The researchers used purposive sampling and virtual, semi-structured interviews lasting approximately 15 to 30 minutes. Seventeen professionals were approached, seven agreed to participate and ten declined. Four participants reported direct experience with secondary-school-aged learners, while the others drew on therapeutic, special-needs, rehabilitation or care and support settings.

Professional experience ranged from one to 20 years, and contact with neurodivergent children and young people ranged from daily to once a fortnight. Exact practice locations and standardized learner ages were not collected, and diagnostic categories were inconsistently reported across caseloads. The authors therefore describe the results as mixed-context professional proxy evidence relevant to Nigerian secondary-school design rather than observations from one defined school or a representative sample of Nigerian schools.

Open-ended interview accounts were analyzed inductively through reflexive thematic analysis, yielding four themes: sensory environmental stressors; environmental distress and spatial dysregulation; restorative and regulatory features; and spatial configuration, transitions and classroom ergonomics. In a separate analytical strand, participants appraised nine researcher-predefined features—acoustics, lighting, colour and visual complexity, sensory zoning, withdrawal spaces, flexible furniture, wayfinding, biophilic elements, and temperature and ventilation—for relevance, functional influence, feasibility and priority. The separation matters because agreement with a named design feature does not show that the issue emerged independently from the interviews.

The second author conducted the primary coding, while the first author provided supervisory review; there was no independent parallel coding, formal member checking or positionality diary, and the primary analyst’s architectural training may have influenced interpretation. Visual and lighting-related problems appeared in all seven open-ended accounts. Participants described glare, distracting windows, abrupt changes in light, fluorescent flicker and excessive visual stimulation.

Six raised auditory overload, citing echoey corridors, loud conversations, alarms, scraping chairs and chalkboard noise. Five described crowding or reduced personal space, especially in assembly halls and busy corridors, while four reported olfactory or tactile sensitivities involving smells, food, cleaning products, textures or touch. Rather than treating noise or light as isolated variables, several professionals distinguished persistent background conditions from abrupt, unpredictable events.

That distinction points to different responses: persistent reverberation may require absorptive surfaces or quieter finishes, while sudden alarms and other events may require predictable signaling, transition buffers and better management of movement through shared spaces. The accounts also depict distress arising when several demands converge. One mental-health professional described a 14-year-old autistic student who became non-verbal, covered their ears and could not follow the usual evacuation procedure during a fire drill involving an alarm, flashing lights and a crowded route.

A special-needs coordinator described a Year 9 autistic student becoming highly agitated after a class was moved into a room containing traffic noise, glare, fresh-paint odor and nearby sports activity. A guidance counsellor reported that chalkboard noise was severe enough to contribute to one learner changing schools. These are professional reports of person-environment interaction, not evidence that a single feature caused each outcome, yet they illustrate how intense or unpredictable environments can combine with an individual’s sensory profile during high-demand situations.

Corridors, doorways, playgrounds and assembly areas were described as places where crowding, reverberation, movement and uncertainty accumulated. Participants reported freezing at thresholds, difficulty processing signs in chaotic corridors, reluctance to enter an unadapted route and withdrawal during transitions. Advance notice of journeys, visual or verbal prompts, straightforward routes and escorting were associated in the accounts with easier movement.

At the same time, all seven professionals discussed seating, orientation or classroom layout, suggesting that neuro-inclusive adaptation need not be confined to specialist rooms or expensive equipment. Strategies included positioning learners away from windows or high-traffic areas, preserving sightlines to the teacher, varying seating arrangements and avoiding tightly clustered desks. Lower-stimulation environments were the clearest consistently emerging supportive feature.

Participants described sensory rooms, quiet rooms, dimly lit areas, classroom focus corners and simply the quietest available space, together with blinds, dividers, soft seating, headphones, fidget items, textured surfaces and reduced visual clutter. The transferable principle appears to be access to control over stimulation rather than one prescribed room type. Professionals also considered organization itself a form of control: separating quieter and more active areas, reducing visual clutter, controlling crowding and adjusting furniture could produce benefits without major building work.

Participants suggested portable and locally feasible measures such as fabric panels, soft floor coverings, blinds, local textiles, furniture-based zoning, picture or color-coded signs, painted navigation paths and small retreat nooks. These examples establish perceived feasibility, not measured effectiveness. Integrating the open-ended findings with the prompted appraisals produced a preliminary three-tier retrofit framework.

