The large convex surface over the stage works with the balconies and reflects sound back down to the performers at a delay time and strength that helps them to hear each other and to have an accurate impression of what they are conveying to the audience.
A custom system of riser platforms fits neatly into the stage geometry, raising the musicians at the rear up a few steps to help them hear each other, as well as for the audience on the main floor to see and hear them as clearly as the players in front. The platforms can be set at several different heights and reversed to make other arrangements.
Details
Getting the architectural details right is important to define the nuances of the sound. The side walls are finished in overlapping waves of gypsum tiles to spread and blend the middle sound wavelengths that carry voice, wind and brass strength. The surface of these tiles has a rough texture to spread and slightly attenuate the highest frequencies and thereby promote warm tone without any brittleness. The heavy tiles and the masonry walls to which they are tightly fastened work together to reflect bass sound energy
Balcony fronts are built up of 2 layers of wood. We determined that planing a slight crown on the boards and scraping shallow, almost microscopic grooves in the surface timber boards would help create the warm sound for which we were aiming. KPMB and the timber subcontractors worked through many samples and mock-ups and finally landed on a technique to scrape the boards so that they would reflect both sound and light with a warm glow.
The timber floor in the audience area is solidly fixed to the concrete beneath in order to preserve bass impact and warmth of tone. The timber stage floor, in contrast, is supported on open timber framing with a substantial airspace to promote resonance of the floor deck. This flexibility helps the musicians to feel each other playing and thus to play tightly together.
Audience seats were specified to minimise sound absorption beyond that required for comfort. Heavily padded cinema seats would have removed too much sound from the room and taint the acoustical quality. It was our goal to deliver all the sound to the audience and musicians; giving support to all the effort and musicianship of the performers. For the same reason there is no carpet in the room.
In order to allow amplified concerts and percussive concerts to come across clearly with less reverberation, we have designed a set of acoustic curtains that can be extended to absorb sound and reduce reverberation. Normally they will not be used for natural acoustic concerts.
Timber veil
The signature architectural feature of the hall is the timber “veil” that forms the ceiling and the layered front of the room. Developed in collaboration between architect KPMB, theatre consultant AMPC and acoustician SSD, these large ribbons link together the technical systems, and yet obscure them, allowing the sound through, yet scattering it.
In order to achieve excellent acoustical warmth and resonance we determined that the acoustical boundary ceiling should be 19m above the floor. However, in order to provide excellent support for the performers to hear themselves and each other, we recommended a large solid ceiling surface approximately 12m above the stage, with relief in the profile. KPMB wanted the room to look lower than its acoustical 19m height. AMPC encouraged KPMB toward design that hides the technology. We all wanted to achieve a continuity of ceiling and avoid the impression of a large panel suspended above the stage.
The result, after much hard work, is like a river of flowing timber. The gaps between the ribbons are large enough to most of the sound through to the upper part of the room. The low and mid frequency sound passes through nearly unobstructed. Very high frequency harmonics are scattered, contributing to warmth. Above the stage, the ribbons are attached to the sound reflecting “canopy” and reflect high frequency sound in different directions to help the musicians hear each other and therefore play in cohesive ensemble.
The construction of the ceiling was as much of a challenge as the design. Each ribbon is made of many square section strands, well bonded and firmly suspended to avoid resonating or absorbing sound.
Silence is golden
To set the stage for the best possible music making, for the most intimate communication of emotion, there can be no mechanical and electrical noise in the room to mask the music or to break the concentration. The widest possible range of loud and soft encourages the widest range of dramatic impact. We give performers the dynamic acoustical space in which to work, from silence and subtle pianissimo to crashing fortissimo. “N1” is an indication that the ventilation and lighting noise are so quiet as to be inaudible. In a hall this quiet, a good performer can get the audience to hold their collective breath in the most emotional of silences.
To achieve such silence, ventilation is delivered through smoothly curved ducts lined with soft insulation to attenuate fan noise. Air is extracted slowly though hidden slots under the seats. Lighting noise is engineered out of the system through the selection of high quality dimmers and light fixtures known to be quiet. All mechanical equipment, all transformers and all pipes are supported on resilient “vibration isolators” to decouple them from the building, and every detail is checked in the field.
With hundreds of students and teachers occupying the building at any one time it is important to separate the teaching and practice studios acoustically from the concert hall. In collaboration with the RCM staff, SSD and Aercoustics have created a sound environment where the sound from a trombone trio in one room does not disturb a violin lesson in the adjacent, but in the corridors some sound from each room contributes to a busy, active music school atmosphere.
The concert hall is a separate building floating on thick rubber pads to isolate it from the subway, from nearby teaching studios and from mechanical equipment rooms. The TTC subway runs almost directly under the site. If we had not isolated the hall, the subways would be audible, as would the chillers in the hockey arena next door.
Early in design process RCM and the design team wanted convincing evidence that the costly floating structure would be necessary, and was worth the cost. SSD and Aercoustics harnessed our technical resources to prepare an “auralisation” – an audible demonstration of the noise as it would be if we did not isolate the hall compared with the noise as it would be if we did isolate the hall. Using calibrated recordings of vibration in the ground, Aercoustics projected the vibration and noise transmission into the auditorium structure across the frequency range. By converting the transmission parameters into digital filters, we made a calibrated audio demonstration in a silent audio studio. The client team was able to determine in a few minutes with high certainty that the isolation was necessary. Aercoustics developed specifications for the special rubber pads to support the building and reviewed the pads during construction. Aercoustics also made sure the studios are individually isolated from each other and the concert hall.
Electroacoustics
Our collaborators Engineering Harmonics have designed an innovative performance sound system that responds to this particular hall design. Two loudspeaker clusters are used for amplified music – one in front and one behind -- and only the smaller, more discreet one is necessary for speech events. The loudspeaker directivity can be reprogrammed, and along with the powerful acoustics of the room, will allow successful amplified sound with lower power. Respectful of both the RCM’s intent that the loudspeakers not visible when not used and performers’ desires for high power and many features, EH has worked with AMPC and KPMB to keep loudspeakers out of the audience view, except when they are needed.
Success and teamwork
Integration of room acoustics design, noise control and sound isolation with our acoustics colleagues Aercoustics brought sensible low-tech, low cost solutions to the design table with solid engineering and experience. Integration of audio and video technologies with the acoustics has been a pleasure with Engineering Harmonics and AMPC working together on the suspensions for the loudspeakers and integration of cable management through the building.
The success of the acoustics and indeed the overall design is due in large part to the RCM commitment to acoustical and performance excellence and their confidence that we could deliver.
Our close collaboration with Anne Minors Performance Consultants and KPMB on the auditorium design has brought together the experience and expertise of concert hall design to create a distinctive music space for the RCM and for Toronto. Anne Minors’ compact and engaging arrangement of people in the space serves as the foundation for exciting artistic communication; in architectural counterpoint KPMB’s flowing ceiling form will probably become the visual signature of the building. The room acoustic will not be seen, but it will be embedded in every note of every performance in the space, so that performers can communicate their deepest emotions to their audiences and both will remember the performance and the hall as one.
