The Des Moines Civic Center is a unique multi-purpose performing arts hall with 2,800 seats on one strongly raked level. The inward-leaning curved pylons of the side walls, a characteristic gesture of the original acoustician, Paul Veneklasen, dominate the hall’s acoustics.
Kirkegaard was hired in 2013 to evaluate the hall, focusing on improved sound for the resident Des Moines Symphony Orchestra. After developing a full menu of possible improvements, Kirkegaard worked with the owner and users to prioritize these sub-projects. Three were ultimately implemented–a new orchestra shell, high-frequency echo control treatments at the side walls, and a complete reconstruction of the hall’s rear wall.
The new orchestra shell is heavier and simpler, with flat upstage towers, gently curved sidewall towers and gently curved ceiling reflectors with integral lighting fixtures. The shell is more projective, with a higher ceiling. The musicians benefit from cleaner reflections within the shell and less buildup of sound, as well as better coupling to the acoustics of the audience chamber.
The side wall treatment is primarily aimed at improving clarity. The thin absorption added to specific locations on the lower side walls absorbs high frequency sound only, softening confusing late reflections.
The rear wall was rebuilt so that it reflects sound diffusively back to the audience and stage. By integrating a series of curtain pockets into the re-built wall, large-scale diffusion and a place to store curtains were provided, maximizing the difference between the absorptive and diffusively reflective conditions.
The acoustical improvement has been dramatic-greater presence and impact, clearer hearing conditions for the musicians, and a sound for the audience that is more reverberant, warmer, and clearer.