The problems of acoustic ecology in the human environment are studied by many researchers around the world, especially the contributions to city noise made by cars. In recent years, more and more electric vehicles that are much quieter have appeared on city streets. Cars and motorcycles are traditionally powered by the rather noisy operation of an internal combustion engine. Electric transport, on the other hand, runs on electric motors powered by noiseless energy sources (batteries, fuel cells, capacitors, etc.). As a result, the electric car creates noise only due to the contact of the tires with the asphalt and due to the turbulent air currents on the car body. All this makes the movement of electric vehicles less noisy and, at low speeds, almost silent. Therefore, electric vehicles are classified by UN Regulation No. 138 as silent vehicles. With the undoubted benefit of this circumstance for the acoustic ecology of the city, there is also a quiet threat to humans – a pedestrian may simply not hear the approach of an electric car. It is for this reason that the legislation of many countries of the world obliges electric vehicles to be equipped with special sound devices – AVAS systems that increase the acoustic visibility of electric vehicles.
Contribute to the latest Thor AVAS survey on pedestrian safety, here.
In recent years, a wide variety of micromobile vehicles have also begun to appear on the roads in large volumes. And, more importantly, on the sidewalks of cities – scooters, gyro scooters, unicycles, segways and everything that, despite its harmless appearance, can sneak up unnoticed (at a speed of up to 30 km/h) to an unsuspecting pedestrian. While the issue of ensuring the safe movement of microtransport vehicles causes great discussion, no country in the world has resolved this in law.
Thor AVAS, together with the Research Institute of Building Physics, is conducting a large scientific study of the safety of electric transport. Their work studies how different vehicles are acoustically visible (heard) to a pedestrian and how it is possible to increase their visibility without causing ecological damage to the acoustic environment.
In-laboratory work takes place in a unique acoustic measuring complex – a large acoustic anechoic chamber. This is a room in which there is absolutely no echo due to the walls and ceiling being covered in a layer of a special sound-absorbing structure more than 1 meter thick.
The room used by Thor AVAS is the largest anechoic chamber in Europe and one of the largest chambers in the world – the floor area exceeds 120 square meters. It is also very quiet in this chamber – so quiet that it is a unique auditory experience, with the background noise level in the chamber only reaching 18 dBA.
During testing, many loudspeakers are placed in a circle around the cell. Together they make up the radiating part of the laboratory setup. Six speakers imitate the noise of the environment, reproducing, for example, the sounds of a city courtyard or a city park, in 5.1 stereo, comparable to a movie theater. Another three-way speaker system simulates the noise of an approaching electric vehicle’s tires.
The approach of a car is simulated at a speed range between 10 and 50 km/h. Imitation occurs by increasing tire volume according to auditory laws. When the distance between the car and the pedestrian decreases, the sound pressure level increases by 6 dB.
Finally, consider the last loudspeaker is the AVAS system, the principle which is the subject of the study. By playing different sounds through the AVAS system, traffic safety conditions can be significantly improved.
The essence of the experiment is to determine how long it takes a pedestrian to hear a car approaching them. Participants of the experiment are given registration panels and the experiment begins. At first, participants in the experiment hear only the sounds of the environment, the park or the yard, because the simulated car is still “far away”. At the moment when participants hear the approaching car, they press the registration button on their remotes. By this pressing, it can be determine how long it took for the pedestrian to register the approaching car, i.e. how much time the pedestrian has to react to the approach and decide on further actions. For example, an electric car without an AVAS system is heard when impact time is between 3-5 seconds, depending on the vehicle’s speed. In such a short time, the pedestrian will not have time to react to the approach of the vehicle and a collision may occur.
When driving an electric vehicle with the AVAS system turned on, it is possible to significantly increase the time for acoustic detection of an approaching car by a pedestrian. The most effective method is to turn the system up to high volume. Very loud and unpleasant sounds can be played through the AVAS system (or alternatively, turn on loud music) and the residents of the next few blocks will know in advance about the approach of the car, which, of course, will have nothing to do with traffic safety. The correct sound of AVAS should ensure the safe movement of an electric vehicle and sound at such a volume that it will not exceed the established rules and sanitary standards for a residential area. However, sounds of the same loudness can have varying visibility. By changing the timbre of the sound, its frequency range, and introducing volume modulations and discrete components at certain frequencies, it is possible to significantly increase a vehicle’s visibility without increasing the volume.
The Thor AVAS study aims to find the best ways to control the visibility of an electric vehicle using the AVAS system. The goal is to create such sounds for the AVAS system which, on the one hand, will not be unpleasant, excessively loud, and attract unnecessary attention, and, on the other hand, provide optimal and speed-independent visibility.