New Mercedes S-Class: Sound of Silence

Mercedes-Benz S-Class Vehicle Acoustics

Perfect vehicle acoustics and innovative sound system

September 7, 2005 8:01 PM
Filed Under: German, Mercedes-Benz

Press Release

Perfect vehicle acoustics and innovative sound system

 

Technical progress in the automobile is audible and tangible – as amply demonstrated by the new S-Class with its unique noise, vibration and tire performance, which ensures one of the most important conditions for the legendary long-distance comfort of the Mercedes’ top model. Engineers from various different areas cooperated closely to achieve this benchmark per-formance. Through the precise alignment of body, interior, drive system and chassis, they have developed an automobile that is agreeably quiet while exuding powerful self-confidence, also in terms of acoustics. This harmonious overall composition gives the Mercedes S-Class a totally new sound. Equally unique is the listening experience of the sound system, which was especially developed for the S-Class: The state-of-the-art digital technology, deployed for the first time in the automobile, enables a new level of three-dimensional sound pleasure.

 

The optimisation of noise, vibration and tire comfort began as early as in the planning phase of the new Mercedes saloon. Using high-performance computer programs, vibrations transferred from the engine and axles were simulated and the body area constructed to avoid generating any unpleasant resonances. An-other important contribution to the high level of stress comfort is made by the rigid body shell structure, which contains up to 50% high-strength and ultra-high-strength high-tech steel alloys. In comparison to the predecessor model, the static tortional flexibility of the body shell has been improved by app. 12%.

 

The focus of the stress tests was the floor plate of the new S-Class, whose innovative relief embossing makes it five times more rigid, thus reducing vibrations to a minimum. The asymmetrically arched floor plate, based on findings from bionic research, was developed and patented by Mercedes engineers and their colleagues at DaimlerChrysler Research.

 

Highly efficient insulation materials, which damp vibrations and absorb sound, further contribute to the high level of ride comfort in the new S-Class. Computer simulation techniques were also used for calculating the use and fitting of materials. Subsequent tests under realistic conditions confirmed the high effectiveness of the insulation measures. The sound level in the rear of the new luxury saloon is two to five decibels lower than in the predecessor model. The tire noise in the interior has been audibly reduced – at 80 kilometres an hour by up to 3 decibels.

 

Overall Mercedes-Benz deploys some 170 fibre, fleece and foam elements for sound insulation in the new S-Class.

 

Body: Exterior mirror developed in the aero acoustics wind tunnel

 

The aerodynamic body of the new S-Class, which with a drag coefficient of 0.26 has one of the most drag-reducing saloons in the luxury class, also offers the best conditions for perfect aero acoustics. Mercedes engineers examined various body areas in the wind tunnel to achieve further progress with innovative measuring techniques. For example, they designed the casing of the exterior mirror in a way that eliminates disruptive wind noises. The form of the A-pillar and the multiple door seals are also the result of aeroacoustic tests.

 

Engines: Package of measures for low sound levels and sonorous sound

 

Noise alignment is one of the main tasks in developing an engine. In order to solve the conflict of objectives between low passing noise and agreeable, sonorous engine sound, a complex package of measures was realised. Two-cartridge air cleaners with integrated resonators, hydraulic engine mounts, more rigid engine supports, a newly developed camshaft drive and a twin-pipe exhaust system are some of the means used to insulate noise and vibration. In addition, by deliberately accenting certain agreement frequencies, the engine engineers further enhanced the typical S-Class sound.

 

Sound system: New digital technology for maximum listening pleasure

 

In cooperation with the harman/kardon® audio specialists, Mercedes-Benz sound engineers developed a powerful sound system, which offers perfect three-dimensional sound pleasure. It is based on the DTCP technology (Digital Transmission Content Protection) which is celebrating its global premiere in the automobile. This method enables the digital transfer of all signals from the source to the amplifier thus alleviating the necessity for digital-analogue conversion. As a result, the modern multi-channel formats of DVD audio, DVD video and DTS-CDs can now be played with absolute fidelity for the first time. The spatial sound impression is provided by harman/kardon® with its professional multi-channel technology LOGIC7®. With unique digital algorithms the system achieves a realistic and enveloping surround experience true to the original master, not comparable to other sound systems, The heart of the harman/kardon® system is a 600 watts amplifier with a digital signal processor.

