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AES Section Meeting Reports

Toronto - January 8, 2013

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Summary

Rob began by highlighting the fact that the Toronto AES and SMPTE group often do a joint session at least once a year. This is one of those sessions.

Briefly, Koerner Hall was built over three years at a cost of some $110 million. The 1,135-seat hall is the jewel of the new TELUS Centre for Performance and Learning at the Royal Conservatory of Music. Since its opening on September 25, 2009, the hall's design, flexible performance characteristics and superb acoustics have been praised by critics and performers alike. The hall achieved the highest possible acoustic rating—N1--rendering it ideal for the finest acoustical performances of classical music, jazz, and world music. The incorporation of variable acoustics makes it equally well suited to amplified music, lectures, and film presentations.

The hall features an innovative and almost invisible 'voice-stick' designed by Engineering Harmonics to maximize intelligibility, rather than sound reinforcement. Aercoustics was responsible for optimizing the acoustics.

As pointed out many times during this meeting, both Engineering Harmonics and Aercoustics worked with Sound Space Design for this project.

This meeting is a celebration of this hall. Rob has recorded here and stated it is a beautiful space to record in.

The first speaker was John O'Keefe of Aercoustics who spoke on behalf of the acoustics team.

Rob provided Mr. O'Keefe's extensive background. He also noted that John was recently inducted as a fellow in the Institute of Acoustics.

John talked about the room acoustics, noise control and building isolation. He was primarily in charge of noise control. Bob Essert from Sound Space Design was the man in charge of this project.

To set some perspective he discussed an editor's note made by Sir Harold Marshall in 1967 (not a refereed paper) to the Journal of Sound and Vibration where he simply asked: "wouldn't lateral reflections be a good idea?" This revolutionized hall design. This is why Koerner Hall is narrow and tall.

(Sir Harold is the first acoustician to be knighted for his contribution to acoustics and science. He changed the format of performing art spaces).

This meant a return to the traditional shoe box design shape of the 19th century which is what Koerner Hall is based on. By attempting to satisfy the single requirement of strong early lateral reflections, the design team brought back a four fold return. A narrow room provides early lateral reflections which leads to source broadening. This design also leads to strong late lateral energy contributing to envelopment. So not only does one have a 'broad' source in front of you but "a cloud of music surrounding you".

In a tall narrow room, the early decay time (the first 10 dB of reverberant decay) is much closer to the reverberation time and as a result the room sounds more reverberant and the decay is smoother. Also, the rate of attenuation of reverberant (sound pressure) level is less than it is in a wide fan-shaped room. Wide rooms used to be the norm.

"Shoe box design covers a multitude of sins!" While a room can have great lateral energy, it may not have quite the warmth, because the lateral energy is 'grazing over' the seats. Here in Koerner Hall, the balconies (which are also at the sides of the room as well as the back) have soffits which provide reflections from the sides at angles from 35 - 40 degrees. "In a building a fire code rules all": The fire exits are also the area that draws out lateral reflections.

The cornerstone of good acoustics is a quiet background level. "Musicians need a quiet room the way a painter needs a white canvas. A quiet room reveals all the acoustical nuances of clarity, spatial impression, of reverberance and loudness, giving the performers a powerful presence". In Mr. O'Keefe's mind "there is nothing more moving than a performer that makes a pause in what they're doing - and have a thousand people.......perfectly quiet". He made this point dramatically clear by very deliberately pausing, himself, when making that statement!

Koerner Hall is an N-1 room. One of the problems was 'value engineering'. In an N-1 room, the ventilation system is no longer the problem but the electrical system.

Building isolation was another concern. This is very close to the Toronto Subway line. But the other concern also came from Varsity arena near by which has a compressor bolted to the ground generating 40 Hz. The building is isolated on 250 rubber pads. He discussed some of the steps needed to achieve this as well as a manufacturing problem that was dealt with regarding the pads.

At the close of his talk, and "in a bit of shameless promotion", he invited everyone to the International Symposium on Room Acoustics the first week of June.

After John's presentation, Rob introduced AES member Mr. Jim Hayward who performed on the stage piano to give the audience the opportunity to audition the hall, and give some idea of its uniformity.

Before playing, Jim discussed an earlier opportunity to perform in the hall and how he managed to find the sweet spot for the piano in 15 minutes. He also had the 'front' of the piano angled away from the back of the hall to avoid odd comb filtering effects that may come off the back wall reflection.

Jim performed the Chopin Prelude in C minor with some extemporization. This provided the audience the capability to hear the full range of frequencies. They were invited to move to different locations between repetitions of the selection to hear the consistency of sound in various places in the hall.

One member mentioned they liked the sound of the applause also!!

Rob presented John O'Keefe, before his departure, with an AES certificate of appreciation. John held it up saying "For Neil" referring to Mr. Neil Muncy who passed away August 2012.

