The evolution of Turner Field: The five-year conversion of Olympic Stadium's PA system to Turner Field's complex sound system presented a real bookkeeping challenge.
Jul 1, 1997 12:00 PM, Ron Baker
In early 1992, Wrightson, Johnson, Haddon and Williams (WJHW) was contracted to develop the sound-reinforcement system for the yet to be built Olympic Stadium in Atlanta for the 1996 Summer Olympic Games. In 1997, with the Atlanta venue now converted to Turner Field, the home field for the Atlanta Braves of Major League Baseball, our involvement with a variety of final sound system design and installation issues continues.
Olympic Stadium, as originally constructed, hosted a number of athletic events, chiefly track and field, as well as the opening and closing ceremonies. It included seating for more than 100,000 configured in a huge oval. Approximately half of the seating was designed to be retained during conversion of the facility to a much smaller, more intimate space for baseball.
The project highlights the amount of time that certain projects can extend. In the early stages, WJHW worked closely in a joint-venture fashion with a consortium of leading architectural firms known as the Atlanta Stadium Design Team (ASDT) under contract to the Atlanta Committee for the Olympic Games (ACOG).
>From the outset, ACOG and the Braves put together a rather comprehensive program that established the essential features and requirements for the stadium. As you might imagine, this list is never as definitive as you'd like it to be, but it did provide us with concepts of the project's overall scope and an idea of what the intended functions of the sound-reinforcement system would be.
Once WJHW came on board, we held several meetings with various participants and individuals of ACOG and ASDT, reviewing with them the advantages and disadvantages of different types of system designs. It was agreed that the system would use a distributed loudspeaker approach, which is more common these days in ballparks and other expansive spaces.
Distributed vs. central 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 the 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 a significant loss of sound quality because of the distance the sound must travel before reaching the majority of the listeners. Some factors, such as humidity, can significantly attenuate the higher frequencies; 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 of 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 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 no 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 not needed, or different program sources can easily be directed to different areas. 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 rise 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 create a system comparable to other new venues.
Dramatic transformation >From a design standpoint, our initial challenge in the Olympic Stadium-Turner Field project was knowing that the building was going to 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 the 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. Renting would allow quick removal and also save some cost. The system for Olympic Stadium can be accurately 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 presented different needs. First there was the Olympics, requiring typical public address sound reinforcement, but also with a requirement that it be able to augment the system used for the opening and closing ceremonies. As a result, the idea was to allow the field system for the ceremonies, which would tie in to provide some added artistic freedom to exploit the overall sound-reinforcement capabilities. Patrick Baltzell, who provided the mix for the ceremonies, ended up using the stadium system to do a surround sound type of effect, enhancing the on-field system.
Back to distributed Once these types of issues were discussed and a course agreed upon by the committee and design team, we then went about the business of actually designing the stadium system. As mentioned, we had decided to take a distributed approach.
When evaluating a building plan as to whether to select this course, the first thing we look at is the geometry of the facility. The venue must have the layout and physical attributes to accept a distributed solution. Basically, there must be sufficient surfaces and locations where loudspeakers can be positioned to adequately cover the spectator seating area.
In some venues this is easy; 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 that is being projected 100 feet (30.5 m) away or more.
There is no magic formula for doing this; 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 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 is a 4:1 ratio, and sometimes only a 3:1 ratio. Once you get outside of this ratio, the loudspeaker will probably be too loud for the nearest seats.
After determining where loudspeakers should be positioned, we work closely with the architect to ensure that the proposed sound design won't conflict with other building elements. Often problems such as signage and satellite scoreboards don't show up on preliminary building plans.
The idea is to avoid an aesthetic backlash, where a loudspeaker location 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; 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 loudspeakers, it's best to start with basic knowledge. Loudspeakers are available in a variety of common coverage angles, such as 60 degrees x 40 degrees, 90 degrees x 40 degrees and slight variations of these. So right from the start you can determine the primary tools with which you're designing.
Another important consideration is aesthetics. Early in the project, we supplied the architect with our requirements for spacing between the loudspeaker cabinets. The architect came back with a request that the loudspeakers 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 maybe placing them completely behind the audience. These options must be weighed. One position may work best from a psychoacoustic standpoint; another may better fit the coverage patterns of the available devices. It's also another factor that we try to optimize while using the fewest number of cabinets.
