Optimizing the Driver Experience With Active Noise Cancellation

Downloaded audiobook — check. Podcast — ready to go. And then your end customer hits the highway and has to turn up the volume high enough to risk blowing an eardrum. In short, another driver/passenger experience takes a hit due to road noise.

As in-vehicle capabilities grow increasingly sophisticated, the need to tackle road noise becomes even more crucial.

Bringing Peace and Quiet to the Cabin

Active Noise Cancellation Technology Diagram

Active Noise Cancellation Technology Diagram

Active noise cancellation (ANC) technology has been around for several years and makes vehicle passenger compartments noticeably quieter. By negating noises that are constant or predictable, whether originating from the vehicle interior or exterior, the system can broadcast cancellation wave forms via the vehicle speakers to cancel the unwanted noise.

One example of unwanted noise is the sound created by tires rolling on the road surface.  This sound is impacted by the tire design, materials, pressure and wear, as well as the road surface itself. Today’s improved noise cancellation applications use a plethora of accelerometers and microphones to capture the input signals in order to generate a real-time reference wave form that can be inverted to cancel the unwanted noise. Sensors can be mounted along the noise transfer path in various locations around the vehicle: along the interior or exterior of the passenger compartment, on the under body or under the hood, virtually anywhere unwanted noise may be initiated. In the case of tire/road noise, sensors would be mounted on the subframe near the suspension points where the vibration energy would enter the vehicle structure.

Molex’s Rugged and Effective Noise Cancelling Solutions

Molex Road Noise Sensor

Molex Road Noise Sensor

Molex Road Noise Cancelling (RNC) Sensors are designed to meet the stringent needs of various harsh environments. Our exterior- mounted sensors, such as the RNC Sensors, are design for an IP6K9K rating according to the ISO20653 specification, salt mist/water exposure, and impact loading, making them especially suited for the underbody mounting conditions.

The Molex family of accelerometer sensors are designed around low noise floor accelerometers that enable them to sense a lower energy level vibration or movement. This correlates to the accelerometer sensing vibration noises at very low speeds of vehicle movement. The yellow blocks in the following image show the region of the wave form that would not be captured by other accelerometer technologies.

Yellow indicates the region of the wave form not captured

Yellow indicates the region of the wave form not captured

It is important to have the sensors mounted as close as possible to the noise source. Once an excitation is sensed by the sensor, there is a race to get the input through the processing unit to the speakers and broadcast the cancellation sound to reach the occupant’s ears by the time the excitation travels through the vehicle sound path to reach the occupant. As an example, it may take only 0.009 seconds for the sound of the tires to reach the occupant. Molex uses its extensive sensor mechanical housing experience to design various packages to fit the mounting locations necessary throughout the vehicle to get as close as possible to the noise source.

Collaboration Between Molex Sensors and Analog Devices’ A2B Technology

The Molex family of sensors utilize the Analog Devices’ (ADI) Automotive Audio Bus (A2B) technology, which is a cost-effective, low latency networking technology allowing the digital signal to be transferred from the sensor to the processing unit in under 0.002 seconds thus providing time for processing and broadcasting of the cancellation sound.

Molex RNC Sensor System Latency is less than 150µs

Molex RNC Sensor System Latency is less than 150µs

A2B technology efficiently connects up to 32 input channels to the central processing unit. A channel can be understood as one axis of an accelerometer or one microphone sense element.  This allows a plurality of Molex RNC Sensors to be connected in a chain, allowing coverage of a large sense area. This also reduces the amount of cabling needed to connect the sensors to the processing unit, reducing wire harness costs and weight.

Molex RNC Sensor’s Daisy Chain Harnessing Compared to Competitor’s Home Run Harnessing

Molex RNC Sensor’s Daisy Chain Harnessing Compared to Competitor’s Home Run Harnessing

The Molex family of RNC sensors also utilize technologies that maximize the resolution of the data file. The combination of the sense element technology and the network provides a higher sample rate and precise measurement points, thus delivering more accurate data to the processing unit to have a better representation of the original noise source.

Sensors focused toward active noise cancellation are an important piece of the system’s overall efficiency.  With sensors that capture the noise close to the source, regardless of the location, and the capability to transfer the data signal quickly and accurately, the Molex family of RNC sensors are positioned well to reduce unwanted noise and improve customer satisfaction.