How Apple designed AirPods 4 for effective ANC

The story of AirPods actually begins with the iPod.

Along with Apple’s popular personal music player, the company released its first pair of earbuds. Sure, they were wired and very basic, but the accessory laid the foundation for what would become AirPods. Along the way, EarPods were bundled with the iPhone in 2007, and a redesign in 2012 produced something closer to what would become the first-generation AirPods in 2016. The company’s work to improve the fit of EarPods continues to pay off as Apple prepares to ship the noise-canceling AirPods 4.

“We started out trying to learn a little bit about human physiology and what shapes would fit people’s ears best,” Kate Bergeron, Apple’s vice president of hardware engineering, told me about those early days. “We started doing MRIs and trying to figure out how to collect data, but we didn’t have a clear idea of ​​how many scans we were going to have to do, or how many different types of ears we were going to need.”

Over the years, Apple has developed more efficient methods of collecting data, allowing it to build its database of ear shapes faster than it did when EarPods first debuted. Bergeron said she expects the company to “continue this journey” forever when it comes to developing new versions of AirPods.

During what Bergeron described as “the dark days of COVID,” a small group on the AirPods team was trying to solve a dilemma. They wanted to integrate effective active noise cancellation (ANC) into the open design of “regular” AirPods. The team had already succeeded in doing so on two AirPods Pro models and the AirPods Max earbuds. But this time, it was essential to retain the open nature of AirPods while providing the technology needed to block out distractions.

So, over the course of several days in 2021, Bergeron and AirPods marketing director Eric Treski met in one of Apple’s acoustic labs for a demo. At this point, the team wasn’t sure they had something viable, but they wanted to hear the CEO’s thoughts nonetheless.

“We were blown away,” Bergeron recalls. “We thought, ‘We absolutely have something here, we have to get on it and we have to do it.’” The acoustic and computational work needed for an effective ANC algorithm was happening simultaneously with iterations aimed at improving the fit and overall comfort of the AirPods 4.

After testing the AirPods 4, I can say that the fit and comfort have improved since the third-generation model. But Apple has also expanded the earbuds’ capabilities with the H2 chip and microphones in the AirPods Pro 2. This combination of advanced technologies allows Apple to constantly monitor the fit in a user’s ear, updating the ANC algorithm in real time so that noise blocking is still effective even when the AirPods move around.

“The performance is even higher on the computational side than on the AirPods Pro,” Bergeron said. “The ear tip gives you a pretty consistent fit.”

Apple’s journey with ANC began with the development of the first-generation AirPods Pro, which launched in 2019. Effective active noise cancellation was typically more common on over-ear headphones, with a few exceptions, but Apple realized that making a distraction-free listening experience “pocketable” was appealing to its users. Of course, the company followed up with its own earbuds, the AirPods Max, before the powerful second-generation AirPods Pro.

Treski explained that the ANC setup, or the third generation of Adaptive EQ as he described it, continuously manages and adjusts all the EQs for active noise cancellation and audio quality at the same time – and in real time. So in addition to the revised shape, the acoustic architecture of the AirPods 4 also helps deliver effective ANC on open earbuds.

“It’s really, really hard to create such exceptional ANC quality in a product without an ear tip,” he said. “The power of the H2 allows for that, so we’re using the H2 chip a lot to manage the ANC quality and listen to ambient noise from the mics to make sure we’re canceling it out as much as possible.”

The lack of eartips on the AirPods 4 also creates a challenge for Transparency Mode. Treski noted that it’s “arguably even harder” than mastering ANC on open-back earbuds, because you have to blend the ambient sound from the microphones with what you naturally hear through your unplugged ears. There’s a perfect blend that will sound real to your brain, but it also has to be done with extremely low latency so that the automatic adjustments don’t cause any delays in what’s coming through the AirPods.

The new shape of the AirPods 4 also helped improve the overall sound quality of the earbuds. The front end of the earbuds, which the team calls the “snorkel,” Bergeron revealed, is very different from the AirPods 3. Because the previous model was more open, she explained, engineers had more freedom to maneuver. With the new version, the speaker had to be adjusted so it wouldn’t bounce sound back to the internal microphone that monitors noise inside your ear. That’s why the speakers are now aimed toward your ear canal and are slightly recessed.

“To get a better fit, we had to adjust the driver and the front of the product,” she said. “Mechanical engineers are in charge of packaging the whole product, trying to fit everything in. Acoustic engineers say, ‘OK, based on these constraints, this is the best place we can put the driver.’”

The AirPods 4’s design overhaul extends to the case as well. Apple has managed to slim down the accessory while simplifying how you interact with it. The end result is “the same magical experience,” Bergeron noted, but the lack of a button allowed engineers to eliminate overall thickness and rely on an accelerometer. Removing the button also gets rid of a place where liquid could potentially get in, so the case has the same IP54 rating as the new AirPods.

“We will definitely get a double victory there,” Bergeron said.