NVH: Silent agreement

Mar 13, 2014
The feeling of well-being in an automobile not only depends on the available space, good seats and a pleasant interior design, but also on the noise levels and noticeable vibrations. The new C-Class offers its passengers outstanding qualities in this area.
Squealing brakes, clattering windscreen wipers, a rumbling suspension, strange noises from the air conditioning system – in a car such acoustic accompaniment gets on people's nerves. While we do not consciously register many noises and vibrations when riding in a car, they can still have an unpleasant effect on us.
In technical terms these disturbances – consciously registered and unknowingly endured – are collectively referred to as NVH. This abbreviation stands for noise, vibration, harshness, and describes all oscillations that can be heard as noises or felt as vibrations in the car, although some oscillations in the frequency range between about 20 Hz to 100 Hz can also be felt. The cause of NVH are oscillations of a source such as e.g. those induced in the suspension by the road surface, which are transmitted to other structures of the vehicle and in turn excite vibrations in these.
Excellent comfort with harmonious background noise
The brand quality of Mercedes-Benz traditionally includes an optimal design for quiet running and vibration comfort. This comfort not only underscores the high-value appeal, but is also a factor in the high level of driver-fitness safety.
Thanks to meticulous detail work the new C-Class meets these high standards. This does not mean that the Saloon is necessarily quieter than other automobiles in all situations, but it is more pleasant and harmonious overall. Some noises are expected by the vehicle occupants because they serve as orientation, such as e.g. the noise of the power-closing windows or the click of a switch. Confusing on the other hand is a hissing noise whose source cannot be located or suddenly vibrating body shell components. This attracts attention and distracts the driver from focusing on traffic. On the C-Class the Mercedes engineers were not satisfied until there was nothing left that could disturb or confuse, and the chosen test persons confirmed the Saloon's feel-good sound.
The basis for this comfort that enhances performances and caresses the senses is provided by the new intelligent body shell concept of the C-Class with fewer components compared with a conventional design, which makes high overall vehicle rigidity possible. The result is exemplary load introduction rigidity where the body shell attaches to the powertrain and the suspension. This minimises low-frequency tyre noise, reduces structure-borne sound and helps to reduce wind noise as well as powertrain noises. Furthermore, with regard to improving interior quiet running in the higher frequency ranges (from 300 Hz), noise-insulating and noise-absorbing elements of various foam and fibre materials are installed all over the body shell. They include new component concepts on the firewall, the floor covering and the large foam absorber on the parcel shelf.
Optimised actuating and operating sounds
The comfort-focused and performance-enhancing interior acoustics include purposefully designed actuating and operating sounds. That is because the low driving noise brings noises to the fore that otherwise would not attract attention – such as a hissing of the ventilation system. This is particularly true when the vehicle is at a standstill at a traffic light or in a tailback and the ECO start/stop function has switched off the engine. On the other hand, the driver expects certain sounds as feedback when using vehicle functions such as e.g. the power windows. Warning and notification sounds also must send an instantly understandable message. The goal is therefore to give these sounds a high-quality, suitable and unmistakable design while reducing others to the point where they are no longer bothering.
Together with the detail optimisation of door and vehicle body shell, door module and seals, a new generation of door locks, redesigned under acoustic aspects, provides the basis for a low-frequency door noise with a satisfying click that signals precise locking. Corresponding kinematics in the lock ensure a pleasantly quiet and precise sound of the central locking system.
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