The Science of Sound in the Stadium
Just mention Chicago's Wrigley Field or Boston's Fenway Park and baseball buffs wax nostalgic. These are two of the last "old-time" ballparks -- they seem smaller, the stands closer to the players. You can practically reach out and touch the pitcher's mound, and the announcer might as well be sitting in the next seat.
Fans will line up all night in the rain to score tickets to games played on these venerable diamonds. Over the past five years, attendance at Wrigley has run 60% above that at the Windy City's other ball field, Comiskey Park. "Intimacy and charm has an appeal to fans," observes Jim Brown of Audio Systems Group in Chicago (see "The Boys of Summer Play It by Ear").
Brown should know. He's an acoustics designer who specializes in stadiums and other large spaces. A sound system he helped design for Wrigley in 1986 (and updated in 1989) plays a big role in creating an ambiance that approaches being at a farm club game in Utica, N.Y. Abandoning the standard practice of mounting huge loudspeakers on the scoreboard, Brown distributed four rows of much smaller speakers over the entire grandstand. It's a sound system that's dedicated to announcements -- not to exciting the crowd with loud music.
The sophisticated sound system helps create an auditory illusion that shapes the crowd's perception of the space. In reality, Wrigley has only 10% fewer seats than most ballparks constructed in the past decade. "Chicago Cubs management has long subscribed to providing a family-oriented experience," notes Brown.
But not every stadium wants to be so staid. Many of the newer ones are decked out with special lighting effects and sport huge video displays of the action on the field. And they're used for other sports and events besides baseball. Sound systems must be able to handle rock concerts, single singers, religious events, circuses, and tractor pulls.
Whether its Wrigley or the Superdome, the game for acoustics engineers is still the same: delivering clear, uniform sound -- which can be bent, absorbed, and reflected -- to about 60,000 seats as well as to concessions and concourses. And do it without disturbing the neighbors.
In addition, crowd sounds are piped into glassed-in skyboxes and suites and fed to the broadcast media. The press needs to hear the official scorer and the wireless microphones worn by referees and umpires. These systems must be able to switch between the game announcer to broadcast, and provide play-by-play replay. "Each ballpark brings some of the same challenges -- and often its share of new ones," Brown told a recent meeting of the Acoustical Society of America in Chicago.
One such challenge is compensating for the effects of an atmosphere that's constantly in motion. High humidity and temperature absorb sound. And the wind changes its direction. Sound aimed at a section of seats in the grandstand can be deflected and come down to earth more than a mile away. "The fans don't hear the park announcer clearly but the neighbors in the lakefront high-rise do," says Brown. The effect on the fans? "The sound can fade in and out between words or from one musical measure to another."
Another bugaboo is that people absorb sound and hard surfaces reflect it. In a partially filled stadium the empty seats create a pattern of random sound that creates background noise. Sound bouncing off rear walls of the stadium, especially those with a concave structure that can focus the sound like a lens, can reach the audience on the far side of the field, creating an echo that can make speech hard to understand.
To avoid such problems, Brown and other sound designers have switched to systems of distributed speakers that can be aimed and adjusted individually, such as those at Wrigley. But since each fan hears sound from multiple speakers, they must be placed so that all the sound arrives within thousanths of a second, which means a distance of about 35 feet.
If sound spills into a distant area -- say from the upper deck into the lower stands -- it will create a delay, an artificial echo. "One of the most important aspects of system design for large spaces is where the sound goes after it passes the audience it is intended to cover," Brown points out.
Then there's the issue of volume. Some announcers vary the pitch of their voices as the game gets more interesting while others remain calm and collected. Sound technicians control the level of excitement -- without creating excessive variation.
Moreover, the announcer must always be heard over a noisy crowd. This is controlled by feedback from remote microphones that pick up the crowd sounds. "If the system is set to sound right when the crowd is quiet, it won't be heard with two out and the bases loaded." says Brown. "And, if it's set loud enough for an exciting part of the action, it will be blasting the fans out of their seats when the crowd is quiet."
"Wise designers realize that the sport is star of the game, not the sound system," he continues. Indeed, about the only thing producers of designer sound can't control is the roar of the crowd.
By Alan Hall in New York
Edited by Beth Belton