The AirPods story actually begins with the iPod.

With Apple’s popular personal music player, the company shipped its first set of earbuds. Sure, they were wired and very basic, but the accessory laid the groundwork for what would eventually become AirPods. Along the way, the EarPods would be bundled with the iPhone in 2007, and a 2012 redesign produced something more akin to what would eventually become the first-gen AirPods in 2016. The work the company did to improve the fit of EarPods continues to pay off as Apple prepares to ship the noise-canceling AirPods 4.

“We had started trying to learn a bit about human physiology and what shapes would fit better in people’s ears,” Apple’s Vice President of Hardware Engineering Kate Bergeron told me about those early days. “We started doing some MRI scans and trying to figure out how to gather data, but we didn’t have a sense of how many scans we’d be looking for, or how many different kinds of ears we needed.”

Over the years, Apple has developed more efficient methods for gathering data, so it was able to build out its database of ear shapes quicker than in the early days of EarPods. Bergeron explained that she expects the company to be “continuing that journey” forever when it comes to developing new versions of AirPods.

During what Bergeron described as “the dark days of COVID,” a small group from the AirPods team was trying to solve a dilemma. They wanted to bring effective active noise cancellation (ANC) to the open design of the “regular” AirPods. The crew had already successfully done so on two models of the AirPods Pro and on the AirPods Max headphones. But this time around, it was essential that the open nature of the AirPods remain while also providing the technology to block out distractions.

So in 2021, over the course of several days, Bergeron and AirPods marketing director Eric Treski met up at one of Apple’s acoustic labs for a demo. At that point, the team was unsure if they had anything viable, but they wanted the executive’s feedback on it nonetheless.

“We were just blown away,” Bergeron recalled. “We said ‘we absolutely have something here, we need to go after this and we’ve got to make it happen.’” Acoustic and computational work that was required for an effective ANC algorithm was happening simultaneously with iterations on improving the fit and overall comfort for the AirPods 4.

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

“It’s even computationally more intense in many ways than it is with the AirPods Pro,” Bergeron said. “The ear tip gives you a fit that’s pretty consistent.”

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

Treski explained that the ANC setup, or the third generation of Adaptive EQ as he described it, is constantly managing and adjusting any equalizers for both 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 is also instrumental in providing effective ANC on the open earbuds.

“It’s really, really hard to create this great ANC quality in a non-ear-tip product,” he said. “The power of the H2 allows that, so we’re actually doing a lot with the H2 chip to manage ANC quality and listen from the mics for environmental noise to make sure we’re canceling as much as possible.”

The lack of an ear tip on the AirPods 4 also creates a challenge for transparency mode. Treski noted that it’s “arguably even harder” than mastering ANC on open earbuds since you’re having to blend ambient sound from the microphones with what you’re hearing naturally through your unplugged ears. There’s a perfect mix that will seem real to your brain, but also it has to all be done with extremely low latency so the automatic adjustments don’t lead to any delays in what comes through the AirPods.

The new shape for the AirPods 4 also provided an opportunity to improve overall sound quality on the earbuds. The front end of the buds, which Bergeron revealed the team calls the “snorkel,” is very different from the AirPods 3. Since the previous model was more open, she said, the engineers had more freedom to operate. With the new version, the driver had to be adjusted so that it didn’t reflect sound to the internal microphone that monitors noise inside your ear. That’s why the drivers are now pointed down your ear canal, and why they’re slightly recessed.

“In order to get the improved fit, that necessitated adjusting the driver and the front of the product,” she said. “The mechanical engineers are doing the packaging of the entire product, trying to fit everything in. Acoustic engineers are saying, ‘okay, based on those constraints, this is the best place that we can put the driver.’”

The design overhaul on the AirPods 4 extends to the case as well. Apple was able to slim down the accessory while also simplifying how you interact with it. The end result is “the same magic 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 one place where liquid could potentially get in, so the case has the same IP54 rating as the new AirPods.

“We get a double win there for sure,” Bergeron said.