Expanding on the same concept used in noise-cancelling headphones, Toyota has developed a noise cancelling system for its Japanese-market Crown Hybrid
that nearly eliminates engine sound within the passenger compartment. The system uses a complex system of microphones, speakers and sensors located around the cabin.
Like the headphones, the new Toyota system works by using small microphones to monitor surrounding sounds, then plays back frequencies mathematically calculated to be the exact opposite of the ambient noise through the speakers, causing both sound waves to collide and cancel each other out. The Toyota system has an extra sensor that takes into account engine rpm.
Debuting in the Crown Hybrid, the system was developed to cancel the annoying hum of the engine at low rpms when driving around town.
Toyota isn’t the first to develop such a system for cars. Lotus had developed similar systems as far back as 1990, and a trio of Mazda engineers having written a scholarly paper to the Society of Automotive Engineers detailing a nearly identical system in 1994. Acura, too, has a similar system dubbed Active Noise Cancellation (ANC), which it uses on a number of models.