Studies on recycled materials emerged during recent years. This paper investigates samples’ sound absorption properties for panels fabricated of a mixture of paper sludge (PS) and clay mixture. PS was the core material. The sound absorption was measured. We also consider the influence of an air gap between panels and rigid backing. Different air gaps (50, 100, 150, 200 mm) simulate existing acoustic panel systems. Finally, the PS and clay composite panel sound absorption coefficients are compared to those for a typical commercial absorptive ceiling panel. The average sound absorption coefficient of PS-clay composite panels (α_avg. in the frequency range from 250 to 1600 Hz) was up to 0.55. The resulting average sound absorption coefficient of panels made of recycled (but unfinished) materials is even somewhat higher than for the finished commercial (finished) acoustic panel (α_avg. = 0.51).

Studies on recycled materials emerged during recent years. This paper investigates the properties of sound absorption and transmission loss of the structures of the perforated plastic panel (PPP) backed with the rubber granule panel (RGP). Under production conditions, such a structure could be produced using only waste. The normal incidence sound absorption and transmission loss of the structure was measured using ISO 10534-2 and ASTM E2611-17 standard methods, respectively. In this study, the plastic panel perforation holes were tilted in steps of 15°–45° compared to the vertical axis of the sample. Different thickness rubber panels were used as backing (12 mm, 22 mm and 27 mm). The results showed that the sound absorption and transmission loss increased with the angle of the perforation pore. To compare the different structures, the multi-criteria analysis using the technique for order of preference by similarity to ideal solution (TOPSIS) approach was done. The RGP thickness, sound absorption coefficient (SAC) and sound transmission loss (STL) were weighted as a criterion. The results of the multi-criteria analysis showed that the optimal structure for a possible application is PPP45°+ RGP 22 mm, which was ranked highest of all alternatives. The first peak of SAC reached 0.97 at 1000 Hz. In the frequency range of 250–1000 Hz, STL values reached up to 10.4 dB and in the frequency range of 1–4 kHz – 20.1 dB. The results obtained using RGP and PPP show promising development potential for sound absorption and insulation applications.

Since society is moving towards sustainable development, interest in secondary use of waste has recently become significant. This paper investigates a process to develop an acoustic material, using two types of waste. Composite acoustic panels were developed using waste tyre textile fibres (WTTF) and paper sludge (PS), and polyvinyl acetate (PVA) were used as a binder. Non-acoustic (bulk density, airflow resistivity) and acoustic (sound absorption coefficient, sound transmission loss) parameters were studied. Composite acoustic panels with different proportions of WTTF/PS/PVA (sixteen samples) were subjected to testing for the sound absorption coefficient according to ISO 10534-2 and sound transmission loss according to ASTM E2611. The density of all samples varied between 155.2 and 709.9 kg/m³, the thickness between 14.4 and 20.5 mm, and the airflow resistivity between 29.5 and 101.5 kPa∙s/m². The results reveal that the proportion of various waste materials in mixtures can improve the acoustic performance of panels. The combination that gives the highest α_avg. with a value of 0.50 was experimentally found to be 70% WTTF mixed with 15% PVA and 15% H₂O. The average sound absorption coefficient with a value of 0.46 was also found to be 25% WTTF mixed with 25% PS and 25% PVA and 25% H₂O. In sound transmission loss, the most effective was 50% PS and the 50% PVA composite, the TL_eq was 28.3 dB, while the composites together with 30% WTTF, 20% PS and 25% PVA, and 25% H₂O showed 18.9 dB loss. The results obtained using WTTF and/or PS wastes are attractive and show great and promising development potential.

Environmental issues near roads become more and more important in our society daily life. One of the most critical environmental issues is traffic noise. The present paper study louvred noise barrier designed by authors. The louvred noise barrier provides sound attenuation while allowing airflow and sunlight through it. Since the airflow resistance of the barrier is low, it requires a shallow foundation compared to conventional noise barriers. The sound attenuation performance of the louvred noise barrier was tested experimentally in a sound transmission chamber. Airflow resistance simulated using a computational fluid dynamics model. The simulation and experimental study were done with different louvred noise barrier setup: change of louvre blade angle and sound-absorbing material thickness. The results showed potential for future development for the field testing. Sound attenuation was highest in 2500 Hz and 3150 Hz octave frequency bands. Depending on the louvred barrier setup, sound attenuation was up to 28 dB(A) in mentioned frequency bands. The equivalent sound pressure level reduced up to 17 dB(A). The results showed that an increase in the louvre blade angle increases sound attenuation and increases airflow resistance.

Traffic calming is the combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behaviour and improve conditions for non-motorized street users. Vibration measurements were performed by the authors of this paper near the roads with traffic calming devices. The measurements were taken throughout two seasons: in the winter and in the summer in order to evaluate the influence of soil freezing on traffic-induced vibrations. The only car measured was Fiat Doblo (weight 1,405 kg), and its driving speed when passing a speed bump or a speed table was controlled (20 km/h; 30 km/h; 40 km/h). The results show that the Peak Particle Acceleration (PPA) values were higher in the winter season compared with the summer. The vehicles passing over the speed tables induce lower PPA values than those passing over the speed bumps.

Wood is a sustainable renewable material that is widely used in the building sector. Due to recent trends in green initiatives in European and other countries, wood waste is becoming more popular for sound absorption and insulation because of its renewability. Recycled wood material granulated charcoal is an effective acoustic treatment. In this study, we investigated the sound absorption coefficients of raw wood and granulated charcoal species: birch (Betula pendula), pine (Pinus sylvestris), and oak (Quercus robur). The impedance tube method was used to characterize the sound absorption properties of the granulated charcoal. The maximum bulk densities of the materials investigated were 567 kg/m³ for birch (B. pendula) wood and 247 kg/m³ for granulated charcoal. The airflow resistivity of wood and granulated charcoal was found using the static airflow method according to the standard. The grain size distribution of charcoal was also determined, with the highest percentage (25–29%) of the birch and pine grain distribution of charcoal species having a size of 400 µm and 30.7% of the oak a size of 1 mm. All species had the lowest grain size value, i.e., 900 µm (1–4%). The sound absorption of granulated charcoal does not depend on the carbonization temperature at 400, 500, or 600 °C. Granular charcoal of 25 mm has a better sound absorption thickness coefficient for birch at 600 °C (0.57 at 315 Hz) compared to wood of the same thickness. The effectiveness of absorption for wood and granular charcoal depends on the type of wood (birch > pine > oak), grain size, airflow resistivity, and bulk density.