Tier 1 comprises acoustic control, lighting control, withdrawal or escape spaces, and sensory zoning, because these features showed the strongest convergence between spontaneous accounts, resource-limited priorities, functional importance and practical implementation. Tier 2 contains flexible furniture and wayfinding or predictability, which were judged useful and implementable but less consistently selected as immediate priorities. Tier 3 includes biophilic respite, visual simplification or color, and temperature or ventilation, which participants generally considered relevant when prompted but less often prioritized for immediate action or, particularly for ventilation, potentially more capital-intensive.

Tier placement was interpretive rather than based on numerical scores, and prompted relevance alone did not determine ranking. The framework is therefore a practice-informed proposal for testing, not a validated design standard or universal ranking for every school. Implementation was consistently constrained by more than construction costs.

All seven professionals mentioned financial limitations, while space shortages, ageing infrastructure, fixed building footprints and poor original planning also shaped what was possible. Institutional readiness mattered as well: incomplete staff buy-in, competing school priorities, limited decision-maker awareness and a lack of practical know-how could impede change even when a retrofit was technically possible. The findings support a staged logic in which low-cost reorganisation and targeted improvements precede expensive replacement of lighting, ventilation, acoustic systems or entire spaces.

The most promising options must still be tested building by building because sensory preferences vary, and no single environmental prescription will suit every learner. Staff engagement, maintenance capacity, climate, available space, institutional culture and user priorities all affect whether an intervention can be implemented and sustained. The study has important boundaries.

It did not directly involve neurodivergent students, observe classrooms, measure acoustics, lighting, temperature or ventilation, or test student outcomes before and after a retrofit. It also did not establish statistical generalisability, thematic saturation, or identical design needs for autistic learners and people with ADHD, dyslexia, learning disabilities or other sensory processing differences. The autism-specific ASPECTSS framework was applied only after the themes had been developed, as a post hoc interpretive lens, and Attention Restoration Theory provided another conceptual lens for discussion of retreat and nature-based spaces; neither was tested as an instrument in this study.

Future work should combine direct student participation and co-design with clearly defined demographics, multiple school sites and objective environmental assessment. Until then, the study offers a locally grounded map of professional concerns and a testable retrofit sequence: control sound and light first, preserve somewhere to withdraw, organize space for predictability, and evaluate the results with the learners who will use them.

Subject of Research: Professional-identified sensory and spatial barriers and retrofit priorities for neuro-inclusive Nigerian secondary schools

Article Title: Professional perspectives on sensory and spatial barriers relevant to neuro-inclusive secondary school environments in Nigeria

Article References: Olagunju, O. O., & Ogundele, A. T. (2026). Professional perspectives on sensory and spatial barriers relevant to neuro-inclusive secondary school environments in Nigeria. Frontiers in Built Environment, 12, 1965117. https://doi.org/10.3389/fbuil.2026.1965117

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1965117

Keywords: neuro-inclusive design, sensory environment, school architecture, Nigeria, autistic learners, acoustics, lighting control, sensory zoning, retreat spaces, qualitative research, Professional, perspectives

A team at the Fraunhofer Institute for Nondestructive Testing IZFP in Saarbrücken and Technische Universität Ilmenau has now borrowed a trick from an unexpected place — the satellite navigation system GPS — to break that bottleneck. In a study published in Frontiers in Acoustics, Marius W. Schäfer, Giovanni Del Galdo, and Sarah C. L. Fischer demonstrate that orthogonal spread code sequences, the same family of codes that keeps GPS satellites from jamming each other, can drive every channel of an ultrasonic testing system simultaneously. The signals overlap in the specimen, yet post-processing separates them cleanly, turning a sequential chore into a fully parallel one.

The underlying idea comes from code division multiple access, or CDMA, a cornerstone of digital communications. In direct sequence spread spectrum, each channel is assigned a different code sequence, and orthogonality — the mathematical property that lets decorrelation separate the signals within the cross-correlation ratio — is achieved by modulating orthogonal codes onto channels sharing the same frequency band. Alternatives exist. Time division multiple access waits for each ultrasonic signal to fade before the next channel fires, which becomes painfully slow as channels multiply. Frequency division splits channels into separate bands, but narrowband transducers make channel-to-channel transmission difficult, and wideband transducers leave only a sliver of bandwidth per channel. Simpler keying schemes such as phase, frequency, or amplitude shift keying work for single transmissions but degrade badly when signals overlap. CDMA, the authors argue, is best suited to ultrasonic testing because it keeps transmission time short while preserving accuracy across a large bandwidth.

