We usually translate the sound into print as a crack!, but if you were to give it a comic book onomatopoeia, you might choose a meatier bop!, or a raw ponk. However you render it, it’s the unmistakable sound of a tightly-stitched cowhide sphere meeting a wooden barrel with the force of a car crash, a sound that echoes up to the cheap seats whenever a perfectly-timed swing meets its target. It’s a violent sound, combining the thud of the leather ball flattening into the bat’s surface with the satisfying snap of every fiber in the wooden bat absorbing the ball’s kinetic energy. When you hear that sound ring out - that cacophonous sound of organic materials colliding in mid-air, like a rhino charging into a wooden fence, or a dry branch being snapped over a snare drum - everything’s right in the world for that brief moment.

It gives me goddamn chills just thinking about that sound.

And just like other telltale signs of spring - robins singing, trees blossoming, snowbanks receding into piles of slushy cigarettes butts - hearing that crack for the first time every March means that we’re finally clawing our way out of the dregs of winter.

Well, we made it. Spring Training’s here.

The crack is back.

That Sound

It is, first and foremost, a gratifying sound - something that taps into the most primal wiring in our brain to hear things go “boom”. And if baseball bats didn’t make that sound, I don’t think baseball would be the same. Other sports certainly have their distinctive sound effects: the squeak of sneakers on the hardcourt, the ka-pow of a booming slapshot from the blue line, the crunch of helmets and bones pounding together at the line of scrimmage, the thwack of a tee shot, the dueling ugh!’s of a tennis match. Really, any sport isn’t the same once it’s divorced of those signature rhythms and cadences. But there’s something different about the sound a baseball bat makes. It goes beyond just a satisfying “bang” sound, and into something more meaningful, something sewn into the DNA of the sport itself.

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If you’ll let me get a bit metaphorical for a moment, think of the baseball bat as a musical instrument, a sort of long, thin wooden drum, and think about how it produces a different tone based on where the ball hits it. The pitcher, the outfielders, the fans way up in the $12 seats - they’ve all finely tuned their ears to the specific frequencies of that instrument, the crack that signals a ball hit right in the meatiest part of the bat’s sweet spot, versus the dull ponk of a foul ball up on the handle, or the muffled thunk of a grounder off the bottom of the bat. A routine thunk doesn’t even make you look up from your nachos, but a crack lifts your ass out of your seat.

Picture yourself as an outfielder. By the time you get your first reliable visual clue to determine whether a ball sailing towards you is a pop-fly into shallow center field or a long drive headed for the warning track, it’s already a couple of seconds into the ball’s trajectory, looking right up into the sun as the ball nears its apex. Even at full sprint, that’s too late to either have to take off and cover a hundred feet into the infield or a hundred feet back towards the fence within the two seconds you have left before the ball drops. You need another clue, which is where you use your ears.

According to researchers who’ve studied the science of the sounds of baseball (more on them in a minute), the sound of the hit will reach the outfielder’s ears within 0.3 seconds of contact, well before the first visual indication of the ball’s trajectory, which he’ll get 1.5 seconds into the ball’s flight. Decoding that sound will give the fielder plenty of information on whether it’s the loud crack of a line drive roped over his head or the clunk of a shallow bloop. That sound is the universal language of baseball, and scientists are looking into where that language comes from.

The Science

In a sport that’s been dissected from every conceivable angle by mathematicians, statisticians and scientists, it should be no surprise that researchers in the relatively niche scientific field of acoustics have occasionally dabbled in baseball. Researchers who study the science of sound have analyzed and dissected the sound of a bat crack, eliciting dissertations, panels and debates. In what may be the first example of a research paper on the phenomenon, Dr. Robert Adair of Yale University presented “The Crack-of-the-Bat: The Acoustics of the Bat Hitting the Ball” at a meeting of the Acoustical Society of America in 2001. (It’s available here.)

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Dr. Adair explains that the main “crack” we hear doesn’t come from the wood grain of the bat, but rather the violent pulse of air being pushed out as the ball flattens against the face of the sweet spot. A poorly-hit baseball that connects outside of the bat’s sweet spot tends to glance off the bat with less energy, but a ball that lands flush against the sweet spot squishes flat against the bat, bouncing right back off of it like a trampoline and sending out a miniature sonic boom of air.

