A sound source that mimics the acoustics characteristics of a human talker is required in objective assessments of speech intelligibility in person-to-person speech communications (PP) scenarios. The few special speech test sources available that meet the strict specifications of the relevant standards are costly and can be inaccessible to practitioners. This can prevent investigations or can lead to non-special and more affordable loudspeakers to be used as alternative sources without knowledge of their suitability. This study evaluates the validity of non-special loudspeakers in PP assessments and supplements a previous preliminary examination by consolidating and expanding early findings. Speech Transmission Index Public Address (STIPA) assessments were conducted employing three representative non-special loudspeakers and one standardized reference speech test source under laboratory conditions. Absolute errors of STIPA measurements were analysed and evaluated against two just perceivable difference (JND) threshold levels. The mean absolute errors obtained for all non-special loudspeakers for almost all scenarios were within one JND of any of the two JND levels. The striking and consistent low level of error found validated the proposition that non-special and affordable loudspeakers may be used as suitable speech sources in pilot or survey-grade speech intelligibility assessments in place of a special standardized speech source when that source is not available, or in full investigations when the relevant standard to adhere to allows the use of those alternative speech sources.

We sought to determine the effects of classroom loudspeaker position, model of loudspeaker, and talker accent on mental effort or cognitive load, word clarity, sound quality, and word recognition. Thirty-one typically-developed university students whose native language is English rated and transcribed recorded sentences produced by a native English talker and a native Dutch talker speaking English. The listeners were seated in acoustically pre-calibrated locations in a classroom and were presented 10 sentences at conversational level in each of four randomized conditions: from a conventional classroom loudspeaker in front or mounted above them, and from a loudspeaker optimized for speech reproduction placed in front or mounted above them. At the front of the classroom was a muted video recording of one of the talkers delivering an online lecture. Results showed front-located speakers yielded less cognitive effort, better sound quality, and better word clarity—showing importance of congruence of loudspeaker/talker position.

Human and non-human subjects are exposed to micro plastics through drink, food, and air. Micro-plastics propagating through atmosphere are breathable particles during inhalation and exhalation leading to deposition of them in the deep lung via the alveoli of the lungs. Teabags are made of plastics that are not recyclable and biodegradable. Therefore, we intend to remove used teabags from the natural environment by repurposing them to make sound attenuating panels for building and architectural industries, contributing in this way to a sustainable circular economy. The panels were designed and developed from consumed teabags as porous material by filling a frame to investigate acoustics wave propagation through them at normal incidence. Experimental testing was carried out on circular teabag panels in an impedance tube using a transfer function method to determine their sound absorption coefficient and transmission loss. Furthermore, the impedance gun method was used to determine the absorption properties of square panels. Results show that 75 mm thick circular panels give an absorption coefficient higher than 0.8 between 400 and 1600 Hz. Up-to 9.8 dB sound transmission loss of circular panels is obtained at higher frequencies. Absorption coefficients for square teabag panels are very good despite a coincidence-dip seen at 800 Hz. The satisfactory sound absorption and sound transmission characteristics of acoustic panels made of consumed tea bags can make this recycled material a cost-effective solution in the production of sustainable acoustic treatment in indoor spaces. The results suggest that recycling of consumed teabag as the panel could be applied as alternative sound absorbing materials.

The present work introduces a novel approach to designing metamaterial for low frequency and high frequency wave attenuation by repurposing plastic waste. The metamaterial is constructed using a duct-like structure with a periodic arrangement of bottles of different sizes. This configuration leads to the formation of a local resonant band, which spans from 240 to 340 Hz. In both the numerical model and the experimental setup, a harmonic excitation is given to the proposed configuration and transmission loss is computed as a function of frequency. The experimental results support the findings obtained from numerical simulations, confirming the effectiveness of the designed metamaterial. One crucial aspect discovered in this work is that introducing space between the bottle’s neck and the side wall of the structure causes the bottles to act as Helmholtz resonators. Thus, in turn, this results in an additional band gap at low frequencies, complementing the existing Bragg’s band gap achieved by the periodic arrangement of bottles. The ability to change the size of the bottles gives control over the position of the band gap, allowing for greater flexibility in tailoring the metamaterial to specific noise attenuation requirements. The applications of these plastic bottle-based metamaterials are wide ranging, especially in improving the indoor acoustic environment of buildings. This work opens up a new avenue for further exploration and innovation in the field of sustainable and environmentally friendly metamaterials.

Outdoor environmental noise is a major source of annoyance in urban areas and exposure to it can increase the risk of severe health issues. Consequently, it has been the focus of research for decades. Even though people spend the majority of their time indoors, most studies use outdoor noise levels and do not include indoor noise measurements to estimate real exposure levels. This study conducted simultaneous indoor and outdoor noise measurements for 24 h in four multi-unit residential buildings to identify the levels and sources of outdoor noise heard indoors and quantify the effects of outdoor noise on indoor levels. The measurements were conducted in unoccupied suites that are most exposed to traffic and other outdoor noise sources. Surveys were administered following building occupancy to collect information regarding perceived acoustic comfort levels due to outdoor noise. The indoor LAeq,24h in three of the study buildings were above 40 dB(A) and exceeded WHO’s noise level limits. Regression analysis showed that outdoor noise only explains 14%–58% of the variability in indoor noise levels. This is mainly because of heating, ventilation, and air conditioning (HVAC) system noise which resulted in consistently high indoor noise levels despite variations in outdoor noise. Analysis of the survey showed a poor correlation between reported annoyance and measured noise levels. But annoyance strongly depended on other factors such as suite location and noise sensitivity. The findings show that outdoor noise measurements alone may not be good predictors of exposure levels and the effects of outdoor noise on occupants.

