Whether they’re driving cars or someday relaxing in autonomous vehicles, people are seeking better sound quality for their infotainment options. Automakers are responding by adding more speakers and increasing their power while exploring noise cancellation, high efficiency amplifiers and alternative speaker technologies.

Two or three dozen speakers are now being designed into luxury cars, and some infotainment system offer 1000 W of power, rivalling the performance of home entertainment systems. Continental has even developed a concept system that eliminates the bulk and weight of speakers, using certain surfaces in the vehicle to resonate sound.

This technology, as well as advanced designs that use conventional speakers, involves many factors. Pricing, volume, weight and vehicle acoustics complicate the engineering challenge for those creating radio head units and speaker systems.

Noise cancellation focus

Engineers at Tier 1 suppliers are taking a more holistic approach to blend these factors into systems that fit power and pricing budgets, often working more closely with automakers. Tool developers including COMSOL and Siemens are helping engineers better understand how all factors work together.

“3D modeling and prediction has advanced to a point where we can start to predict performance of a transducer, especially in low frequencies,” said Brad Hamme, Senior Manager of Acoustics at Harman. “This, combined with more collaboration with OEMs, has allowed us to predict the performance of a transducer as heard by all occupants of a vehicle. As we move towards the system goals of less mass, better vehicle integration, and increased sound quality, we can predict and then propose unique solutions that help reduce compromises to sound quality based on traditional packaging constraints.”

Vehicle cabins pose complex challenges as engineers attempt to match the sound quality of home entertainment systems, since engine and road noise cause substantial disruptions in audio quality. Electronic technologies are increasingly augmenting sound deadening materials.

“The noise cancellation technology specifically focuses on these two types of noises to bring overall noise effect down in the cabin, giving more clarity to both in-vehicle communication between passenger, as well as audio play back from the sound system,” noted Bijal Joshi, Software Engineering Manager, Voice Solutions, at Continental Infotainment & Connectivity. “Reducing this noise also helps reduce passenger fatigue that can be experienced by extended exposure to the road noise.”

Noise cancellation is among many areas in which electronic technologies are changing demands for physical components. The amount of sound deadening material that add bulk and weight can be reduced by using noise cancellation, often with better results.

“Wind, engine, and road noise are all part of what makes audio systems more difficult to get right,” Hamme said. “Combating them with direct cancellation instead of a traditional masking approach yields greater sound quality.”

Mass and packaging solutions

Weight is also a factor that might prompt a transition to next generation audio amplifiers. Many home audio systems have used Class D devices for years, but cost has limited their acceptance in mainstream vehicles. Class D amps use output transistors as switches to control power distribution, making them more efficient than traditional Class A and B designs. That efficiency also reduces heat, which is a problem for commonly-used amps as automakers strive to lessen weight.

“Class A and B components will remain a less-expensive solution,” said Bill Cleaver, Principal Engineer at STMicroelectronics. “The thing you lose with Class A and B is weight. You need to add the weight of a heat sink. Class D lets you get more power to the speaker without a heat sink.”

Audio amps also come into play when acoustic engineers are deciding whether to go with a few powerful speakers or distributing several smaller speakers around the cabin. That’s another factor that’s prompting developers to place more emphasis on a system approach to audio design.

“Manipulating voltage can allow for more efficient speakers which then have greater output per transducer,” Hamme said. “We also have arrays of smaller transducers which can be packaged in more unique ways compared to a single large transducer."

He explained that better vehicle integration also helps his team optimize their systems designs, whether due to a sealed integrated enclosure or less body rattle from integrated support built into a transducers frame, for example.

Looking into the future, design teams are looking at techniques that reduce or eliminate these speakers. High quality sound can be generated by vibrating specific surfaces in the vehicle.

“There are new approaches of producing sound inside the car by using large surfaces,” Friedrich said Jens Friedrich, Acoustics Engineer at Continental Engineering Services. “Additionally, new algorithms will also improve the overall sound quality. The approach of using surfaces inside the car as panel speakers will help to reduce the amount of parts due to large surfaces that radiate sound.”