Juan Miguel Barrigón Morillas

The impact of environmental noise on the health and well-being of people living in cities is an issue that has been addressed in the scientific literature to try to develop effective environmental policies. In this context, road traffic is the main source of noise in urban environments, but it is not the only source of noise that pedestrians hear. This paper presents an experimental study using in situ surveys and acoustic measurements to analyse the capacity of acoustic variables related to sound energy to estimate the occurrence and importance of noise effects in urban environments. The results revealed that average sound energy indicators can be considered most significant in terms of the perception of the noise effects studied on pedestrians. When estimating noise effects from them, frequency weightings related to flat or nearly flat spectra (Z and C weightings) were found to provide better results than an A weighting; however, it was also concluded that if the average energy is considered, the use of a temporal I weighting did not lead to improvements. The perception of how noisy a street is, it is strongly associated with a low frequency, and annoyance was the effect that generally showed the strongest significant correlations with acoustic indicators. The indicators of minimum sound levels explained a larger proportion of the variability of noise effects than the indicators of maximum energy; they were even better in this regard than any of the average energy indicators in terms of explaining the variability of startle and annoyance in the ears, and they were found to be equivalent when interruption of a telephone conversation was assessed. Both acoustic variables associated with sound energy in different parts of the audible spectrum and Leq in each one-third octave band showed significant correlations with the effects of noise on pedestrians. Similarities in the structure of the spectra were found between some of these effects.

This review analyzed scientific publications on noise pollution in 22 Arab countries from 1983 to 2022. The objective of this study was to assess the current state of research on noise pollution in the Arab world, identify trends and gaps in the literature, and subsequently formulate a thorough research agenda. A comprehensive search of the Scopus database was conducted using relevant search terms and inclusion criteria. Out of 249 results, 104 studies were selected. The data extraction from the 104 studies includes the country where the study was conducted/designed; the publication year; the journal of publication; sponsorship details; and the research methodology used. VOSviewer software (VOSviewer 1.6.18) was used to visualize the literature data and co-occurrence networks, collaborations, and research fronts. The analysis revealed that Saudi Arabia, Jordan, and Kuwait were the most active countries in noise pollution research, while Sudan and Libya had the lowest number of publications in this field. Additionally, countries like Somalia, Syria, Yemen, and Mauritania had no publications on this subject. Research on noise pollution in this region mainly focuses on noise in urban zones and workplaces, particularly in Saudi Arabia, Kuwait, and Jordan. Topics vary across other Arab countries. The results highlight the increasing significance of noise pollution research in the Arab world, particularly evident in recent periods. However, scientific output from Arab countries remains significantly limited compared to other global contexts. This study emphasizes the pressing requirement for increased investment in noise pollution research, aiming to achieve knowledge of the acoustic situation in Arab countries in order to develop strategies to mitigate population exposure to noise pollution, improve the well-being of citizens, and protect public health.

Noise barriers are common noise mitigation measures usually implemented near roads or railways, with proven efficiency. This work presents a study of a porous concrete material incorporating expanded clay as aggregate, to be used on the sound-absorption layer of noise barriers. A theoretical material model is calibrated using experimental data and then used to estimate the diffuse field sound absorption from the normal incidence sound absorption estimation/measurement. Validation of such estimation is performed by comparing to reverberant room measurements. Numerical simulations are carried out using the boundary element method (BEM) and the CNOSSOS-EU calculation method to assess the performance of different types of barriers incorporating this material. L-shaped and vertical barriers are tested, as well as low-height and conventional (taller) barriers, employed in the context of a railway noise scenario. Different results are obtained by the two methods, mainly due to the different underlying physical principles. Good insertion loss values may be obtained using both conventional and low-height noise barriers together with the porous concrete material if a careful choice of its location within the barrier is made.

The pandemic of coronavirus disease (COVID-19) led to the need for drastic control measures around the world to reduce the impact on the health of the population. The confinement of people in their homes resulted in a significant reduction in human activity at every level (economic, social, industrial, etc.), which was reflected in a decrease in environmental pollution levels. Studying the evolution of parameters, such as the level of environmental noise caused by vehicle traffic in urban environments, makes it possible to assess the impact of this type of measure. This paper presents a case study of the acoustic situation in Cáceres (Spain) during the restriction period by means of long-term acoustic measurements at various points of the city.

Birds generate vocalisations (songs and calls) to communicate. Acoustic communication may be hindered by habitat features so birds can use several strategies to favour sound transmission. Sound transmission depends on the acoustic properties of their habitats. Scree slopes, also known as ‘pedrizas’, are frequent in the Mediterranean forests of south and central western Spain. As the acoustic properties of these rocky grounds might favour sound transmission, we propose that birds might actively use ‘pedrizas’ to increase sound transmission. We assessed the following prediction of the hypothesis: the number of vocalisations recorded should be higher near the ‘pedrizas’ than in forest areas far away from ‘pedrizas’. Using portable recorders in the Mediterranean forest of Monfragüe National Park, we found that the number of recorded vocalisations was higher near the ‘pedrizas’. As this result was not due to differences in species richness, we consider it supports the prediction of the hypothesis. This is new evidence that birds might use a natural element within their habitat to increase sound transmission.

A characterization of the sound absorption of a sustainable material with scarce current use such as natural virgin cork is presented in this paper in order to explore further possible applications in the design of acoustic solutions. Different samples of virgin cork not bonded and various decorative panel formats were tested under random sound incidence conditions in a standardized reverberation chamber. The samples in which the outer bark of the cork was facing upwards showed a better behavior as an acoustic absorber, with sound absorption coefficient values generally greater than 0.6 for frequency bands between 1 and 5 kHz. The results obtained were compared with samples of some recycled materials available in the scientific literature, such as sheep wool and PET.

Noise pollution must be considered to achieve sustainable cities because current levels of exposure to environmental noise are a considerable risk to the health and quality of life of citizens. Urban features and sound levels were registered in 150 streets in the Chilean cities of Talca and Valdivia to analyze the relationship between both types of variables. Urban variables related to street location, urban land use, street geometry, road traffic control, and public and private transportation showed very significant correlations with the noise levels, and multiple regression models were developed from these variables for each city. Models using only urban variables in Valdivia and Talca explained 71% and 73%, respectively, of the variability of noise. The prediction error was similar in the different types of urban roads and did not exhibit significant differences between models developed in different cities. The urban models developed in one city could, therefore, be used in other similar cities. Considering the usefulness of these variables in urban planning, these models can be a useful tool for urban planners and decision-makers to implement action plans regarding noise pollution.