Living in Westchester, Chris Bankoff said, he's used to two types of noise: the occasional house party by Loyola Marymount University students, and the engine roar of planes taking off from LAX.
What he didn't expect to hear Aug. 2 was the low-frequency thumping of music coming from HARD Summer, a house- and techno-music festival held at Hollywood Park in Inglewood, about 5 miles from Bankoff's home.
When he first heard the beats on that Friday, he thought it was a party nearby and brushed it off. But the next afternoon, Bankoff said, the sound resumed and was even louder than the day before.
"I could hear the change in rhythm," he said. "It was just like someone parked out in front of the house playing loud music in their car."
In North Redondo Beach, about 9 miles from the entertainment venue, Sondra Segall thought she was hearing construction work. The noise didn't bother her, but she wondered how she was able to hear it.
Residents in Manhattan Beach, El Segundo and Hermosa Beach also took to the Nextdoor App and Reddit in droves to ask or complain about the noise. The El Segundo Police Department received more than 100 calls Friday and 200 on Saturday; the number dropped to 50 calls on Sunday, possibly in response to the community alerts and social media posts.
Neither the festival organizer, Insomniac Events, nor Hollywood Park replied to requests to comment before publication.
Although Inglewood's noise ordinance places limits on the concert volumes, it says those limits do not apply to events at Hollywood Park that end by midnight. So the artists at HARD Summer, who ended their sets around 11 p.m., probably performed at or above airport-runway volumes.
HARD Summer organizers told KABC-TV in a statement, "While we always operate within legally acceptable decibel levels, we have sound monitors deployed in the field to monitor and respond to all noise complaints."
The energy in sound waves diminishes the farther they travel from the source. So even if the music was amplified to the threshold of pain, the volume should have dropped below that of a hushed conversation within a few miles of the concert.
So, what happened?
El Segundo City Manager Darrell George said in a statement that he reached out to Inglewood City Manager Mark Weinberg, who said the event's organizers made mistakes when they set up the performance spaces that exacerbated the "bass reverberation."
Inglewood Mayor James T. Butts Jr. issued a statement nearly a week after the first complaints, saying the sound and vibration issues experienced were "related to certain bass frequencies" that can be affected by "stage position, reflection off of buildings, and atmospheric conditions including wind." Butts added that putting a stage on the elevated American Airlines Plaza "was a major contributor to the issue," and said the area will be off-limits to concerts in the future.
Judging from the anecdotes shared by residents, increased bass reverberation isn't what people in the South Bay were hearing, said Vincent Olivieri, professor of sound and design at U.C. Irvine.
"'Reverberation' refers to the millions of reflections off of different surfaces that give spaces their particular sound," Olivieri explained. It's the reason a cave, with hard stone walls that cause lots of acoustic reflections, sounds like a cave and not a living room, he said.
"The reverberation explanation also doesn't account for why it appears that only folks to the southwest of the venue heard it," he said.
If Inglewood's explanation doesn't hold water, then how could residents as far as 9 miles southwest of the venue hear the low-frequency vibrations of HARD Summer? Experts in audio engineering and acoustics theorize about how the sound could have traveled so far.
How the sound might have traveled
The festival's musical acts played on five stages set up in the parking lots surrounding SoFi Stadium. With this type of outdoor show, there are no walls to interrupt the flow of sound outward, said Tony Hoover, principal for McKay Conant Hoover, acoustical and audiovisual consultants.
And unlike indoor entertainment venues, there's no roof to contain the sound, he said.
Deep bass is a big part of hip hop, techno and electronica music, said Barry Rudolph chair of the Los Angeles section of the Audio Engineering Society. He said he's sure the festival used powerful amplifiers and huge speakers to reproduce the sound fully and at high volume.
"Loud and long sound waves can vibrate surrounding local structures into resonating with this additional sound energy," adding to the problem of sound bleeding from the stages into the community, he said.
It's like hearing a car coming down the street with a window-rattling stereo — you hear the music before the car comes into view, Rudolph said.
