Tim Maly spoke to a vibration performance engineer with GM and found that the sounds you you think are engine or mechanical noses might not actually be sounds your car is making.
We’re made to hear what we expect to hear. If you’d like to learn a little more about this, Roman Mars’ 99% Invisible has a great episode on the manufactured sounds that go into sports.
Strangely, to give people the impression that the Impala’s engine was working as intended, GM had to partially mask its real sound.
In general, to improve fuel economy in a car, you want to reduce the engine’s RPM. Over the past few decades, the auto industry has been doing that. In the 90s, says Gordon, a 4c engine might be cruising at 3,400 RPM. Today, it’s below 2,000.
But as you reduce the speed that the drive shaft is rotating, you lower the frequency of the sound it’s making. There comes a lower limit where the engine is making what Gordon calls “groan-y and moan-y” noises which people find unpleasant. The car sounds broken.[…]
Some sounds in the car are completely artificial. The telltale clicking of a turn signal was once an artifact of the mechanical process that turned the light on and off. But that mechanism has long since been replaced by an electronic circuit that operates silently. Still, audible feedback is valuable so the car plays an MP3 file of a turn signal over the speakers.