 

A further innovation is the metal matrix loudspeakers developed especially for the S-Class. This high end cone material is three times stiffer than traditional loudspeakers which results in a more transparent, resonant free sound. The sound system for the Mercedes top model includes 14 of these high-performance loudspeakers, which are integrated into the vehicle structure, providing unadulterated distortion-free sound.

 

harmann/kardon® is a leading manufacturer of top class audio systems. Since its invention of the world’s first high fidelity receiver - the Festival D 1000 - in 1954, the American company has been among the audio sector’s pioneers.

 

At a glance: The new S-Class sound system by harman®/kardon

 

Amplifiers
High-performance DSP amplifiers with 13 channels and 600 watts – 11 time 40 watts for the main channels plus 2 time 80 watts for the subwoofer channels

 

DSP with discrete LOGIC7® audio-processing and fully digital copy-protected audio transmission via fibre-optic cables (MOST DTCP)

 

Media and formats:

 

Dynamic volume control (DVC) with dynamic equalising

 

Loudspeakers
Instrument panel:

Front:

Side:

Back:

 

harman/kardon® — manufacturer of the sound system

 

A leading manufacturer of top class audio systems, harman/kardon® has been among the pioneers in the audio sector since the company invented the world’s first high fidelity receiver, the Festival D 1000, in 1954. The American company’s guiding principle hasn’t been technological leadership for its own sake but rather technology that benefits customers and delivers higher sound quality. To ensure the most greatest possible accuracy of realistic sound reproduction, Harman is a one-stop supplier of all types of components, from recording equipment to professional studio and storage technology to the highest quality playback products.

 

Today, Harman International combines top, world renowned brands in the most important areas of music production and reproduction under one roof, including harman/kardon®, Becker®, AKG®, Infinity®, JBL®, Mark Levinson®, Lexicon®, Revel® and Studer®.

Vehicle Acoustics: Agreeably Pleasant Sound

 

 

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.

Engine noise: Quiet performance and well-designed sound

 

Mercedes-Benz engine designers worked to avoid noise and design sound with state-of-the-art measuring technology and great meticulousness. Nearly all of the well over 200 separate parts of the powertrain were subjected to acoustic testing and assessed for volume and frequency, from crankcase to engine mount, from piston to injection valve.

 

The goal of the engine specialists was to obtain an agreeable sound pattern in every driving situation. To achieve this, the absolute values of the noise development were measured and acoustic interference sources eliminated, which in themselves are not loud but with load and speed changes can make their presence disagreeably felt at certain frequencies, and thus have a subjective effect on the sound pattern.

 

For example air intake: with its frequency spectrum, the engine intake noise spreads strongly in the direction of the vehicle interior and can thus impair pas-senger noise comfort. One result of the analyses using state-of-the-art measuring techniques aligned to the actual audible impressions is the newly developed intake pipe from nylon fabric, deployed for the V6 and V8 engines of the new S-Class. In contrast to the smooth plastic that was used previously, this material is sound-absorbing and considerably reduces noise intake.

 

The issue of noise alignment is increasingly become one of the main functions in engine development – mainly because engineers must solve the conflicting objectives of how to achieve lower passing noise and agreeable, sonorous engine sound. With the six and eight cylinders of the S-Class, the Stuttgart experts rigor-ously followed the concept of noise reduction and sound design. For this reason, various measures were developed to reduce engine noise – from two-cartridge air cleaners with integrated resonators above the insulation mat under the engine hood and newly developed hydraulic engine mount to the twin-pipe exhaust system. At the same time, the experts were concerned with creating a typical S-Class sound, by accenting specific agreeable frequencies, primarily with the targeted harmonisation of the exhaust system.

