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Making that throaty V8 sound from an engine that isn’t

A fallout from the quest for improved gas mileage is smaller engines, typically 4-bangers, which lack the vroom of a V8 power plant. These small engines with their putt-putt sound are popular in LA where fuel prices are well above the national average. Now, innovative automakers are embellishing the engines with-would you believe-fake sounds. The concept is not only being added to lower-priced sporty vehicles but also to high-powered and high-priced vehicles.

Parked, the BMW M5 conveys an image of raw power; however, when underway, BMW engineers deemed the acoustic image to be lackluster. Thus, they linked the vehicle’s stereo system’s digital signal processor into the engine management system; this allows the audio system to simulate the sound of a twin-scroll, twin-turbocharged V-8 engine in sync with the actual 560 HP power plant humming away underneath the hood. When one revs the engine or hits the gas when the traffic light turns green, the car stereo synthesizes the bark and roar that one would not hear when sitting behind the wheel. BMW claims that its Active Sound Design system accurately reproduces the sound of the engine over the full range of RPMs, torque loads, and vehicle speeds.

Porsche has a long reputation of powerful, mean-sounding engines in its venerable 911; however, when the automaker switched from an air cooled to a water cooled engine that unmistakable sound was lost. In fact, Porsche acknowledges that the 911’s unique sound quality of the vehicle was a criterion ever since its debut in 1963. For the new 2012 Type 991 series, Porsche engineers focused on creating a sonic profile to satisfy all possible operating states, ranging from engine starting and idling (presenting an image of power without being obnoxiously loud) to a wide-open racetrack roar when the pedal is pushed to the medal. Unlike BMW, Porsche desired a genuine sound not an electronically synthesized one. Thus, the engineers developed a new Sound Symposer, which is standard on both versions of the 991. An acoustic channel picks up intake vibrations between the throttle valve and air filter; a membrane incorporated in the channel reinforces the vibrations and transmits them as an engine sound into the cabin. The result is a direct acoustic link between the cabin occupants and the engine, providing optimal transmission of the load-dependent sounds. The system can be activated or deactivated by the driver via a “Sport” button that controls a valve ahead of the membrane. In addition to amping up engine sounds, the sound of gearshifts can be enhanced.

For performance enthusiasts with Porsche tastes and a Focus St pocketbook there is the-well-the Focus ST. Ford engineers added a special sound tube, called a sound symposer, which amplifies the throaty sports car-minded motorists relish. Although the name is the same as Porsche’s moniker, the technology is different. Ford engineers developed a method to naturally amplify the specific lower range of engine frequencies found between 200 and 450 Hz that are music to the ears of performance junkies. The sound symposer utilizes a composite “paddle” that vibrates with intake air pulses. Ford has employed the sound tube concept on previous iterations of the Mustangs; however, the sound symposer used in Focus ST is unique because of its electronically controlled valve, which opens and closes based on driver inputs: engine speed, accelerator pedal position, and gear selection. In lower gears, the valve is mapped more aggressively; however, in higher gears the effect is decreased to enable quieter cruising. This isn’t possible with conventional, passive sound tubes.

In contrast to the BMW’s Active Sound Design is Honda’s Active Noise Cancellation technology employed in its Odyssey minivan; the system uses the vehicle’s speakers to cancel out cabin noise with out-of-phase sound waves, and an inversion of the Prius’ Proximity Notification System, which uses external speakers to make the silent hybrid’s presence known to pedestrians.

In addition to Honda, other automakers are embracing noise-enhancing technology for electric vehicles. Many owners of electric vehicles find their quietude a plus; however, there is a downside. Vision-impaired pedestrians and others who rely on aural cues are at increased risk. Currently, the Nissan Leaf has emits a sound when the vehicle starts up, accelerates, or backs up. For its Volt, which currently has a warning bell that can be activated by the driver, General Motors Co. is considering options for a continuously broadcast sound. Five years ago, Toyota Motor Corp. began working on sounds for its HEVs, initially looking at using the vehicle’s horn, having it tweet or make short toots at low speeds. In the near future, the government will require these quiet cruisers to emit some type of noise at low speeds, when their battery-driven motors usually run silent. A study authorized by the National Highway Traffic Safety Administration in 12 states reported a 50% higher rate of accidents involving pedestrians for hybrids than for standard gasoline-powered. The agency is formulating regulations that will require sounds on battery-powered vehicles by the end of 2016. This upcoming mandate has caused auto makers to develop the perfect sound. Some sounds under consideration include those of jet engines, bells, birds, flying saucers, and revved-up sports cars.