Proposed Sounds for Electric Vehicles
Electric and hybrid electric vehicles are one of the most promising solutions to long term emission targets in the automotive industry, and the electrification of transport is a growing trend. Potentially more efficient and much greener than internal combustion engines, advances in battery and powertrain technologies mean better performance and better range than ever before.
Another significant advantage to electric vehicles is that they operate almost silently, reducing noise emissions both inside and outside the car. While this is a desirable feature for several reasons, it can also present additional problems - particularly where pedestrians and other road users are concerned. The natural noise of the combustion engine acts as a key warning system of the presence of the vehicle, and additionally, the tone of the engine when accelerating or slowing down gives vital clues to the speed and likely manoeuvrers of the vehicle.
Sound for electric vehicles is an interesting concept, and free from the restraints of an ICE, manufacturers have experimented with various ideas. Many see the opportunity for brand recognition and styling with internal sounds which mimic engine noise, giving the driver a feeling of familiarity or the impression of driving a powerful or sporty vehicle. External sound is also becoming a key area of development, with different sounds and warning systems being developed to alert pedestrians and other road users of a vehicle's approach.
The Regulatory Landscape
As far back as 2011 the European Union drafted guidelines for Acoustic Vehicle Alerting Systems (AVAS), with the aim of recommending to manufacturers systems to be installed to provide an audible signal to pedestrians and vulnerable road users. In 2013 a draft law was approved to tighten noise limits for cars to protect public health, and also to add alert sounds to ensure the audibility of hybrid and electric vehicles. The amendment stating that:
“The sound to be generated by the AVAS should be a continuous sound that provides information to pedestrians and vulnerable road users of a vehicle in operation. The sound should be easily indicative of vehicle behaviour, and should sound similar to the sound of a vehicle of the same category equipped with an internal combustion engine.”
In 2014 the legislation was passed that requires AVAS to be mandatory in all new hybrid and electric vehicles by 2019.
Earlier in 2016 a new regulation was adopted by the UNECE World Forum for Harmonization of Vehicle Regulations (WP.29), which requires acoustic and warning devices on hybrid and electric cars. The ‘Regulation on Quiet Road Transport Vehicles’ aims to minimize the risk posed by silent cars, without creating a disturbing level of traffic noise.
According to the regulation, quiet cars should be fitted with an AVAS to create artificial noise in the speed range from 0-20 km/h. Above 20 km/h the noise of wind and tires on the road are audible thus negating the need for a warning system. The regulation also introduces the minimum AVAS sound levels, spectrum and frequency shift, depending on the vehicle’s forward or backwards speed. When the car’s speed increases the sound becomes louder -– 50 dB at 10 km/h, 56 dB at 20 km/h, and 47 dB for reversing - so that pedestrians can audibly judge the speed. To provide for environmental protection, the regulation also specifies the maximum overall sound limit. Loud enough to warn pedestrians of an oncoming vehicle, but quiet enough to protect against noise pollution.
Potential Dangers of ‘Silent’ Vehicles
Clearly the key issue for silent cars is that pedestrians may not hear them coming, and dangerous situations may arise. This is an even greater problem when considering the blind and visually impaired. Various studies have indicated that silent vehicles are more likely to be involved in an accident than traditional ICE vehicles, and charities supporting the visually impaired have lobbied for legislation to mitigate that risk.
A study commissioned by UK charity Guide Dogs and carried out by TAS Partnership Ltd suggested that electric vehicles were a growing danger. The study found a 54 % increase in accidents where pedestrians were injured by silent vehicles from 2012 to 2013. A YouGov survey commissioned by the same charity found that 76 % of the general public agreed that quiet vehicles make the roads less safe for pedestrians with visual impairment. Furthermore, around three quarters of those surveyed said that quiet cars made roads less safe for old people and children.
The Royal National Institute of Blind People (RNIB) has been supporting the European Blind Union and World Blind Union in campaigning the UN for tighter legislation on alert systems. The organisation lobbied for the recent WP.29 regulations to be more protective of blind and visually impaired pedestrians, but noted its disappointment that the legislation included an option for manufacturers to fit a ‘pause’ switch for the AVAS system, whereby it can be temporarily disabled.