 

With the newly developed V6 diesel engine in the S 320 CDI, the second-generation commonrail technology ensures quiet performance and permits double pilot injection. In less than a millisecond, small pilot volumes of fuel flow into the cylinders and effect an even better preheating of the combustion chambers before the main injection. This results in smoother combustion development and considerable lower operating noise of the diesel engine.

 

Vibrations and acoustics comfort: Audible progress in the Interior

 

It is not only the airstream which generates vibrations and noise. Axles, steering, tires, engine and powertrain also have a large impact on acoustics comfort. These components are also examined in the noise laboratory and optimised in meticulous detailed work. Examples:

In order to prevent the low-frequency vibrations generated by the road sur-face, Mercedes engineers examined not only the engine mount, spring bearing and shock-absorber mount, but also for the first time included the seats in their calculations. The result is an optimised seat structure and specially coordinated seat cushions which compensate for the disturbing low-frequency resonances with their dampening effect.

 

To avoid road and tire excited steering wheel vibrations, the Sindelfingen experts developed a vibration absorber for the steering wheel.

 

At the front the interior is shielded with two acoustically effective systems: with absorber made from high-quality resin foam at the firewall and with a “soundproof” dashboard, which is completely insulated in the front area, thus transferring no disturbing noises from the engine into the interior. The channelling areas for cables and wires were also sealed hermetically.

 

The Mercedes engineers also reduced the tire rolling noise which is perceptible primarily in the lower speed range (up to 100 km/h). This was done by the targeted deployment of high-quality insulation materials. Together with the high induction stiffness at the coupling points to the chassis, they reduced the noise level in the interior against the predecessor model by up to three decibels.

 

Overall some 170 fibre, fleece and foam elements are used for sound insulation in the new S-Class.

 

Test Centre: with up to 260 km/h through the Hall

 

Acoustic waves and vibrations are tracked in twelve state-of-the-art test chambers and measuring facilities in the Mercedes-Benz Technology Centre in Sindelfingen.

 

One of these is the external noise test chamber which is used for test cars making the “accelerated drive-by test” without moving. A total of 21 microphones set up in long rows to the left and right listen to every detail of the vehicle. As the car does not move, the engineers consecutively switch on the microphones in line with the vehicle speed in order to simulate the drive-by. This is an intelligent measurement technique which guarantees the highest level of repeat accuracy.

 

In order to meet the prescribed test conditions, the external noise test chamber must have an impressive size, even though the vehicle is stationary. Indeed, with a floor space of 18 times 25 metres, it is larger than a tennis court. Hundreds of metre thick, grey insulation elements made from rock wool cover the walls and the roof of the seven-metre high hall in order to exclude each and every sound reflection. Even possible external vibrations that could falsify a measurement were rigorously excluded: the hall floor which weighs well over 1,000 tons is placed on a huge air suspension system.

 

Unlike open air conditions, secondary noises or weather influences must not be allowed to impact the measurements in the state-of-the-art measuring hall. The simulation of actual driving conditions for the rolling noise measurements is guaranteed by a roll test chamber anchored in the floor. On its realistic road surface test vehicles reach top speeds of up to 260 km/h. As a supplementary drive, two 180 kW electric motors bring the large roll mass of the roll in movement. At the same time a 200 kW airstream blower provides the necessary cooling for the engine.

 

In their tests, Mercedes acoustics experts are interested not only in the volume passers-by perceive of an automobile passing by. They also intensively examine the noise world that the driver and passenger experiences, sometimes for hours without interruption. To do this, they also place passengers in the vehicles for measuring trips in the large hall: dummy heads that exactly match their human model. However, in the auditory channels there are not eardrums, bones and nerves, but highly sensitive capacitor microphones. They allow not only a spatial recording corresponding to the auditory perception of the ear, but also serve to obtain precise sound pressure and frequency measurements.

