Keep it quiet - it's the new Mercedes-Benz CL

In addition to the noise configuration and sound insulation of the engine, exhaust system and chassis, it is the car's excellent aero-acoustics in particular that will make it a very quiet driving experience for drivers and passengers.

"Aero-acoustics, the discipline with the aim of reducing wind noise, is a relatively new field in automotive development, one in which Mercedes-Benz has been playing a leading role in recent years," said Johannes Fritz, Director, Sales and Marketing, Mercedes Car Group, Middle East. "The good aerodynamics of Mercedes passenger cars are also noticeable in acoustic terms, for if the airstream passes across the outer skin with minimal turbulence in the interests of low drag, this also leads to less noise."

It was with this in mind that Mercedes-Benz engineers designed airflow-efficient A-pillars, developed a more rigid bodyshell with reinforced outer surfaces and achieved a new sealing concept for the doors. This exemplary noise insulation is also helped by the side windows, which have a thickness of six millimetres in the new CL-Class coupé.

Many other components were also developed with a view to aero-acoustic efficiency: for example the windscreen wipers, which are positioned very low down, out of the airstream, when not in use. A narrow stem between the exterior mirror housings and the doors also prevents wind noise, and a specially designed rubber seal between the rear window and the boot lid also makes for aero-acoustic efficiency. The tilting/sliding sunroof features serrated wind deflectors whose ridges create designed-in longitudinal air turbulence, thereby reducing thrumming noises when the roof is open.

To carry out their aero-acoustic measurements, Mercedes engineers developed a new procedure involving a three-metre parabolic mirror fitted with numerous microphones, which acts as a sound reflector. From five metres, the microphones at the focal point of the mirror record the noises caused by the airstream as it passes around the vehicle body.

A video camera makes the area under examination visible on the computer screen. At the same time the system superimposes the wind noises onto the video image as different-coloured areas, depending on the sound volume and frequency. This enables sources of irritating noise and its distribution to be identified and examined.
During the development of the new CL-Class this innovative aero-acoustic measuring procedure was supplemented with well-proven artificial head technology.

This dummy with an artificial head, whose anatomically accurate 'ears' were equipped with capacitor microphones, was seated behind the steering wheel making both spatial sound recordings and precise measurements of sound pressure and frequency possible.

Subsequent evaluation of the test results showed how effective the noise reduction methods were. The acoustically sensitive area at the driver's head level appears as a dark blue, particularly quiet zone on the computer screen of the parabolic mirror microphone system. At a wind speed of 140 km/h, the interior noise level in this area is below 66 decibels.