Whereas some acoustic roughness can be located quite easily, in other cases the exclusion principle has to be applied. Parts are removed until the noise disappears and the evil-doer is found. A lot depends on a sharp ear, sensitivity, patience and last but not least the creaking and cracking expert's experience. Peithmann: "The loud noises disappear first, then new sources of noise emerge that we were not able to detect beforehand."
There are so many ways and so many areas in the car in which unwanted noise can develop. The roof post lining may rub against the roof rail lining, the seat height adjuster may scrape past the seat trim fastenings when actuated, a terminal strip may knock against the frame or the glass in the instrument cluster may start to rattle. For the members of the creaking and cracking team there is probably no noise they haven't yet heard.
Over the years the team has compiled a "creaking and cracking catalogue" which is accessible via the Audi Intranet as part of the knowledge management programme. It serves Audi engineers as a basis when developing a new model, in order to avoid designs with unwanted creaking and cracking potential from the very start. The experts can even identify certain sources of noise when looking at the design of the digital model on the computer screen - well before any actual hardware which might crack, rattle, clatter or squeak is produced. "Certain design features and component or material combinations can be excluded immediately, just by looking at the CAD data," says Peithmann.
Nevertheless, at this point of time and given the current state of the art it is not possible to compile a complete "creaking and cracking analysis" for a car with the aid of computer simulation. "This degree of simulation is not practicable, for example noise-specific material behaviour when exposed to different climatic influences," explains Carsten Vortanz. Even in the future, the numerous test drives and trials with ultra-modern test technology and last but not least the sensitive ears of the creaking and cracking team will remain an essential basis for the high acoustical quality of all Audi models.
Noise Database for Audi Dealers
Customer Service at AUDI AG registers customer-relevant noise on the road from the driver's position by means of dummy-head stereophony and makes the details available to dealers and workshops as a database via the Audi Servicenet. In this way, noise complained of in customers' cars can be compared with noise sources and directions already stored in the database.
The purpose of this is to simplify the often hour-long search for and analysis of noises in customers' cars. Noise analysis was often a difficult task for the dealer. If it proved impossible, the car had to be returned to the manufacturer. The Servicenet also describes the relevant measures that enable Audi dealers to eliminate the various noises on the spot at their premises.
This procedure is already in use for functional noises generated by the engine or brakes, but with regard to detecting, analysing and eliminating creaking and cracking noises it is still in the test phase.
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