Choosing the right codes was the first hurdle. The researchers compared three candidate sets: random binary sequences, random Gaussian sequences, and Gold codes, which are generated by combining two maximum length sequences with different seeds using shift registers. With six linear-feedback shift register elements, the Gold code set yielded 63 codes, or 65 orthogonal sequences including the two initial ones — enough for 65 potential parallel channels. The cross-correlation statistics told a clear story. All three sets averaged a cross-correlation maximum of roughly 25 to 26 percent, but the worst case separated them dramatically: 36.0 percent for Gold codes against 52.4 percent for random binary and 51.0 percent for random Gaussian. Gold codes simply never let any two sequences become uncomfortably similar, which is precisely why GPS relies on them.

The experimental platform was a custom-built two-channel ultrasonic testing system designed to behave in a fully linear manner, a property achieved by driving the transducers in differential mode with operational amplifiers. The transducers themselves are 3:1 piezoelectric composites of PZ29 ceramic and araldite epoxy, with a nominal center frequency of 5 MHz, mounted on a 60 mm-thick steel block using ring magnets and engine oil as the coupling fluid. The system includes an arbitrary signal generator based on 2048-element look-up tables and a 16-bit data acquisition section, operating at a digital frequency of 125 MHz — one sample every 8 ns. Measurements ran in pulse-echo mode, with a digital rectangular filter allowing a passband between 2 and 11 MHz.

The first experiments revealed a sobering truth about physics. Two Gold codes measured independently had a sharp auto-correlation maximum and a cross-correlation distance of 72 percent in the digital domain. Once converted into ultrasonic signals by the real hardware, that distance collapsed to 25 percent — far too ambiguous for reliable time-of-flight determination. The culprit is the system’s transfer function: gain and phase variations across the bandwidth distort the transmitted codes, destroying the carefully engineered correlation properties. Direct evaluation of raw ultrasonic echoes, the team found, is simply not suitable for separating overlapping coded signals.

The solution was compensation. By applying the inverse of the system’s transfer function to the recorded echoes, the researchers restored much of the original code character. The auto-correlation distance climbed back to 60 and 70 percent, and the cross-correlation side lobe distance reached 50 percent. In the two-transducer validation, both codes were correctly detected in every evaluation window — the echo from the opposing transducer, the backwall echo from the recording transducer, and the reflected echo from the opposing channel — even though the signals were inverted at the specimen boundaries. Remarkably, correlating the compensated echoes directly with the digital codes also worked, showing that single-echo computation is not even required for a successful code decision.

To prove the method scales, the team simulated a nine-transducer setup by superposing nine Gold code sequences with random time offsets between 0 and 8000 ns and random amplitude factors between 0.5 and 1, mimicking the overlapping echoes of different amplitudes that arrive at a receiver in a complex test object. After compensation, every code was localized with an error of less than 4 ns — half the system’s sampling interval — using a polynomial fit to resolve fractional delays. Only one code, scaled to the lowest amplitude with an unfortunate overlap, came close to the cross-correlation level, with a side lobe distance of just 7 percent. The uncompensated ultrasonic signal, by contrast, mostly failed evaluation, exactly as the earlier single-code experiments predicted.

The compensation is not free. Applying the inverse transfer function amplifies noise alongside the signal, and bandwidth limitations mean some parts of the code are never fully reconstructed. The average cross-correlation maximum for compensated ultrasonic signals was 44.8 percent, better than the 66.5 percent of uncompensated signals but still well above the 24.5 percent of the ideal digital codes. The authors also flag practical constraints: when many channels fire at once, the summed sound pressure may push the material beyond its linear acoustic range, introducing nonlinear effects that the linear transfer function cannot cover. Constructive overlap at a receiver can also overdrive amplifiers or the ADC, so gain must be reduced or code selection and clever delays used to manage the interaction area — a delay even shorter than the code duration can help while keeping the measurement in a single cycle.

Even with those caveats, the implications are striking. Compared with recent approaches — Golay codes for medical imaging, TOP-CS sequences for low-power ultrasonics, Hadamard and chirp schemes simulating 256 channels — this work offers a short code duration of about 1 second and 65 usable orthogonal codes, letting specimens with small geometry and high sonic velocity be evaluated without echoes colliding with ongoing excitation. Techniques such as full matrix capture, which fires transducers sequentially and suffers accordingly long acquisition times, could profit enormously; even running a fraction of channels in parallel cuts execution time by the number of simultaneous senders. The authors see particular promise in hazardous environments, where reducing personnel exposure time matters more than anything, and note that coded sequences improve the sharpness of correlation maxima — and therefore image sharpness — while CDMA modulation performs well in multipath environments and resists narrowband interferers. The next step, they say, is porting the method to state-of-the-art test systems, potentially using on-board FPGAs to separate superimposed coded echoes in real time.

