By Prof. Ercan Altinsoy, Chair of Acoustic and Haptic Engineering, Technische Universität Dresden
Hearing is an important sense in our daily life and enables us to interact with our environment, objects and other persons. The sound signals deliver us several information. Therefore, hearing and vehicle sounds play an important role for the traffic safety. The timely detection of the vehicles by pedestrians is a prerequisite. However, electric vehicles move almost silently up to a speed of 20 km/h. In order to reduce this risk for all traffic participants including especially children, visually impaired and elderly persons, and cyclists, quiet vehicles should emit artificially generated sounds. For this purpose, standards have already been defined by various national and international authorities with regard to the sound character. The regulation of United Nations Economic Commission for Europe (UN Regulation No. 138 - ECE/TRANS/WP.29/2016/26) and US, Federal Motor Vehicle Safety Standard (FMVSS) 141 are two of the most prominent.
The legislations define the minimum A-weighted sound pressure level per 1/3-octave band. Although the results of several scientific studies were taken into account to prepare the above mentioned standards, we will experience in the following years if the required sound pressure levels will guarantee the intended traffic safety. To gain experience with the defined minimum sound level requirements particularly at very noisy traffic situations is very important. All car manufacturers and suppliers developed successful technical solutions for the implementation of AVAS. At the same time, some technical problems will still be important in the near future. Some of these technical problems are the speaker directivity characteristics, speaker frequency response and sensitivity variations and the placement of the speaker. However the most important aspect is the sound design.
Car manufacturers design individual warning sounds taking into account the defined minimum sound pressure level and frequency requirements. Some of these warning sounds can be easily recognized as a vehicle sound by pedestrians and people and some of them cannot. Some of these sounds inform pedestrians about the operating conditions, such as velocity, acceleration, deceleration, with great success and some of them don’t. Another important topic is the environmental impact. The sound design plays an important role on the perceived annoyance of the warning sounds. Some of these warning sounds can be very annoying for residents.
Over the following years, the society will have the chance to evaluate the perceived annoyance of different warning sounds. The least annoying warning sounds will be preferred by drivers and at the same time by car manufacturers. This will lead to the warning sound design gradually being less unpleasant. The EU Project eVADER and several research groups, including my own, try to improve the technical implementation solutions and the regulations. A possible modification of the standard can include the automatic adaptation of the AVAS level depending of the background noise. Another important future aspect is the detection of pedestrians and emitting a directional sound beam only in the direction of pedestrians to avoid unnecessary noise pollution.