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Experiences

Sound Check

Date — 29 November, 2013

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Sound_check_engine_AMG_972x426

The thunderous roar of a big engine. It starts off as a high-revving, throaty sound, and within seconds, changes from a deep throbbing into an aggressive, red-hot hammering. To the expert, the sound is immediately recognizable: it comes from the C 63 AMG, the big V8 naturally aspirated engine made by the high-performance subsidiary of Mercedes-Benz.

The car it belongs to remains invisible for the moment. For we are not out on the open road but in the acoustics laboratory at Mercedes AMG in Affalterbach. The small town just a few miles northeast of Stuttgart and half an hour away from Mercedes headquarters has a population of under 5,000. AMG, founded in 1967 and started as a small racing company, has long been part of the Mercedes Group and today employs around 1,200 people. In the engine assembly department, specifically trained and highly skilled master mechanics completely handcraft AMG engines – following AMG’s unique credo “one man – one engine”. Once the engine is completed,the master mechanic attaches AMG’s famous engine plate – bearing the master mechanic’s name. These unique power units are coveted by motor enthusiasts all over the world not only for the performance but also for their sound.

The high-performance machines are developed in the company’s own R&D department. There, gigantic V8 biturbo power units are mounted in racks for transport. Menacing-looking metal sculptures, open hose connections, raw cable harnesses. Tools in clinical-looking, rollfronted cabinets, long rows of shelves with spare parts and test components. Engineers and mechanics in black polo shirts with the white AMG logo emblazoned across their chests. The mix here is an unlikely one of state-of-the-art technology and elbow grease. This hall is virtually silent. But from afar, the roaring of a test engine trickles through the walls at a frequency that makes it clear from the pitch that the engine on the test stand is being driven to its limits.

Sound_check_soundwave_972x426
—The shape of sound: At Mercedes AMG acoustics laboratory, sound waves are visualized to help create the distinctive AMG engine sound.

Moving to the acoustics room, we find walls flanked by huge loudspeakers with a row of professional-looking headsets on the table in the middle of the room. The technology here would normally be found only in a serious recording studio. Marcus Hofmann explains. “We all know what an AMG sounds like. That’s easy. Hardly any other manufacturer produces that cool, gutsy sound. But we wanted to find out what makes it so special: what’s its genetic make-up?” Marcus Hofmann’s job is to identify and document all the possible sources of obtrusive vibrations in a car, which naturally includes the sound of the engine. That sound is as much a part of the overall impression left by a car as its looks.

Acoustics engineer Uli Kohlmann opens up a table on a large wall-mounted monitor: it is AMG’s acoustic archive. The sounds of all the V8s and several engines from the competition are cataloged here in various situations: idling, accelerating, overtaking at normal speed and overtaking while accelerating.

The bullish snort of a V8 thunders out of the loudspeakers: a deep, guttural, rumbling sound, the turbocharger in full song. A G 63 AMG. “Those side exhaust pipes really are the business,” chuckles Marcus Hofmann.

But here they can reproduce the sound of the AMG engine not only acoustically but also visually. A brightly colored graphic is projected onto the wall. “That’s a Campbell diagram: it’s what you might call the acoustic fingerprint of an AMG. Engine speed – in rpm – rises from left to right while the pitch is shown on the vertical axis. Blue means that the frequency at this engine speed sounds quiet. Green indicates an increase, and yellow and red show that it’s getting louder and louder. The lower frequencies sound louder at slower revs but as the engine speed increases, the high frequencies become more pronounced.” We look at the colorful diagrams, fascinated, but plainly clueless. Another AMG engineer laughs: this time, it’s Ralph Illenberger, who is responsible for the design of all of AMG’s exhaust systems, and the man behind the sound. “I think Marcus Hofmann and I are the only guys at AMG who understand a Campbell diagram in theory and can also read it. We take a look at it, and we know just from the pattern – in other words, the frequency distribution – how the engine will sound.” In other words, whether it’s ugly or shrill. Whether the tones neutralize each other, or whether it has those wonderful crescendos and diminuendos. Whether the frequencies are harmoniously balanced. Whether it sounds clean and simple or gives you the goose bumps. Whether it gives you a “nails-down-the blackboard” shudder, or whether there are too many moments where it sounds neutral and, ultimately, boring.

THE SOUND OF A TYPICAL AMG ENGINE IS A POWERFUL, MUSCULAR RUMBLE.

—Ralph Illenberger, responsible for the design of all of AMG’s exhaust systems

The first step to perfect sound is the elimination of all interference noise and vibrations. That goes without saying. The real work is developing the sound. Ralph Illenberger explains: “We know exactly which parameters and conditions dictate the sound. Let me give you an example: a classical US eight-cylinder has that warm V8 rhythm because each cylinder has twin valves. These act as a muffle, so together with the low revs you get this soft, laid-back sound. With our four-valve engines, it’s the opposite. They’re high-revving and generate enormous exhaust pressure combined with a high-speed exhaust flow. If our engines didn’t have such huge exhausts with exactly timed connections between the manifolds, our engines would sound incredibly harsh, with a really brutal backbeat. Cylinder capacity and firing order also play a major role. A Ferrari V8 gets its famous screech at high engine speeds because, in terms of the firing sequence and ignition angle, it’s actually like two four-cylinders hooked together. That, too, generates a totally distinctive sound. In our case, the math behind the control makes a significant contribution to the sound of a typical AMG engine. That powerful, muscular rumble has its origins here.”

