New Mercedes S-Class: Sound of Silence

Press Release

Vehicle Acoustics: Agreeably Pleasant Sound

• New perfection for noise, vibration and tire comfort
• 12% more rigid body as basis for audible progress
• Body details developed in aero acoustics wind tunnel
• Sophisticated sound insulation for agreeable acoustics in the interior
• State-of-the-art test and analysis methods in the Mercedes test centre

Get in, drive and enjoy – this is the unique experience offered by the new S-Class. After only a few kilometres, it becomes apparent that Mercedes-Benz has achieved a new level of driving comfort with this luxury saloon.

Seats, materials, air conditioning, steering and air suspension chassis make an immediate impression as comfort attributes, making car driving such an agreeable experience. But there is a lot more to this impressive driving pleasure than meets the eye – extensive engineering effort in a wide range of areas, with intelligently combined and perfectly coordinated results that lead to the overall harmonic picture.

Mercedes experts define a key element of comfort with three letters - NVH - Noise, Vibration and Harshness - noise, vibration and tire comfort. From the planning phase right up to production, NVH was integrated in the entire development processes. Engineers from various areas worked took an interdisciplinary approach to achieving the ultimate level of noise comfort: a new Mercedes sound - agreeable and quiet while still self-assured and with a strong character - the new S-Class.

The body shell created the conditions necessary for the sound of comfort. Even before its construction, high-performance computers examined how the body components reacted to vibrations caused by the engine or from the axles. The result is a structure of state-of-the art materials that achieves new record levels of rigidity. In concrete terms, the static tortional flexibility of the body shell – a key requirement for high vibration comfort – is up by 12% against the previous S-Class. The bending resistance is 6% higher than that of its predecessor.

Vibrations: Patented relief-embossed floor panel

The precise calculation enabled aligning the body structure with other components such as axles or steering so as to eliminate any resonances detrimental to comfort. The Sindelfingen engineers paid special attention to the platform, which forms the stable backbone of the passenger cell with eight longitudinal profiles, four cross members and a three-part tunnel reinforcement.

For the first time, the sheet metal bars within this multiple structure are not even, but sport an innovative, asymmetric embossed relief, which was precisely calculated, giving the sheet metal five times more rigidity than the predecessor model. The embossed relief reduces vibrations to a minimum, thus greatly enhancing the exemplary ride comfort of the new S-Class.

The asymmetrically arched floor plate is a Mercedes patent developed by Sindelfingen engineers together with their colleagues at DaimlerChrysler Research. It is based on findings from bionics.

In a later development phase, the Mercedes engineers again implemented a targeted NVH tuning, developing further effective insulation measures that damp vibrations and absorb sound. One example is the large-area under-floor panelling, which is made up of noise-dampening textile fibres.

Computer programs and test chamber tests helped to test the effectiveness of these and other measures. Sound pressure was calculated in the low-frequency range at various points of the interior through simulations, and the efficiency of a variety of insulation materials was tested. In this way, Mercedes engineers optimised the acoustic comfort in the rear of the new S-Class, obtaining an audible result. The sound level is two to five decibels below the values of the predecessor model.

Aeroacoustics: Fine-tuning in the airstream

Aeroacoustics is a relatively new discipline which is of particular importance. Since aerodynamics experts now have a wind tunnel with extremely low inherent noise, they can deal with generating the lowest possible aerodynamic drag, optimising the life coefficients, deflecting dirt from mirrors, lamps and panes as far as possible, as well as with noises resulting from the flow around the vehicle body and its detach-able body components. In recent years, Mercedes-Benz has made great advancements with work on this important specialty area of vehicle acoustics.

The streamed aerodynamic body of S-Class, which has reached a new record in this vehicle class with a drag coefficient of 0.26. It is also acoustically superior since less noise is generated when the airstream is directed over or around the sheet metal without any turbulence to achieve the low aerodynamic drag.

But the S-Class developers have left nothing to chance. This is why aeroacoustic experts and body developers collaborated very closely, even in the planning phase of the luxury saloon, creating the design prerequisites for a considerable aeroacoustic reduction of noise. Examples include the more rigid body shell, rein-forced exterior surfaces and a new door concept of independent internal and external modules. This sound basis was followed by successful detailed optimisation in the wind tunnel, which functions in a particularly quiet manner as a result of sophisticated air ducting, acoustic soft trim and the air speed controlled via the rotational speed. With a nozzle section of 22.5 square meters, wind speed of up to 260 km/h can be realised on the vehicle. Engineers can easily generate gusts of wind and sidewind flows in this wind tunnel.

Under these quiet working conditions, the Mercedes engineers tracked down wind noises using a newly developed measuring method. A three-meter acoustic concave mirror equipped with several highly sensitive microphones and a video camera, scanning over large areas of complete body areas assisting in the localisation of disturbing sound sources. Thus, for example, on the side window the microphones at the focal point of the concave mirror captured across the whole surface all the wind noises, which appeared on the computer screen in colour depending on volume (level) and frequency. Simultaneously, the camera image is also transferred to the computer, which enables a precise localisation of critical sound sources. This makes orientation measures simpler and more effective.

One example of the measures resulting from these concave mirror measurements is the casing of the exterior mirror of the new S-Class. The narrow bar which joins the mirror casing and the door was designed in such a way that the wind noises are compensated for by the airflow over the bar. In addition, the door gap is multiply sealed in important areas up to four sealing levels to ensure that no wind noises are perceptible in the interior. The form of the A-pillar and the special rubber seal between the rear window and the boot lid are also the result of noise analyses in the aeroacoustics wind tunnel.

For the tilting-sliding roof and the new panoramic sliding roof, the Mercedes specialists developed jagged wind deflectors. Their notches generate air turbulence in a longitudinal direction, effectively suppressing the disturbing throbbing noise from the open sliding roof.