Subject of Research: Ultrasonic Testing

Article Title: Compensated orthogonal spread codes for full parallel usage of multi-transducer ultrasonic testing systems in NDE

Article References: Schäfer, M. W., Del Galdo, G., & Fischer, S. C. L. (2025). Compensated orthogonal spread codes for full parallel usage of multi-transducer ultrasonic testing systems in NDE. Frontiers in Acoustics, 3, Article 1620233. https://doi.org/10.3389/facou.2025.1620233

Image Credits: AI Generated

DOI: 10.3389/facou.2025.1620233

Keywords: ultrasonic testing, non-destructive evaluation, Gold codes, CDMA, coded excitation, signal processing, NDE, acoustics, Compensated, orthogonal, spread, codes

The objects examined include five crescent-shaped brooches fitted with chains and clanging plates, seven ring pendants made of interlinked rings, a unique double-shelled ornamental disc from grave 778 with paired anthropomorphic clapper plates, a lantern-shaped pendant from grave 733, a belt chain from grave 669 belonging to a belt of the Schrotzhofen type, a slitted crotal from a horse bridle in grave 196, a slitted poppy-shaped pendant, an ornamental phalera from grave 750, and a broad-rimmed bronze bowl from grave 496 that originally carried four clapper plates and a clapper ring on its rim. All were cast in copper alloys using the lost-wax method or hammered by hand, and all were recovered from women’s graves in the Hochtal cemetery. Three additional pieces from the museum’s collection, a ring pendant and two neck rings with clapper elements, originate from the Central Balkans and date to the transition from the Late Bronze Age to the earliest Iron Age.

Although these are costume ornaments rather than musical instruments, the researchers classified them using the Hornbostel-Sachs systematik of 1914 and its later revisions. Every object proved to be an idiophone, a self-sounding instrument in which the material itself, thanks to its stiffness and elasticity, produces the tone without membranes or strings. The brooches with chains and clapper plates belong to the frame rattles and pendulum rattles, while the crotal is a vessel rattle in which a loose rattling body, in this case a small white quartz pebble, strikes the vessel wall. The ornamental disc with its paired plates striking against each other also counts among the concussive idiophones, comparable to small cymbals. The classification, the study notes, remains cumbersome for archaeological sound objects and urgently requires a systematik adapted to the needs of archaeology.

To measure the sounds, the team recorded all 21 jewelry idiophones in a purpose-built sound-damped chamber while shaking them continuously. Three-second excerpts were filtered with a 500 Hz high-pass filter to remove low-frequency noise and then analyzed with professional software to extract acoustic and psychoacoustic parameters. These included the sound pressure level, the peak frequency, the spectral centroid as a measure of brightness, sharpness, roughness, tonality expressed as the tone-noise-ratio, and impulsiveness. Psychoacoustic parameters capture the subjective perception of the sounds by human listeners, expressed for example in units of loudness such as sone and phon.

The results divide the corpus into two acoustically distinct groups. The ten objects whose sound is generated by clashing plates, thin metal sheets on brooches, pendants and the belt chain, produce on average quiet and noise-dominated sounds with weakly pronounced partial tones. The nine objects with interlinked rings, the ring pendants and neck rings, are on average far heavier, weighing up to 378 grams per group average against 118 grams for the plate group, and produce louder sounds averaging 76.4 dB SPL and 25.7 sone, with clearly pronounced partial tones that make them sound more tonal. The plate objects average 62.2 dB SPL and 11.5 sone. The heaviest neck ring, a torc from Sinošević in Serbia with T-shaped terminals, hollow poppy-shaped elements and bird-head pendants, weighs a massive 1,503 grams and demands an upright posture to wear well, straining the cervical spine during prolonged use, as the author observed when donning the pieces herself.

