Audio testing with Harman’s Golden Ears
04 November 2017
Perfecting the acoustics of automotive interiors is a complex process. Harman’s acoustic engineers explain why it still requires a human touch.
There’s an irony when it comes to in-car audio. Automotive interiors are a notoriously challenging environment in which to deliver high quality sound, yet that’s where a lot of us spend the most time listening to music.
The job of designing and developing car audio systems for some of the world’s leading brands falls to the acoustic engineers at Harman International. They’re the brains – and the ears – behind names like Bang & Olufsen, B&O PLAY, Revel, Bowers & Wilkins, Harman Kardon, JBL, Canton and Mark Levinson.
Grzegorz Sikora, Senior Manager, Acoustic Systems Engineering Europe, Car Audio at Harman International said, “a car audio system has to cope with a lot of different challenges. It’s by no means an easy job. Something as simple as changing the seat material or the interior fabrics can alter the acoustics on an otherwise identical cabin, which means sound tuning for each model has to be crafted individually. Not only that but the audio system must sound right across all seats within the car and under all driving conditions. Sound experience has to be consistent, whether the car is moving or stationary.”
For the Harman car audio team and OEMs, it takes several years to develop a sound system. All components must be selected to fit a specific audio brand, the car brand and the car type. Placing loudspeakers in the car is a challenge in itself. For example, the positioning of tweeters is governed by a very different set of rules to the positioning of woofers and subwoofer. Acoustic engineers collaborate very closely with transducer engineers and mechanical designers to find optimal positions. This can even lead to some significant changes to the vehicle. It’s not unknown for the team to request changing the type of material used in the doors.
After many iterations, simulations, discussions and evaluations, the engineers receive a first prototype of the car, including sound system, around a year before production. At this point Harman engineers have to check all the system’s components and the car’s mechanical integrity, ensuring that all hardware is suited to the specific car.
“When we first get access to the pre-production prototypes, our priorities are to check the design and capability of the system. At this stage, the sound system is like a block of marble, waiting to be sculpted and reveal its final sound,” explains Sikora. “Around six months later we will then get the car back for another three weeks to continue the development.”
In general, sound system design happens at the crossroads between engineering and art. However, at the beginning, it’s almost purely an engineering process. Firstly, the bulk of the tuning is carried out by a computer-aided sound tuning suite, developed in-house by Harman. During the process, several hundred parameters are set based on the a-priori knowledge of the electro-acoustical parameters, targets and cabin sound field simulations. Harman engineers place approximately 6-12 microphones around the main listening positions in the car. The vehicle’s speakers are then fed with a specifically designed series of pulses, tones and noises, which the system picks up via the microphones. Analysing this data, the software can calculate the optimal frequency spectrum for individual speakers and the best levels for the various channels, within the boundaries set by engineers.
“We design sound systems for the pleasure of our human auditory system. Contrary to a popular belief, the mechanism of our ears is not so optimal. The majority of hearing and sound interpretation happens in our brains that makes up for deficiencies of ear mechanics. Therefore, the human factor of the process is vital since the scientific progress of modelling our brain is not up to this task yet,” comments Sikora. “With a computer-aided sound tuning suite we can dramatically cut down the time taken to reach a starting point through objective measurements, giving the engineers more time to focus on the details and making sure they won’t strain their ears. The final tuning is best crafted manually – it’s a design process.”
Harman engineers who carry out this work have earned the nickname ‘Golden Ears’ among their colleagues. Each one undergoes years of academic and on-the-job training to ensure they’re able to pick up on minute differences in acoustic properties. One of them, Stefan Varga, is responsible for the design and development of B&O PLAY sound systems for Ford, with the latest recipient of this meticulous tuning exercise being the B&O PLAY Sound System in the all-new Ford Fiesta. Due to debut later this year, it’s the first product of Ford’s recently announced partnership with Harman International.
As with all Harman-developed systems, the 10-speaker B&O PLAY Sound System set-up has received hundreds of hours of development and fine-tuning so that it delivers a bold sound experience that’s unique for a car in this category.
“Reproducing the signature of the B&O PLAY sound experience in a small car is a challenging task,” comments Varga. “We have to ensure that the system integrates perfectly and that the sound meets the acoustic properties of the cabin. It has to deliver a consistently high sound quality whether you’re commuting through the city or cruising down a country road. We visit OEM test tracks and lots of different roads with varying surfaces. The speed, number of passengers in the car, type of engine and tyres, and even weather conditions all affect the audio. Even lowering a window can have a big effect. It all needs to be considered and adjusted for.”
Not only do sound systems have to work across a wide range of conditions, they also have to deliver optimum sound quality for any type of content. The Harman engineers evaluate each system for a variety of different musical genres, not to mention radio play and podcasts. To a certain extent, the choice of samples is a matter of the tester’s personal taste but they’re also chosen to reflect the vehicle’s demographic.
“We have a standard selection of music but each engineer has ‘go to’ tracks,” says Varga. It’s crucial for each engineer to know every track that is being used, he explains: “There are several things that we look for in a piece of music. We evaluate these things in a controlled listening environment and learn how they sound as a reference. There might be a very precise staging and localisation of instruments or sounds, a unique sounding singer, a natural and big sounding orchestra or simply the mono voice of a radio play. I also like to use pieces I recorded myself, as I know them very well.”
Almost every conceivable genre of music is covered, ranging from hip hop to classical. In the case of the Ford Fiesta, the engineers spent a year listening to more than 5,000 tracks to ensure the premium 675-watt technology sounded great whether enjoying Adele, Foo Fighters, Jay-Z or chilling out to classical music, no matter how quietly or loudly it’s played.
Each model is the product of years of design collaboration with the car manufacturers and months of hands-on work. More importantly, it’s also the result of decades of cumulative experience within Harman; sophisticated development tools may help to streamline the process, but ultimately it comes down to the skill, precision and experience of sound designers.
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