Applied Acoustics

Abstract Electric and Hybrid Electric vehicles (EV and HEV) seem to be the future of transport in smart cities and the key for the total reduction of noise disturbance and pollution in urban areas. However, several problems have to be solved to guarantee the safety of these types of vehicle. Up to now, the use of HEV has shown the dangers of a “quiet” transport system in urban environments; in fact, it has been estimated that an HEV is twice as likely to be involved in a pedestrian crash as would be an internal combustion engine (ICE) vehicle in the same situation. With the aim of improving their safety, different kinds of warning sounds are being designed to increase the detectability of EV and HEV without themselves becoming new annoying sound sources. The sound directivity, frequency of emission and intensity of warning sound systems will guarantee their efficiency and limited noise impact. Several research works bring to the fore a significant variation of the pedestrian response time to different acoustic stimuli. However, it is necessary to examine the suitability of these warning sounds according to the urban environments in which they are going to be emitted. Distinct areas inside the city have different soundscapes whose spectral content can vary significantly, masking some of the sounds suggested as an alert. This paper analyses in detail the main characteristics of several warning sounds proposed by the industry, conducting a comparative study of the different design trends. A total of 131 sighted listeners were exposed to a virtual road-crossing test. The behaviour and appropriateness of warning sounds are analysed depending on the urban environment. For this purpose, three clearly different soundscapes have been selected: stopped vehicles at a traffic light, a pedestrian shopping area and the vicinity of a playground. The results highlight the wide variability in pedestrian reaction time for the different warning sounds used. Some signals considerably improve the detectability of the vehicle, providing results even above the ICE vehicle ones. However, other warning sounds do not decrease the reaction time with respect to the EV. In addition, a clear dependence is observed between the detectability and the soundscape involved, changing the results for the same warning sound depending on the acoustic environment.

The acoustics of churches is a cultural heritage to be preserved as carefully as the artistic and architectural aspects of this particular category of buildings. The acoustic characteristics of an environment could be measured according to different techniques varying from the numerical quantification, by means of acoustical parameters, to the recording of the binaural or ambisonic impulse responses of several combinations of source–receiver locations. The complexity of this kind of buildings can lead different researchers to choose dissimilar ...

For many years the problem of noise generated by trains has had an increasing importance; in this paper, attention is focused on the noise generated by the train wheels due to their vibration. Today there are many kinds of railway wheels which are affected by different noise generation mechanisms. If the traditional and well known solid wheel is considered, a lot of data is already present in the literature both concerning the vibration and the noise point of view. On the other hand, the widely used resilient wheels are not so well known in their vibratory and acoustic behaviour as in the case of solid ones. The extensive experimentation presented and commented in this paper looks for a confirmation of some literature data first, and then it gives new results. Particularly the vibro-acoustic characterization of different kinds of wheels (both solid and resilient ones) has been carried out, in order to have a comparison between the behaviour of the newly built wheels and the older ones, representing the state of the art. Besides it has been shown that a detailed modal analysis of the suspended wheel coupled to sound measurements can give useful information about the wheel noise emission in its normal operating conditions.

Children and teachers are organisms involved in information exchange within an environment called a classroom. The biological task for the auditory system is to alert important changes. Audition is always active and specialises in sudden, extreme, or quickly approaching sounds that might necessitate action.
High intensity sound (even within legal levels) might induce physiological stress on hearing and voice organs when competing with ambient noise, psychophysiological stress on heart rate and metabolism, or psychological reactions such as annoyance.
A recent German study showed that the acoustical conditions in elementary classrooms often do not fit the specific needs of children, who are more sensitive to acoustic problems due to reverberation and noise than adults.
If the soundscape matters to school children, how can we create optimal acoustics in classrooms for communication, learning, and development? This is a great multidisciplinary challenge, calling for us to bridge environmental psychology, acoustic design, and education.
In this presentation, I will explain concepts such as SPL, reverberation radius, and Lombard effect, and share preliminary results from a pilot study in Singapore kindergartens.