Here's a video of the Nissan Leaf driving forward (along with the sound it makes)In developing the sound system, Nissan studied behavioral research of the visually impaired and worked with cognitive and acoustic psychologists. After looking at applied original technology developed to reduce vehicle noise and conducting tests in Japan and abroad, the Approaching Vehicle Sound for Pedestrians system was created.
The sine-wave sound system sweeps from 2.5kHz at the high end to a low of 600Hz, an easily audible range across age groups. Nissan worked to avoid a sound range that would add unnecessary noise to the environment (around 1,000Hz).
Depending on the speed and status (accelerating or decelerating) of Nissan LEAF, the sound system will make sweeping, high-low sounds. For instance, when Nissan LEAF is started, the sound will be louder, so a visually impaired person would be aware that a nearby car was beginning operations. And when a car is in reverse, the system will generate an intermittent sound. The sound system ceases operation when Nissan LEAF tops 30km/h and enters a sound range where regular road noise is high. It engages again as Nissan LEAF slows to under 25km/h.
The system is controlled through a computer and synthesizer in the dash panel, and the sound is delivered through a speaker in the engine compartment. A switch inside the vehicle can turn off sounds temporarily. The system automatically resets to "On" at the next ignition cycle.
Here's a video fo the Nissan Leaf backing up (along with the sound it makes)