Ah, the crack of the baseball bat¿it is for the devoted fan as evocative of the game as the seventh-inning stretch. And for the outfielder, it can provide important clues to where the ball will go. Indeed, as Yale University physicist Robert Adair noted on Friday in a presentation made at a meeting of the Acoustical Society of America in Chicago, "sometimes the difference between the sharp acoustic crack-of-the-bat and a sullen acoustic clunk-of-the-bat can be worth a run or two."
To visually determine how far the ball will fly, the outfielder must wait about two seconds after the ball is hit before the angle at which the ball rises¿an indicator of the distance it will travel¿becomes apparent, Adair says. But by then, it can be too late for him to start running to catch it. Thus, rather than look for the ball, players listen. When the batter hits the ball, the outfielder hears either a "crack" or a "clunk," as Adair puts it. The crack, he explains, comes from about 100 cubic centimeters of air being forced out from between bat and ball at less than a 2,000th of a second, resulting in a sound with a frequency of about 500 Hertz. The clunk is a combination of the crack and the duller 170-Hertz-sound created by a vibration in the bat that occurs when bat and ball make contact far away from the bat's so-called sweet spot.
Knowing whether the batter hit the ball well (crack) or not (clunk) lets the outfielder know whether he should run farther out or farther in to catch the ball. That telltale sound, Adair has determined, reaches the outfielder after only 0.3 second¿1.7 seconds faster than the visual cue. In that time span, he notes, the outfielder can run more than 50 feet¿easily the difference between catching the ball and watching it hit the grass.