Walking A Fine Line Array

In Uncategorizedby tfwm

The buzzword of the day in sound reinforcement is line-array systems. Manufacturers have been feverishly working to bring these products to market since the introduction of this acoustic phenomenon to the touring market just a few years ago. Though the physics of line-array systems is nothing new (these principles were defined in the 1930’s) what is new is the application.

The majority of touring acts currently use line-array systems consisting of 4 to 10 or 12 enclosures (loudspeakers) stacked vertically and suspended from the ceiling on either side of the stage. The physics of sound tells us that when two or more transducers are placed so that they are radiating sound at certain frequency ranges (based on the distance between the transducers), the radiation pattern of the sound will become narrower in the plane in which they are arrayed.

Today’s version of the touring line-array system uses this principle to project sound over long distances, while keeping sound off the stage below. Unlike a traditional loudspeaker system, which drops 6 dB in level as the distance from the loudspeaker to the listener is doubled, line arrays can reduce this drop to 3 dB, depending on the size of the array and frequency. This feature works very well in outdoor settings, or for a touring company that is presenting concerts in an arena, and that has time and budget constraints which may not allow for the use of delay-fill systems.

At the same time that these systems have become popular, many churches have identified the need to install new sound systems to accommodate their changing worship styles. Churches that are incorporating contemporary music into their services, or using this style exclusively, are prime candidates for new systems.

Contemporary worship music may feature the use of instrument tracks, rather than live accompaniment, or instrumental ensembles that primarily include synthesizers, bass, guitars and drums.

To maximize the success of this style for their congregations, churches need to have not only sophisticated sound systems, but systems that are very different from those used in more traditional churches that rely solely or primarily on choirs, organs and string or wind ensembles in their worship services.

When church officials go shopping for a new system, they may base their choices on picking up a copy of Pro Sound News to see what the latest trends are. They may think that the best choice would be a line-array system like the ones now used so widely by groups in the touring music industry, which typically stage concerts outdoors or in arenas or other large venues.

However, equating needs with those of rock-and-roll bands or going with the latest rage, may not provide a sound basis (no pun intended) for selecting a loudspeaker.

Church decision makers should strive to better understand the factors that contribute to how a line-array system works. Perhaps a line-array system is not appropriate for their situation. Decision makers should be much better equipped to make wise decisions about the significant financial investment that a sound system represents. I am not suggesting that line array systems have no place in churches. On the contrary; they can be very effective tools if they are correctly applied. My main hope is for churches to do their homework when selecting a sound system- because for some applications it may not be entirely appropriate.

One promoted advantage of the line-array system, as it is currently being marketed by manufacturers, is that it theoretically allows systems to cover long distances without delay speakers. Manufacturers claim that the pattern of the array can be adjusted so that the sound does not hit the rear wall of a facility, but this ability does not apply across a wide range of frequencies.

The problem in most churches is that they have rear walls that bounce the sound back. The result is a big echo at the front of the room, which is disorienting to the audience and to the musicians (see Fig 1- print version).

I once attended a demonstration set up by one line-array manufacturer in a theater. The system worked beautifully in the back and the middle of the auditorium, but in the first few rows, listeners could hear an echo off the back wall, and on stage the echo was much worse. Of course, it needs to be noted in these cases that it all comes down to proper system aiming- and perhaps in this case the presenters did not have sufficient time to engineer the system for the room. It did however illustrate potential problems with the use of a line array in that particular installation. For churches, all potential solutions should be evaluated in terms of cost vs. performance in a variety of areas .

The traditional approach to covering seating areas in the rear of a typical space (generally beyond 50 to 60 feet from the front row) is to use additional delay-fill loudspeakers. The speakers may be suspended from the ceiling about 35 to 40 feet from the stage and are aimed down into the seating area.

An advantage of a delay-fill system is that loudspeakers do not have to be turned up as loud to provide even coverage to the rear of the room because listeners are much closer to the speakers. The delay fills should be positioned so that the echo is greatly minimized and the sound is projected downward, striking the rear wall at an angle that causes the reflection to bounce into the seating at the rear of the room, where it is absorbed (see Fig 2- print version).

Of course, with additional radiating sources, there is always the risk of potential pattern overlaps and cancellations, so again, be wary of speaker placement.

Sound system designers must consider a number of issues that are unique to each facility. A key consideration is the room geometry, which includes the distance from the stage or platform to the rear wall, the height of the ceiling, the location of the seating, and the locations in which loudspeakers can be placed. Obviously, loudspeakers must be placed so that sound is not directed to areas where there are no seats, such as walls and ceilings, and systems must be installed so that the main loudspeakers do not generate a great deal of sound on the platform or in the choir loft.

Acoustics are another important issue. Reverberation time (the amount of time it takes for sound to die away) must be considered. Generally, the longer the reverberation time gets, the greater the need for the designer to either use larger, more-directional loudspeakers or to move the loudspeakers closer to the listeners.

Another factor is the surface materials – stone, wood, or other materials used for walls and ceilings; the number and types of windows and/or curtains; and the flooring, whether wood, carpeting or other type of flooring. Knowing what those surface materials are and where the new loudspeakers will be placed will help determine whether there will be echoes or flutters.

Performance requirements must also be determined. In more traditional churches, the best choice may be a central cluster system of loudspeakers, in which the main loudspeaker array is placed over the middle of the platform or pulpit area.

In contemporary churches, by contrast, a three-cluster configuration of loudspeakers is very commonly used. The center cluster is used for vocalists and for those who are speaking, such as ministers and laypeople. The loudspeakers on the left and right are typically used to reinforce instruments in stereo because that sound is what worshipers are accustomed to experiencing in their home audio systems and even in their cars.

Depending on room geometry, line arrays can be very effective for covering the front two thirds or so of a room. In fact, I am currently working on the design of a new system for a prominent theater where I am suggesting line arrays for the main left, center, and right arrays. The room geometry fits the horizontal pattern of these arrays very nicely and eliminates the need to array loudspeakers horizontally. This provides very coherent imaging and very smooth coverage across the room. However, I am not attempting to cover the top of the balcony from these locations over the stage. I’m still using delay fill loudspeakers to cover under the balcony and the upper balcony seating.

Churches must also make their choices based on a system’s sound quality, reliability and cost. Cost is almost always an issue. Systems for contemporary churches are much more expensive than systems for churches with more traditional music styles. If a church’s budget is limited, it may have to narrow its choice to a center-cluster loudspeaker system, and it may not be able to install such enhancements as left-right stereo arrays and subwoofers.

It is always useful to hear loudspeakers in action. The best way is to listen to different brands in similar facilities. Church members and staff who are involved in the decision-making process would do well to attend worship services in other churches and listen to the quality of various systems. It is important to note that the biggest variable in any system’s performance is the skill and experience of the person driving the console. World class systems can sound terrible if operated poorly, and marginal systems can sound good with a decent operator.

With a complex set of technical requirements such as these and the unique features and desires of a given church, selecting a system can be daunting. Learning the craft of sound system design takes years of training and experience. It is a task that involves paying considerable attention to the acoustics of the room.

Churches may be better served by securing the services of a qualified sound contractor or consultant. These professionals have spent much of their lives learning the physics of sound, electronics, and acoustics, all of which contribute to the design of a good sound system.

Look for companies and individuals with good references for the type of facility you have. Check those references to see whether their clients are satisfied with their work. Then follow your chosen designer’s recommendations. Doing your research will result in a much better system for your church. Perhaps it may incorporate line-array technology after all. Anything is better than buying whatever so-and-so is touring with this year because you heard it was cool. When you’re preparing to pay good money for a sound system, you’re really walking a fine line.