SSSHH…KEEP IT QUIET! VAUXHALL REVEALS ASTRA’S SILENT SECRETS

Much has been written about how quiet and refined our all-new Astra is, and here’s how it was achieved – welcome to the quietest place in Germany!

The final phase of testing for production-readiness requires a trip to the Acoustic Lab at the Dudenhofen Test Centre, in Germany, where engineers evaluate all Vauxhall/Opel new models before sign-off to production in a state-of-the-art anechoic chamber.

Reducing NVH (noise, vibration, harshness) in the new Astra’s cabin was always a high priority, and Astra is put through an extensive and precisely defined requirements list. Apart from the appropriate sound of the engine or rolling noise, this includes the sound made by closing a door or the clicking of the indicator. The tests also include idle behaviour, the Start/Stop function and driving under part or full engine load, for example. Highly-sensitive microphones record every noise so they can be analysed afterwards.

“Dummy Head” Testing

Another vital part of the testing scenario are the ‘dummy heads’ - plastic effigies of the human head and shoulder area perfectly replicate all the acoustically relevant elements of the human outer ear. An array of microphones fitted in the ears of the dummy heads record and replay noises in the same way that a ‘real’ human would perceive them. This enables stereo recording and replaying, as well as differentiation between the upward and downward direction of noise, making the dummy’s hearing virtually three-dimensional. To achieve the desired vehicle sound that is pleasant for occupants, a binaural transfer path analysis and synthesis is conducted to distinguish between airborne and structure-borne noise source paths. From this, engineers can identify, for example, which screw needs to be turned to achieve the agreed target value – first virtually and then in reality. If both cases produce satisfactory results, the Astra has cleared the next hurdle on the way to production readiness.