Intelligibility

Speech

Two basic characteristics of speech concern any listener. Speech is most enjoyable, and most effective, when it is understandable and pleasing to listen to. Sound system designers and acousticians refer to the understandability of speech as INTELLIGIBILITY. Speech intelligibility is affected by many factors. It is most affected by the reverberant characteristics of the room itself. Generally speaking, the longer it takes sound to "die down" in a room, the more reverberant that room is considered to be. Speech is less understandable in rooms that are highly reverberant. In other words, the more reverberant a room is, the lower the speech intelligibility.

Traditional Music

For centuries, church music has been primarily organ, piano and choral elements. You may also consider acoustical instruments such as woodwinds, brass and classical guitar as elements of traditional music performance when traditional, liturgical styles of music are performed. Where speech intelligibility is degraded by highly reverberant rooms, traditional music is enhanced by higher reverberation in worship spaces. Generally speaking, the higher the reverberation time, the better the sound quality of traditional music performance. Perhaps now you are beginning to understand the basic problems associated with the combination of speech and music in a traditional worship environment.

Contemporary Music

There is an ever-growing trend toward incorporating contemporary music styles in worship services. Many churches, historically founded in traditional, liturgical worship, have begun to embrace contemporary worship as an enhancement or to add "special music" elements to their worship service options. It is important to understand that contemporary music worship is also affected by room acoustics. Although there are many subtle aspects to optimum contemporary music worship, the primary goal is to make certain that vocal lyrics are understandable. Here we go again with intelligibility. Only this time, the intelligibility is further degraded by additional instrumental sound levels. Put this in an environment with relatively high reverberation and the results can be disastrous.

The Sound System to the Rescue

A properly designed sound system that is installed and aligned correctly will greatly IMPROVE problems associated with room acoustics, music and speech. But did you notice that I DID NOT say that a sound system will ELIMINATE those problems?

A sound system can help reduce the effects of highly reverberant levels in a room by doing one or more of the following:

1. Increase the Directionality of the Sound Source
   Have you ever noticed that when you are shouting to someone across the room, if you are not understood, you can cup your hand around your mouth and improve the intelligibility of your voice? A sound system can do the same thing. If necessary, a sound system designer can use speaker components that are highly directional. This does two things. First, it increases the amount of direct sound reaching your ears. Second, it focuses more of the total sound energy into areas where people are sitting (Fig. 5). People absorb sound much better than hard walls, ceilings or floors. The less the amount of energy that is directed toward reflective surfaces, the lower the reverberant level in the room. This helps improve speech and vocal intelligibility.
2. Decrease the Effective Distance Between the Sound Source and the Listener
   Stand next to someone in a reverberant room. He is easy to understand during conversation. Now move across the room. His speech is now much less understandable. In general, the closer you can get the sound source to the listener, the higher the intelligibility will be. In many cases, this is the only effective approach for sound system design. For example, if the sanctuary is fairly reverberant and the distance from the sound system to the last pew is at least 60 feet or greater, chances are the only solution for providing good speech intelligibility is to use a separate speaker system (Fig. 6). The system is elevated over the rear seating areas or balcony, using specific electronics to match the sound arriving from this "satellite cluster" with the sound arriving from the front speaker system.
3. Reduce Unnecessary Sound Energy
   Not every event that occurs in the church will result in every seat being occupied. In fact, for small weddings, funerals or other similar events, less than 20% of the seating areas may be used. In these situations, the sound energy that is directed toward unused seating is not only useless, it actually will contribute to the reverberant energy in the room, which will in turn degrade intelligibility. A sound system can be designed so that specific speaker components can be turned off individually to reduce the reverberant level in the room.

Sound Systems Will Note Eliminate Acoustical Problems in a Room

As a professional sound system contractor, we have the tools and experience to determine how simple or complex a sound system must be in order to provide adequate intelligibility. We can measure the reverberation characteristics of the room and, combined with other structural and acoustical information, we can predict whether a particular speaker system will provide sufficient intelligibility.

Sometimes the acoustics of the room will prevent the use of any cost-effective sound system solution. At this point, the customer has several options. We discuss those options with the client and help determine the best overall solution. In some cases, simple acoustical treatment can be included in the sound system design package. There are times, however, when a professional contractor will put the customer's best interest first and recommend that an acoustical consultant be brought into the project. It has been our experience that when acoustical design and implementation is required, the best results occur when the acoustical consultant and the sound system contractor work together to develop a solution that combines acoustical treatment and electronic sound reinforcement technology.

The Bottom Line

No matter what specific acoustical problems your church may have, there is only one prudent method for finding the best solution:

• Hire a professional sound system contractor that can accurately measure the acoustical characteristics of the room. If the project involves new construction there are computer software tools that can be used to predict the reverberant characteristics of a proposed facility.
• Make certain that you provide us with ALL the pertinent information regarding styles of worship, including any future plans to incorporate new forms of music worship.

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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