Statistical analysis revealed strong correlations between loudness and tonality, between roughness and impulsiveness, and between brightness and peak frequency. Louder objects carry more tonal partials, objects with sharper impulses sound rougher, and objects with a high peak frequency are perceived as brighter. Only a weak correlation emerged between weight and sound pressure level, since the corpus mixes very different types of sound ornaments. A comparison between the Iron Age crotal from grave 196 and a Roman bell found in grave 765, which is clearly of Roman origin and probably lost by grazing cattle in the Hochtal centuries after the cemetery fell out of use, shows dramatic differences. The bell is subjectively about eight times louder, at 83.6 dB SPL and 62.1 sone against 64.8 dB SPL and 8.1 sone, and rings with a spectral centroid of 3.8 kHz, far darker than the crotal’s 10.6 kHz, with partial tones that sustain for several hundred milliseconds after a single strike.

The study argues that these ornaments were worn on festive occasions rather than during hard daily labor, comparable to a Sunday best, although visible wear traces on many objects suggest everyday use was also possible. Because the clapper elements strike against each other with every movement, the jewelry functioned as a rattle that announced the approach and presence of the wearer. The communicative and symbolic messages encoded in prehistoric dress were thus perceived not only visually but also acoustically. Ring pendants, known exclusively from women’s graves in Upper Austria, Salzburg and southern Bavaria, served as breast ornaments and may have symbolized wagon journeys, themselves markers of elite status in an age when wheeled transport was largely reserved for the upper strata of society.

The symbolism runs deeper still. Crotals and poppy-shaped pendants, found in the Hallstatt culture only in women’s graves, imitate capsule fruits such as opium poppy heads and pomegranates, both ancient emblems of fertility, prosperity and eternal life owing to their vast numbers of seeds. Rings embody the cycle of life, infinity, eternity and a particular kind of power, invested with magical, apotropaic and healing forces that transform them into psychological instruments of rule by divine legitimation. Anthropomorphic clapper plates may represent protective spirits and guardian figures, while the cymbal pairs on the magnificent brooch from grave 505, decorated with 18 pairs of point-bossed cymbals, may depict sun discs, the giver of life, a motif that appears in combination with water birds, interpreted by Georg Kossack as magical signs of salvation, throughout the religious imagery of the Hallstatt culture.

The psychological dimension of adornment completes the picture. As Georg Simmel observed, one adorns oneself for oneself, and can only do so by adorning oneself for others. Wearing jewelry strengthens the self-confidence of the wearer, and pieces with symbolic content may amplify this effect. The ringing costume ornaments of Hallstatt, the study concludes, served the self-enhancement of their wearers through ornament, color, sound and symbolism alike. All 19 objects from the Hallstatt graveyard were recovered from women’s graves, all testify to high craftsmanship, and all remind us that the soundscape of the Iron Age was not confined to instruments and rituals but resonated from the very bodies of its people. The sound recordings of the individual objects are available for listening in the repository of the Natural History Museum Vienna.

Subject of Research: Archaeology

Article Title: Klingender Trachtschmuck aus dem eisenzeitlichen Gräberfeld Hallstatt: Analysen und Diskussion zu Funden aus dem Bestand der Prähistorischen Abteilung, NHM Wien. In Memoriam Anton Kern, HR, Dr. (1957–2023) Abteilungsleiter i. R. der PA

Article References: Pomberger, B. M., Mühlhans, J., & Grömer, K. (2025). Klingender Trachtschmuck aus dem eisenzeitlichen Gräberfeld Hallstatt: Analysen und Diskussion zu Funden aus dem Bestand der Prähistorischen Abteilung, NHM Wien. In Memoriam Anton Kern, HR, Dr. (1957–2023) Abteilungsleiter i. R. der PA. Annals of the Natural History Museum Vienna, 126, 41-64. https://doi.org/10.3897/anhmw.169220

Image Credits: AI Generated

DOI: 10.3897/anhmw.169220

Keywords: Hallstatt, Iron Age, archaeology, acoustics, psychoacoustics, idiophones, jewelry, Natural History Museum Vienna, bronze, symbolism, Klingender, Trachtschmuck

The study, published in Frontiers in Acoustics by Rui Zhang of the Jinan-Qingdao High-speed Railway, Hui Li of Shandong University’s School of Qilu Transportation, and colleagues including corresponding author Shengyou Yang of Shandong University’s School of Civil Engineering, tackles a problem that has grown acute as rail networks accelerate. Research cited in the paper indicates that once a train’s operating speed exceeds the critical threshold of 300 km/h, aerodynamic noise accounts for more than 50 percent of the total sound pressure level, surpassing wheel-rail noise as the leading source. At 350 km/h, the sound pressure level measured 12 meters from the track can reach 82 dB(A) or more—loud enough to create resonance inside passenger carriages and to sustain sound pollution within 200 meters of the railway, with prolonged exposure posing documented risks to human health.

