rowing program demands and space requirements in urban schools require contemporary gymnasiums to be multifunctional. Their diverse uses today include sporting events, student assemblies, drama productions, band concerts and after school education/daycare to name a few. These uses fall into two broad categories namely, gymnasium use and auditorium use.
Acoustical quality requirements for these two categories are unfortunately not quite the same. Gymnasium use suggests a level of acoustical liveliness while auditorium use requires speech intelligibility, which is defined as the percentage of speech material correctly identified by an average, normal-hearing listener working in their first language. Satisfying one purpose degrades the acoustical quality requirement of the other and hence a compromise is vital.
American National Standards Institute (ANSI) standards do not specify performance criteria for larger enclosed learning spaces such as gymnasium in detail. Converting a gymnasium for multiple use (or multifunctional) is onerous but becoming an essential investment due to growing program and space requirements in most urban schools. Existing gyms were generally designed for sporting events, having less acoustical treatments than required for other activities.
In established schools however, a complete acoustical overhaul of the gymnasium to accommodate its multifunctional use may not be possible because of economic and time considerations. Under these circumstances, the introduction and specific placement of varying amounts of acoustically absorptive materials on the interior surfaces of the gymnasium walls and ceiling is considered to be to be a viable and adequate alternative.
It is assumed that the background sound level generated by HVAC and other sources will still be properly controlled incorporating appropriate rated enclosures (wall, window, ceiling assemblies, etc., meeting or exceeding required minimum STC ratings), and silencers, etc. Under these circumstances, the only significant remaining acoustical issue to be addressed for a multi-functional gymnasium is its reverberation time.
Acoustical Reverberation Time and School Environments
The reverberation time has traditionally been the key factor in quantifying the acoustic environment of a space. In most teaching spaces, the optimum reverberation should be fairly low (approximately 0.6 seconds), so that reflected sound decays rapidly, which allows for better speech conditions. In spaces for sporting or music events, longer reverberation times have been found to be preferred (up to 2.4 seconds) in-order to provide some excitement and liveliness.
Reverberation time at the low end of the range may provide acceptable speech intelligibility in a classroom or lecture room-like setting with students at a relatively close distance, but is likely to detract from the excitement of an athletic competition or the enjoyment of a music recital. Thus, setting an assessment criterion for a gym, which must accommodate varied activities, is not straightforward. Published literature suggests that the optimum range for good speech intelligibility is 0.6 to 2.0 seconds, (for classroom, lecture hall, small theatre-like settings and 0.6 seconds being ideal for core learning spaces) while the optimum range for a ‘live’ space such as auditorium, concert hall, symphonic, etc. is from 1.4 to 2.6 seconds. Thus a compromise is required for multi-use gyms, in order to serve both purposes.
Achieving a Reverberation time of 1.5 seconds or less across the speech frequency range would be a reasonable target without significantly compromising speech intelligibility. Whereas, achieving an Reverberation time of 1.5 seconds or more would be considered as a reasonable target without significantly compromising the excitement required for regular gym activities. Slightly longer reverberation times at lower frequencies are acceptable, as this will have little effect on either overall levels or intelligibility. Similarly shorter reverberation at high frequencies are typical due to the large physical volumes and air absorption without degrading speech intelligibility or the quality required for excitement.
Acoustical Engineering Five-step Process
In summary, establishing good acoustics in a gymnasium with auditorium and classroom uses is achievable but challenging given the cross-purpose acoustical requirements. Through experience and investigation HGC Engineering has determined that the following five-step process will most likely lead to a desired acoustical outcome.
- Determine the existing acoustic treatments and measure the levels of reverberation to confirm their performance.
- Determine the additional absorption required to achieve the determined criterion
- Choose the absorptive treatments considering their low, mid and high frequency absorption coefficients and the level of reverberation already present in those frequency bands.
- Determine an appropriate distribution of material based on acoustical modelling which considers all three directions (generally it is advisable to distribute the materials fairly evenly around the wall and ceiling considering the existing level of absorption in each direction), and confirm the resulting reverberation levels through testing after installation.
- Ensure that the installation proceeds as per the manufacturer’s recommendations or the materials may not achieve the desired level of absorption and excessive reverberation could result.
This is an adapted version of a paper that was originally published in
the Journal of the Canadian Acoustical Association.