Eli5 how noise cancelling in cars works

Question

Given that the general noise in cars (background hum of an engine on a freeway) is fairly predictable could a tech exist that just plays a generic opposing sound in a regular car, such as an mp3 track. This would enable your average user to experience this through a car stereo

In: 2

Answer 1

The problem is, the sound isn’t the same in every seat of the car, and with noise cancellation you need the cancellation to be taking place as close to the ear as possible or else propagation delays will ruin the effect.