August 1, 2014
By Steve Titus, B.A.Sc., P.Eng., Aercoustics Engineering
Traditionally, courthouses were prominent buildings at the core of a community, usually edifices constructed of stone and wood. The acoustic environment in the courtroom was “live” in order to allow a judge and courtroom...
Traditionally, courthouses were prominent buildings at the core of a community, usually edifices constructed of stone and wood. The acoustic environment in the courtroom was “live” in order to allow a judge and courtroom participants to project their speech. Over the years, however, as modern technology evolved and the needs of the courts changed, these grand spaces became closed-in, oppressive rooms. They had limited access to natural light and poor acoustics. It was difficult for people to hear the proceedings at a time when every word was critical.
Courthouses in the City of Thunder Bay were in a similar predicament. Therefore, rather than retrofit two separate courthouses – the Superior Court of Justice and the Ontario Court of Justice – the Ministry of the Attorney General sought to consolidate these services under one roof in a new building. In April 2014, a state-of-the art, six-storey, 23,690-m2/255,000-sq.ft. courthouse opened in downtown Thunder Bay. With enhanced security features and an increased number of courtrooms, the centrally located facility offers more convenient public access to various justice services under one roof.
Toronto’s Aercoustics Engineering was part of the Plenary Group/Adamson Associates team involved in redefining the presence and performance of the modern day courtroom in this project. It was an opportunity to solve multiple issues. The Ministry needed to balance restoring the grandeur and presence of historical courthouses while avoiding any oppressive ambience and poor acoustics.
This was also the first new provincial courthouse to be built using steel construction. From an acoustic and vibration perspective, steel-framed buildings pose distinct challenges when trying to achieve high degrees of sound isolation.
Departure from existing guidelines
The first requirement was to design a courtroom that allowed a judge to be heard without the need for an electronic audio-visual (AV) system. Existing courthouses give A/V equipment precedence over natural acoustics. The courtrooms are often kept dark and quiet to accommodate trial recordings and equipment. But the Thunder Bay Courthouse designers took the opposite approach by focusing on the natural acoustics first and then integrating A/V. While A/V has its place in the courtroom, there needs to be a balance between the technical requirements and natural speech.
Aercoustics accomplished this balance by using acoustical treatments to ensure voices could be heard without any A/V enhancement. This approach was a complete departure from existing guidelines and the result was bright, open rooms with enhanced natural acoustics. The space has a high signal-to-noise ratio and ensures that the acoustical energy is distributed through the courtroom space. The speech level has to be much higher than the ambient noise in the room, so background sounds like ventilation noise or external noise are kept to a minimum. For example, the mechanical system was designed with low velocity ductwork and by selecting equipment that was silenced to meet the background sound level goals.
In addition, perforated acoustical wood panels were located in key locations on the wall, and acoustical ceiling tiles were used to ensure that speech intelligibility was relatively uniform throughout.
The parameter that was used to characterize speech intelligibility is known as Distinctness (D50). The D50 is defined as the fraction of energy that arrives within the first 50 milliseconds of the direct sound. It is presented as a percentage, where a D50 of 50% usually represents good speech intelligibility. The courtrooms here tested on average at a D50 level of 70%. As a result, the rooms are exceptionally quiet, enabling people to speak normally and hear clearly without the need for technology, but allowing for full functionality of the A/V system.
The A/V system is used to record trails and must accurately record the proceedings, otherwise mistrials can be granted. Also it is used for remote witness testimony. The equipment includes microphones, speakers, cameras and sophisticated control units with advanced algorithms.
To overcome the acoustical challenges of the building’s steel structure (in steel structures there are often cavities in the flutes where walls meet decks, for example), Aercoustics had to specifically determine the concrete thickness for the floors and ceiling assemblies to ensure that STC-55 could be achieved in the courtrooms. To ensure there were no perceptible vibration levels from pedestrian traffic outside the courtroom, Aercoustics also reviewed the structural design and developed a finite-element model of the courtroom structure and a feature staircase.
Aboriginal Conference Settlement Suite
The Thunder Bay Courthouse is also the first in Ontario to incorporate an Aboriginal Conference Settlement Suite. The suite was designed with input from elders and leaders within the aboriginal community. The space pays tribute to their traditions and is designed to support the healing process.
The suite was perhaps the most challenging aspect of this project due to its unique shape – a circular room in plan, with an elliptical dome above. Unlike round council chambers, where generally the speaking people are on one side and the audience on another, here speakers are seated all around the room.
Aercoustics was tasked with creating the best acoustic design for a room with no front or back – which meant that speech could come from anywhere in the room. There were concerns that the unique shape of the suite would result in negative acoustical effects known as “whispering” or focusing, which is defined as a phenomenon that creates a high concentration of energy at a specific location.
The solution was to design a unique geometric relief of wall panels around the circumference of the room. The panels retain the architectural and cultural importance of the circular format and consist of vertical wooden slats of varying depth. Carefully designed to an exact geometry and size, these optimized panels diffuse or break up the sound waves to distribute the energy and prevent a whispering and focusing effect.
In addition, the elliptical dome was treated as acoustically absorptive because reflections from this surface would have made it difficult to hear anyone speaking.
Keeping out noise from the atrium
Beyond serving the judicial process, the new courthouse incorporates an atrium that that is also meant to be used for community functions, which can be noisy. Using a 3D computer model of the central atrium, Aercoustics was able to predict the impact of noise intrusion into the courtrooms and created cleverly hidden acoustic treatments. Perforated metal in the balustrade, for example, helps to absorb some noise, and doors have seals to protect the noise from spilling from the public area into the courtrooms. As a result, any conversations or events taking place in the atrium do not disturb court proceedings. For example, Aboriginal drumming performed in the atrium during the courthouse ceremonial opening could not be heard inside the courtrooms.
The 15 accessible and barrier-free courtrooms have sophisticated infrared hearing equipment for those who are hearing impaired, and braille signage. Most courtrooms also have simultaneous interpretation, with one booth permanently built into a jury courtroom.
Aercoustics’ philosophy has always been to design great rooms that work without amplification or reliance on A/V systems. One of the key lessons learned from this project was that the appreciation of rooms with excellent natural acoustics where A/V can also be integrated is universal. We have extensive experience of creating such spaces for performing arts centres, but it is only in recent years that we see other sectors embracing this approach as well, such as educational and institutional buildings like this courthouse.cce
Steve Titus, B.A.Sc., P.Eng., is president of Aerco
ustics Engineering in Toronto. E-mail firstname.lastname@example.org.
Building owner: Ministry of the Attorney General
Architect: Adamson Associates
Acoustical design: Aercoustics Engineering (Steve Titus, P.Eng., Sarah Mackel, B.A.Sc., Kiyoshi Kuroiwa, P.Eng.)
Structural engineer: Read Jones Christoffersen
Mechanical engineer: VRM Engineering
Electrical engineer: H.H. Angus
Audio-visual: Sight N Sound Design
Contractor: Bird Construction