Why Automakers Are Reinventing How Electric Vehicles Sound

When the new Mustang Mach-E pulled up next to Darren Palmer at its public debut in Los Angeles last month, the sound of the electric vehicle’s engine made the hair stand up on the back of his neck. The low bass. The varied timbre. The grumble of a powerful turbine. Says Palmer, Ford’s director of electric vehicle product development: “It’s a distinctive sound.”

Wait, aren’t electric cars silent? Mechanically, yes. Since electric cars don’t get their power from combustible gas engines, they tend to be eerily hushed. But by 2020, federal mandates will require that all hybrid and electric cars make a sound at low speeds for pedestrian safety. And with the number of visually impaired and blind Americans expected to double in the next 30 years, giving these quiet rides some noise is essential, not to mention that our brains are wired to react to sound more quickly in moments of danger.

But for car makers, sound is about more than just safety. Sonic branding is on the rise, with the right auditory aesthetics triggering the brain’s amygdala, the part of the brain responsible for mood, emotion, and memory. The idea is, the right audible experience can even affect our behavior, our purchases, and our perception of flavor, scent, and texture.

Car manufacturers have been spending years testing musical styles, notes, and timbres for their vehicles. They’re hiring professional musicians, psychologists, and neuroscientists to hit the perfect note with gearheads—one that elicits an emotional response or reinforces a feeling of luxury, security, or satisfaction.

Take Jaguar’s 2019 all-electric I-Pace car, which sounds somewhat like a spaceship, thanks to the synthesizer sound created by music producer Richard Devine. He drew inspiration from the pod racers in Star Wars, as well as the sound of electrical motors on modern fans.

To create the Jaguar sound, Devine went through a process of trial and error, creating two different sounds for two sets of speakers on the vehicle’s exterior and interior. “What the passenger and driver hear inside the car is actually quite different than what pedestrians hear outside the car,” Devine says.

Devine also spent time developing sound for the car’s alerts, whether it was the touchscreen navigation system sounds or blinker sounds. “I had to come up with a sonic language for the car,” he says.

Harley-Davidson, meanwhile, detoured from its distinctive rumbling engine sound when it delivered the LiveWire, its all-electric motorcycle earlier this year. Attempting to appeal to millennials, the Milwaukee company has acknowledged the sound might disappoint die-hard Harley fans.

“You may love or hate it—but you recognize it regardless,” says Steve Keller, director of Pandora’s sonic branding consultancy, Studio Resonate.

Since the early 2000s, sound aesthetics have been increasingly important to the design of machines, whether it’s the quiet interior of a car or the whir of a coffee maker. And across automotive history, people have connected sound with cars. The noise of a car engine conveys power or distinction—at least it did while they had engines.

But even without a growling beast under the hood, sound matters. “We’re in the experience economy that really emphasizes the sensory elements of a car,” Keller says.

For instance, Hyundai spent 18 months creating a corporate six-tone sequence for its cars with the goal to make communicate a brand that’s “essential, refined, and confident.” Ford, meanwhile, hired members of the Detroit Symphony Orchestra to create the alerts in its 2019 Lincoln Aviator. The percussion, violin and viola chimes aim to create a feeling of luxury and sanctuary. Porsche has used a “sound symposer” inside the engine compartment that channels the engine noise into their cars interiors, while Volkswagen implemented the “soundaktor” audio systems to reproduce a buzzy noise made by older vehicles with less sound insulation.

Faking sounds, however, can turn off to consumers, automakers have found. In 2016, Volkswagen models featuring a sound actuator that simulated engine noise in the cabin faced backlash, and consumer began removing the “pesky” devices, even posting before and after videos. And in some cases, if a car sounds more powerful than it actually is, it could be literally dangerous. An out of tune vehicle might cause the driver to overestimate the car’s ability to get through an intersection or eke past a semi-truck on a two-lane highway.

As more electric vehicles hit the market—14 new e-vehicle models are expected in 2020—audio aesthetics will create an even bigger resurgence in car audio. Says Palmer: “The silence of electric cars opens a new canvas.”

What Ford ultimately put on that canvas for the new Mach-E became a company-wide effort when executives decided in 2018 that the new e-vehicle would be a Mustang. The car has a long history and devoted fans who have strong opinions about how a Mustang should sound and feel.

“It’s all about the emotion, that car,” says Palmer, “and that’s why it’s lasted for 50 years.”

While Ford’s designers focused on the door handles, the curve of the body and feel of the seats, Palmer’s 100-person team spent a year coming up with the audio aesthetics. They listened to engine roars in Batman movies and the electronic sounds of Blade Runner movies. They installed Bang & Olufsen sound bars and 10 speakers inside the vehicle. They queried consumers at various stages, often acting on their opinions instead of those of experienced car designers.

Two weeks before the L.A. launch, Palmer stepped into the F.I.V.E. Lab, Ford’s in-house virtual reality studio, where he donned a headset and became immersed in a fictional world in which he sat behind the wheel of the car and listened to the engine rev. It mixes a “starship accelerating” whir with a subtle but grumbling background thrum. In another VR scenario, he stood outside a cafe and a Mustang Mach-E pulled up next to him.

“I said, ‘Oh God, that sounds so good,’” Palmer says. “It was totally new, and it sounded completely natural.” And that, of course, is always the sign of a good fake.

The Sound of Silence: Why Automakers Are Changing the Noise That Electric Vehicles (Don’t) Make

More must-read stories from Fortune: