Toyota has added an “active noise control” system to the Toyota Crown Hybrid which works similiar to the way noise canceling headphones work.
Toyota says during slow city drives of between 20 to 40km/h where engine RPM is between 1,000 to 3,000rpm, muffled noise of between 50 to 150Hz can typically be transmitted to the car, impairing the car’s interior comfort.
Three microphones in the car’s interior picks up this noise and sends it to the active noise control system. The system then generates an antiphase sound signal from a set of speakers to counter the noise. Three speakers are used located on the left front door, right front door and one rear woofer. Distance between the mics that pickup the noise and the head of a passenger as well as the shape of the car’s interior has to be taken into account. Toyota says this can reduce noise levels by between 5 to 8dB.
Although there are similiaries between the Crown Hybrid and the Lexus GS450h’s hybrid drive system, the active noise control is not necessary in the Lexus GS as the engine RPM in the GS is higher at the same speeds. This is because the Crown Hybrid’s ratios are tuned for better mileage.