To make sure every
A soloist extraordinaire enters the stage. A hush of silence fills the air, as the audience hardly dares to breathe. Suddenly the voice is heard, its virtuoso quality immediately evident with one coloratura, then another, while a layer of tension builds in the quiet bass tones. A crescendo sets in a few bars later as the voice accelerates through nearly every musical pitch, from bass and tenor to soprano. The finale erupts in an unbridled furioso, and all who hear it are left with goose bumps. Then the recording stops, and Dr. Bernhard Pfäfflin smiles. “Marvelous, isn’t it?”
That short soundtrack of a 911 solo displays a number of qualities that every
Each model should have a sound that matches its character. A GT3 has to rock, that’s for sure. Another important criterion, according to Pfäfflin, is that “the car has to sound like its output.” No synthetic pop music, therefore, but real tones from genuine instruments. Nevertheless, the sound bodies are mixed in such a way that a harmonious pattern emerges for every style of driving.
In order to achieve this, Pfäfflin doesn’t wait until the automotive engineers and engine developers build the first prototypes. The quest for good sound begins much earlier. While both the powertrain and the car are still in the digital creation process, acoustics specialist Bernd Müller is already calculating countless variants of exhaust systems and mufflers—or, to be precise, the effects of different combinations on the sound of the car. Müller is responsible for the gas exchange acoustics at
For someone like Müller, who has lived and breathed acoustics for two decades now, the work would be done were it not for the company’s drivetrain developers, who keep coming up with major new engine innovations. They have introduced a broad range of turbocharged engines, the first four-cylinder engine in many years, and plug-in hybrid cars, and soon there will even be an all-electric sports sedan. These steps are of great significance for the
The tuba in the exhaust system
The new turbocharged boxer engines with 3.0 liters of displacement give the new 911
Moreover, the turbochargers, which spin at up to 200,000 rpm, develop their own very specific sound effect: the well-known turbo whistle. This is not bad in itself, because it alerts drivers to the imminent boost. But it’s important to prevent annoying prolonged tones at high speeds on the freeway. Müller has mastered these two challenges with the help of some technical measures. For example, the wastegate, which regulates the flow of exhaust to the charger, is adjusted in certain respects to meet acoustic demands.
Asymmetry and resonance
The basic tone of this engine is largely determined by its number of cylinders. A fourcylinder engine fires twice for each revolution of the crankshaft, so what initially dominates the acoustics is what is known as the second engine order. Left to its own devices, this type of engine would sound somewhat rough, which is why the Weissach acoustics experts, together with the engine designers, came up with an elegant trick. They have given the exhaust manifold—which channels the exhaust first into the turbocharger—a deliberately asymmetrical design. This creates overtones (secondary orders) that generate a much rounder and more pleasant sound.
The 718’s exhaust system refines the sound further. After passing through the catalytic converter, the exhaust mass flow is split between two pipes of unequal length. The shorter one ends in a classic muffler, which primarily lowers the overall volume. The longer one leads first to a Helmholtz resonator, named after Hermann Ludwig Ferdinand von Helmholtz, who lived and worked in Berlin in the nineteenth century. Like many of his contemporaries, he was a polymath. His particular interests included nerve cells, the conservation of energy, and magnetic fields. One of his most important discoveries was the resonator that bears his name. This air-filled container has a single opening. When airwaves—or sound—flow past the opening, the air inside the container starts to vibrate and generates a tone. Depending on its geometry and dimensions, the natural frequency of the resonator can add or eliminate certain tones—so precise adjustments can be made to achieve sophisticated sound. The result is what emerges from the two tailpipes to meet the human ear.
Composing for the electric motor
The first question that Pfäfflin and Müller asked themselves was how to reflect the character of the car. It’s a given that whatever they compose, they will not violate
“Every customer has a very individual approach,” says Pfäfflin. “But how can you assess a symphony that you haven’t yet heard? Our customers also always expect
By Johannes Winterhagen
Photos by Markus Bolsinger