In his own laconic style, Illenberger tells us more. How modern turbo-powered engines need to be really loud so as to make them heard against the muffling effect of the turbocharger. And how tuning and tweaking the eventual sound of the engine takes place in a second step. What influence different car designs have on the sound of the engine, or how the same engine in the aluminum shell of an SLS AMG sounds completely different in the steel chassis of a C 63 AMG. He explains the different ways in which the sound of the engine penetrates into the interior of the vehicle and is dispersed there, the legal regulations that need to be complied with and the role the car’s positioning plays. For the ultrasporty AMG, the exhaust needs to sound raw, gutsy and uncompromising. For the AMG models designed for everyday use, it will be a more bullish, more finely modulated sound. Illenberger chuckles: “In some cars, it’s clear you can give it the full works. And we have no qualms about doing that, when it’s right. But there are some cars where it just wouldn’t fit. Even the sweetest-sounding engine will get on your nerves after 500 miles on the highway. Because of that, we spend a lot of time discussing the right balance of emotion and comfort.”

Sound_check_engine_V8_AMG_280x280
—The M159 is a powerful version of the legendary V8 automobile engine used today in the Mercedes-Benz SLS AMG

We all know what an AMG sounds like. That’s easy. Hardly any other manufacturer produces that cool, gutsy sound.

—Marcus Hofmann

Sound_check_Sound_diagram_280x280
—Sound waves travel through air in much the same way as water waves travel through water. In fact, since water waves are easy to see and understand, they are often used as an analogy to illustrate how sound waves behave.

So much for theory. But exactly how do you go about changing the sound of an engine? How do the engineers conjure up the right tone? With the help of a few simple examples, Ralph Illenberger patiently explains what he changes on an exhaust system. With this model, a slightly thicker pipe, with another, a thinner one. Here a little insulation, there none. Here, a little stoppage in the pipe. There, 18-millimeter slits in the pipe instead of 24. In one model, the sound may be right when you have an 18-millimeter-thick connecting piece between the two main pipes, in another, it may be just 15 millimeters thick. And how does Ralph Illenberger know so precisely what he must use to generate which effect? “Experience,” he says, “and intuition. You simply have to have a feel for it.” Although various models for calculating it have been developed in recent years, you can only calculate using the data you have available. And you only know for sure whether you’ve got it right when you put the system in the model and hear the actual sound.

An entirely different challenge for the sound engineers in Affalterbach is posed by the development of the SLS AMG Electric Drive and other possible models without combustion engines. Ralph Illenberger laughingly rolls his eyes and lifts his hand in mock defense for this is no longer with him.

“Even an electrically powered AMG should have that characteristic AMG sound,” explains Marcus Hofmann, “but it’s obviously going to be different from a V8.” He brings in an electronic sound clip with different overlays: an aggressive, pumping sound interlarded with a more relaxed groove – electronics enriched with a little V8 acoustics. “The SLS AMG Electric Drive might sound like that,” says Hofmann. “Even in the age of the digital car, you can still hear a typical AMG sound.”

Explore More Articles
HALF_WAY_TO_THE_MOON_Trucks_972x426
HALF WAY TO THE MOON

For the MERCEDES AMG PETRONAS Formula One™ Team, following the Grand Prix circus means transporting 30 tons of material in 10,000 individual parts and at least 60 employees to venues on five continents. Of course, they have to ensure that everything arrives there on time what calls for a system and improvisation in equal measure.

Grande Complication Dial Explained
Small World

Time moves the world. The IWC Portuguese Grande Complication is an understated, beautifully designed way of summarizing time as the motor of all change: a time machine that shows a tilted globe on the dial.

89800 Calibre Movement
Eternity in Digits

The IWC-manufactured 89800 caliber, which made its debut in 2009, redefined the digital date display. The triple-disc mechanism in the perpetual calendar features large-format displays for the date and month and, slightly more discreetly, the leap year cycle. All are ingeniously synchronized.

Top Secret

In a small town in central England, over 500 specialists spend their time developing and building silver arrows for the MERCEDES AMG PETRONAS Formula One™ Team. Almost every one of the 3,200 parts in each car is custom-made.

Ingenieur: the story of a legend

When the Ingenieur from Schaffhausen was launched in 1955 it created a storm. But its actual history goes back much further: to 1888.

Movements Come to Life

All mechanical watches can be fascinating because of their intricate movements. Even simple watches, ones that only tell time, are extraordinarily complex mechanisms that have hundreds of miniscule parts that work harmoniously together. A complicated watch, one that performs additional functions, is by definition even more complicated.

From Atomic Physics
to Quality Management

A doctor with a degree in atomic and molecular physics plays a surprising and important role at IWC.

Flying high with big date and month displays

A fabulous combination of sportiness and elegance, the Spitfire Perpetual Calendar Digital Date-Month is the high-flyer of the IWC Pilot's Watch collection. The date and month could not be easier to read and the mechanics inside the case are an endless source of fascination.