The delicate sound of silence

I once had a rattle in my A4 Sedan that drove me mad until I found its source. The car had been as wonderfully quiet as every other Audi I’d ever driven when it arrived brand new from Ingolstadt, but one day, inexplicably a faint rattle started up somewhere over on the front passenger’s side. After much investigation, stopping, starting, maintaining certain revs as well as emptying the glovebox looking for a culprit, I eventually found a hardened butter-menthol lozenge that had somehow found its way in behind the actual glovebox bin. Needless to say I blamed the kids, removed the offending lozenge and went back to the blissful interior I had enjoyed from the start.

The relief at having found the culprit was palpable, so imagine the immense job satisfaction felt by the members of the offical Audi ‘Rustle and Rattle team’ – those individuals charged with ensuring that each Audi model is delivered without so much as a hint of a squeak or rattle anywhere.

This dedicated team of acoustic professionals leave no stone unturned in ensuring that the celebrated Audi interiors are not disturbed by unidentified sounds that could otherwise cause untold frustration.

It’s all part of the exhaustive testing regimen at Audi that includes subjecting cars to the rigours of extreme temperatures and conditions as well as conducting literally millions of kilometres of on-road testing.

The search for the cause of an unidentified noise can lead the team through the entire vehicle. A noice that might start at the front of the car, can be carried back via components of the car and only be audible at the C-pillar. In addition to this sort of search, the team has to detect critical material pairings, obstruction problems and the effects of aerodynamics in order to localise acoustic disruptions.

The team’s insights can have wide-ranging impacts, sometimes leading to changes in component quality while at other times they might discover production errors. When necessary, they turn to specialists from other fields like production or engine and transmission development for assistance in tracking down a sound and as well as their own experience and expertise, the team use a range of special equipment in their work.

Vehicles are driven on special vibration tracks with different uneven road surfaces as well as driving in traffic to see how the vehicle responds and what, if any, undesired sounds might be discovered. They use vibration rollers which can simulate driving over cobblestones for example as well as employing hydropulse equipment which triggers a selectable frequency band that conveys impulses across the wheels and the chassis into the car. Because the intensity can be varied, the team can literally make just about anything vibrate and produce sound.

Another piece of equipment called the ‘shaker’ is also used and can initiate vibrations directly on the body of the car, allowing the team to avoid the sorts of sound dampening that comes from tyres, shock absorbers and the vehicle’s chassis. 

This technology and the use of test stands give the team the ability to introduce the vehicle to simulations under laboratory conditions that are previously recorded on the test track, but without the disruptive conditions like wind, motor or rolling noises and with the option of reproducing the same sounds and conditions time after time.

It’s an exhaustive, often repetitious process that, if done correctly, results in, well… silence. That is, an Audi interior that provides the perfect backdrop for driving or conversation or listening to music or, depending on the model, listening to the engine note. No frustrating sounds that can’t be accounted for, just that wonderful, automotive cocoon for which the brand is famous.