You may own a pair of Bose QuietComfort noise-canceling headphones or earbuds. You may also be aware that Bose has been helping manufacturers trim the mass and cost of isolating powertrain noise by letting the vehicle's audio speakers broadcast out-of-phase sound waves that cancel powertrain noise the way headphones eliminate white noise on airplanes. Bose is now taking on the much tougher task of canceling road and suspension noise with a system called QuietComfort Road Noise Control.
Nothing's easier to cancel than white noise in an airplane. It doesn't vary all that much so it's predictable, easily measured, and the speaker doing the canceling is right next to your ear. Engine noise varies a lot but is similarly predictable with fully electronic engine-control. The sound of a single bump has probably hit your ear long before a microphone could measure it and order up an opposing sound. But chassis noise sources are more predictable, like those generated by the tires and transmitted—perhaps exciting other new and predictable resonant frequencies in components between the tire and the cabin. Rubber hitting the road generates continuous tones that rise and fall with speed. And while they may vary widely on different road surfaces and conditions, the sound made from one microsecond to the next can be predicted and canceled. Gm Flexplate
Every vehicle is one big matrix of compromises, and Bose is pitching QuietComfort Road Noise Control (RNC) as a cake-and-eat-it means of reconciling tradeoffs like: Quiet interior versus costly/heavy sound deadening, and sharp handling dynamics with rigid-mounted subframes and firm bushings versus the quiet, smooth ride isolation of squidgy bushings. And of course, cost figures into all such tradeoffs.
As challenging as it is to predict road noise, it's even trickier to project how much your trick noise-canceling tech will boost sound quality and/or handling. So Bose enlisted the aid of Ricardo Engineering to explore and quantify the potential benefits QuietComfort Road Noise Control.
Three vehicles were purchased, the sound and dynamic handling attributes of each were quantified, then each was modified and evaluated again.
Four reference builds were engineered for each vehicle. Three focused on differing primary objectives, to illustrate best-case scenarios for when Bose gets involved early in the design phase. A fourth build shows what's possible when adding RNC to an existing vehicle, or when brought in quite late in the design process.
Broadly speaking, vehicles heavily optimized for quiet refinement generally offer the greatest cost and weight savings via RNC, while also deriving the greatest ride/handling improvement (because these attributes have often been sacrificed in the name of quelling noise, vibration, and harshness—a.k.a. NVH).
Other design choices heavily impact the savings RNC can achieve, including: Steel versus aluminum subframes and suspension components, isolated versus rigid subframes, size and packaging of bushings, and use of tuned absorbers and/or acoustic tires. The chart shows the specific savings, which can be as great as $133 or 14 kg (31 pounds), or as much as a 2-point (20 percent) improvement in ride/handling attributes.
Because Ricardo has consulted for numerous OEMs and benchmarked myriad vehicles, it's able to take the results from these three tests, and—based on known body and chassis characteristics of other vehicles, project how much cost or weight RNC could help eliminate from other vehicles.
A big QuietComfort RNC advantage is that it never "wears out," whereas quelling noise with sound-absorbing, foam-lined "acoustic tires," for example, runs the strong risk that these tires will be replaced by cheaper, noisier ones that reduce customer satisfaction. With RNC, when the owner replaces tires (or shocks, or other wear items), the sound-sampling nature of RNC should automatically cancel the new and different noise.
None of these three vehicles featured a factory Bose audio system, nor were any stock speakers replaced. But because road noise occurs at very low frequency, the team needed to add subwoofers in some cases, and because of the size of most passenger compartments, RNC usually needs one under the passenger seat and one in the cargo area.
We got a chance to take a ride in an RNC upgraded Tesla Model 3 with firmer bushings, reduced passive sound-deadening, and two Bose subwoofers added to the seven stock speakers. It featured an on/off switch to gauge the difference RNC makes. We were cautioned not to expect the same effect as switching headphones on and off, and indeed the difference is WAY subtler than that. Tire-slap noise on concrete (a 30-40 Hz frequency) was quite effectively eliminated, but as expected, pothole noises were unaffected. Noise-level differences on most other surfaces were difficult for aging ears to discern, and there was no opportunity for before-and-after handling comparison, but we're assured the steering is sharper and there's less body roll in quick maneuvers.
Ls7 Harmonic Balancer Parts added to the bill of materials are minimal—some microphones in the cabin and wheelhouse areas, and possibly some subwoofers. If consulted early enough in the design process, Bose contends the licensing, development, and parts costs may be offset by materials that are no longer needed. Bose is actively talking to OEMs ( and we should note that Tesla is not yet a customer). If one of them signed up today, a two-year clock would start ticking before you'll be able to have your handling cake and eat it (in peaceful quiet).