Still, Rudolph doubted that the low frequencies from HARD Summer would travel as far as 9 miles. More credible, he said, is that the thumping bass traveled about 1 mile from Hollywood Park in all directions (unlike higher frequencies, he said, low frequencies are omnidirectional).
And yet, there's no shortage of people far from Hollywood Park who've said they heard the festival's rhythmic rumbling on Friday and Saturday.
Hoover said it's not unheard of that sound would travel several miles, but he was stumped to learn that people 9 miles away heard the thumping.
He described the sound emanating from Hollywood Park as "sort of like a great big bubble of sound that keeps getting bigger and bigger." But as the bubble of sound expands, it gets weaker, which is why the volume drops as you move away from the sound's source.
The bubble can be reshaped, though, by wind and temperature, both on the ground and in the layers of air above it.
Temperature comes into play especially on a warm to hot day, Hoover said.
After the sun sets, the air at the ground level will cool, but the air at higher elevations will usually remain much warmer (a "temperature inversion"). These different temperature bands can cause sound waves to bend or refract downwards toward the ground because of the difference in the speed that sound waves travel in warm and cool air, said Jason Corey, associate professor of music for the University of Michigan.
Furthering the temperature-inversion explanation, Olivieri said sound waves or sonic energy can be influenced by microclimates.
Think of a heat dome but on a smaller scale. Under the right conditions, a collection of warm air can sometimes serve as a overhead mirror bounding sonic energy down. This is particularly likely to happen during summer festivals.
As the sonic energy leaves an outdoor concert venue, a portion travels up toward the atmosphere. Here, sonic energy leaving HARD Summer toward the southwest could have hit a pocket of warm air that was halfway between the venue and the affected neighborhoods, Olivieri said.
"That pocket of warm air can serve as a kind of acoustic mirror and refract [the sonic energy] right back down" into the affected neighborhoods] he said.
Corey agreed, saying that during a temperature inversion, "sound from a concert venue that travels up into the warmer air layer and bends downward after passing over buildings and other obstacles reaching the ground miles away from the concert."
Hoover was skeptical, saying that the wind and a number of other factors would have to line up exactly right to create the temperature-inversion effect, especially at such long distances. But Olivieri said that if the bass signal was louder than it should have been, and if the sound bounced off a high-temperature micro-climate system back toward the neighborhoods to the southwest, that might help explain why those neighborhoods heard the pulsing bass while others did not.
The long-distance rumbling of a concert isn't a new phenomenon, it's something that's becoming increasingly prevalent because of improvements in concert sound technology, said Dave Revel, president of Technical Multimedia Design, a consulting firm that often assists venues with noise mitigation.
He added, "It’s a logical progression of technology, but it has brought about challenges to community noise because now you have very large, powerful sound systems that can reproduce a wide range of frequencies."
When it worked events at the Rose Bowl and the Fairplex, Revel said, Technical Multimedia Design found that people as far as 4 miles away were able to detect music, especially the bass.
The role played by noise ordinances
Another potential factor in this incident is Inglewood's noise ordinance.
Volume is measured in decibels, or units of sound pressure. But there are different standards for measuring decibels when regulating noise — among them, one of which focuses on the frequency range of human speech, and another of which is more attuned to a full range of frequencies, including bass frequencies.
Generations of community noise ordinances are based on the former standard, which focuses on frequencies common to human speech, Revel said. "They never anticipated music that [would have] bass in it."
The city of Inglewood's ordinance falls into that category. The challenge, Revel said, is that it relies on a standard that "doesn't take into account all the frequencies and certainly doesn't take into account the low frequencies that travel further."
Concerts and festivals can operate well within the law because "the law essentially ignores the bass."
In 2015, Revel's company was hired by the Fairplex in Pomona to assist with noise mitigation at the HARD Summer festival there in July after complaints of "unbearable noise levels" months earlier, the Daily Bulletin reported.
Revel said he remembers measuring the sound during the event.
"We actually were within the community noise limit for the entire concert, but people's windows were rattling," he said. "People who lived right next door to the concert, and you had their windows rattling because the bass was insane."
This story originally appeared in Los Angeles Times .
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