 

During the tests, the dummy head transfers data to a computer which reproduces the measuring results as coloured diagrams – more precisely designated spectro-grams. What appears to the layman as a colourful juxtaposition of curves and lines provides the engineers with information about causes of the disturbing resonances, which they can then eliminate in a targeted fashion. In the early eighties, Mercedes-Benz was in the vanguard in deploying dummy head stereo-phony. Using this technology, it has achieved notable progress in the area of acoustic comfort, which is audible in the new S-Class.

Sound system: Concert Hall on Wheels

 

 

The sound system specially developed for the new Mercedes-Benz S-Class offers acoustic excellence equal to that of a live concert experience. In cooperation with the harman/kardon® audio specialists, the Mercedes-Benz sound engineers created a new three-dimensional sound pleasure with a technology deployed for the first time in an automobile. Even in the most critical acoustic environment, in the close quarters of a vehicle cabin, the system ensures a previously inconceivable realistic 360-degree music experience on every seat. No matter whether you enjoy 5.1. or stereo recordings on DVD or CD.

 

It is a whole bundle of finely tuned technical measures which allow this audible progress. Thus a technological innovation is celebrating its world premier in the automobile: the so-called DTCP technology (Digital Transmission Content Protec-tion). This digital encryption allows the fully digital, content-protected signal transfer via fibre-optic cables from the source to the amplifier. As a result, all signals are transported and processed digitally. This means that during transmission, there is no interference of any kind which could detract from the sound experience.

 

As this technology avoids the need for a signal conversion from digital into analogue, driver and passengers of the new S-Class may now enjoy for the first time in an automobile the modern multi-channel formats of DVD audio and DVD video as well as DTS-CDs. All multi-channel recordings on DVD and CD such as Dolby-Digital, DTS, MLP and PCM are transferred directly and without loss in quality to the high-performance processor of the amplifier.

 

An optimum sound impression on all seats is provided by the professional LOGIC7® surround technology from harman/kardon®. It was originally developed for high-performance sound processors in professional recording studios. Now the advanced sound processing method creates an optimum multi-channel audio reproduction in the new S-Class. With special digital algorithms, the LOGIC7® technology achieves a considerably more homogenous sound field than other high-end audio systems. It accurately distributes the surround information as intended in the original recording over the 13-channel system architecture, specifically designed for the S-Class. The perceived sound source is moved away from the individual speakers. This means drivers and passengers enjoy the impression of a larger space with wide sound stage and an authentic surround experience regard-less of seating position.

 

A concert hall atmosphere on every seat

 

The LOGIC7® technology even creates a surround sound experience from standard stereo CDs –representing the preponderate share on the music market. Stereo recordings still contain plenty of ambient information from the original master which are with standard CD playback not audible though. The multi-channel surround sound technology LOGIC7® uniquely extracts and recreates this information via all channels of the S-Class system. The system distributes the surround information contained in the two channels over the 13 channels in a way that the sound is distributed markedly more accurate to the loudspeakers and the original recording is considerably more precisely reproduced than in traditional sound systems. Without any artificial effects, you can simply hear what has always been on the stereo CD. The impression is stunning. There is a concert hall atmosphere on each seat in the new S-Class. All the instruments of a piece of music can be accurately located, revealing an impressive and realistic surround sound experience.

 

Amplifiers with 600 watts performance and digital signal processor

 

The 600 watts amplifier, located in the rear of the saloon, is responsible for perfect distribution of the music signals. It features a Digital Signal Processor (DSP), which manages the frequency response with calculating capacity equal to that of a PC, ensuring a well-balanced sound impression at any time.

 

The amplifier generates temperatures of up to 130 degrees during operation. In order to ensure undisturbed operation even under extreme conditions, the Mercedes-Benz and harman/kardon® sound engineers have developed for the new S-Class a particularly complex cooling system with precisely defined heat sinks for the amplifier.