Jeff Bamford of Engineering Harmonics spoke next. After introducing him, Rob provided Mr. Bamford's background. Jeff is also on the Executive Committee of the Toronto AES.

Martin Van Dijk, the senior consultant, was also available tonight to answers questions.

Mr. Bamford's presentation was similar in kind to Mr. O'Keefe's: while there are many systems that are part of the performance hall, Jeff addressed the portion he was directly involved in which was the loudspeaker system.

Projects of this type (preforming arts) typically take 5 to 7 years to complete. It's important to stay true to the original intention.

This room ultimately has two different purposes in terms of the sound system: speech reinforcement and for light music. This is the function of the "Voice-stick" and "Main Cluster" respectively.

With voice reinforcement, one must be careful how the system interacts with the room. Loudspeakers have to be architecturally concealed and clusters need to be retractable. The Voice-stick allows coverage in the main room and is also retractable. It consists of 3 columns of speakers angled at 120 degrees between each column. This also allows coverage into the back area.

The Main Cluster (also called the Pop Cluster) is centre-mounted for main sound reinforcement. It's a curved JBL array and is a music performance system. It's intended to be as visible as possible to have proper coverage in the room.

Columns are also concealed at either side of the stage as well as the back of the hall and near the balconies. Tie lines for portable speakers are available throughout the hall.

Some of the other audio systems include performance intercom and hearing assistance.

Jeff discussed the testing of the voice-stick which was initially done at Roy Thompson Hall. Modeling was done with EASE. Aiming was discussed next. The look of the clusters had to fit in with the 'decor' of the room.

The "voice stick" consists of three off-white Renkus-Heinz IC16 ICONYX digitally steer-able array systems. There are also two additional IC16 arrays, hidden behind the front walls on either side of the stage.

The "pop cluster" consists of eight JBL VerTec 4887A and augmented by two VT4881A subwoofers. The entire eight-box array flies out of sight through an overhead trap door when not in use.

In response to some questions:

It was the intention to create such a reverberant hall. This hall is an instrument. Performers also 'play the room'. The natural acoustics in this room are extremely important.

The subs are flown in the ceiling and are also retractable.

There was a brief discussion about the reverberation and the sound of the room with the side curtains drawn and with them closed. (In between one of Jim Hayward's piano performances, the curtains were drawn to let the audience hear it in its natural state for music).

One member noted that Mr. Bamford was much easier to understand standing on the stage as opposed to behind the microphone referring to the very reverberant sound. Jeff stated when he was behind the mic he could hear the system and because of that moderated the volume of his voice, and without the mic he was 'forced' to project.

The frequency dispersion was talked about next and the consensus seemed to be that there was more fullness towards the back of the hall as opposed to the first two or three rows. Mr. Hayward suggested the piano may have been angled too far away from the back of the hall.

During this, the curtains were put back up, and many people mentioned that the speech intelligibility was better. However, they did prefer the reverberant sound for the music!

Martin van Dijk spoke a bit about the voice stick and also answered more questions.

He also spoke about the necessity of some sound reinforcement. Many halls are built very finely tuned. So much so that different composers from different eras sound better in some spaces than others ie: one hall may be 'optimized' for Mozart while another for Mahler.

Addressing the reverb discussions, the room becomes more reverberant because the voice stick is exciting areas that would normally have more people in the room, because the voice-stick addresses the need for intelligibility for the patrons in the balcony areas.

"For amplifying concerts, is the house system used or do outside companies provide sound systems?": Originally that scenario was not provided for however it has happened once in four years. Martin discussed the "many days and nights he spent with Westbury tuning this room" and trying to understand what was really going on beyond the models.

How are two beams gotten out of a single array?: Each speaker is its own point source that can be combined with an adjacent point source. If all the speakers "know" about the adjacent speaker, in a virtual sense one can create different points of origin within the array. The horizontal beam is fixed. The focal point encompassing the high mid frequencies is at the top of the array and aimed down just above the listeners' ears.

While speech is in mono this is a stereo system. It has separate high frequency drivers that go out to 10kHz and can be used for music reinforcement.

This is a powered system. AC comes to the speakers: each column has 16 two-way drivers in them. Each driver has a 25-watt power amplifier and a channel of DSP. A network cable is also brought down. Signals are delivered via analog paths and Cobranet.

Once the system is setup, it doesn't need much software to control it although one can do so in real time if one decides to do that via a separate Windows program communicating on the network system.

Referring to how different halls can be designed to suit different eras of composers, Rob asked where and how the line is drawn to determine that outcome. Martin responded that is largely decided by the organization that is commissioning the project and the acoustician they bring on board.

Rob presented Jeff & Martin with an AES certificate of appreciation. (Jim Hayward was also presented with a certificate at a later time).

The audience was invited to tour the facility individually and ask questions until closing time.

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