A Vehicle’s Sound System Can Be a Matter of Life and Death

A Vehicle’s Sound System Can Be a Matter of Life and Death

- in Automotive
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A Nissan Leaf electric vehicle at the Geneva Motor Show in March. Since electric motors are virtually silent, the Leaf has a system that emits a sound to alert pedestrians when it is driven at low speeds.

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Harold Cunningham/Getty Images

Adjusting the acoustics of modern automobiles is not only about comfort or pizazz. There are safety considerations, too.

Advanced driver-assistance features like lane departure warnings, automated braking systems and vehicle or pedestrian proximity alerts generate their own bells and chimes. But such sonic alerts can create dangerous distractions, leaving drivers unable to determine which sounds are critical.

“We spend a lot of time tuning those beeps and pings and assessing the quality of the chimes,” said Alan Norton, senior technical leader for audio quality at Ford Motor.

Electric vehicles, with their virtually silent motors, present a separate set of challenges. Especially at low speeds, an electric vehicle provides no audible sounds that might alert pedestrians, cyclists or other drivers to the car’s presence.

“Normally, you expect to hear a car coming,” said Grant Courville, a senior director at the software company QNX.

And so, for several years, designers of electric vehicles have experimented with added sounds called external pedestrian alerts that would warn those nearby that a car was approaching.

The electric Nissan Leaf uses such a system, aptly named the Approaching Vehicle Sound for Pedestrians. It is set off automatically at speeds below 16 miles per hour, emitting a noise from a speaker in the front of the car that sounds like a muted version of a Harrier jet taking off.

At 19 m.p.h., the Leaf’s wheels generate enough noise to turn pedestrians’ heads, so the speaker shuts off. (In reverse, the Leaf sounds like something from a “Star Trek” fan’s garage, emitting a phasers-on-stun sound effect.)

As yet, though, there is no industry standard for electric vehicle warnings, which is why many electric cars — including the Tesla Model S — do not have them.

The National Highway Traffic Safety Administration has been instructed by its parent, the Department of Transportation, to develop a rule for such pedestrian safety sounds. But the agency has several times postponed putting such a rule into effect.

One difficulty, audio engineers say, is that lower-frequency sounds, which travel farther at lower volumes, lack the kind of directionality that could tell someone stepping off a curb where a car was coming from. Conversely, higher frequency sounds tell listeners where the sound is coming from but require more volume to alert people that a car is headed their way.

Within vehicles, meanwhile, audio programmers continue to work on systems to reduce potentially hazardous sonic distractions. In sport utility vehicles with three rows of seats, for example, it can be difficult for a driver to talk to someone in the very back.

“You’re probably tempted to turn around and take your eyes off the road,” Mr. Courville said.

So QNX has developed a system that detects when the driver is speaking, and it uses a nearby microphone to pick up his or her words and send them through the rear speakers.

“You shouldn’t have to yell for in-car communications,” Mr. Courville said.

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