A similar noise cancellation system according to my knowledge was developed by Volkswagen in the 1960's. They put a speaker on the two inner sides of the headrest on both the front seats, so that a speaker was directed towards each ear. A sound having a frequency equivalent to the typical drivetrain noise of a Volkswagen was emmited through each of these speakers thus providing a noise free ride to the driver and the front passenger.
Best regards,
Mickey B. Mama