Noisy Lessons

Reading an article on acoustics in the July 2012 issue of The Construction Specifier reminded me of a number of useful lessons learned in the process of designing and administering public school construction projects. Here is one:

Basic Acoustical Treatment for a School Gymnasium: Although acoustical treatment on walls and ceilings is commonly omitted or is eliminated through value engineering, it is typically crucial for a gymnasium. Some basic guidelines provided by an acoustical consultant on a school project 20+ years ago have proven helpful on several other projects. The guidelines related to a gym with a single basketball competition court, a substantial bleacher area, and a clear height of approximately 25 feet to the underside of the roof structure. The guidelines were simple: Cover approximately 15% of the wall area and 50% of the overhead (roof/ceiling) area with a well distributed array of acoustical panels. The panels were the equivalent of 1.5-inch thick wood fiber (Tectum) mounted on furring and backed by a layer of batt insulation. The distribution of the panels is important in order to adequately reduce sound reflection in the large space. We utilized a checkerboard pattern of panels on the upper half of all walls, and we covered every second joist bay of the underside of metal roof deck.

In practice, the 15+50 surface applied acoustical treatments described above have generally been more successful than “built-in” alternatives like acoustical concrete masonry units (e.g., “SoundBlox”) and acoustical metal decks (including (1) those with perforated flute walls and laid-in fiberglass strips and (2) cellular acoustic deck with a perforated bottom plate and internal insulation).

The 15+50 surface applied acoustical treatments described above have also proven to be acceptable “fixes” for existing or newly constructed gyms of similar size that suffered echo chamber effects and were considered too noisy for normal use.

(It should be noted that the basic guidelines described above will not be effective in every situation, and larger or different spaces are likely to need different percentages and/or different types of acoustical treatment. In addition to acoustical consultant resources, there are good published resources available to architects; one such publication is Architectural Acoustics – Principles and Practice (available as an NCARB monograph).)