Most passengers like to hum along with the radio on a highway drive. As long as the car isn't humming too.

There are few things more annoying than a high-pitched squeak while driving. As car engines become quieter—with electric engines basically silent—those little hums and whistles from the wind and road become more noticeable.

"Today people want to be able to converse within the vehicle, talk on their phone, get their messages and not deal with the road noise associated with that," said Carla Bailo, CEO of the Center for Automotive Research. "It will continue to increase drastically. And then when you talk about EVs, when you get rid of the sound source (from the engine), all the other noise becomes apparent. Silence is going to become one of the most important things."

One company's problem is another's opportunity. And the solutions required to eliminate cabin noise—specifically seals—fall right in the wheelhouse of rubber product manufacturers.

They're ready for the challenge.

"When the engine becomes quieter by going electric, so many other sounds that we don't even notice because of the regular engine noise become more apparent," Orotex President Ken Miura said through a translator. "We will be able to help. I am certain that our product needs won't be disappearing."

Chris Couch, vice president of innovation and product groups at Cooper Standard Automotive Inc., said data from its customers indicates that, after the engine, the largest contributor to cabin noise is wind noise through the window and glass-run system.

And for sealing suppliers like Cooper Standard, Toyoda Gosei Co. and Henniges Automotive Inc., that's a good thing. Even more so since, beyond the glass-run system, Couch said the inner door weather seal and the side sealing package of the door are the next biggest opportunities—both right in the crosshairs of sealing suppliers.

"There's a lot of opportunity with weatherstrip products," said Joe Mannino, senior vice president of technical at Toyoda Gosei. "They are essential components of vehicles and are one of our core rubber product lines. However, they tend to be looked at as a commodity. In order to differentiate our products from the competition, we look to add value by improving two incompatible properties—weight reduction and sound insulation."

But everything in automotive is a balancing act. Fred Jamieson, vice president of engineering and program management at Henniges, said that while EPDM is the best material to stop sound, it's also heavy compared to thermoplastic vulcanizate alternatives.

Suppliers also have a limited amount of space to work with. If the weatherstrip is too bulky, not only does it affect lightweighting efforts, but it's going to make the door harder to close.

"The difficulty comes in the engineering, making sure those seals mate together properly," Henniges President Larry Williams said. "The closing effort of the door is going to increase when you put more rubber in there. That is something our customers pay particular attention to. They don't want you slamming the door, but they want them to close. That's a big focus right now, trying to reduce the closing effort of the door while increasing the content."

All of them agreed—material science is going to be critical to help balance these incompatible properties. New materials that combine the sound insulation properties of EPDM with the lightweighting attributes of TPVs will win more business.

Cooper Standard released one such material to the market in 2017—Fortrex. The compound provides a two-decibel reduction in noise, which Couch said represents about 50 percent, and is lighter weight than a traditional EPDM.

Weatherstrips produced by Henniges are used to keep cockpits quiet.

"We like this problem because it's part of our sealing product portfolio," Couch said. "Our solution for this involves material science."

Sealing may have stolen the spotlight from the engine, but it's far from the only rubber product that impacts cabin experience. Frank Mueller, CEO of Vibracoustic GmbH, which specializes in noise, antivibration and harshness products like air springs, said reducing noise from the tires interacting with the road is a major focus.

Tire makers are implementing new technology to help quiet their products. A Goodyear spokesman said via email that the firm applies sound-dampening in the cavity and innovative tread and sidewall designs to help quiet the ride.

"Noise frequencies can transfer through the tire itself, the vehicle suspension, the road surface and through the air around the tire into the passenger area," the spokesman said. "Goodyear engineers study lateral grooves in the tread, which produce tones, and the overall tread pattern that may create a pattern noise. They vary the size of the grooves to produce a wide scale of frequencies, minimizing negative recurring tones. Evaluating tread groove widths, angles and other factors leads the engineers to finding the right balance."

Nizar Trigui, chief technology officer at Bridgestone Americas Inc., the American subsidiary of Bridgestone Corp., said in an email that everything that the tire encounters on the surface gets transmitted through the vehicle to impact ride quality.

Bridgestone is developing technology with motion control systems while also enhancing its current products to improve vibration control and reduce NVH.

"Reducing noise within the vehicle is interesting," Trigui said. "The engine provides a 'masking' effect for several other noises contributing to the riding experience, such as wind and road noise and other sounds within a vehicle. Electric vehicles cause riders to notice other sources of noise since the engine sounds are not prevalent, so manufacturers need to create a new level of refinement for all structural and mechanical vehicle systems in these vehicles to improve the riding experience."

Mechanical noise is just one part of the equation. As more technology gets integrated into the vehicle, OEMs have to worry about more white noise intermeshing among the components.

Joe Walker, global technology director, materials and laboratories for Freudenberg-NOK Sealing Technologies, said this kind of noise can still affect the performance of the engine.

"Those have to be isolated and shielded from each other so you don't get destructive interference between the computers and the sensors," Walker said. "It's similar to why they don't want a lot of cell phones to be used inside airplanes."

The problems caused by white noise vary, but Walker said they could be quite annoying. For instance: Whenever the radio scrambles because the car drove under old power lines.

A more extreme example would be if radio frequency interference was allowed to disrupt adaptive cruise control or the car's speed monitoring system, causing a more serious safety issue. Walker said new materials and product designs will need to incorporate shielding technology by modifying the seal to help prevent noise from getting through.

"The way you'd create a material to seal against oil is not necessarily going to be effective at shielding against this electro-interference," Walker said. "It requires new material design, new product design and close collaboration with sub-assembly suppliers so you can make the most appropriate use of these new materials in the application."

And this trend isn't dying anytime soon. Vehicles today are more connected than ever.

"Just look at the explosion that's happened in infotainment that's happening inside vehicle systems now," Walker said. "You have everything from GPS to sophisticated radios, DVDs and internet access. Every vehicle is its own traveling hot spot. I think we'll see that the demand for these more sophisticated materials and designs will continue to grow. It's not just being driven by fully electric vehicles."

As more electric vehicles reach the road and the industry grapples with automated vehicles, one thing is clear—passenger's needs will shift.

"Driving an electric vehicle will intensify your senses in terms of what you're going to realize when you drive," Mueller said. "It's going to be a different kind of driving. It won't be focused on the sporty handling, it's going to be more about the comfort about going from Point A to Point B."

Which makes a quiet cabin all the more necessary.

Fully electric vehicles, like the BMW i3, will have less engine noise, making wind and road noise more noticeable and increasing the need to reduce them.

"If you don't have a steering wheel, the perception of performance changes," said Shashank Modi, research engineer at CAR Group. "Today, performance is what's the acceleration from zero to 60 and how does your car handle. But in the future, performance may be what's your comfort in the interior, how quiet is the interior. NVH could play a big role and I think the market for rubber sealing will be very positive in the future."

Couch said while OEMs have talked about quieter solutions, and companies like Cooper Standard are delivering them, car makers have not changed their specifications yet. He added that Cooper Standard believes that will come in time, with or without autonomous technology.

Even if the industry never reaches the extreme of automated vehicles, engines are getting quieter, electric powertrains have reached the market and more technology inside the cabin will continue to make silence a priority.

"The interior is one of the most important factors when choosing a car," Mannino said. "As automation becomes more common and autonomous vehicles become a reality, what we do and how much time we spend in the vehicle will change. This will make the interior and cockpit experience more important."

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