BMW Active Sound Design makes diesels purr

The boffins at BMW are trying their hardest to make the dreaded diesel “knock” a thing of the past.
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Active Sound Design was initially fitted to a petrol-powered MINI prototype last year, allowing the four-cylinder engine to sound like a straight-six or even a high performance V8.

Now the Bavarians have applied ASD to a BMW 635d test vehicle, optimising the car’s audio character for a sportier, more dynamic sound across the rev range.

ASD works by refining the natural sound of the engine with an electro-acoustic system. Based on continually updated engine and driving data, a digital signal processor creates additional sound components for a more audibly pleasing and harmonious overall impression.

BMW manager for airborne sound, acoustics and vibrations, Albert Kaltenhauser, said the latest developments allow high performance diesel engines to sound as good as they drive.

“Today's diesel engines are capable of a lot. They're efficient, highly effective and high-torque, but until now they were lacking the right sound. With Active Sound Design, they're finally achieving the sound that they deserve based on their performance characteristics,” he said.

BMW has carried out numerous experiments placing test drivers in two identical cars: one with ASD and one standard. The sportier sound created by the ASD-equipped vehicle convinced many drivers that the car accelerated harder, was more fun to drive and had better performance and enhanced driving dynamics over the standard diesel.

The reality is a car with identical driving behaviour and equivalent fuel consumption.

BMW has a team of sound designers, engineers, physicists and psychologists developing ASD and has found maintaining authenticity the greatest challenge, as the human ear is very precise and has a fine line between what is satisfying and what is undesirable.

“Even minimal changes to vehicle sound can have a big impact, since human hearing subconsciously evaluates acoustic surroundings like a high performance analyser and all changes are continuously registered in the brain.”

BMW is not alone in its pursuit of noise control, with General Motors already applying active noise cancellation to its 2.4-litre Chevrolet Equinox to reduce low-speed booming sounds.

Given that the current alternative is significant powertrain re-engineering, expect systems like ASD to become a light-weight mainstream solution for the not-too-distant future.