“BMW has been perfecting its acoustic engineering techniques for the past 15 years, understanding what effects various choices in panels and dampeners have on the final sound of the car.
For example, the new BMW 4 Series Gran Coupe is “a sporty car, so the door isn’t supposed to sound too heavy. It can’t sound too light, because a light door wouldn’t convey the right aspects of quality and safety. But it’s not supposed to sound too heavy, either. It should have a precise sound.” By contrast, “the BMW 7 Series would be a bit softer maybe, a bit darker in the sound as it’s our flagship sedan.””
Source: Medium Re-Form