As well, Adair looked into the tiny vibrations that ripple up and down the bat at a specific frequency upon impact. (That frequency was calculated as being 170 Hz, if you’re interested - roughly the same vibration frequency as a vibrating cellphone.) But why does a home run sound different than a pop fly? Adair found that when a hitter manages to connect on a pitch with the sweet spot of his bat, those vibrations, which also create the audible “clunk” sound within the bat, don’t occur - for the batter, it might feel like the bat went right through the ball. But when a ball is hit outside of the sweet spot, either off the end of the barrel or in on the batter’s hands, those 170 Hz vibrations buzz through the bat. That’s what leads to not only the common “stinging” feeling familiar to anyone who’s fouled off a pitch, but also to that audible “clunk” sound that separates a pop-up from a line drive. (Another researcher at the same conference put forth his theory that those bat vibrations were at 160 Hz and not 170 Hz, but, well, welcome to academia.)

From there, more researchers with an interest in both acoustic science and baseball (a surprisingly large overlap, it would seem) started contributing their own research. Dr. Daniel Russell is a professor of acoustics at Penn State, and a large portion of his research has been focused on the science of baseball bats. He’s researched everything from aluminum vs. wood bats to corked vs. uncorked bats to how bat weight affects velocity, and, naturally, he’s also studied the vibrations and sounds of bats. His article on bat vibration included a fascinating clip from Easton’s testing facility of a batter hitting a ball off the end of the barrel at 1,000 FPS, and in the slowed-down footage, you can actually see the wooden bat wobble back and forth like a wet noodle after contact is made.

One of the things Russell looked into is aluminum bats, and the “ping” sound that they make versus the “crack” of a wooden bat. (Before we go any further, I feel we should just come out and say it: the aluminum bat “ping” sound sucks. A clangy, metallic “ping” has nothing on the timeless satisfaction of “crack”. But I digress.) What Russell found while studying college baseball players who used metals bats was telling.

When comparing aluminum bats with newer composite bats (which are similar to aluminum bats, but made of graphite or carbon fibre) he found that players were dissatisfied with the newer composite bats, since they felt they didn’t have the same explosiveness off the bat. In fact, the composite bats were hitting the ball just as hard or even harder than the aluminum bats, but the difference was that composite bats don’t make the same “ping” sound as aluminum. Because the hitters couldn’t get a nice, satisfactory sound out of their bat when they hit the ball at the sweet spot, they perceived their hits as being inferior. Doesn’t that say it all, really? Baseball, divorced of a big loud noise that everyone in the stadium can savor after a booming hit (even if it is a lousy aluminum “ping” and not a proper wooden “crack”), isn’t really baseball at all.

The Feeling

Picture the greatest home run you’ve ever witnessed from your favorite player. Some childhood hero of yours just demolishing some shitty reliever’s fastball. Now, replay that fuzzy memory in your mind, but take out the sound of the bat hitting the ball. It just feels wrong, right?

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Watching baseball is an exercise in craving that sound as a sort of near-Pavlovian stimuli. Our brain is constantly receiving hundreds of messages from our sensory system, and our sense of sound is a big part of filling in the gaps of what we see. We need our ears to provide backup when our eyes are telling us “holy shit, that looked like a gigantic hit.” When we hear a sizzling tray of fajitas, we’re conditioned to get hungry. Likewise, when we process a visual of a slugger turning around on a hanging slider and then hear a big, echoing sound of a crack, our brain paints the picture of a ball sailing a goddamn country mile. And so, like Pavlov’s dog, that sound makes us twitch to life from the stands before we can even see the trajectory of the ball, jumping to our feet and spilling beer and popcorn everywhere in a big, vulgar outpouring of feelings.

It’s the sound of liberty, a good goddamned American sound, like a freshly-baked apple pie being blown away with a handgun.

And with February rolling over to March, that sound is back, positioned to retake its place as the soundtrack of summer.

Thank fuck.