We try 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 to improve coverage.
Once 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, somefairly specific and definitive analysis takes place, where we look at aspects such as precise side spacing between the loudspeakers and the sort of horn radiation patterns that are required.
As with many projects, the Olympic Stadium and Turner Field design called for multiple vendors, so in the specification we developed relatively generic solutions that were not limited to a particular brand or model. In writing the final specifications, we offered two and in most cases three different vendors for the transducer components.
Projecting ahead As mentioned, roughly half of the original structure would be left untouched following the Olympic Games, so within that constraint, half of the system was dealt with in a conventional manner. In other words, this portion of the system was treated just like any other stadium project we've worked on, where the system is optimally designed and then submitted for review.
The other half of the venue, however, was an entirely different story. We projected to when the facility would be in baseball mode (based upon the architectural drawings) and tried to select some loudspeakers that would carry over. These were temporarily installed, pulled during the renovation, then re-installed near the completion of the changes. It was complicated trying to design for the two different modes while trying to use some of the same components, and then further keeping track of the chronology, construction phases and different modes.
The system basically fit three different categories: permanent sections that would not be affected by the renovation; sections that would be installed, then removed and re-used; and sections that were temporary, for the Olympic Games only. Keeping track of all of the quantities of equipment involved presented a real bookkeeping challenge.
Also, the client insisted that the documents for the two different configurations be maintained separately. As a result, we had two full packages of documentation, portions of which were identical, and other parts that were unique. Just dealing with the quantities of drawings and files for this was a big undertaking.
As with most Olympic venues, this project mandated from the beginning that all design elements be done on AutoCAD. Any time we sent blueprints back for bid documents, they had to be accompanied by AutoCAD disks as well.
Although AutoCAD is common now for these types of projects, this wasn't the case when we embarked on the project five years ago. The computer power wasn't readily available, and a serious investment was required just to acquire enough to handle the 100 MB of CAD files associated with the project (to this point). Managing the thousands of CAD documents and drawings was a major undertaking in itself.
Two decks, three levels The section of the stadium unaltered during the conversion of the venue is a two-deck "conventional" grandstand centered at home plate and extending down to the foul poles in the outfield corners. The two decks contain three levels of seating, including a field or "main" level, the club level in conjunction with private suites, and an upper deck level.
A canopy covers the upper deck, important in our decision to use a distributed system because we often rely upon this type of structure to support the loudspeakers intended to cover the upper deck. Without the canopy, we would need to formulate an alternative structure to support the loudspeakers.
In Olympic Stadium mode, long runs of single-deck seating extended past the portion of the two-deck grandstand that was retained for Turner Field. This area was backed by lighting towers that provided the means to mount loudspeakers, but the real question was whether to rent temporary devices or to use ones that would transfer to the new configuration. We made this decision largely based upon the total number of loudspeakers that the stadium would require in final baseball mode. When these ran out, we went to rental stock.
The far end of the stadium, which would be completely eliminated during the transformation, presented a tougher question.Configured in one continuous curving slope extending approximately 130 feet (39.6 m) from top to bottom, it didn't fit into the distributed system plans. In addition, there was not a structure from which to hang loudspeakers, either in front of or behind the seats.
We decided that the only viable solution was to erect poles along the back of the seating area from which to fly temporary loudspeakers. The preferred choice would have been in front of the seats, but this would have obstructed the view.
We knew there would be level variances from front to back in this section, with the loudspeakers flown 25 feet (7.6 m) above and firing down at distances of up to 130 feet (39.6 m), but this problem couldn't be avoided. Although levels for the installed system are maintained at a broadband consistency of plus/minus l dB, they were measured at plus/minus 4 dB from the farthest seat to the nearest in the temporary section.
The custom route During the design process, Eastern Acoustic Works (EAW) was named an official supplier to the Olympics by ACOG. Following this, we began discussions with their engineering department (Kenton Forsythe and Jeff Rocha in particular) about product design issues and requirements of the various loudspeakers that would be needed.
As an original requirement, we needed loudspeaker prototypes for evaluation to insure that aspects such as coverage angles, performance criteria and overall sizes and shapes of the loudspeakers were consistent with what we had envisioned. This was particularly important because some sightlines were very tight.