To capture the physics at this speed, the team built a full-scale three-dimensional computational model in ANSYS Fluent that simulates a wind tunnel test of a train traveling at 350 km/h. The train geometry was based on the surface parameters of the CRH380A, measuring 3.38 meters wide, 3.70 meters high, and 74.28 meters long. The researchers deliberately simplified the model—treating the train surface as completely smooth and omitting structural details such as windows, doors, and bogies—while preserving the representative aerodynamic shapes that generate the noise. The computational domain exceeded the requirements of the CEN European Standard for railway aerodynamics, and the mesh was refined on the vehicle surface to a maximum size of 0.1 meters and a minimum of 0.05 meters to resolve the critical aerodynamic regions.

The turbulence modeling choice matters here. Because the curved wall surfaces of a train introduce distortion when calculated with the standard k-ε model, the team employed the Realizable k-ε turbulence model, which introduces constraint terms that prevent non-physical negative pressures caused by excessive time-averaged strain rates and incorporates quantities related to rotation and curvature—making it better suited to the rotational and mixed flows swirling around a speeding train. Because the train speed exceeds 0.3 Mach, compressibility was included in the analysis, with the SIMPLE algorithm handling pressure-velocity coupling and second-order upwind discretization applied to convection and dissipation terms.

On top of the flow solver, the researchers layered the Broadband Noise Source Model, an approach founded on Lighthill’s acoustic analogy theory from aeroacoustics. This model uses the statistical attributes of turbulence to characterize the vortex motion and acoustic radiation traits of noise sources, correlating the turbulent flow field with the acoustic field. It is valid under conditions of uniform isotropic turbulence, high Reynolds number, and low Mach number—precisely the regime of a high-speed train in open air. The model’s efficiency makes it a staple for preliminary noise prediction, and it allowed the team to compute the surface acoustic power distribution of the entire train, which peaked at the front of the vehicle where wind turbulence is most intense.

That peak at the train’s nose enabled a crucial computational shortcut. The integrated sound power level derived from the Fluent results came to 0.53295 watts, and because the sound power is concentrated at the front of the train, the problem could be simplified into a two-dimensional line sound source in COMSOL Multiphysics, with a line source intensity of 0.0071 watts per meter. The COMSOL model placed point A as the noise source and point B as the monitoring point, corresponding to the front of the vehicle, with perfectly matched boundaries simulating an infinite field. The accuracy of this hybrid approach was verified against real wind tunnel tests conducted in the 5.5 m × 4.0 m acoustic wind tunnel at the China Aerodynamics Research and Development Center in Mianyang, Sichuan, where a 1:8 scaled three-car train model was tested at 83.33 m/s in a fully anechoic chamber. The simulated sound pressure level at the monitoring point was 91.27 dB against 89.83 dB from the test data—a 1.4 dB error, comfortably within the acceptable range of 2 dB.

With the model validated, the team examined six scenarios: no barrier at all, a low-height vertical barrier, a high-height vertical barrier, a semi-enclosed barrier with a two-thirds opening, a semi-enclosed barrier with a one-third opening, and a fully enclosed barrier. The barrier material was modeled as built-in aluminum, with the barrier surface assumed flat and the track section near the barrier treated as straight. The results showed that the fully enclosed sound barrier delivered the lowest sound pressure levels at all testing points, achieving noise reductions of 4.5 to 6 dB, while the vertical barrier followed with reductions of about 4 dB. The fully enclosed barrier maintained reductions exceeding 4.5 dB up to 20 meters away, making it the clear leader across all frequency ranges.

The frequency-domain analysis revealed subtler structure beneath that headline ranking. Once the frequency surpassed 31 Hz, the no-barrier condition remained the highest across all frequencies, while the fully enclosed barrier stayed lowest at every frequency. But the semi-enclosed barriers behaved differently depending on the band: in the high-frequency range, the two-thirds-opening barrier actually outperformed the vertical barrier, ranking just behind the fully enclosed design. In the low-frequency range, however, its performance collapsed—at 16 Hz it recorded 91 dB, producing an overall sound pressure level that exceeded the other conditions. As frequency increased, noise reduction effectiveness correlated positively with the degree of confinement, with the ranking at 1,000 Hz aligning exactly with the level of airtightness. For high-frequency noise, in short, a higher sealing degree yields improved reduction; for low-frequency noise, greater confinement does not enhance the effect.

