The science of how sound travels around SF during outdoor concerts

Many residents remember last year’s festival for the deep, pulsating bass that infiltrated the city from Noe Valley to Twin Peaks, and even carried across the bay, rattling windows in Alameda and Oakland. 

While some embraced the sound as a symbol of the city’s vibrancy, others flooded social media with complaints about the “shockingly loud” electronic music. Others sent noise complaints to San Francisco’s Entertainment Commission, which regulates entertainment venues and events in the city. The agency told SFGATE it received nearly 200 noise complaints over the two days of the festival, the most it’s ever received for a single event. By comparison, Outside Lands receives 100 complaints on average annually, while Hardly Strictly Bluegrass — also happening this coming weekend — tends to generate only a few. 

Last year’s complaints have led the organizers to make significant adjustments in advance of this weekend’s event, including setting up sound monitors around SF and Alameda and establishing a dedicated hotline for festival-related noise complaints. 

They’ll certainly have their work cut out for them. A wide array of factors determine how far the sound of a given show carries, some easier to control than others; sound engineers who manage outdoor events will tell you that their work is both a science and an art. While equipment design and implementation can be adjusted, other factors are more challenging to account for, such as weather patterns that can amplify sound over wide areas. 

When the sound engineers get that artistry wrong, the consequences can be dramatic. During a performance by Beyonce and Jay-Z at Oracle Park in 2014, sound carried all over SF, triggering a record number of noise complaints (a record broken by last year’s Portola Festival). When Metallica played outdoors at Civic Center in 2018, nearby residents reported not being able to sleep over the noise. And I’ve personally enjoyed listening to Oracle Park shows from Dead & Company to Lady Gaga without buying a ticket, because they’ve been audible in my backyard, near Dolores Park. 

Perhaps the biggest factors that determine how far sound carries are the design and placement of the loudspeakers, according to Arica Rust, a freelance sound systems engineer.

“There are methods of deploying a loudspeaker system to focus sound, even at low frequencies, in a specific direction,” Rust, who has helped manage sound for local events such as Outside Lands and the Treasure Island Music Festival, wrote in an email. 

The professional loudspeakers used at large-scale events are usually equipped with software that can predict with remarkable accuracy how far and wide sound will carry, which sound engineers can use to ensure the energy is focused on the audience. When noise spreads across the city, it’s often because the high-tech equipment is being misused, Rust said.

“I think part of the issue of poor deployments is due to people not understanding how to properly use the tools at their disposal because of lack of time and resources,” she wrote. “Due to the overall labor shortage in the industry once the lockdown eased, many companies are strapped for people, but it’s important to invest in the education of your workforce.” 

After the 2014 Beyonce concert at Oracle Park, the venue’s organizers made adjustments to the speakers, successfully mitigating noise: An AC/DC concert the following year received only 12 noise complaints.

Of course, musical genres that are louder and more bass-heavy can generate more noise pollution — likely part of why Outside Lands receives more complaints than Hardly Strictly Bluegrass, despite both festivals featuring musical acts on multiple stages in Golden Gate Park across three days.

“Outside Lands features a huge variety of performances, including rock and pop and hip hop and DJ sets. You’ll find more thumping beats/heavy bass there,” Tamara Aparton, a spokesperson for San Francisco Recreation and Park Department, wrote in an emailed statement. “Hardly Strictly is mostly bluegrass, country, and singer-songwriters. Some of the performances are acoustic.”

Still, Rust said that a good sound engineer can control even the heaviest bass. “Even with EDM shows, there’s a way of arraying the subwoofers to steer the sound in a certain direction and cancel it in other directions,” she said over the phone.

It’s much trickier to control for atmospheric conditions, which can dramatically affect how far sound carries. Both the Portola Music Festival and the 2014 Beyonce concert occurred when the city was blanketed by a layer of cool air sitting under a layer of warmer air, known as an inversion layer, which usually develops when an ocean breeze pushes cool air inland. That blanket can trap sounds close to Earth and bounce them around the Bay Area. 

“It’s something that basically keeps a lid on the sound. It prevents the majority of sound from going up in the atmosphere, and instead refracts the sound back toward the surface,” said Dalton Behringer, an meteorologist with the National Weather Service’s Bay Area office in Monterey. 

A blanket of fog over the city is usually an indication that an inversion layer is present, and that was definitely the case at last year’s Portola Music Festival, when the fog was low and heavy, holding the sound close to the ground. This weekend, forecasters aren’t anticipating the typical SF fog pattern, as a cold front is expected to drop down into California that will likely help mix out the marine layer, Sean Miller, a meteorologist with the weather service, said. An inversion layer could still develop with the system carrying cold air into the region, but Miller said it’s unclear where it will set up and it would likely be higher in the atmosphere, impacting the sound less than a layer closer to Earth.

The wind, meanwhile, can dictate which direction the sound travels. “If you have a slight breeze in one direction, then the sound will carry with the breeze,” Behringer said. “If the breeze is blowing away from you, if you’re upstream from the sound source, that could muffle it from you. If you have a more turbulent wind, you could have a waffling of sound where the sound muffles in and out.” 

After last year’s drama, the organizers behind the Portola Music Festival say they’ve learned a lot about how to minimize sound pollution from this year’s event, and that they’re prepared, should another inversion layer develop. 

“For Portola 2023, we have adjusted our stage and speaker configuration, and we’ll be monitoring audio levels at strategic locations in and around the festival site and in San Francisco and Alameda counties,” Erin Bilbo, a spokesperson for Goldenvoice, said in an emailed statement. 

The team is placing sound meters in Alameda and San Francisco neighborhoods that had issues with noise last year and will make adjustments accordingly throughout the day, according to Maggie Weiland, executive director of the Entertainment Commission.  

While anyone with noise complaints during the festival can call 311, festival organizers have also established a special community hotline number staffed by individuals, who will field noise complaints and send them directly to the sound engineer team. The engineers will “try to mitigate it in real time,” Weiland said. That hotline can be reached at 877-324-8151, Friday through Sunday.

Weiland thinks that it’s worth fine-tuning the logistics to keep major festivals here, which she sees as an important part of the vibrancy of the city — and they also have the potential to bring in significant revenue. 

“Pre-pandemic, the entertainment and nightlife industry was bringing in $7 billion in economic impact for the city of San Francisco annually,” she said. “… We’d like to build capacity for more events of this scale. We need to learn from it.”