Proposed Sounds for Electric Vehicles
A number of carmakers have trialed alert and warning systems in electric vehicles already, and the industry continues to design and develop improved technologies. Early examples include GM’s ‘Safe Sound Alert’ which it introduced after collaboration with the National Federation of the Blind. In 2010 the automaker introduced its ‘Pedestrian-Friendly Alert System’, which was manually activated on the Chevrolet Volt - using the horn to emit warning chirps to pedestrians.
Nissan’s Vehicle Sound for Pedestrians (VSP) system was developed for the Leaf in 2011, and uses a sine-wave sound system that sweeps from 2.5 kHz at the high end, to a low of 600 Hz. The sound system emits sweeping high-low sounds depending on speed and whether the car is accelerating or decelerating.
New ideas and concepts for vehicle sounds are also demonstrating the ability to control the direction of sound so as to provide warnings with minimal impact on noise pollution.
The EU-funded eVADAR (Electric Vehicle Alert for Detection and Emergency Response) project tackled this exact challenge. The project developed a prototype of an intelligent alert system for electric and hybrid vehicles. The system detects pedestrians and other vulnerable road users at risk of collision and directs a warning sound specifically at them.
The sound is optimiszed to be clearly audible to the targeted individuals, but barely perceptible to other road users. The optimal sound volume is determined for each warning and depends on the level of background noise, ensuring that the alert is loud enough, but no louder than it needs to be. The timbre of the sound has been tweaked for the best possible compromise between high detectability and low noise pollution.
The research involved major car manufacturers - PSA Peugeot Citroën, Renault and Nissan - automotive suppliers, universities, research institutes and the European Blind Union, which supplied input of road users particularly reliant on sound.
Directional sound is produced by an array of loudspeakers that boost the sound in a specific direction and cancel it out in others. The system detects road users by means of cameras and radars already being used in driver assistance systems in many vehicles. The information is fed into a control unit developed by eVADAR, which communicates with the associated acoustic system. The warning sound is then emitted from six speakers at the front of the vehicle. Ambient sound is measured by microphones and this is factored in to ensure that the warning sound is clearly audible at the location of the at-risk individual, but no louder than necessary.
To guarantee maximum safety, the targeted warning is accompanied by a low-level omnidirectional sound, and depending on future legislation additional sounds could also be integrated to indicate that a car is reversing.
Peugeot Fractal Concept
Manufacturers have also been working on their own designs and concepts, with one such example PSA Peugeot Citroën’s Fractal Concept.
The concept is based around sound identity to create a very specific brand and image. Much of the technology is relevant to the internal sounds, with the ‘location’ of sounds projected to certain areas to convey information to the driver. The voice from the navigation system, for example, appears to come from some way in front of the vehicle, but as it moves along the sound source shifts to the cabin and then to the side of the car in which the driver needs to turn.
PSA Peugeot Citroën collaborated with sound designer Amon Tobin to develop an acoustic identity for external vehicle noise. The Fractal’s external sound signature keeps the car in sync with other road users, such as pedestrians and cyclists, who are alerted to the car’s presence by different sounds specific to its status - acceleration, deceleration, and cruising speed.
One of the most prominent commercial solutions already on the market is the HALOsonic system developed by Lotus Engineering and HARMAN.
HALOsonic technology encompasses the cancellation of sounds, as well as the creation of sound through Electronic Sound Synthesis (ESS). Sounds are produced outside the car for pedestrian safety, and inside the car for improved driver feedback and enhanced driving experience.
The External ESS side of the system is developed specifically to provide safety for other road users and to meet forthcoming legislation. It works by synthesizing an engine sound with volume and pitch appropriate for the speed and direction of the vehicle. The sound is projected from speakers mounted at the front of the vehicle, giving pedestrians an early warning of its approach. The sound is projected only in the direction of travel, fading away almost instantly once the vehicle has passed.
The HALOsonic system is customizable so that automakers can integrate their own unique sounds to project the image and style of their particular brand.
The Future Will Sound Familiar (to Pedestrians)
With legislation already in place, all electric vehicles of the future will have to emit a level of sound to make them safer for pedestrians and other road users who may otherwise not hear them coming.
In the absence of an internal combustion engine - which may be tuned to emit a particular sound, but is by its nature of a particular noise - the option to customize systems with unique sounds provides designers with a new freedom in terms of customization and branding. These image-enhancing concepts will be endless for internal noise, but will be limited for external noise which will have to meet certain guidelines to suit legislation and to ensure vulnerable road users are protected.
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