According to Italian regulation, the Ministerial Decree of 11 October 2017 about Environmental Criteria, reference values for acoustic indoor quality descriptors in public buildings are imposed. Regarding school environments, indoor acoustic quality targets refer to reverberation time, clarity, and speech intelligibility, whose representative acoustic descriptor is the speech transmission index (STI). This paper presents pyeSTImate, a Python-based tool for speech transmission index prediction in lecture rooms. The tool returns fully simulated results from the dimensions and material characteristics of classrooms with parallelepiped geometry and without limitations in size. Extensive experiments have been conducted with different simulation methods, evaluating the accuracy by comparison with in situ measurements selected from primary, secondary, and university classrooms in school buildings of the Marche Region in Italy. The combination of simulated speech transmission indexes with a prediction method based on an artificial neural network has also been evaluated. The analysis of the performance demonstrates the computational robustness of the tool that enables its use for the analysis of existing rooms, as well as for the renovation and design of new spaces.

Investigations in solid-state physics show that metamaterials, a kind of periodic material, can produce a band of frequency gap. When a sonic wave’s frequency falls into this frequency gap, it cannot propagate. Enlightened by the concept of frequency gap, researchers recently investigated various metamaterials. The search for bandgap(s) is critical in such innovations. The present letter presents the analysis of the band of frequency gap(s) for two and three-component systems as 2D period materials using the Finite Element Method. The investigation highlights the influence of geometrical parameters on the bandgap. Modelled metamaterial uses a core of aluminium, a coating of natural rubber and a matrix of air. For the lattice constant’s specified value, with the core’s increasing size, the bandgap shows to increase. The general effect of the coating leads to the flattening of the dispersion curve. For the square lattice and circular core, the bandgap appears around a net core size (with and without coating) of around 30%–32% of the lattice constant. Multiple frequency bandgaps appear of substantial sizes at the core’s threshold size, that is, when the core’s net radius is equal to half of the lattice constant. The softer material coating is found as a potential alternative to tune and control acoustic metamaterials. With a three-component system, bandgaps appear comparatively at significantly lower frequencies. Lower edge frequencies for such bandgaps are found to be independent of the core and coating size.

Single-leaf panels made from homogeneous and isotropic materials are commonly used in buildings. However, it is often necessary to add various layers of the same or different materials in order to increase the acoustic insulation. This article presents a prediction method for the calculation of the sound reduction index that comprises single panels and multilayer panels joined together using spot techniques, such as by screws. The method is based on previous single-leaf panel models extended to multilayer structures. The predicted values are compared with panel measurements obtained according to ISO 140-3. The sound reduction index R in third octave bands, the weighted sound reduction index Rw, and the spectral adaptation terms ( C, Ctr) are examined. In addition, predictions from two commercial software tools are evaluated and compared. Statistically, the results show that the proposed method gives values that agree well with the measurements, both for single and multilayer panels.

Traffic noise transmission through the open windows of naturally-ventilated classrooms can reduce speech intelligibility and can negatively impact academic performance. The findings of a numerical study are presented. Software was used to assess effective noise attenuation solutions for naturally-ventilated classrooms exposed to traffic noise. A typical situation in urban schools in Gauteng, South Africa, is considered in which classrooms are ventilated by large open windows in accordance with national building regulations and norms and standards for school design. The aim of the study was to establish a heuristic framework for early design decisions regarding how far from the road a classroom building should be set, and the effective height and position of a solid noise barrier to ensure a suitable ambient noise level inside a classroom with open windows. Efficacy was measured with reference to an indoor ambient sound level of 40 dBA. The findings show that with the insertion of barriers, the required ambient level was achieved for a classroom at least 68 m from the road, if the barrier is at least 3.5 m high. However, it was found that a significant insertion loss (>6 dB) and an improved signal to noise ratio could be achieved for classrooms as close as 17 m from the road with a barrier of at least 2 m high. Though not broadly generalizable, the findings provide a heuristic guide applicable for designing new schools or selecting attenuation interventions in existing city schools that are similar to those used in the study.

This research set out to broaden the pool of evidence regarding the acoustic conditions at schools in South Africa. A review of local and international literature, standards and design guidelines shows that the ideal classroom acoustic conditions of 35 dBA ambient and 0.7 s reverberation time are required to enable a suitable environment for teaching and learning. A review of local literature revealed a very small body of knowledge regarding actual acoustic conditions and monitoring of classroom acoustics and that these cases demonstrated ambient noise levels in classrooms (whether occupied or unoccupied) to be above the recommendations of the relevant South African National Standard (SANS 10103). The limited local research promted the need for this case study. The findings of a province-wide survey of urban schools showed that traffic noise is the main source of noise disturbance in schools. A case study of five schools showed that the average outdoor noise level at schools exposed to traffic throughout the day is 63.3 dBA and the average indoor noise level at these schools when classrooms are unoccupied is approximately 58 dBA, which is significantly higher than the requirement. The reverberation time in classrooms was between 0.6 and 1.75 s. It is concluded that the current acoustic conditions in South African urban schools is poor when evaluated against the South African National Standards. However, since this is based on only five case studies, a broader study is required to understand the general conditions and establish suitable mitigation measures.