Audi has already set a high standard in terms of in-car audio systems through collaborations with premium suppliers Bang & Olufsen and Bose. Now its development engineers are looking to usher in the next revolution of in-car hi-fi with the Audi Sound Concept. To help bring a physical principle called "wave field synthesis" to the automobile, the company has crammed a standard Audi Q7 with 62 speakers - five woofers and five tweeters plus 52 mid-range speakers.
Wave field synthesis is a spatial audio rendering technique whereby “artificial” wave fronts are synthesized by a large number of individually driven speakers. Such wave fronts seem to originate from a virtual starting point and, unlike traditional spatialization techniques such as stereo, the localization of the virtual sources doesn’t depend or change with the listener’s position. In other words the entire interior of the car would be a “sweet spot”.
Wave field synthesis goes to the movies
One of the driving forces in the field of wave field synthesis is the Fraunhofer Institute for Digital Media Technology (IDMT) in Ilmenau, which first demonstrated that wave field synthesis can be made to work in a real-world application at the Linden Lichtspiele Cinema. Each of the 192 individual speakers at the movie theater is driven separately by a fast computer – at the precise moment in which the virtual wave front would pass through its point in space. Some signals are delayed by milliseconds, depending on the location of the speaker. The result is that each moviegoer experiences perfect audio spatialization in optimal sound.
The product name for the technology developed by IDMT for the cinema is Iosono. Since there are no Iosono-encoded feature films yet available, audiences can only experience the full potential of the technology by watching an Iosono-encoded trailer titled, Creating Waves.
Looking to bring wave field synthesis technology to its automobiles, Audi began its development work in collaboration with IDMT five years ago. The current status of the project is the Q7 prototype, which is parked in a workshop.
Most of the Q7’s luggage compartment is taken up with a powerful amplifier and thick cables that connect it to three PCs. The 62 speakers installed in the car include five woofers and five tweeters plus 52 mid-range speakers in the instrument panel beneath the windshield, in the roof pillars and in the doors. Five units are integrated into each door sill, with specialists needing to make cutouts in the sheet metal, fabricate new bezels and lower the interior door release handles to fit them all in.
As with the Iosono cinema system, Audi can only enjoy the full potential of the system using specially created wave field audio media because there is no corresponding audio media available on the market. The media used to demonstrate the system comprises up to 32 tracks, with specific spatial information for each of those tracks. Although a few film studios are already producing films using wave field synthesis says head engineer of the Audi Sound Concept, Peter Gleim.
When Gleim plays the sample a sound like a thunderhead issues from the speakers – a mix of music, traffic noise and animal sounds. A female narrator guides the listener through the acoustic hubbub, dancing past the listener on the right and at other times on the left. The whole time the listener’s ears are surrounded by the sounds of driving cars and roaring lions. A marching band seems to march from side to side through the Q7 before finally a helicopter flies a lap around the cabin below the headliner.
Everything old is new again
Wave field synthesis is not dependent on special material to demonstrate its strengths, however. It also coaxes entirely new acoustic images out of conventional stereo signals. As Gleim explains, “We can simulate any wave front. With stereo, we can generate a sound as if the two speakers were located far outside the car. And we can also add any desired spatial impression computationally – not as a sound effect, but as a mathematically precise simulation.”
Gleim demonstrates this with vocals seeming to come from far off to the left, seemingly from the corner of the workshop, and a guitar coming from the opposite side. This impression remains wherever the listener is seated in the Q7.
Not an optional extra just yet
Don’t expect a wave field synthesis sound system to be offered as an optional extra in your new Audi for a while yet. “Our goal was to show what is technically feasible; to explore the limits,” explains Denis Credé, Head of Sound Development at Audi. “What we are learning will be integrated into the sound systems of tomorrow. It’s like with racing: A lot of what is first tried out on the race tracks of this world later shows up in modified in production vehicles. The Audi Sound Concept project is like racing for sound systems.”
Until then audiophile Audi drivers will have to make do with the Bang & Olufsen advanced sound system comprising 14 active speakers, including two acoustic lenses with anodized aluminum grilles, and 1,100 watts of amplifier power.
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