Audi adopts wave field synthesis in audio prototype
Audi has already set a high standard in terms of in-car audio systems through collaborations with suppliers such as 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 synthesised by a large number of individually driven speakers. Such wave fronts seem to originate from a virtual starting point and, unlike traditional spatialisation techniques such as stereo, the localisation 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”.
One of the driving forces in the field of wave field synthesis is our old friend, 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.
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.
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 Peter Gleim, the head of the experiment 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.”
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.