Stadium Sound:
The Overview On Different Approaches

by Ron Baker, WJHW
with Keith Clark, Editor, PSW Install Sound

(Editor's note: Ron Baker and I collaborated on the following article about four years ago, just as WJHW was finishing the sound design for Turner Field in Atlanta, which had first been developed as the primary stadium for the 1996 Olympic Games and then converted for use by the Atlanta Braves of Major League Baseball. Thanks to Ron’s considerable acumen, the article contains a wealth of basics regarding sound reinforcement for stadiums. - Keith Clark)

The classic approach in large sporting venues has been to place a loudspeaker cluster more or less in center field (in a baseball venue) or on top of an end zone scoreboard structure (in a football venue). The cluster then fires toward the vast majority of seating areas. Logically, the distance that the sound travels (several hundred feet) means that each member of the cluster is able to cover a large segment of the seating area.

The advantage of this approach is that it is highly economical, simply because it employs the fewest number of loudspeaker components. But the down side is significant losses of sound quality due to the distance sound must travel before reaching the majority of listeners. Factors like humidity can significantly attenuate the higher frequencies, while thermal conditions and wind can cause sound to fade in and out, or to "swirl".

In addition, the sheer distance the sound must travel can create a delay of 0.5 seconds or more on the field. This creates some synchronization problems for performers, such as those providing the national anthem.

Yet another factor that can come into play is the environmental impact from a noise standpoint. Obviously, a large-scale cluster has to be very loud to reach every seat, so there is likely potential for a fair amount of spill outside the confines of the stadium, an aggravating situation for the surrounding community.

On the opposite end of the spectrum there is the distributed system. Numerous benefits can be derived from this approach, which places the loudspeakers much closer to each listener. Frequency response is much broader, while delay times are usually dramatically reduced. With a distributed system, you're typically looking at delay times of more than 0.2 seconds, significantly improving the situation for performers in addition to better matching the images on the stadium's video screen.

A distributed system also provides a good level of control over sound. Portions of the system can be turned off when no needed, or different program sources can easily be directed to difference areas of the venue. The bottom line is improved control over the entire production.

The down side is cost. The number of loudspeakers dramatically increases, as does the associated amplification and wiring. Cost and maintenance of these items also goes up correspondingly.

Yet we’ve found that cost is becoming less of an issue with owners and managers of new facilities, who have learned that improved sound quality is what the public is expecting. As a result, they are now more likely to allocate the necessary funds to do a comparable job.

Meeting Different Needs

Olympic Stadium before it was converted to Turner Field. Looking from the temporary seating to the grandstand that was outfitted with a distributed system and retained.

In the grandstand, looking out to the temporary region, and beyond that, Fulton County Stadium, former home of the Atlanta Braves since demolished.

From a design standpoint, our initial challenge in the Olympic Stadium/Turner Field project was knowing that the building was going to initially be configured much larger than the final version. Further, it would have to undergo a rapid transformation in less than eight months so that it could be ready for baseball season’s opening day in early April 1997.

Our general concept was that portions of the facility that would remain untouched during the changeover would receive a final sound system, while the temporary areas would be largely covered by rented system components. This would allow quick removal and also save some cost.

So the system for Turner Field can accurately be described as something of a hybrid. However, we determined that even the rental portion of the system would be done in a distributed fashion, with conventional, non-custom devices as opposed to the more specialized loudspeaker devices used for the permanent part of the building.

The system also needed to meet two different uses, which at times present different needs. First there were the Olympic Games, requiring typical public address sound reinforcement, but with a requirement that it be able to augment the system utilized for the opening and closing ceremonies. As a result, the idea was to allow the field system for the ceremonies to tie in to provide some added artistic freedom to exploit the overall sound reinforcement capabilities.

Distributed System Criteria

Once these types of issues were discussed and a course agreed upon by all parties, we then went about the business of actually designing the stadium system. We decided to take a distributed approach.

When evaluating the building plan as to whether to select this course, the first thing we look at is the geometry of the facility. That is, the venue must have the layout and physical attributes to accept a distributed solution. Basically, there needs to be sufficient surfaces and locations where loudspeakers can be positioned to adequately cover the spectator seating area.

In some venues this is easy, while in others it is not. We look at mounting positions and then evaluate the ability to reach the farthest listeners, the nearest listeners and so forth. The goal is to avoid any condition where a listener close to a loudspeaker is being overwhelmed with sound while it’s trying to project 100 feet away or more.

There is no magic formula for doing this; largely, it comes down to the trial and error process gained over years of designing distributed systems. However, a general rule of thumb that we follow is that for any given loudspeaker position, the farthest listener that the loudspeaker should have to reach should be no more than four times the distance to the nearest listener that the same loudspeaker is to cover. So, it’s a 4:1 ratio, and sometimes only a 3:1 ratio. Once you get outside of this ratio, it’s likely that the loudspeaker will be too loud for the nearest seats.

After determining where loudspeakers should be positioned, we work closely with architect to make certain that the proposed sound design won’t conflict with other building elements. Often things like signage and satellite scoreboards don’t show up on preliminary building plans.

The idea is to avoid an aesthetic backlash, where a loudspeaker location or locations won’t be tolerated. In working with architects, we’ve found this to be a give and take process. Some positions they’ll let you have, while others are absolutely out of the question.

The bottom line is that the loudspeakers tend to drive the development of the entire system. Until the loudspeaker layout is roughed out, you don't know how much cabling will be needed, where it will run, how many power amplifiers will be required, where they'll be located and so forth.

In determining the types of loudspeaker(s), it's best to start with basic knowledge. Of course, loudspeakers are available in a variety of common coverage angles, such as 60 x 40, 90 x 40, and ever more variations. So right from the start you can determine the primary tools with which you’re designing.

Looking Good Is Important

Another important consideration is aesthetics. Early in the project, we supplied the architect with our requirements for spacing between the loudspeaker cabinets, and he in turn came back with a request that they align with columns so as not to detract from the intended look. Achieving this took a slight adjustment, but saved a lot of trouble in the long run and did not significantly detract from the intended performance of the system.

Selecting the location that offers the best coverage is another factor to consider. Sometimes you have the option of putting a loudspeaker directly over the heads of the audience, or perhaps setting the loudspeakers in front of them and firing back, or perhaps placing them completely behind the audience. These options have to be weighed. One position may work best from a psycho acoustic standpoint, while another may better fit the coverage patterns of the devices that are available. It’s also another factor that we try to optimize while using the fewest number of cabinets.

Yet another factor for consideration is to make sure that each loudspeaker cabinet is adjustable in the vertical domain. If there are slight errors in the computer model of the layout, or if the selected devices don’t quite match up to what was expected, then the loudspeakers can be pivoted for improved coverage.

One the loudspeaker design is roughed out with a protractor, we then move into building a computer model of the facility and sound design. For this project, we used the EASE program to predict coverage angles and so forth. During this process, some fairly specific and definitive analysis takes place, where we look at aspects like precise side spacing between the loudspeakers and what sort of horn radiation patterns are required.

As with many projects, the Turner Field design called for multiple vendors, so in the specification we developed relatively generic solutions that were not limited to a particular band or model. In writing the final specifications, two - and in most cases - three different vendors were offered for the transducer components.