November 20, 2012 By Dan Daley
Acousticians will always list their ears as their primary tools, but as good as those highly developed organs are for them, they’re backed up with a very sophisticated array of software-based systems that let them predict and track reflected sound in almost any kind of environment.
Some programs are specifically intended for use by acousticians, such as the CATT-Acoustic’s v.9 program, that Damian Doria, a principal in Artec Consultants, an acoustical consulting firm based in New York City, used to handle prediction and auralization requirements for projects such as the new symphony halls in Carmel, Indiana and at the Miami Arts Center.
Another, more recent addition to the architect’s arsenal, is Autodesk’s Revit Architecture, a Building Information Modeling (BIM) software that allows the user to design with both parametric 3D modeling and 2D drafting elements. BIM is a Computer Aided Design (CAD) paradigm that employs intelligent 3D objects to represent real physical building components such as walls and doors, and allows the impact of parametric objects on acoustical reflections to be predicted in a 3D environment.
There are other software-based tools that pick up the job when it comes time to design a systems for a space. Bob McCarthy is president of Alignment & Design, a Missouri firm that creates sound system designs using various software programs, including SIM audio analysis and optimization software, which McCarthy developed develop while working at Meyer Sound, as well as Rational Acoustics SMAART, whose acronym - Sound Measurement Acoustical Analysis Real Time - underscores its Fast-Fourier Transform (FFT)-based algorithmic operation that can be applied to three operational modes: transfer function, real-time analyzer (RTA) and impulse response. In fact, the number of choices that acousticians and audio systems designers have to choose from in terms of software - other products include Renkus-Heinz’s SysTune, AFMG’s EASE, and SATLive.
These software-based analytical and measurement tools are used by both acousticians in measuring and modeling spaces, then used by systems designers to build those audio system, first on paper or in CAD and then in reality, and they are used again to validate the design of finished systems and then to fine tune them in place. They’re used in various configurations, depending upon the point in the process, and are abetted by even more specialized programs, such as Bruel & Kjaer’s Dirac software, which measures speech intelligibility.
“The entire process is like one big circle and [the software] is used at every step,” says McCarthy. In fact, he surmises, the measurement and analysis technology that’s now available to the industry exceeds what it needs to accomplish in most scenarios. “At this point, the tools are better than the knowledge base of the users,” he comments. “The consistency of the technology is at the point where if you run two of them in parallel processing with a Y cord, you’d get the same results. The math goes back to the 18th century - the technology just lets us get it faster.”
But, if sound in a reflective space is able to be so precisely predicted, mapped and analyzed, why does sound seem to be the most subjective of all the crafts that make up the universe of systems? Probably because we are trying to precisely define that which we can only perceive subjectively. “It’s not like light; it’s invisible,” McCarthy says of sound. “As a result, it’s a tough medium to understand the physics of.”
Mark Graham, a principal at Wrightson, Johnson, Haddon & Williams (WJHW) in Denver, goes deeper in his response. “The objective versus the subjective when it comes to analyzing sound and its reflectiveness is more a matter of psychoacoustics,” he says. The math can be incredibly precise on the slide rule but its application inevitably compels rules of thumb rather than unblinking algorithms. For instance, at the New Meadowlands NFL stadium in New Jersey, the deeply segmented levels that make up the bowl are fertile grounds for sonic reflections as sound from any point source penetrate deeper into them.
That’s why a distributed system, using thousands of speakers dispersed relatively closely to the audience, is the best strategic solution. But short of placing a speaker over each seat, which would be prohibitively expensive, the practical math suggests that as long as any audience member is within no less than 10 dB of the level of the direct sound ad within 30 milliseconds of its arrival, any adverse acoustical effects are effectively nullified.