Halosonic External Electronic Sound Synthesis

The Concern

Lotus Engineering and Harman International have developed technologies to synthesise external sound on electric and hybrid vehicles to counteract the growing concern these 'quiet' vehicles pose to pedestrians and cyclists. A simulation of a real engine sound is used on the 'HALOsonic' Hybrid technology demonstrator vehicle, making it instantly recognisable that the vehicle is in motion.

Electric and hybrid vehicles, a favourite choice of the environmentally conscientious have recently come in for criticism from blind and partially sighted people. Due to the almost silent operation of hybrid vehicles at slower speed when running on electric power, the independent travel of the blind and partially sighted may be put at risk as they cannot hear these quiet vehicles as they approach, making crossing a road or walking through a car park hazardous.

The Solution

The 'HALOsonic' Hybrid technology demonstrator uses a standard Toyota Prius, one of the highest volume and most advanced hybrid vehicles to demonstrate the sound synthesis application and compensate for the lack of engine noise emitted by the vehicle when running on an electric motor. What has resulted is the same environmentally conscious hybrid vehicle, without the potential risk to pedestrians and cyclists.

The solution that Lotus has devised is a novel reapplication and development of its Electronic Sound Synthesis technology. This is a part of the Lotus suite of patented active noise technologies which comprise three main systems, Active Road Noise Cancellation, Engine Order Cancellation and Electronic Sound Synthesis.

The Technology

External Electronic Sound Synthesis provides specified electronic sound models which can be applied to an external speaker system to improve pedestrian safety. This is especially important for electric and hybrid vehicles which can be difficult to hear at lower speeds due to their drive mechanism. A synthesised sound, dependant on speed, is projected from speakers at the front and rear of the vehicle, making it instantly recognisable that the vehicle is in motion.

To synthesise the engine sound, a road speed signal is taken from the vehicle and a waterproof loudspeaker system is positioned behind the grille allowing the sound to emanate from the front of the vehicle. The sound can also be synthesised from the rear of the vehicle in the same way, allowing warning when the vehicle is reversing. When a car is operating on the electric motor only, throttle and speed dependent synthesised sound projects an engine sound in front of the vehicle. The technology was designed around the behaviour of a conventional engine, using an existing engine sound which makes it instantly recognisable with the pitch and frequency helping to identify vehicle distance and speed.

If the hybrid's engine starts operating, at higher speeds or throttle demands or lower battery levels, the control system automatically stops the external synthesis. When the powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantaneously sets the system running again. It is all completely automatic and the driver hears almost none of the additional sound. In order to generate a realistic engine sound, recordings of a suitable donor engine are made and analysed to establish the characteristic frequencies at different engine speeds. These frequencies are then entered into the synthesis controller in the form of a 'voice' which outputs the sound through an amplifier and out through the loudspeakers. Alternatively, more futuristic sounds for electric vehicles can be created using sampled sounds and generated waveforms.

HALOsonic

The HALOsonic suite of patented noise management solutions comprises three main systems, each of which can be used individually or in combination.

The first two systems are Active Road Noise Cancellation (ARNC) and Engine Order Cancellation (EOC). Both of these look to reduce noise levels in the cabin, particularly at frequencies that are audibly unpleasant. In the case of road noise, the system reduces broadband noise levels at frequencies below 250Hz whereas EOC tackles harmonic frequencies generated by ignition events in the engine.

Input signals from the engine (for EOC) or sensors mounted to the suspension system (for ARNC) are fed into the electronic controller, as are sound signals, measured by microphones located in the cabin. The software algorithms of the controller then calculate what sound is needed to provide cancellation and the speakers of the in-car entertainment system are used to put this into the cabin. All this takes just a few hundredths of a second and repeats and adapts constantly through the complex control system, seamlessly and instantaneously adapting to changes in speed or road condition. The cancellation system operates on the input signals so other noise in the vehicle such as the audio system and speech are not interfered with or cancelled. The result is a quieter, more pleasant cabin.

The third system is electronic sound synthesis, the purpose of which is to enhance the sound in the cabin, or enhance the sound at the front of the vehicle to increase pedestrian safety. The control system uses engine speed signal, a throttle position sensor and the in-car entertainment system to add sound. In this way a car could be made to sound sportier or be given the pleasing sound characters of, say, a flat 6 or V8 engine. Coupled with EOC and ARNC, the interior sound in the cabin can be tuned to enhance the driving experience and match the brand attributes of the vehicle.

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