Music/Sound Without Speakers Like Violin for Automotive Reduces Weight

Inspired by the functional principle of string instruments, Continental claims it is reinventing the car audio system. The international technology company is replacing conventional loudspeakers with actuators that create sound by vibrating certain surfaces in the vehicle. In comparison to conventional speaker technology, the speaker-less audio system brings many advantages. The company calls the technology Ac2ated Sound.

At considerably lower weight, with dramatically reduced box volume and lower electricity consumption, the new Continental solution delivers excellent acoustics and a totally new sound experience. Experts such as the renowned Landsberg-based master luthier and graduated physicist Martin Schleske have given the sound system top scores for its performance.

By bringing speaker-less sound into vehicles, Continental has taken up a challenge. Irrespective of the vehicle segment, drivers’ expectations towards car audio systems are usually very high. This is the reason why current audio systems typically require many speakers to deliver 3D sound through many channels. From a design point of view, it is not easy to integrate these many point sources.

“In the age of electric vehicles, car manufacturers are looking for innovative solutions to drastically reduce the weight of their vehicles and gain space for passengers and new technologies. On the other hand, design and sound quality should not suffer from this goal,” said Johann Hiebl, head of the Continental business unit Infotainment and Connectivity. “Our approach is to treat the car itself as an instrument. We use compact actuators to excite suitable surfaces to generate a natural, 3D sound experience. The challenge lies in the profound understanding of NVH in the widest sense, which is required to achieve excellent acoustics. Typically experts have either the vehicle expertise or the acoustics expertise. Continental has both in-house plus the manufacturing know-how.”

In direct comparison to a conventional high-end vehicle audio system, a speaker-less solution can reduce the system volume by a factor of ten or higher, while bringing down the system weight to a fraction of a speaker solution. The invisible car audio technology can be integrated into any car model from high end sedans to small electric vehicles.

The mix of tweeters (high frequency speakers), midrange speakers and subwoofers, which make a conventional high-end car audio system, frequently interrupts the original interior surfaces with the typical look of a speaker front.

“It is not necessary to integrate speakers with oscillating membranes when you have all the surfaces you need to do the job already in the car,” said Dimitrios Patsouras, director competence center NVH at Continental Engineering Services. “The rationale behind this invisible audio system is to avoid this kind of duplication and utilize existing components for even better results.”

The sound waves are generated by compact actuators, which are similar to the core of a conventional speaker. These transducers consist of a magnet and a coil that generate micro-vibrations. However, instead of an oscillating membrane which is part of a current speaker, larger existing components and surfaces in the vehicle are excited by the transducers to radiate the sound.

“If you take a violin for comparison, the bow and strings are the transducer. The violin’s bridge equals the location and bonding of the transducer to the surface which equals the instrument body,” Patsouras said. “Specific areas in the vehicle lend themselves to each of the required three main frequency ranges. The A-pillar is suited for high frequencies, while the door panels have the right properties for generating medium frequencies. Similar to speaker technology, we use large components such as the roof lining or rear shelf to generate low frequencies.”

To achieve a good 3D sound, conventional high-end car audio systems can easily require between 10 and 20 or more speakers. With a conventional speaker design, this gives the system a weight of up to 33 pounds and a total box volume of 10 to 30 liters. Continental’s speaker-less audio system can weigh as little as two pounds and requires as little as one liter of total box volume.

“The main benefit is the quality of the sound. Even experts listening with an astute ear have given us the highest praise for our invisible system’s acoustics,” Patsouras said.

In a demo vehicle, Continental is also presenting the scalability of the system by switching between an entry-level low-cost system using three audio channels, a mid-system using four to six channels and a premium solution using up to 12 channels. In doing so, the front seats are used as sound bodies to intensify the bass experience and to provide passengers in the rear seats with a totally new audio experience. Continental’s speaker-less audio system can easily be compared with a high-end speaker solution from a premium manufacturer.

Speaker-less technology offers further potential beyond car audio. It can also provide a sound source for human-machine interaction concepts, such as navigation instructions or the indicator sound.

“Speaker-less technology can also be used for sounds as part of the human-machine interaction concept with the added benefit of generating the sound where the driver’s attention should ideally be,” Patsouras said. “We see great potential for the speaker-less system as a part of functional audio concepts.”

Continental will also demonstrate its multimedia products during the International Motor Show, IAA in Frankfurt/Main