The mechanism behind these differences lies in how sound waves interact with barrier geometry. As sound waves encounter a barrier, three physical phenomena take place: diffraction, transmission, and reflection. High-frequency waves, with their shorter wavelengths, tend to diffract around the barrier’s edge, their energy diminishing geometrically with propagation distance. The sound-insulating capabilities of the barrier material limit transmission, while a sound-absorbing surface layer converts incoming sound energy into thermal energy through a porous design, reducing secondary reflections. Behind the barrier, the sound field splits into a sound brightness area outside the geometric shielding range and a sound shadow area on the noise-back side—the region crucial for protecting noise-sensitive targets through combined diffraction attenuation and transmission suppression.

The cloud maps of total sound pressure level made the consequences of top openings vividly clear. Increasing the opening at the top of the barrier caused a significant rise in the sound pressure distribution behind it: as the degree of diffraction grew, the sound shadow area shrank and the noise intensity within it rose, reflected in the warming colors of the region to the right of the barrier. A fully enclosed barrier blocks both direct sound and top-diffracted sound, producing the largest shadow area and the lowest levels. In a semi-closed structure, the top opening allows noise to escape behind the barrier through diffraction paths, weakening the shielding effect—a leakage that becomes pronounced when the opening is large. Strikingly, at distances greater than 10 meters, the noise intensity at the monitoring point with a two-thirds opening actually surpassed the intensity recorded with no barrier at all, meaning a poorly sealed barrier can be worse than nothing in the far field.

The practical implications are direct. The researchers conclude that for trains traveling at 350 km/h, fully enclosed sound barriers—with their greater noise reduction efficiency—are the optimal choice in noise-sensitive areas, even though they carry the highest construction cost. In regions where noise is a relatively lesser concern, lower-cost vertical barriers are advisable. The study also notes that analyzing frequency distribution is crucial when deploying vertical or semi-enclosed barriers, since their effectiveness varies across the spectrum. The team’s hybrid simulation technique—fine aerodynamic meshing only around the train in Fluent, high-density acoustic meshing only near the barrier and observation zones in COMSOL—significantly enhanced computational efficiency while preserving fidelity, offering a template for future studies of noise control on the world’s accelerating railways.

Subject of Research: Researchers in China used coupled ANSYS Fluent and COMSOL simulations, validated against wind tunnel tests, to show that fully enclosed sound barriers provide the best noise reduction against high-speed train aerodynamic noise, followed by vertical barriers, with sealing degree critical for high-frequency noise control.

Article Title: Study on the noise reduction effect of sound barriers on the aerodynamic noise of high-speed trains

Article References: Zhang, R., Li, H., Yang, J., Chen, X., & Yang, S. (2025). Study on the noise reduction effect of sound barriers on the aerodynamic noise of high-speed trains. Frontiers in Acoustics, 3, Article 1616806. https://doi.org/10.3389/facou.2025.1616806

Image Credits: AI Generated

DOI: 10.3389/facou.2025.1616806

Keywords: high-speed rail, aerodynamic noise, sound barriers, computational fluid dynamics, acoustics, noise control, COMSOL, ANSYS Fluent, noise, reduction, effect, sound

The central challenge the authors describe is that a porous sound absorber is not one material but two: a fluid phase, typically the air trapped in the pore network, and a solid phase, known as the skeleton, which may be a polymer foam, a fibrous mat, or a granular assembly. Predicting how such a medium behaves when sound waves strike it requires knowing the parameters of both phases. The seminal work of M. A. Biot in the 1950s provides the theoretical framework for coupling the two, but the practical business of measuring the underlying numbers is where laboratory ingenuity comes in. For an isotropic material, the fluid phase is described by quantities such as open porosity, static air-flow resistivity, tortuosity, viscous and thermal characteristic lengths, and static thermal permeability, while the solid phase requires its mass density, Young’s modulus, loss factor, and Poisson’s ratio.

These parameters are not arbitrary. The widely used Johnson-Champoux-Allard-Lafarge model, or JCAL, needs six fluid-phase parameters to compute the dynamic mass density, which captures visco-inertial dissipation, and the dynamic bulk modulus, which captures thermal dissipation. Combined with the four elastic parameters of the skeleton, this yields the ten-parameter Biot-JCAL model, the workhorse of modern vibro-acoustic prediction. Simpler models exist for materials with particular morphologies: the Delany-Bazley-Miki model needs only flow resistivity and porosity, while the limp model for very soft materials such as cotton-candy-like foams requires nothing more than the skeleton’s mass density. The review emphasizes that choosing the right model is itself a characterization decision, because the number of parameters a laboratory must determine depends on the physics assumed.

