Toyota has employed the ‘Active Noise Control’ system on its Crown Hybrid vehicle, using three microphones located on the roof of the interior of the car to detect the muffled noise of the engine.

The system then generates antiphase signals from three speakers, two located on the right and left front doors and one rear woofer on the rear shelf, to counter the noise. The system which was implemented after the car’s engine was found to be noisier than expected, reduces the interior engine noise by about 5 to 8dB, the company said.

“We collected the data such as the distance between the microphone and the head of a passenger, the distance between each speaker and the head of a passenger, and the shape of a car interior,” Toyota said.