An improvement on old methods
Using an array of 12 loudspeakers in a quasi-spherical arrangement, the room can recreate acoustical environments in three dimensions. The perceived quality of the simulation no longer depends on knowledge of a listener’s cranial dimensions, and so spatial realism of the simulation is significantly improved when compared to headphone simulations.
For a recent performing arts project, this allowed validation of the design to a degree that was unachievable in the past. When combined with a VR simulation, reflections from overhead surfaces and the rear wall were remarkable to perceive when these aspects of the design had formerly been nothing more than lines on a page. On a recent feasibility study for the acoustical renovation of the Montréal Olympic Stadium, where an acceptable reverberation time design target was hard to determine, simulation provided the necessary information to develop an effective design, while allowing the client to understand exactly what they would get for their money with different levels of treatment.
Another key aspect leading to the improved realism is the quality of the low frequency reproduction in the 20 to 100 Hz range. Convincing low frequency reproduction of sources such as subway rumble or bass instruments is lacking in headphone simulations since bass is heard but not felt as it would be in real life. The issue is an acoustic phenomenon known as room modes or standing waves.
At modal frequencies where the wavelength in air corresponds to dimensions in a room, energy will build up in the space, and it will ring. All rooms have modes, and these modes can radically change what is heard at specific frequencies depending on the listening position. Moving a few feet can change not only the level by as much as 10 to 20 dB (quiet versus loud), but also the character of the sound (‘tight’ to ‘boomy’). This level of variation can be misleading and would be unacceptable in a precision simulation environment.
A special system was therefore developed for reproduction of low frequency sources. Multiple subwoofers have been placed throughout the room so that at seated height anywhere in the room, the level varies only slightly (+/- 3 dB) from the target frequency response. This ensures an accurate simulation. The use of multiple subwoofers has many advantages over methods used in the past for low frequency control. In some recording studio control room designs, as much as 50 per cent of the floor area might need to be consumed by acoustical treatment to provide a similar level of control at low frequencies.
The entire playback system is controlled using a dedicated digital signal processing (DSP) unit, performing all processing needed to provide a uniform low frequency response and to ensure all speakers are configured with the correct delay and equalization settings. The configuration is fixed and inaccessible to users of the system to avoid the potential issue of an accidental change of settings. The processor is fed over Ethernet using the Dante protocol that allows up to 1024 channels of uncompressed digital audio to be transmitted to the listening room. If desired, a simulation and two-way communication with the client could be conducted using a laptop from any room in the office.
As a result of this level of control, any project affected by low frequency noise can use the technology to get a clear picture of how the intrusion will sound. For example, this approach was used to simulate subway noise intrusion for Toronto’s Koerner Hall with and without isolation. Subways are not the only noise source that can be simulated. This technology has been used in various projects such as simulating helicopter noise through different windows, walls, and ceiling assemblies for a hospital. Weight drop noise from condominium gyms, basketball courts above classrooms, set construction shops beside recital halls, and rock music recording and rehearsal facilities are other applications where this technology has been applied to gain a better feel for the numbers and understand the true implications of various design recommendations.
In conclusion, simulation rooms can be a valuable tool for building professionals. The insight provided will result in savings in time, cost, and frustration. With a true picture of how a building will sound, risk and expectations can be managed more effectively.
Ben White, B.E.Sc., has worked as an acoustical consultant at Aercoustics for four years. He was responsible for the design of the Bridge, a new virtual reality (VR) acoustical simulation environment at Aercoustics, among other in-house technical initiatives. White has worked as acoustical project manager on the Centre for Technology and Innovation at Humber College, the new Rogers Radio Studios, Lynx Music studios, and many other projects in the institutional, performing arts, and media/broadcast spaces. He can be reached at benw@aercoustics.com.
Steve Titus, B.A.Sc., P.Eng., brings more than a decade of experience to being CEO of Aercoustics Engineering, a privately held firm specializing in acoustics, vibration, and noise control. 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 the St. Lawrence Market North redevelopment. Titus is co-chair for Canstruction Toronto, and sits on the finance and audit committee of the Consulting Engineers of Ontario (CEO). He can be reached at stevet@aercoustics.com.
