THE ART AND SCIENCE OF CONCERT HALL ACOUSTICS

III. STATE OF THE SCIENCE

Starting in the early 1990’s, various companies worldwide began producing programs with which to model concert halls. A series of round robin competitions in 1995 proclaimed that the commercial programs ODEON and CATT, in addition to one unspecified research code, were the most accurate in the competing field (Vorlander 689).

These programs would allow an acoustician to define plane surfaces in order to build a hall in a computer. The acoustician would then assign each surface material characteristics and the degree to which it absorbs, reflects and deflects sound waves. A source can then be defined, including its location, shape of directivity of sound and the overall gain in sound power. The emphasis is therefore not on details, rather, on large surfaces that will certainly reflect sound waves (Lynge 18).

For this project, the program ODEON was used to model a variety of hypothetical and reality based halls. Simulations were run as “jobs” with one or more sources sending their signal through the room. Results were exhibited as point receivers and grid receivers. A point receiver would give the values for the above-mentioned variables at a sampled listening post. It would also illustrate the decay curve for how the sound died out, a reflectogram of when sound impulses reached the listener, soundroses for both the horizontal and vertical axis, and a visual representation of the simulated rays and their paths to the receiver. A grid response would put as many receivers as specified in the hall, and demonstrate the values for the above-mentioned variables in a colored visual representation (Lynge 47). Several examples of a grid response can be found in this report.

The technology has reached a state where it can model some hall characteristics and eliminate bad ones, but it has failed to examine the full range of such elements. For example, sources agree that hall shape is an important feature, especially for good lateral reflections. Modeling has been used to verify the known fact that a fan shaped hall gets poor lateral reflections while shoebox shaped hall does much better. This is because the reflections off the side walls will be spread in a more even manner towards the audience (Figure III.1).

Figure III.1. Half of a shoebox hall and half of a fan-shaped hall, demonstrating why lateral reflections are stronger in halls with narrow parallel walls.

Thus, this technology has been used to eliminate the fan shaped hall from the acoustical architect’s options. Interestingly, modeling has been used to also verify that a reverse fan shape has a positive impact on lateral reflections (Kahn 3-4).