Silence the road, enhance the ride

Imagine yourself sitting in your car, driving along the highway and on small country roads. What noises do you hear? The answer probably depends on whether you have an electric vehicle or a car with a conventional combustion engine. What many people don’t know is that without the sound of a combustion engine, noise coming from the tires becomes much more noticeable for the driver and the passengers. Road noise cancellation reduces in-cabin noise coming from the tires. This significantly increases driving comfort in electric cars, especially if you want to listen to music or have a conversation.

Most electric vehicles are therefore equipped with noise dampening material. This, however, comes with additional weight. The SMA380 from Bosch follows a much more advanced approach: The small sensor measures the sound waves coming from the tires on the road surface. This vibration data makes it possible to calculate and emit corresponding inverse sound waves that cancel out the noise via the vehicle’s speaker system before it reaches driver and passengers. Let’s take a closer look at this fascinating technology.

“With no running engine, other noises dominate the soundscape in the cabin of electric vehicles – the noise of the tires on the road surface being the loudest. The SMA380 road noise cancelation sensor from Bosch offers an efficient and light-weight alternative to noise dampening materials.” Sabrina Reuter, Project Manager in MEMS development

Latency is one of the key parameters for active noise cancelling in automotive applications. This is where Bosch’s SMA380 3-axis acceleration sensor with low latency comes into play. The sensor efficiently measures the noise level by registering the sound waves close to the wheels and providing the data to corresponding systems. These can then calculate the overall frequency of the noise and emit the inverted frequency at exactly the same time the road noise reaches the vehicle cabin.

The SMA380 accurately measures low-g vibrations with a latency of about 100 µs. This latency allows the system to transmit acoustic data from all four wheels very fast and helps send the necessary counter-frequency just in time. Besides its low latency, the SMA380 comes with a small footprint of only 2.3×2.8 square millimeters, which provides for easy integration into the vehicle, and features a high temperature stability of -40–125°C.