All about acoustics

How do define ‘perfect sound’ and just as importantly, how do you reproduce it inside a vehicle? For the team at the Audi sound lab, that is the task they are faced with as they seek to work around the obviously physical constraints of a vehicle’s interior and create an environment where the occupants can enjoy optimal sound reproduction, regardless of which seat they occupy within the vehicle.

To do this, they must first calibrate their ears, align them to the perfect sound of a musical composition under optimal conditions in the reference listening room – a place that has been meticulously designed according to ideal acoustic parameters.

They then do the same inside a vehicle, to check whether he and his team have succeeded in transferring this perfection to the sound system of an Audi.

But how do you define perfect sound in the first place? According to Klaus Brummet, Head of Sound Development and Infotainment Design at Audi.

“No highs that are too sharp, no bass that is too boomy. But still precise, of course, the timing must be right, you must be able to hear the exact sounds,” says Brummet. 

“With clarity, brilliance and a certain transparency. A musical composition with many instruments and vocals should not be a meaningless mixture of sounds, but your ears must be able to differentiate and assign each and every single one of them. Can I differentiate between different voices, can I hear individual people sing?”

But achieving a sound as perfect as possible inside a car is a challenge for the Audi sound specialists: “Because the interior of a vehicle is anything but acoustically optimal,” Kluge explains. “Too many smooth surfaces, too many reflections.”

But there are some benefits, too, Klaus Brummet points out: “We know exactly where the listeners are sitting, we can define exactly where the loudspeakers are located for best listening pleasure, and we can tune the sound precisely to that. That’s why our claim is – In your Audi, the listening pleasure is better than in your living room at home. We can precisely harmonise the acoustics inside the vehicle and ensure that the full richness of detail of a musical composition becomes audible and can be properly enjoyed.”

When first defining a vehicle concept, Brummet and his colleagues have to pay attention to ideal acoustic conditions: Where are the loudspeakers located, how are they placed in relation to the windshield, how are they angled, does a head-up display perhaps take space away from a tweeter, is there an optimal positioning for the subwoofer for an ideal sound inside the vehicle so it will trigger the desired emotions?

This concept lays the foundation for the sound experience inside the vehicle, but the experience ultimately thrives from the fine-tuning of the interior, perfected in the Audi sound lab. After all, the sound from the 18 loudspeakers must be as good in the passenger seat or the back seat as it is in the driver’s seat. To achieve this, it is precisely defined which individual loudspeaker sends a certain signal with a certain delay and at a certain level, so that an overall sound image reaches the ear that naturally reproduces all frequencies authentically with rich and high-quality acoustics.

Two key Audi partners are involved in this tuning process: the high-end sound specialist Bang & Olufsen and the Fraunhofer Institute for Integrated Circuits IIS in Erlangen. Both partners work for several weeks per vehicle model to fine-tune the sound in the interior.

After linearising the loudspeakers via the speaker management system, the Bang & Olufsen specialists adjust each individual loudspeaker in an entertainment tuning process in a way that, without a surround algorithm, a 2D sound will precisely reproduce the sound impression from the reference listening room inside the vehicle.

The sound engineers from the Fraunhofer Institute then make individual adjustments to the spatial effects for each sound system in each vehicle. Using a patented algorithm, they filter out spatial information from the music tracks, output it via the treble and surround loudspeakers, and can thus increase the intensity of the track’s spatial impression. They call it up-mixing to 3D sound.

The goal of all these efforts: to create the most immersive sound experience possible, a soundscape that engages listeners from all directions – making you feel that the interior of the vehicle seems significantly higher and wider than it actually is. 

Klaus Brummet disappears briefly into a sound chamber and returns with a curved headrest. Two integrated loudspeakers can be seen behind the perforated surface. “It’s a preliminary design”, he reveals: “When the sound comes right from the back of your head, you start to feel light, as if there were no headrest behind you, as if you were in a free space.”

You could also transfer phone calls and navigation instructions to these speakers, which would then be separated between the driver and front passenger and heard only from the headrest. This would be the first step for individual audio zones per seat – another innovation that could be much nearer than you think.