As a general philosophy, it's best to try to use conventional devices for projects of this nature. However, all of the loudspeakers had to be configured horizontally primarily because of the sightline issue; that is, the components are mounted side by side as opposed to one above the other. In addition, a custom approach was further dictated by the need for some of the loudspeakers to provide an uncommon coverage pattern.
As a result, we took the route of working with EAW on development of several custom loudspeaker models. The first of these was the AOS110, which includes a 12 inch (305 mm), low-frequency woofer and a 90 degrees x 50 degrees high-frequency horn with driver and a passive crossover to optimize power response.
We evaluated this loudspeaker at our facility and found its performance to be quite acceptable. This was followed by the AOS130, a high-output loudspeaker with a 15 inch (381 mm) woofer and a 60 degrees x40 degrees horn with driver and a passive crossover. Again, we tested it at our facility and found it to exceed expectations.
The AOS100, loaded with dual 12 inch (305 mm) woofers and dual high-frequency horns with drivers, proved too large to be tested at our facility. Instead, we opted to review basic performance criteria and drawings rather than deal with the logistical problems created by their size.
The final loudspeaker, the AOS90, was different enough that we took advantage of the newly completed stadium in order to do an on-site evaluation. The two separate high-frequency horns (one short-throw, the other long-throw) were arranged so that they could be adjusted in the vertical plane, along with provisions for electronic delay so that the optimum transition point between the two could be achieved.
This was certainly a unique situation. Because the building was far enough along in its completion to be able to do a live mockup, it allowed us to obtain a much more realistic view of final performance as opposed to either of the more abstract methods - reviewing data or live testing in our facility. Ultimately, it resulted in a better loudspeaker device and also gave us confidence that the product would fully meet all of our expectations.
Another advantage gained from this early access to the building involved optimized final aiming of the loudspeakers. We found that several of the loudspeakers couldn't be mounted where we had originally planned, despite all of the careful work with the architects. As a result, we were able to select alternative mounting positions where live mockups allowed us to take actual field measurements. These in turn provided valuable input for revised locations and angles that worked best in attaining smooth, complete coverage.
Defined coverage areas The upper deck of the stadium is covered by three loudspeakers, each with its own defined coverage area, suspended in a vertical line from the canopy. The front cabinet, the AOS130, fires forward and covers roughly the entire front half of the upper deck seating area. The next one-fourth is covered by an AOS110 firing almost straight down. The remaining one-fourth is covered by another AOS110, firing backward.
In a significant portion of the grandstand (from roughly first base to third base in baseball mode), a fourth loudspeaker, the AOS100, was added above the AOS130. It provides coverage to the front half of the seating sections along the playing field. The AOS100s were necessary in this region because signage and scoreboards wouldn't permit locating loudspeakers any closer, such as on the face of the second deck.
The club level is covered by two AOS110s mounted at about the midpoint of the underside of the balcony. One is aimed forward and covers the front half of the seating area; the other fires back and covers the rear half. On the field level, a single AOS110 mounted on the club level underside fires back to cover the last five rows of seating. Another AOS110 is aimed almost straight down and covers the middle five rows. Grandstand areas outside of the first to third base stretch receive coverage from a single AOS90 mounted to the front face of the club level. The loudspeaker's downward horn covers nearby seats; the other horn is pointed outward to the edge of the field.
Most of the new seating sections, located in the outfield and constructed during the conversion to Turner Field, offer similar loudspeaker placement and mounting conditions. AOS110s are mounted on overhang structures to cover all seating. In the bleacher seating area, there are no overhangs, so coverage is supplied by compact two-way loudspeakers mounted on the scoreboard structure.
Virtually all of the loudspeakers were painted dark green to blend in with the steel structures to which they're mounted. The AS090s mounted on the face of the club level were painted white to match the color of the structural concrete.
Signal processing is fairly conventional, particularly for a project of this type. We employed a lot of parametric equalization to provide added tailoring for specific areas. For power, we required that the type of amplifiers selected have provisions for computer control and monitoring from the control position because of their far-flung distribution throughout the facility.
Almost complete During the conversion to Turner Field, the sound system control position had to be moved about 50 feet (15 m) to a new location on the club level. As an unplanned change, this presented a significant challenge to the contractor, who had to access new cable and conduit runs in a completed facility. However, this challenge and several others were overcome to ensure that the system was up and running by the Braves' opening game in early April. Although some fine tuning of the system continues, the project should reach its conclusion by fall of 1997.
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