Meet the people who make sure a Porsche sounds like a Porsche. A visit with the sound designers in the acoustics lab at the Weissach Research and Development Center.
This article original appeared on Porsche and written by Michl Koch
This is clearly not your average sound studio. The walls are covered with gray, wedge-shaped sound-insulating elements; in the middle, a Mahogany Metallic 911 is mounted on a dynamometer. In front of it, the device resembling an oversized microphone is actually an acoustic camera. Welcome to the realm of Porsche’s sound designers.Here in the acoustics lab in Weissach, Dr. Bernhard Pfäfflin, head of development for vibration technology and acoustics, and his team compose the unmistakable Porsche sound. The sound room provides a perfect environment for them to record sources of noise without reflections and to pinpoint sources of noise emanating from the car through the use of the acoustic camera. The recordings are collected in a sort of technical media library.
The acoustic camera makes it possible to locate sources of noise and make sounds visible.
Head acoustics engineer Dr. Bernhard Pfäfflin listens carefully by the 911.
These soundtracks—including the thrilling melody of the naturally aspirated boxer engines, the crescendo of the valve trains, and the tempered trumpeting of the exhaust system—can be mixed on the computer and fine-tuned in a manner similar to a musical recording. When a new model is being developed, the sound experts know what it will sound like even before the prototypes hit the track. And, of course, there are always improvements to be made to comply with ever-stricter noise restrictions being imple-mented in countries around the world. The challenge is to make cars noticeably quieter to the outside world while simultaneously transmitting the wondrous sound of the Porsche drivetrain to the interior with clarity and verve. Designing this sound is the passi-on of the Weissach acoustics engineers.The term “sound design” can be somewhat misleading, as it suggests that the sound of the car in action can simply be constructed and played back like a recording. But the song of the Porsche engine is not artificially created; it’s authentic, as Pfäfflin emphasizes. “The task is to present the existing acoustics in the most favorable way. It’s not an end in itself. Instead, we strive to accentuate the message that an engine transmits naturally in the most suitable way—or to carefully filter and insulate certain overtones that threaten to overwhelm the overall harmony.”The Weissach team uses applied physics dating back to scientist Hermann Ludwig Ferdinand von Helmholtz, who lived and worked in Berlin some 150 years ago. His insights into acoustics are still valid today. As a matter of fact, sound experts still swear by the formula, “If you’ve got a handle on Helmholtz, you’ve got the sound under control.” The Helmholtz resonator, which von Helmholtz developed to help him identify frequencies and musical pitches, has been used by Porsche for years to help create the ultimate sound in every model. This modern version is a little box in the intake duct which varies the sound depending on the load and engine speed by means of an electrically controlled valve similar to the keys on a saxophone.But one principle remains ironclad: it can’t sacrifice power or torque and it can’t increase the weight—let alone decrease effi-ciency. “We’re relentlessly uncompromising here at Porsche. Of course the feedback that good sound engenders is extremely important. But performance continues to be our highest priority,” says Porsche’s top acoustics expert.
To ensure that no extraneous sounds are picked up during recording, the insulated walls absorb sound waves.
Another system the acoustics team uses to highlight the Porsche sound is the sound symposer. This is not a speaker, but rather a sort of sound path, a line for tones consisting of a plastic hose with a gas-impermeable membrane. That’s how it transports the passionate trumpeting of the intake pipe, for example, into the cockpit. Because most drivers perceive the engine note differently, it’s possible to dial in just the right amount—using a flap valve and the gas-impermeable seal through a membrane that works something like the human eardrum.What does that mean in practice? As soon as the driver hits the Sport button on the center console, sharpening the responsiveness of the transmission, engine, and suspension, the flaps in the sound symposer and the Helmholtz resonator open to allow unrestric-ted flow, intensifying the natural sound of the Porsche engine. If the intensity of the sound becomes too dominant, you can switch back to comfort mode and cruise along quietly. The acoustic feedback doesn’t just add a bit of oomph to the driving experience—it also sharpens the driver’s perception of the engine’s degree of exertion. The driver should have a direct and unvarnished take on exactly how much of the Porsche’s vaunted torque and acceleration is currently being used. Bernhard Pfäfflin takes a scientific approach: “The objective is to accurately convey the operating state of the car to the driver. This state can change very rapidly through strong acceleration or the exceptio-nal brakes. At the same time, specifically designed acoustics can assist the driver in assessing and interpreting this performance spectrum more precisely.”
Placing the dummy head on a monopod simulates the perception of a standing person.
One thing that the sound makes clearer is acceleration. An overly quiet car—acoustics experts refer to this as decoupling—could lead the driver to underestimate speed. A lack of sound could lure some drivers into thinking that they are moving quite slowly at 200 km/h. Such a misapprehension not only could make it more difficult to adhere to the speed limit; on highway exits with tight curves, for example, a precise sense of the car’s degree of exertion plays a very important role. This sense of speed makes it much easier for the driver to assess the appropriate limits. With largely decoupled acoustics, the driver can only rely on the speedometer, whose abstract signal can lead to misinterpretations.The acoustics engineers spend a great deal of time filtering out irritating noises. Bernd Müller, sound designer for the Carrera model line, explains, “In the beginning, a new engine sounds like a rolling caravan of oil pumps.” Porsche models have several of these pumps on board, and these pumps distinguish each new prototype with the mechanical whine that characterizes all gear-wheels. “At this point the key is to insulate these noises so that they don’t disturb the driving experience.”
The dummy head on the passenger seat records sounds that the human ear would perceive.
To soften the high-pitched clickety-clack of the valve train, for example, the acoustics pros painstakingly develop ribbed valve covers. Likewise, power motors for the steering, air-conditioning system, and windshield wipers have nothing to do with dynamic car control and should ideally fade away into the orchestra pit of oblivion.Now you might think that the rear- and mid-engine model lines—the 911 and the Boxster/Cayman—make the acoustics engine-ers’ job significantly easier than those with front engines. After all, with their boxer engines’ inclination toward more raw overto-nes, they produce a notably sporty sound backdrop that always sounds a bit like a race car and whets the appetite for some high-revving fun.“With the Cayenne, Panamera, or Macan, the distance between the engine and the driver is a bit greater,” Pfäfflin says. “But the core of our activities remains the same: we make audible what the engine is doing, although the V-engine series make for a more subdued spectrum. The motivation for our work is unchanged: as soon as the feel for the engine load is clearly and unambiguously transmitted to the driver, he drives better—and is usually happier as well.”Artificially generating sounds and adding them to the drive spectrum through speakers is absolutely out of the question. It’s a bit like the German beer purity law, the “Reinheitsgebot,” which prohibits all artificial aromas and additives. What you hear is only what the engine begets: Pure Porsche.