[Acoustic quality and urban health-more than just noise and silence]

The acoustic environment before and during the SARS-CoV-2 lockdown in a major German city as measured by ecoacoustic indices

The SARS-CoV-2 pandemic drastically changed daily life. Lockdown measures resulted in reduced traffic mobility and, subsequently, a changed acoustic environment. The exceptional lockdown was used to analyze its impact on the urban acoustic environment using ecoacoustic indices. Using data from 22 automated sound recording devices located in 9 land use categories (LUCs) in Bochum, Germany, the normalized difference soundscape index (NDSI) and Bioacoustics index (BIO) were explored. The NDSI quantifies the proportion of anthropophonic to biophonic sounds, and BIO quantifies the total sound activities of biological sources. The mean differences and standard deviation (SD) were calculated 5 weeks before and 5 weeks during the first lockdown. Pronounced peaks for the NDSI and BIO before lockdown that diminished markedly during lockdown were observed, however, with distinct differences in terms of the LUC. The mean NDSI increased from 0.00 (SD = 0.43) to 0.15 (SD = 0.50), the mean BIO decreased from 4.74 (SD = 2.64) to 4.03 (SD = 2.66). Using the NDSI and BIO together reveals that changes of the acoustic environment during lockdown are mainly driven by decreased anthropophonic sound sources. These results suggest that further studies are needed to tailor ecoacoustic indices more accurately to conditions of the urban environment.

An Experimental Study on the Performance of Corrugated Cardboard as a Sustainable Sound-Absorbing and Insulating Material

The continuing development of industrialization and increasing population density has led to the emergence of noise as an increasingly common problem, requiring various types of sound absorption and insulation methods to address it. Meanwhile, the recycling of resources to ensure a sustainable future for the planet and mankind is also required. Therefore, this study investigates the potential of corrugated cardboard as a resource for noise reduction. The sound absorption and insulation performance of non-perforated corrugated cardboard (NPCC) were measured, and modified corrugated boards were fabricated by drilling holes either through the surface of the corrugated board alone or through the corrugated board in its entirety. The sound-absorption/insulation performance both of perforated corrugated cardboard (PCC) and perforated corrugated cardboard with multi-frequency resonators (PCCM) were measured using the transfer function method and the transmission matrix method. To determine the effectiveness of NPCC, PCC, and PCCM in noise reduction, the sound pressure level was analyzed by applying it to a home blender. The results showed PCCM’s sound absorption and insulation performance to be excellent. On the basis of these findings, we propose the use of PMMC as an eco-friendly noise-reduction material.