The sound of electric power

The sound of electric power

The sound a vehicle makes, or does not make, is an important ingredient in its identity and many worry that near-silent electric cars may be seen as devoid of personality.

Ricardo engineers have developed systems to give EVs their own authentic sound and a distinct identity for their brand.

in a world poised on the brink of automotive electrification across the
board, sound quality has become even more important. Most drivers accept that, though EVs are fun to drive, the noise made by an electric car does little to convey the essence of a brand. Ricardo thought so too and in 2013 embarked on a project called Realistic Augmented Sound by Ricardo
(RAS-R). Rather than creating unrelated synthetic sound like some existing
systems, RAS-R ‘listens’ to the electric machinery powering an electric vehicle and subtly modifies it to create a pleasing sound signature, a signature directly linked to the dynamic behaviour of the car.

Deliberately engineering the sound a car makes is not new, but objectives sought by engineers have changed considerably over time. Sixty years ago, the emphasis ranged from doing everything possible to subdue powertrain noise in the case of the Rolls-Royce, to simply quietening exhaust noise down to acceptable levels. Once that was accomplished with family cars and sports cars, their sound signature was left to chance and the choice of equipment.

Buyers could be fairly confident that an Alfa Romeo fitted with a twin choke Weber carburettor, for example, would make an exciting sound. As time has passed, the subject of sound, or noise, has become more complex
for two main reasons. One of those is legislation. Manufacturers face much greater restrictions and cars are subject to more complex regimes such as driveby noise tests. The second is technology. For efficiency, virtually all new internal combustion engines are turbocharged. This has the effect of subduing the induction note that would once have made a significant contribution to the more pleasing side of a car’s sound signature. For a performance car, induction sound is arguably more
important than the exhaust note, certainly to the driver.

Ricardo has designed many systems to enhance the natural sound of combustion-engine powered cars. These include active exhaust systems
with internal flaps, which produce a precisely engineered sportier note during acceleration. Ricardo also developed the intake sound generator system to extract the natural induction sound from the intake manifolds of the McLaren MP12-4C, creating a more spirited engine note inside the cabin than the turbocharged V8 would produce unaided.

Electric cars offer more of a challenge. An electric motor does not produce a soundtrack that occupants normally associate with a car, and it also bears
a similarity to mundane machinery like domestic appliances. Electronically
generated sound is one solution to augmenting electric vehicle sound, but
Matthew Maunder, Ricardo technical specialist for noise and vibration, is sure of one thing: sound that is engineered into the car must be absolutely
authentic. For that reason, he does not believe that synthetically generated
sound is the answer, especially for EVs.

“Synthetic sound systems use processing power to replace a sensor, so to some extent it’s a cost reduction initiative. Arguably, it gives more freedom
to produce exactly the type of sound you want,” he says. “We’re limited with RAS-R to some extent because the sound is authentic, but we do have strong capabilities to modify the basic sound. I would argue that perhaps starting from a clean sheet, as you do with synthetic sound, gives too much freedom.

“If the sound you hear as a driver deviates from the behaviour of
the vehicle even for a moment,” he continues, “then the brain identifies it
as a separate perceptual object and, in the driver’s mind, these will never mate up again.” Synthetic sound generation systems that have been developed to date can take signals from the vehicle CAN bus, or a throttle position sensor, “but there might be a delay or lag or the synthesizer might make a sound that doesn’t relate exactly to what the car is doing. At that point, the driver’s brain rejects it because the sound just becomes a noise,” says Maunder.

RAS-R is absolutely authentic because its source is the sound made by
the vehicle powertrain. Initially, work was done on combustion engine systems with an automotive grade microphone positioned inside the intake manifold. The signal is processed, modified and relayed into the cabin via loudspeakers. The important thing is, it’s authentic and not synthetic. “It works well,” explains Maunder, “because that bark is still there
inside the intake manifold but it can’t get out because of the turbocharger.” The driver hears a sound more akin to that of a naturally aspirated engine, but tuned to the quality, shape and intensity decided upon by the vehicle manufacturer.

The human brain is good at sensing the slightest degree of undesirable lag
present in even the best turbocharged engines. The augmented sound system helps with that too, instantly delivering a change in engine note in response to the driver’s actions, and creating the impression for that split second thatengine response is instantaneous too.

Read the full article in RQ 2018 Q1