A perception-based study of the indoor and outdoor acoustic environments in India during the COVID-19 pandemic.

This work presents the results of a perception-based study of changes in the local soundscape at residences across India during the last 2 years of the COVID-19 pandemic and their effects on well-being, productivity during work from home (WFH), online education, anxiety, and noise sensitivity. Using emails and social media platforms, an online cross-sectional survey was conducted involving 942 participants. The responses showed that a greater percentage of participants felt that the indoor environment was noisier during the 2020 lockdown, which was attributed to increased home-entertainment usage, video-calling, and family interaction. The outdoor soundscape was much quieter during the 2020 lockdown due to drastically reduced traffic and commercial activities; however, during the 2021 lockdown, it was perceived to be comparable with pre-COVID times. While changes in indoor soundscape were shown to affect peace, happiness, and concentration while increasing annoyance, the reduction in outdoor noise positively impacted these aspects. The responses indicate that indoor soundscape changes adversely affected productivity and online education. Consequently, only 15% of participants now prefer the WFH model, while 62% have reservations about online education. In some cases, the responses demonstrate a significant influence of demography and suggest the improvement of the acoustic design of residences to support work.

Anthropogenic noise variation in Indian cities due to the COVID-19 lockdown during March-to-May 2020.

This paper analyzes the impact of a nationwide lockdown enforced during March-to-May 2020 to prevent the widespread transmission of COVID-19 on the local anthropogenic noise level variation in Indian cities. To this end, data obtained from the National Ambient Noise Monitoring Network (NANMN) was used to analyze the long-term daily evolution of average day- and night-time levels at selected locations across seven major cities. The results indicate that when the strict lockdown phase 1 was declared, all industrial (I), commercial (C), and residential (R) zones experienced either a gradual or sudden decrease in noise levels while the silence (S) zone was unaffected. Depending on the zone, the weekly trend graphs reached a minimum either during phase 1 or conditionally relaxed phase 2. Across I, C, and R zones, the average maximum day- and night-time reduction with respect to the pre-lockdown period ranged from 4 to 13.8 dB(A) and 4 to 14.1 dB(A), respectively. As anticipated, with a gradual ease in restrictions from phase 2 onwards, the levels climbed back almost linearly, and during unlocks, the daily variation resembled the pre-lockdown trend. Furthermore, the responses to an online COVID-19 noise perception survey supported the NANMN results and suggested that the lockdown was quieter.

An experimental application of aeroacoustic time-reversal to the Aeolian tone.

This paper presents an experimental application of the aeroacoustic time-reversal (TR) source localization technique for studying flow-induced noise problems and compares the TR results with those obtained using conventional beamforming (CB). Experiments were conducted in an anechoic wind tunnel for the benchmark test-case of a full-span circular cylinder located in subsonic cross-flow wherein the far-field acoustic pressure was sampled using two line arrays (LAs) of microphones located above and below the cylinder. The source map obtained using the signals recorded at the two LAs without modeling the reflective surfaces of the contraction-outlet and cylinder during TR simulations revealed the lift-dipole nature of aeroacoustic source generated at the Aeolian tone; however, it indicates an error of 3/20 of Aeolian tone wavelength in the predicted location. Modeling the reflective contraction-outlet during TR was shown to improve the focal-resolution of the source and reduce side-lobe levels, especially in the low-frequency range. The experimental TR results were shown to be comparable to (a) the simulation results of an idealized dipole at the cylinder location in wind-tunnel flow and (b) that obtained by monopole and dipole CB, thereby demonstrating the suitability of TR method as a diagnostic tool to analyze flow-induced noise generation mechanism.

Enhancing the focal-resolution of aeroacoustic time-reversal using a point sponge-layer damping technique.

This letter presents the Point-Time-Reversal-Sponge-Layer (PTRSL) technique to enhance the focal-resolution of aeroacoustic Time-Reversal (TR). A PTRSL is implemented on a square domain centered at the predicted source location and is based on damping the radial components of the incoming and outgoing fluxes propagating toward and away from the source, respectively. A PTRSL is shown to overcome the conventional half-wavelength diffraction-limit; its implementation significantly reduces the focal spot size to one-fifth of a wavelength for a monopole source. Furthermore, PTRSL reduces the focal spots of a dipole source to three-tenths of a wavelength, as compared to three-fifths without its implementation.

Multiple line arrays for the characterization of aeroacoustic sources using a time-reversal method.

This letter investigates the use of multiple line arrays (LAs) in a Time-Reversal Mirror for localizing and characterizing multipole aeroacoustic sources in a uniform subsonic mean flow using a numerical Time-Reversal (TR) method. Regardless of the original source characteristics, accuracy of predicting the source location can be significantly improved using at least two LAs. Furthermore, it is impossible to determine the source characteristics using a single LA, rather a minimum of two are required to establish either the monopole or dipole source nature, while four LAs (fully surrounding the source) are required for characterizing a lateral quadrupole source.