Sound Systems: Gymnasium

Reflect for a minute on the quality of sound in your school’s gym. Is the sound system good? Can you hear and understand what is announced? Is the volume even, or is it too loud in some seats and unintelligible in other areas? If it is loud enough, is the sound distorted? After a brief thought, you likely concluded that your present gym sound system could use improvement. Unfortunately, there are not many good gym systems. If you have a good one, count your blessings!

A gym sound system must be versatile. Gymnasiums are used for a wide variety of events: sports, the dance line during halftime, convocations or assemblies, graduation ceremonies, concerts, musicals, dramas, etc. A sound system is needed for all these events. Each of these applications has unique requirements and places different demands on a sound system. It is difficult to expect one sound system to meet the exact requirements for each type of event. To provide proper sound reinforcement for these applications, several sound systems or configurations may be required. Due to the space limitation, this article will focus on a sports system set up. Please contact us for more information about the other system configurations.

Demands of a Sports System:

The sports sound system must provide:

1. Enough volume

2. Sound clarity (intelligibility)

3. Even coverage

These three objectives are extremely interrelated. In other words, they must all be met or the sound will not be satisfactory.

LOUD ENOUGH

A challenge the system designer must overcome is background noise from the crowd. It is just not appropriate for a crowd to hold in their shouts of enthusiasm during an exciting game. Besides, the team needs to hear the cheers and excitement from the crowd. However, the crowd noise must be taken into account by the designer, or the system will not fulfill the demands. Figure 1 illustrates the measured sound pressure levels in some common situations. The average noise level at a game may be in the 75 to 85 dB range. Loud cheers can be considerably higher. It is commonly accepted that for excellent intelligibility, the signal or announcement should be 25 dB louder than the background noise. Therefore, the sound system must produce 100 to 110 dB in the bleachers—at the listener’s ears. Unfortunately, a system capable of levels this loud can be very hard on the budget and the ears. What if the crowd roars with excitement and the background noise raises to 100 dB? It is impractical to expect the sound system to overcome that noise level.

Figure 1
Average sound pressure levels of common sounds

What can be done to lower the background noise? Acoustics play an important part in the crowd-noise factor. Crowd noise in a gym with little acoustical treatment will seem louder than in one which has been acoustically treated. Better acoustics also contribute to better intelligibility. Solving an acoustical problem can be expensive, but it is the best solution in a non-acoustically treated room. Also, the audience will appreciate the sound in a room with good acoustics.

INTELLIGIBILITY

Above, we stated that an announcement needs to be 25 dB higher than the background noise to be clearly heard. But, so many times when the volume is simply turned up, it gets distorted and is impossible to understand what is spoken. What help is available? The following are pieces of equipment to help solve this problem.

Compressor/limiter:

This equipment will help prevent distortion by lowering an excited announcer’s voice. When the volume peaks are limited, the average sound level can be increased without fear of distortion.

Autoleveler:

This is a derivative of the compressor. It compensates for quiet voices and for loud, excited voices. The highest quality models have features which make this product very attractive!

Automatic Noise Sensing Leveler:

These units have a sensor which monitors the crowd noise and adjusts the volume of the sound system to compensate for changes. Now the crowd won’t be blasted when the room is quiet and yet can still hear the announcer during the energetic moments.

Speech Processor:

A speech processor digitally processes spoken words to greatly increase the sound clarity. The end result is the ability to hear more clearly under high noise conditions without hurting the ears of the audience with high volume.

Equalization:

By properly adjusting the quality of the sound, better clarity can be achieved. This is done through an equalizer. An equalizer is a set of tone controls which give the sound operator the ability to adjust the tone of the sound system. The result is better, more natural sound which is easier to understand.

SOUND SYSTEM COVERAGE

The goal of a sound designer is to provide the same volume and quality to every listener in the room. However, in reality, this is not quite possible yet. But with today’s computer modeling programs and equipment, we are very close to this goal. Poor coverage occurs when some people hear the announcement clearly, others get blasted and yet others cannot hear at all. Every loudspeaker covers a specific area (Figure 2). If a listener is in the coverage area, s/he may hear clearly. If the loudspeakers are not positioned and aimed accurately, there may be areas that are not covered. In those areas, people will not hear well.

Figure 2
Speaker Coverage Patterns

by Ron Huisinga © 1996 Internet Sound Institute (www.soundinstitute.com). This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com

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