In this article, the authors present the geometry and measurements of the properties of an acoustic metamaterial with a structure composed of multiple concentric rings. CAD models of the structure were developed and subsequently used in numerical studies, which included the study of resonant frequencies using the Lanczos method and an analysis of sound pressure level distribution under plane wave excitation using the finite element method. Subsequently, experimental tests were carried out on models with the same geometry produced with three different materials (PLA, PET-G, and FLEX) using a fused deposition modeling 3D printing technique. These tests included: determining insertion loss for a single model based on tests using the measurement window of a reverberation chamber and determining transmission loss through tests in a semi-anechoic chamber. Sound wave resonance was obtained for frequencies ranging from 1700 to 6000 Hz. Notably, the experimental studies were carried out for the same structure for which numerical tests were conducted. The physical models of a metamaterial were manufactured using three different readily available 3D printing materials. The results of laboratory tests confirm that the created acoustic metamaterial consisting of multi-ring structures reduces noise in medium and high frequencies.

In order to design a stable and reliable voice communication system, it is essential to know how many resources are necessary for conveying quality content. These parameters may include objective quality of service (QoS) metrics, such as: available bandwidth, bit error rate (BER), delay, latency as well as subjective quality of experience (QoE) related to user expectations. QoE is expressed as clarity of speech and the ability to interpret voice commands with adequate mean opinion score (MOS) grades. This paper describes a quality evaluation study of a two-way speech transmission system via bandwidth over power line – power line communication (BPL-PLC) technology in an operating underground mine. We investigate how different features of the available wired medium can affect end-user quality. The results of the described study include: two types of coupling (capacitive and inductive), two transmission modes (mode 1 and 11), and four language sets of speech samples (American English, British English, German, and Polish) encoded at three different bit rates (8, 16, and 24 kbps). Our findings can aid both researchers working on low-bit rate coding and compression, signal processing and speech perception, as well as professionals active in the mining and oil industry.

On September 25–29, 2023, the LXIX Open Seminar on Acoustics OSA2023 was held in Karpacz. The conference was organized by the Wroclaw Branch of the Polish Acoustical Society (PTA). Simultaneously with the OSA2023 conference two accompanying events were held: Signal Processing Symposium SPSympo23 and 5th Polish-German Structured Conference on Acoustics PGSCA2023. 240 specialists from Poland and abroad took part in the OSA2023, SPSympo23, and PGSCA23 conferences delivering 96 papers and 6 plenary presentations.

Water is widely used in the mining industry, particularly in mineral enrichment processes. In the process of magnetic separation or flotation of crushed ore, a concentrate (an enriched product), and tailings (a product with a low content of a useful component) are obtained. One of the main tasks of enrichment processes is the efficient use of water resources. This is achieved by reclaiming and subsequent reusing water contained in ore beneficiation products by extracting it in industrial thickeners. Optimizing this process makes it possible to reduce water usage in the mining industry, reduce costs of mineral enrichment processes, and address extremely urgent environmental protection problems. To evaluate the process of sedimentation of the solid phase in the pulp within the thickener, measurements of parameters of longitudinal ultrasonic oscillations and Lamb waves that have traveled a fixed distance in the pulp and along the measuring surface in contact with it are used. The proposed approach allows for the consideration of pulp density, particle size of the solid phase in the ore material and the dynamics of changes in these parameters in the thickener at the initial stage of the sedimentation process. Based on the obtained values, adjustments can be made to the characteristics of its initial product, leading to reduced water usage and minimized loss of a useful component.

This study used experimental measurements and the finite-element method (FEM) simulations to investigate transient underwater radiated noise induced by the impulse excitation of water surrounding a watertight steel-structured circular cylindrical shell submerged in the 176 × 8 × 4 m towing tank. The excitation was caused by dropping an iron block onto a structural bracket in the shell to generate structural vibration. The experimental results were found to be consistent with the FEM results, with the difference between the experimental and simulated sound pressure levels being less than 3 dB. Moreover, it was determined that the structural vibration also generated airborne noise in the cylindrical shell, but this contributed much less than the impulse excitation to the induction of underwater radiated noise. Finally, analysis of the sound field of the underwater noise radiation showed that it was influenced by the wall thickness of the watertight steel cylindrical shell and that of the reinforced bracket seat structure. In particular, the structural reinforcement position proved to be the diffusion breakpoint of the underwater sound radiation. This demonstrates that compared with the studied structure, a thicker and more complex reinforced structure will transmit less or incomplete sound radiation into water.