Church Sound Systems and Acoustics

Designing Solutions That Won't Compromise Speech Intelligibility or Music Quality

By Craig Janssen with David Kahn

Printed without Permission as copied from Systems Contractors News - Nov. 1997

The reason for posting this article is to confirm the fact that there are many audio and acoustical professional that do indeed agree on how to do church sound. I met Craig a few years ago and discovered that he went through the same learning as I have. His work is counted as some of the best in the world.

It's no secret that many churches are plagued with acoustical and sound system problems. For whatever reason, sound system and acoustics designers have often ended up on opposite sides of the fence with respect to who is to blame for these problems.

Sound systems designers typically want large amounts of absorption to be placed in the room to ensure good speech intelligibility while the acoustics designers commonly focus on the musical performance of the room and as such fight against adding absorption.

Our company provides consulting services (both sound systems and acoustics) for many church clients, thus we have had to work out design solutions that do not compromise either speech intelligibility or the musical quality of the spaces. We thought it would be useful to write an article that elaborates on the issues at hand.

It is very common for churches to add considerable acoustical treatment in the form of sound absorbing materials in an attempt to improve acoustics. Such treatment is sometimes part of the original design, and sometimes it is added "after the fact" in an attempt to reduce the problems inherent in a poorly designed room or sound system.

Intelligibility of the spoken word is almost always improved with the addition of sound absorbing materials. Unfortunately the addition of such treatment usually has a negative impact on the music acoustics and other important acoustical aspects of the worship experience, such as congregational participation. These conflicts provide what can appear to be an un-resolveable dichotomy of interests.

With good room design and a coordinated sound system design, we believe, the addition of sound absorbing materials, which almost always has a negative impact on the natural acoustics, is not, inherently necessary for excellent intelligibility of the spoken word.

PROGRAMMATIC REQUIREMENTS

Speech intelligibility is essential in almost any worship facility while good music acoustics are Of course also desirable. Assuming that the music program does not consist of exclusively amplified instruments, the natural acoustics of the are required to support the musicians, including the choir, organ and other instrumentalists and singers.

The natural acoustics should also support congregational participation and worship. Even in churches that incorporate a very contemporary musical style with many amplified instruments, it is typically still very important for the space to support congregational participation.

There could be reasons, however, to desire a more absorptive environment, thus requiring use of some sound absorbing materials. Some of the more contemporary churches that typically run with "high-power" sound systems require lower levels of reverberation and hence more sound absorption. Also, in very large churches seating, say, over 3,000, or in existing churches that are poorly designed, sound absorbing materials can be required to reduce the level of late sound reflections (echoes).

In general, reverberant churches usually have better acoustics for music (non-amplifled), and are usually more exciting to sing in.

Reverberant gathering spaces tend to support congregational participation and generate a sense of community. However, reverberation also tends to reduce the intelligibility of the spoken word and reduces the sense of intimacy desired for preaching.

In many churches, one feels a sense of community during praying and singing together, while in other churches one feels isolated and not part of a congregation during worship. The acoustics of the space can and do have a significant impact on the program of the church.

From this simple programmatic approach, there seems to be a contradiction of acoustical requirements in a church. Many aspects of worship require lots of reverberation, while the important requirement for good speech intelligibility or contemporary music performance requires just the opposite. This dichotomy presents an interesting and demanding challenge to the acoustics and sound system designer for a worship space.

Basic Theory EXPLAINED

One way of describing a room's acoustics is with a quantitative measurement of the reverberation time. Reverberation times can vary from under one second in small worship spaces treated with sound absorbing materials and up to maybe ten seconds in some large cathedrals.

Reverberation time depends on both the size (volume) of the church, and on the sound absorptive properties of all the interior finishes. Larger spaces (with more volume) usually have longer reverberation times. Seating area is considered, in acoustical terms, a sound absorptive interior floor finish. Therefore, the greater the seating capacity (for a given room volume), the shorter the reverberation time. Of course the addition of other sound absorbing materials on the walls and ceiling, and on the floor (carpeting), also reduces the reverberation time.

We have observed that the concept of reverberation time has been considered by many in the sound system and acoustics design world to be a major factor in their designs. However, reverberation is a complex phenomenon that cannot be explained simply by reverberation time. Many other aspects of reverberation such as reverberation level or early reflection content are essential if one is to correctly understand the acoustical performance of a space.

Higher amounts of reverberation, more common in smaller rooms, can be very harmful to speech intelligibility. As an example, speech intelligibility in a reverberant racquetball court can be very poor due to the large amount of reverberation one experiences. However, in a very large room (like Grand Central Station in New York City) with a large reverberation time, speech intelligibility is actually quite good since the sound of one's voice isn't loud enough to excite the entire room's reverberation.

Many people believe, and in fact one can still find many textbooks, the blanket theory that reverberation time is directly related to speech intelligibility, no matter the room size. That is, the longer the reverberation time, the worse the speech intelligibility. However, our experience has proven that in many cases speech intelligibility can still be good in rooms which, according to measurements, have large reverberation times.

A more thorough look at other aspects of reverberation can help to explain why reverberation time and speech intelligibility are not necessarily directly related. The basic architectural design of the room determines, among other things, how early sound reflections can travel from a sound source (a speaker, singer or loudspeaker) to the people in the congregation. Some architectural shapes lend themselves to providing more and stronger early sound reflections and it is these early sound reflections that can be very helpful in improving speech intelligibility. One can conclude that the acoustics and sound system designers need to be involved in the design process at a very early stage before even the basic room design and room shape have been established.

DESIGN SOLUTIONS

With a good sound system design, excellent intelligibility can even be achieved in a reverberant environment. Therefore there is far less need to compromise the natural acoustics in order to satisfy the intelligibility requirements. This approach can lead to a much better feeling of community within the congregation. It can of course also result in a considerable cost savings by eliminating the addition of the sound absorbing materials.

Fabric wrapped fiberglass panels, an effective and frequently-used product used to reduce reverberation, usually costs at least five to six dollars per square foot. The cost of many typical custom applications can cost at least double this figure. In a large worship space, this can be a very expensive proposition. Usually a well-designed sound system coordinated with the room design is a much more cost-effective approach. Of course this also has the great advantage of meeting the programmatic requirements for both speech and music.

Although many aspects of a sound system design will impact speech intelligibility, the selection and placement of loudspeakers is certainly one of the most critical design elements. Poorly selected or poorly placed loudspeakers can result in a tremendous waste of money. Again it is essential for the sound system designer and Acoustician to work together with the architect in developing basic room design concepts to ensure that a coordinated design solution is implemented.

So why add sound absorbing materials? Usually this is done to improve speech intelligibility, which invariably suffers in a more reverberant environment. Many years ago before electronic sound reinforcement systems existed, such an approach could almost never be avoided. Now, given the industry experience and available design tools, there is no excuse for a poorly designed sound system or room design, and therefore no need to focus on addition of sound absorbing panels simply to improve speech intelligibility.

The programmatic requirements as they relate to acoustics are in general contradictory. Reverberant environments are in general preferable (depending on the church program), although this generally leads to a reduction in speech intelligibility. With a carefully integrated room acoustics design and sound system design, it is possible to generate a design solution that resolves this contradiction in requirements.

Craig Jansenn is currently the principal consultant at Acoustic Dimensions in Dallas, TX With more than fourteen years of experience in electro-acoustic systems and acoustics design, he specializes in the integration of high-power sound system in difficult acoustical spaces.

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