Baseball’s “Crack” Is More Than Just Bat Hitting Ball

Opening Day is nearly upon us and will be heralded, after the National Anthem and the refrain “Play ball!,” by baseball’s singular sonic signature: the crack of the bat on the ball.

“It gets so that you can tell from the sound of the crack if it’s going to be a home run or not,” says Joe Carpenter, lead mixer for Fox Sports’ MLB games. “The sound of the bat is at the heart of the game’s sound.”

All sports have unique audio aspects, and some are particularly tunable. An interesting piece in the Wall Street Journal explored how the various sounds of golf clubs are purposely engineered. For instance, the muted sound of thick-faced putters can be further softened using cushioned inserts in the club head. A putter will put out a crisp, ring-like sound when a groove milled into its sole. The nickel in the tungsten-nickel–alloy box on the back of Titleist AP2 irons was chosen for its vibration-damping characteristics.

Although baseball is a somewhat less elegant mechanical and acoustical proposition, it places no less emphasis on the sound of its sticks.

“The [acoustical aspects] of a baseball bat are important,” says Chuck Schupp, manager of professional baseball promotion at Louisville Slugger, the largest and oldest of the 28 bat-making vendors approved by MLB. “With wooden bats, you don’t have the same ability to really engineer the sound as you do with aluminum bats.”

Wood vs. Metal
The timbre of metal bats, used in most college leagues, can be varied by the blends of composites and aluminum hybrids used, the weave of the composite materials, the thickness of the bat’s barrel wall, handle stiffness, and other factors.

Wooden bats, though, the only kind allowed in major-league play, are more nuanced. Maple and ash are the woods of choice, with maple a 60-40 favorite of Slugger users; those woods tend to produce a slightly thicker sound than the less-used beech.

Between the two favorite woods, Matt Bynum, new bat product/process development system manager at Slugger, says that maple has a slightly higher-pitched crack sound than ash. Beech and birch wood make very good bats, but their density, which is lower than those of maple and ash, seems to strike a hollow chord for baseball players. “Watch players tap the bats as they’re choosing them,” he says. “They tap on the ground, the walls, their lockers; they all have their own routines. They can tell if it’s the bat they want just by the sound it makes. And they almost always reject the beech and birch bats just on the sound.”

For Elliot Scheiner, whose Bethel, CT-based manufacturer, Star Bound Bats, uses only ash wood, the best-sounding bats are the raw ones, before stain and layers of polyurethane are added. “It makes them sturdier,” he says, “but takes away from them sonically, I think.” And he should know: in another life, he engineered and mixed hit records for Steely Dan, the Eagles, and Foo Fighters.

Bynum notes that the resonance of various bats starts at the cellular level. Ash wood is ring-porous: a cross-section reveals target-like rings of concentric circles, the spring growth rings of the tree itself. Maple bats’ cross-section under a microscope shows the far more random etchings of winter growth.

These characteristics affect not only the sound but also the ballistics of the bat. “When you see a bat break on a pitch on TV, if it goes flying in a dozen pieces, you know it’s a maple bat,” he says, a function of maple’s random cell structure. “An ash bat will break into a couple of pieces kind of along a seam.”

The Batter Effect
Then there’s the person wielding the bat. The sound of bat hitting ball is influenced by various things, such as the mass of the hitter. Bynum says the same bat connecting with a fast ball swung by the Texas Rangers’ Josh Hamilton, who launched 28 out-of-the-parkers in a single round at the 2008 Home Run Derby, will sound different from the same shot powered by a batter weighing 50 or 60 pounds less.

In addition, there is a mechanical coupling between batter and bat, and elements like the size and pressure of the grip, as well as whether the batter lets go or hangs on to a bat immediately after contact,  affects the resonance of the bat and thus the sound of the crack.

Three-Dimensional Audio
Broadcast mixer Joe Carpenter recently did some experimentation on capturing that crack during several spring-training game broadcasts in Glendale, AZ. In addition to the two parabolic microphones he usually uses (loaded with DPA lavaliere mics when the home plate area is relatively constricted or with Sennheiser MKH 8020 omni condensers when he can spread them out more), in the preseason games this year, he has been able to place a mic on the umpire. The results, he says, were three-dimensional.

“You really hear the essence of the ball on the bat like never before,” he says. “It’s very prominent, to the point of being almost unnatural. You can hear precisely where on the bat each ball hits.”

MLB has not yet said if it will allow umpires to wear microphones during regular-season play. But Carpenter says that some stadium designs do allow him to use a third parabolic microphone located behind and slightly off-center of the umpire and catcher and that combination produces some pretty spectacular results, too.

“At the NLCS in Philadelphia last year,” he says, “you could actually hear the players rubbing the pine tar on their hands, and this was on top of the noise of a full NLCS crowd. I started blending that third mic in more, and it was the best home-plate audio I ever heard. You could hear the sound of the Velcro tearing on the batting gloves. It was picking up so much that MLB said to dial it back because it was picking up too much of the what the umpire was saying.”

As home-plate audio becomes more and more intense, baseball’s signature sound will continue to be a major focus. But, for all of the physics, chemistry, and mechanics of bat contacting ball, the bottom line is that every crack of the bat is still a work in progress.

“Every day, the sound will vary based on location, temperature, humidity, wind. It’s all situational,” says Carpenter. “I’ll start with very basic EQ, then just tweak it as the game goes on, trying to make it sound natural. If it’s too crisp sounding, that’s misleading to the listener. You want to get it to where the player hears it. You want to know where the ball’s going to land just because of how it sounds.”