Accurate characterization of ground acoustic impedance is essential for reliable prediction of wind turbine sound propagation over natural and agricultural surfaces. In conventional indirect measurements, a loudspeaker and two microphones at different heights are used to estimate an equivalent flow resistivity by fitting the measured sound pressure level (SPL) differences with those calculated from an image-source propagation model and an acoustic impedance model. Because this fitting is generally carried out over a broad frequency range, the conventional approach is referred to here as the global-band method. However, a single full-band flow resistivity may not represent the frequency-dependent ground response with sufficient accuracy. To improve the spectral representation of the ground boundary condition, this paper proposes a spectral-band method for determining the ground impedance in individual 1/3-octave frequency bands. The method is intended to provide more accurate impedance inputs for wind turbine sound propagation models. The results show that the spectral-band method more accurately captures the frequency-dependent behavior of the effective flow resistivity and ground impedance, significantly reducing the discrepancy between calculated and measured SPL differences. In addition, an empirical formula is established to describe the relationship between the flow resistivity obtained using the global-band method and that obtained using the spectral-band method, so that the ground impedance can be more conveniently specified for simulations at individual frequency bands.
We investigated the acoustic environment of a military command post, focusing on two conflicting needs: protecting speech privacy while maintaining clear internal communication. A finite element model of a 248.17 m3 command post was built, combining geometric acoustics with ray tracing. To reduce diesel generator noise, we introduced parallel unequal-cavity acoustic metamaterials on both the source and the walls. Field measurements showed that enclosing the generator reduced its average sound pressure level from 90.4 dB to 73.8 dB. In simulations, applying the metamaterials to the walls shortened the reverberation time T60 from 0.81 s–2.13 s down to 0.4 s–1.6 s—but the improvement varied strongly with frequency. The largest drop occurred at 500 Hz (1.6 s to 0.4 s), with smaller reductions at 250 Hz and 1,000 Hz, and almost no change at 125 Hz or 8,000 Hz. Broadband speech transmission index (STI) improved from 0.44–0.69 to 0.52–0.95, averaging above 0.65. We then used particle swarm optimization to find the best source position within the already-optimized room. After 50 iterations, the 500 Hz equivalent per-band STI contributions exceeded 0.84 across most receivers and reached above 0.99 at several locations; other bands (250 Hz–4,000 Hz) stayed between 0.60 and 0.75. Overall, combining acoustic metamaterials with intelligent source placement appears to significantly improve the command post acoustic environment—a finding that may inform noise control strategies for similar military facilities.
Short video platforms have quickly emerged as a source of digital media consumption, which is overwhelmingly researched in terms of visual saturation, dependence on algorithms, and performance response. The auditory aspect, and, in particular, the homogenization of the background sound effects, is not researched thoroughly. This review will examine how user auditory fatigue can be caused by acoustic homogenization on short video platforms. It states that the repetition of similar background music structure, transition signal, loudness, timbral textural profiles, and emotionally coded sound patterns produces a platform-mediated auditory scenery with a lack of diversity and continued sensory demand. The article builds a conceptual model based on the insights of acoustics, psychoacoustics, media studies, human-computer interaction, and platform studies to construct a link between acoustic homogenization and auditory fatigue by proposing mechanisms, which include perceptual saturation, augmented listening effort, dynamic compression, enhanced temporal turnover, algorithmic reinforcement, and cross-modal overload. It also examines existing methods of measurement, such as the acoustic feature analysis, subjective fatigue evaluation, behavioral measures, and physiological measures, and points to the weaknesses of the existing empirical findings. It concludes the article by stating that auditory fatigue in short video use must be viewed as a cumulative and ecologically organized response, and not a one-sided response. This review is an interdisciplinary step forward by foreshadowing the aural ecology of short video platforms, as well as suggesting fatigue-conscious future research and platform design and governance of digital well-being.
This paper develops a mathematical optimization framework for broadband vibration attenuation of a simply supported thin plate using a sparse network of passive inerter-dashpot dynamic absorbers. The four attachment locations are fixed a priori away from nodal lines of the retained low-order modes; the optimizer allocates a total absorber mass limited to 4.2% of the plate mass and constrains tuning frequency to 75–580 Hz, damping ratio to 0.035–0.290, and inertance ratio to 0.05–4.50 over the selected 45–650 Hz numerical band. A modal Kirchhoff–Love model is condensed with frequency-dependent absorber impedances, and a nonsmooth Chebyshev H-infinity epigraph objective is treated by log-sum-exp smoothing, differential-evolution exploration, and projected local polishing. For the ten-mode benchmark, the robust design reduces nominal peak mobility from 91.889 dB to 85.096 dB: its 6.793 dB reduction exceeds modal tuning by 0.468 dB and the uniform-inerter layout by 1.604 dB. Across fifty material-and-damping perturbation scenarios, its 95th-percentile peak is 1.757 dB below modal tuning, indicating a practically relevant upper-tail benefit, although experimental validation remains necessary. Because the tenth retained plate mode is 385.356 Hz, results above that frequency are reported as exploratory pending a 15–20-mode convergence study.
Partially filled storage and transport tanks often radiate objectionable low-frequency sound because liquid sloshing, flexible shell modes, and uncertain damping interact in the same operating band. This paper develops a compact hydroelastic vibro-acoustic design method for a vertical cylindrical tank equipped with internal porous annular baffles and external viscoelastic rings. The fluid is represented by Bessel-based sloshing modes, the shell by a Ritz expansion, and the nonlinear free-surface contribution by a cubic Koopman–Galerkin lifting. Interval type-2 fuzzy sets describe epistemic uncertainty in fill height, fluid density, shell stiffness, loss factor, and baffle clogging. A deterministic design and a proposed fuzzy robust design are compared over alpha-plane uncertainty scenarios using peak sound power, band-averaged sound power, wall acceleration, and wave-height constraints. The proposed design reduces the 95th-percentile peak sound power from 57.84 dB in the uncontrolled tank to 48.55 dB, decreases the 95th-percentile band-averaged acoustic level from 28.47 dB to 26.73 dB, and lowers the 95th-percentile wall-acceleration level from 130.48 dB to 120.34 dB. Relative to the deterministic optimum, the robust design has a 0.216 dB higher nominal peak and a 0.173 dB higher 95th-percentile peak. Still, it lowers the 95th-percentile band mean by 1.059 dB and wall acceleration by 0.613 dB. The contribution is the integrated reduced-order design workflow; physical validation remains necessary.
