Just as in-vehicle audio systems are production staples, exterior sound systems may become standard fare on hybrid-electric (HEVs) and electric vehicles (EVs).
The reason external sound may become commonplace on electric-mode operating HEVs and on EVs is because at low speeds the vehicles are quiet—maybe too quiet.
A couple of years ago, the University of California–Riverside (UCR) launched the first in a series of sound tests. With funding from the National Federation of the Blind, the UCR research project centered on participants listening to audio recordings of hybrid-electric and internal-combustion engine (ICE) powered vehicles approaching from two directions at 5 mph (8 km/h).
Research subjects were able to judge the approach direction of the ICE-powered car when it was about 28 ft (8.5 m) away. In contrast, the approach direction of an HEV was not determined until the vehicle was 7 ft (2.1 m) away, noted Lawrence Rosenblum, UCR professor of psychology and one of the project's researchers.
"Across eight experiments testing three hybrid-electric vehicles and three ICE engine cars in recorded and live contexts, sighted and blind subjects found the hybrid cars significantly harder to localize than the ICE cars," said Rosenblum.
So far, no production vehicles in North America use an external sound system, but the issue is being discussed.
"We're researching this right now to determine if the Nissan Leaf will have external sound, and what the sound will be if it does," Brian Brockman, Manager of Corporate Communications, Midwest Region for Nissan North America, said about the EV, which is slated to reach the U.S. market in December.
Visteon is production-ready with an external sound system following a year of research and development work.
"It's an outgrowth of our active sound management program. We found that the amplifiers, speakers, and the algorithms that generate sounds for vehicle interiors were very similar to what would be needed on the outside of an ultraquiet vehicle," David Chi, Associate Director of Business Development–North America for Visteon's Premium Audio Systems, said during a media event at the supplier's southeast Michigan complex.
The production intent hardware of Visteon's external sound system features a 4 x 20-W remote Digital Signal Processing (DSP) amplifier to synthesize and playback prerecorded engine sounds that would interface with the vehicle's communications bus for synchronization with pedal commands and other vehicle operating conditions.
In the demonstration concept, external sound passes through two 4-in (102-mm) speakers located at the vehicle's front and a 6.5-in (165-mm) woofer at the vehicle's rear. "Instead of paper cones—usually the material for speakers located inside the car—the speakers would use polypropylene or another material that can withstand a harsh exterior environment," said Chi.
In a production application, speakers could be packaged behind the front fender, behind the front grille, on the vehicle's crossbeam, or in another semi-protected locale.
"The actual sound would be done in partnership with the automaker since an engine sound is a vehicle's signature," Chi said about the software code that engineers would develop to generate a particular sound.
A future production battery-electric vehicle for the North American and European market may be the first to feature Visteon's external sound system. "We've submitted a quote and hope to win business with an auto manufacturer that intends to have exterior audio on a future vehicle," Chi said.