Porsche’s Sound Symposer–perhaps a rather self-congratulatory contraction of “symphony” and “composer” –is among the more honest of this sort of sound-generation system. Channeled right out of the inlet tract itself, the Symposer plumbs sound waves through a tube directly into the car’s interior when a “sport” button is selected, opening a butterfly valve. With the butterfly valve closed, sound is more muted. Both the 991-chassis 911 and Panamera GTS have Symposers. It’s fairly simple and mostly mechanical in nature.
For the F10-chassis M5, BMW recorded the car’s engine at all rpms and throttle loads, stored all those permutations and makes it available for playback through the car’s stereo. Virtual engine sound on demand for your aural pleasure, courtesy of digital signal processing.
The precise sample is determined by engine load and rpm. But the inescapable point is that the car puts distance between itself and the driver where a true driver’s car does everything possible to remove distance and improve communication.
It’s the automotive equivalent of being at a big football game, sitting on the 50-yard line, yet watching the broadcast on your mobile device. A Foley artists’ special effects film soundtrack for your car.
Other players in the sound effects game include Lexus, but in their most elaborate case, no faking takes place. For their flagship LFA with its F1-inspired V10 powerplant capable of 9,500 rpm (now out of production), engineers wanted the driver enveloped as completely as possible in sound by the high-revving jewel of an engine. Lexus went to the length of contracting Yamaha’s musical arm to hit the high notes, as they were.
Yamaha went about the project thinking of the cabin as the performance hall, the engine itself as the instrument and the driver alone as the audience. Anyone who has driven the LFA can attest to the singular experience of that particular automotive sound stage with its harmonies and overtones as complex as a huge pipe organ or a brass band. Could Mozart have heard it, he’d have gotten completely verklempt.
Volkswagen’s “Soundaktor” in some models like the GTI and Beetle Turbo operates akin to BMW’s system, but it amplifies the engine’s actual sound inside the cabin. It doesn’t re-create or synthesize the signal aimed at the driver and passenger. The sound rises from under the hood through a dedicated speaker.
By the way, intakes and exhausts are not the only sources of noise from cars. The audio signature of automobiles is hardly simple and comes from multiple sources. The engine itself barks not just from the intake and exhaust system but often, and to varied degrees by the hammering of valvetrain lifters and rockers emanating from under the valve covers or from deep within the valley of an internal-cam engine. And older engines with timing chains not well insulated rattle those links in pitch and volume proportions to rpms, the Ferrari V12 being the classic and most musical example.
Engines also obviously transmit vibration to the cabin, adding another non-acoustic sensation to the mix. Spinning gears inside a manual transmission whir in relation to speed. Once up to speed, tire noise rises and tires can also screech as they reach their limits of adhesion. Finally, sheer wind noise rises with speed as well. Tally it up and an internal combustion-powered vehicle is an eight-channel auditory device or an eight-piece band. Nine in the case of hybrids carrying electric motors.
And what about fully-electric cars? Lacking internal combustion explosions constantly occurring, they could use a soundtrack, too.
Ask any pedestrian.