Hop into a new $115,000 Mercedes S-Class limousine and the door will close with a satisfying, vault-like thunk. Do the same in a beat-up version from 1992 and you'll hear a sound that's eerily similar. That's because for the past several decades, Mercedes has been engineering its doors to sound reassuringly, consistently, the same.
This is harder than it sounds. (Pun intended.) As technology has evolved, car doors have too. Everything from the steel exterior (now either aluminum or a light-weight, high-strength steel), to its insulation, to side curtain airbags, to the electronics crisscrossing the interior has all changed. And that means to recreate that "thunk," technicians have had to do a lot of tweaking.
It's a process that begins in the design phase, says Tobias Beitz, manager of operational sounds at Daimler AG. "A good sound is not a matter of weight," he says. "The door sound is mainly ensured by the optimal acoustic design of the door structure, latches, and seals." So, in the split second where the door meets the frame of the car, it first hits the metallic components of the latch, which emit a low clicking sound. Then you’ll hear the louder, dull thud of the dampers and seals catching the door as it locks into place.
There are even variations on the Mercedes theme of door sounds. "We don't necessarily design exactly the same sound for a sedan and an off-road car," Beitz says. "But it should always sound like good quality, be authentic, and be a Mercedes." A G-Class SUV's door might sound heavier than an SLK convertible’s, but no matter what they'll both sound like a Benz.
Unsurprisingly, Mercedes' competitors have similar acoustic programs. Audi, for instance, has a door development team with design engineers and properties developers who fine-tune their own signature sound.
Audi's group also uses dampeners and seals, and calibrates the latch components to emit an equally unique click. In addition, all of their cars use an outer metal skin with harmonic vibration behavior that "ensures a rich sound when the doors are closed," writes Brad Stertz, Audi's corporate communications manager. So, as the door absorbs the vibrations of its impact with the frame, its exterior cladding emits a subtle, pleasant noise.
As lavish as all of this sounds, signature door-engineering isn’t a prerequisite for every luxury car. Rolls Royce, which makes among the most refined sedans in the world, doesn't have a specific door-sound. (Instead, their claim to fame is something closer to a tomb-like silence.)
Still, there is something ineffably special about a team of highly trained engineers who’ve labored for years to ensure that—no matter what—the sound of a slamming door is as iconic as a three-pointed star.