Smoke rises from cars on fire during the widespread protests in Philadelphia Credit: Danya Henninger / Billy Penn

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Philadelphia has been rocked by nights full of fires, commercial break-ins, and robberies as vandals take advantage of the uproar created by protests against institutional racism and the killing of George Floyd.

Many city residents have reported difficulty sleeping through the louder-than-usual cacophony of sirens.

And…the explosions.

Low-frequency blasts continued deep into Wednesday evening, intensifying after dark and carrying through into the early hours of the morning: booms of sonic proportions that, even when captured on cell phone audio, have an almost ominous growl.

“I heard at least a dozen booms between 1 and 1:30 this morning and was still hearing them when I fell asleep close to 2,” said Sarah McLaughlin, a South Philly resident.

Some residents have made an effort to count. From his home in Bridesburg, Ray Skwire kept a diligent tally from 7 p.m. to shortly after midnight on Tuesday.

“I know I heard at least 200 separate blasts, and I’m sure I likely missed a few as well,” Skwire said. “My best guess is it’s fireworks, above and beyond ATMs.”

Philly now has full-on “boom” documentarians who are chronicling the frequency of the sounds, which seemingly come from all corners of the city. Theories have been percolating on social media — largely without evidence — as the hashtag #phillyexplosions continues to trend. Fireworks. ATM explosions. Tactical warfare. People blowing up M-80s for fun.

Could it be a government plot to seed further disorder? Or does it just come down to the weather? Billy Penn looked into the mysteries.

Hundreds of nightly booms, only 50 ATM blasts reported

Many presume the sounds are tied to the rash of ATM break-ins in Philly since last weekend.

But police reports of burglary or explosive attempts do not match the frequency of the sounds occurring in rapid succession all over the city.

The Philadelphia Police Department confirmed 135 incidents related to explosive events around this city as of Tuesday. Commissioner Danielle Outlaw said approximately 50 ATM machines have been damaged or opened since last weekend.

Wednesday evening, Pa. Attorney General Josh Shapiro lauded the first arrest of an individual allegedly connected to the incidents, a man accused of selling dynamite in the city’s Frankford section.

The local division of the federal Bureau of Alcohol, Tobacco and Firearms has been investigating, and believes illegal M250 to M100 explosive devices are being used for these attempts.

But details are scarce, and ATF officials didn’t respond to questions about the other reports of explosions around the city.

“The situation is very fluid at this time as we work on and process this scene,” said John Schmidt, the acting special agent in charge of ATF Philadelphia.

Military psy-ops? No, says PA National Guard

With National Guard forces stationed around Philadelphia, some speculate the booms are a psychological warfare tactic to instill fear and keep people indoors after citywide curfews go into effect.

The most frequent theory: government agencies are deploying Long Range Acoustic Devices (LRAD) to generate the sounds.

One tweet that’s been shared over 3,000 times encourages people to contact Gov. Tom Wolf’s office to complain about the devices being used “to terrorize citizens.” Other posts circulating feature pictures of the Pennsylvania National Guard’s tactical vehicles with red circles around what they believe to be the device near the truck’s turret.

It is true that law enforcement agencies in the U.S. have deployed LRAD as a form of protest control, even in recent days. But those devices emit an ear-piercing, omnidirectional screech — not the ominous booms you’re hearing around town.

Lt. Col. Keith Hickox of the Pa. National Guard told Billy Penn he’s been briefed on “the conspiracy.” But he assured that his troops don’t use LRAD, nor anything capable of replicating that sound.

“We don’t even have sonic equipment in our inventory,” Hickox said of the described devices. “I don’t even think I’ve seen something like that in my career. The only time I’ve seen those is in the ‘Incredible Hulk.’”

Over 2,000 members of the national guard are stationed in the Philadelphia region right now, and the colonel said they’ve reported the explosive noises back to command as well. However, he said, it’s not their job to investigate. That’s all up to the local law enforcement, which currently attributes most of the explosion incidents to ATMs.

While Philly Parks & Rec does deploy a kind of sonic weapon — the high-pitched “Mosquito” devices used to keep teens away from public spaces at night — it’s unclear whether city police do.

The Philadelphia Police Department denied using any “artificial noise” in recent days, but did not answer Billy Penn’s questions about whether sonic noise devices are part of its arsenal.

Fireworks, M-80s and the lightning effect

If we are entrenched in a sonic conspiracy, government officials picked a well-camouflaged setting. In addition to ATMs being blown up, the city is noisier than usual.

Since the protests and unrest erupted across the city, residents in parts of North Philly and Kensington report a days-long fireworks festival in the streets, a kind that is usually only seen on July 4 or other warm-weather holidays.

The recreational use of M-80s — basically like small sticks of dynamite — is common in many neighborhoods, and use has increased in recent days. Reports of vehicle fires and explosions across the city as well, unassociated with demonstrations.

Add all this noise together, and local acoustic experts say you have the answer.

There are two atmospheric factors at play here, according to Felicia Doggett, president and CEO of Metro Acoustics, an acoustics and vibration consulting firm based in Philly.

One: the weather: Sound travels faster at higher temperatures and in higher humidity. With the temperature in the 80s and 90s all week and lots of pre-summer moisture in the air, conditions are perfect for sound to travel long distances. Second, the architecture: Philly has lots of tall buildings downtown and canyon-like streets that can scoop up sound, reflecting it out into the neighborhoods.

Doggett notes that the low, ominous grumbles of the explosions people are hearing indicate they’re coming from far away, and they could be from in any direction.

“It’s like when you hear a crack of lightning,” Doggett said. “When you’re close, you hear a crack. But when the lightning is far away, you hear a growl.”

Water can also carry sound, too. In the summer heat, Jersey residents near the Delaware River have long reported problems with noisy waterfront parties on the Philly side creating a window-rattling effect and keeping them up until 3 a.m.

Few of these explanations may prove individually convincing to the late-night Twitter chatterers.

“We can’t rule out Gritty’s involvement in generating the booms,” said McLaughlin, of South Philly.

For Skwire, the Bridesburg resident who was tallying the booms, it’s just fascinating to watch.

“I was actually quite surprised at the number of people [paying attention to it],” he said. “It’s an interesting little mystery that a lot of people seem to have caught onto out of curiosity, since they hear it as well.”

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Max Marin (he/him) was Billy Penn's investigative reporter from 2018 to 2021. A graduate of Temple University, he has produced award-winning journalism on local politics, criminal justice, immigration...