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Guest Column - February 2008

Turn It Down

Dealing with Acoustical Issues in Recreational Facilities

By Art Barkman


R
ecreational facilities are often noisy and have issues with distortion that minimize the use of the space for other functions along with compromising the use of the space for recreation. This is especially true in educational, municipal and worship-related facilities where these spaces are multifunctional.

While excessive noise levels may not be sufficient to substantially impede the use of the space if its primary function is a gymnasium, giving instruction might be difficult. These conditions often limit the use of the space for other functions. In addition, if the gym is used for spectator events, the distortion makes announcements difficult (or impossible) to understand. Often school gymnasiums are used as an auditorium to accommodate large audiences. Other gyms are specifically designed as multipurpose facilities and may be used as cafeterias or auditoriums.

The cause of these problems is the preponderance of hard surfaces that reflect and amplify sound. These multiple reflections cause the sound (words, music, etc.) to be heard several times with diminishing levels of volume as each reflection passes your ear. The phenomenon is termed reverberation time (RT) and is measured

in seconds—the time that a sound decays by 60 decibels and becomes inaudible. The greater the RT, the greater the distortion, the less intelligible words are and the quality of music is diminished.

Many untreated gymnasiums have reverberation times in excess of 10 seconds, whereas an RT of less than 1 1/2 seconds is desirable and required for clarity. As a reference, recording space RT should be under 0.5 seconds.

When the reverberation is reduced, there is a simultaneous reduction of the volume of sound. Both are highly predictable using mathematical models that consider the volume of the space and the reflectivity of the surfaces (walls, ceiling and floor).

This reflectivity is measured by a tested number that provides a Noise Reduction Coefficient (NRC). This is the simple mathematical average of the absorption of sound at four frequencies: 250, 500, 1,000 and 2,000 Hz. These are the frequencies we make the most and hear the best. A block wall has an NRC of 0.03 (3 percent) whereas an efficient wall or ceiling treatment can have an NRC of 0.80 (80 percent) or higher.

This correction is achieved through the application of sound-absorbing materials to the walls and/or the ceiling. Perceived noise reductions of 30 percent to 50 percent are common given the proper engineering.

The ceiling is the first place to look for acoustical enhancement. Some facilities have a suspended acoustical ceiling and, while its performance may not be optimal the gain in upgrading it (replacing the ceiling panels) is marginal. More significant gains can be had by treating the wall surfaces, which are probably hard. A commonly used suspended ceiling panel will have an NRC of about 0.60—or 60 percent absorption. Replacing it to bring it to bring it to 0.80 or higher is not a good place to spend your money unless it is aged and in disrepair (damaged, water-stained, etc.). Even as such, there are restoration systems that are less expensive and do not downgrade acoustical performance. These would be acoustically transparent paints and snap-on grid covers.

Many ceilings in recreational facilities provide virtually no acoustical contribution. Exposed bar joists and metal deck, gypsum board, preformed concrete and wood are the most common. Flush mounting acoustical panels (actually wall panels applied to the ceiling) work well and can be sized and patterned to avoid lighting, air conditioning vents, sprinklers or other obstructions.

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