 

In contrast to the surround system known as DolbyDigital 5.1, the LOGIC7® technology uses a 13-channel system architecture, thus providers an even better and spatially even more convincing audible impression. The S-Class amplifier provides 13 channels to accurately address the loudspeakers. The electronics operates each channel individually, supplying for example 160 watts for the subwoofer and for each woofer channel in the front 80 watts.

 

Newly developed sandwich-type loudspeaker cones

 

Signal processing and transmission are not the only decisive factors for sound quality though. As any hi-fi fan knows, loudspeakers are a key factor in the quality of any listening experience. For this reason, new metal matrix loudspeakers were developed for use in the Mercedes-Benz S-Class. Their high-quality membranes are three times stiffer in relation to their weight than traditional loud-speakers. As a result they are highly sensitive.

 

State-of-the art material engineering is used for manufacturing this sensitive sandwich-type cone body. In a galvanic process, an aluminium substrate is given a ceramic surface. The soft aluminium core provides damping, the ceramic coating layer for strength. Rigidity, damping and low weight – the most important properties of a loudspeaker membrane are thus combined in an ideal fashion. These metal-matrix cones are eminently suitable for deployment in the automobile where they must be able to cope with extraordinarily high loads. They are resistant to moisture, temperature variations and most chemicals.

 

The new Mercedes-Benz S-Class features 14 of these high-performance loudspeakers. Their computer-modelled metal-matrix radiating surfaces allow virtually no acoustic resonance and discoloration over the entire frequency range. Perfect reproduction of the bass range is generated by a 200 time 320 millimetre oval subwoofer on the rear shelf together with two further 200-millimetre bass speakers in the front doors, each which is flanked by a 100-millimetre mid-range loudspeaker. The high frequencies radiate on the left and right from an additional 43-millimetre tweeter, so forming a fully-fledged three-way system in the front doors.

 

Further loudspeakers: There is a 100-millimetre mid speaker in the centre of the instrument panel. Left and right in both of the back doors there is one 165-millimeter woofer/mid speaker and a tweeter. And in additional to the powerful subwoofer on the rear shelf two additional mid speakers provide sound to the interior of the new S-Class. The amplifier provides the eleven main channels - centre, front left / right, side left/right, back left/right with 40 watts each, from which the door woofers have alone 80 watts and the subwoofer in the rear shelf has additional 160 watts.

 

All loudspeakers are integrated into the vehicle structure in an optimum fashion. To do this one of the methods the sound specialists use is to separate the wet area from the interior with an aluminium module in the doors of the new S-Class. The bass loudspeaker operates in the volume of these wet areas, while the mid loudspeakers use the volume between the door module and inner panelling. In this way, there is no interference. The effort is rewarding and audible. In the new S-Class, the middle tones, so decisive for the sound experience sound particularly clean, pure and without distortion.

 

Sound check with dummy head technology

 

However, top technical performance alone does not guarantee any extraordinary, benchmark music pleasure in the automobile. Rather, the sound system must be precisely adapted to the vehicle interior. To do this, the Mercedes-Benz and harman/kardon® sound specialists examined the anticipated sound situation in a reproduced vehicle, while the new S-Class was still in the design stage.

 

When the first prototypes were available, the sophisticated measurement was intensified. By using modern dummy head technology, tests were conducted to examine how various sounds are perceived by people of different sizes across all frequencies on all seats in the vehicle. However, the subjective sensation of sound was even more decisive. With specially selected music recordings, experts with finely attuned ears assessed whether the measured frequency ranges corre-sponded to the subjective sound impression and the spatial sound experience was aligned to the musical model at each seat. Even the most minute of weaknesses were compensated by changing the specifications to the digital signal processor of the amplifier.

 

Furthermore, the new S-Class sound system had to demonstrate its steadfastness in driving operation on asphalt roads, cobblestones and rough roads. It presented no problems even under extreme temperatures. The system performed as expected, providing a new dimension of sound pleasure in an automobile, even when the vehicle was heated overnight to 50 degrees and the amplifiers worked at full power one hour long generating a volume close to 120 decibels – the equivalent to the sound of a jet taking off from the closest proximity.