Chevrolet Malibu engineers are all ears

(August 11, 2011) MILFORD, Mich. — A room full of audiophiles may not agree on a single style of music, but most concur that ordinary MP3 player ear buds don’t have the technology to deliver concert-quality sound. Likewise, Chevrolet noise engineers threw out conventional tools to evaluate the interior sound quality of the all-new 2013 Malibu sedan.

In the intensely competitive midsize car segment, customers expect refined, quiet interiors. The challenge for engineers is that sound – like music – is very subjective, and people respond to it differently. “To tune the sound properties to appeal to the widest possible audience, we need to make sure everyone hears the same thing,” said Kara Gordon, Malibu’s lead acoustic engineer.

Gordon and her fellow engineers are using better sound reproduction in the lab to help make the 2013 Malibu sedan one of the most refined and quiet midsize sedans available when it launches early next year.

They are doing this by equipping pre-production Malibus with a mannequin-like recording device called an Aachen HEAD. Named for the headquarters of Head Acoustics GmbH in Aachen, Germany, the head is a digital recording tool that closely matches the way humans process sound with both their ears. The Aachen HEAD technology preserves the binaural attributes of the sound, regardless of whether it’s inside or outside of a moving vehicle.

The device mimics the head of an average-sized person and incorporates specially calibrated, highly accurate digital microphones in each ear position. The microphones use a precise, 24-bit recording resolution to enable dynamic range equal with human hearing.

The Aachen HEAD is typically belted into the passenger seat or rear seat farthest from the driver. The recordings are made as the test Malibus are driven on a variety of road surfaces at a range of speeds.

At General Motors’ “Jury Room” in Milford, groups of engineers listen to the Malibu’s interior noise recordings and rate them on several criteria.

The Jury Room is equipped with a high-fidelity audio playback system that features Stax SR-303 electrostatic ear speakers. Unlike those little white buds, the large, rectangular Stax units fit over the ear and feature a large, translucent electrostatic film for precise sound reproduction.

The stock ear buds that come with a digital music player can reproduce sounds from a low end of 20 Hz to a maximum of 20,000 Hz, but all audio devices experience distortion as they approach the limits of their range.

In contrast, the Stax ear speakers’ range goes from just 7 Hz all the way up to 41,000 Hz, well beyond the range of the human ear. However, that extra head room means the speakers are always closer to their sweet spot for the sounds we can hear. That means everyone evaluating the sounds of a Malibu or any other Chevrolet hears the same sounds, regardless of which set of ear speakers is used, giving the engineers more consistent feedback on sound quality.

“The typical acoustic memory of the human ear to discern subtle yet important differences is about 10 seconds – or about the time it takes to go from one vehicle to another. The Aachen HEAD, our Jury Room and high-tech headphones make it possible for us to give our Malibu customers the quietest, most pleasing interior sound quality possible,” said Gordon.

The new Malibu will feature components that prevent tire, wind and road noise from entering the cabin. Several components such as noise-reducing outside rear view mirrors, laminated side glass and noise-absorption pads are strategically placed to make the cabin quiet and improve the overall quality inside.