Direct measurements form the first category of techniques, and three fluid-phase parameters can be obtained this way. Static air-flow resistivity, standardized in ISO 9053-1, is measured by forcing air through a sample of known thickness and area and recording the pressure drop, an application of Darcy’s law borrowed and adapted from the geosciences, where rocks rather than foams were the original targets. Open porosity, the fraction of a material’s volume accessible to the acoustic wave, can be measured by compressing the air in an enclosure containing a sample and reading the pressure increase, a method related to the gas pycnometer used for geomaterials, or alternatively by weighing a dry sample and then saturating it with a fluid of known density, an application of Archimedes’ principle. The review notes that larger samples yield more accurate porosity results in both approaches.

The high-frequency limit of dynamic tortuosity, which quantifies how the winding pore paths lengthen the effective route of sound through the medium, was historically measured by saturating the sample with an electrically charged liquid and measuring the electrical resistance across it. These methods, now largely abandoned, required the skeleton to be an electrical insulator and prior knowledge of the porosity, and they struggled with the very materials that exhibit the highest tortuosity values, whose pore sizes of a few microns resist complete saturation. The remaining fluid-phase parameters, including the viscous and thermal characteristic lengths and the static thermal permeability, must be estimated indirectly, typically by combining impedance tube measurements with a physical model.

Indirect estimation has become the dominant paradigm, and the impedance tube is its central instrument. In the late 1990s, the technique gained popularity when a third microphone placed inside the rigid backing allowed researchers to measure the pressure behind the sample, simplifying the extraction of the dynamic bulk properties. Building on this, Panneton and Olny showed in 2006 that four JCAL parameters governing viscous dissipation could be recovered analytically from such measurements, and the approach was later extended to retrieve all six JCAL parameters from low- and high-frequency asymptotes. The three-microphone technique is currently in the standardization process via ISO 10534-3, a proposition already submitted, reflecting how laboratory practice matures into international consensus. The review also highlights subtleties that can corrupt results: air leaking around the sample can create double-porosity effects that alter the measured properties, and vibrations of the skeleton itself can contaminate the data, which experimenters mitigate with Teflon tape rather than wax, or by adding nails to shift skeleton resonances out of the measurement range.

Ultrasound methods offer a complementary route. By measuring the speed of sound in a sample of known thickness and porosity, researchers can quickly estimate tortuosity and even map heterogeneity across a material. However, at ultrasound frequencies, multiple scattering can appear in media with pore sizes of hundreds of microns, a phenomenon not accounted for in classical visco-thermal models. Clever workarounds have been developed, including successive measurements in two different fluids to separate and exclude scattering effects from the estimates of the characteristic lengths. Time-domain methods, in which reflected or transmitted impulse waves are analyzed, have also been explored since the early 2000s to estimate porosity, tortuosity, and flow resistivity, though the review describes this approach as still in a sparse state of development with perspectives for complementary robust characterization.

On the elastic side, the review reveals a field riddled with practical difficulties. Interlaboratory tests have shown large deviations between values of Young’s moduli and loss factors obtained by different methods, with the main deviations traced to the frequency range and the initial condition, whether imposed load or imposed strain. Uniaxial compression, the most common technique due to its apparent simplicity, is influenced by at least four factors: the possible anisotropy of the material, the temperature and frequency dependence of visco-elastic behavior, the static strain or stress dependence, and the coupling with the fluid phase as air enters and leaves the sample during compression. For fibrous materials, anisotropy is particularly critical because the elastic parameters along the fibers can differ significantly from those perpendicular to them. Moreover, polymer skeletons exhibit glass transition temperatures typically between minus twenty and twenty degrees Celsius, meaning their stiffness changes dramatically across ordinary laboratory conditions, yet few characterizations are performed at multiple temperatures and frequencies.

The review also confronts the frontier of new materials that defy classical characterization. Activated carbon exhibits a sorption phenomenon that makes direct porosity measurement impossible. Natural fibers typically display multiple scales of porosity, as did early 3D-printed materials, though this tendency is decreasing as printing precision improves. Fractal microstructures and nanomaterials present further challenges, with nanomaterials often difficult to manufacture in prototype samples large enough for impedance tube or ultrasound testing. Characterization in extreme environments, including high temperature for muffler and thermo-acoustic applications, high pressure, water-saturated conditions for building and underwater uses, and in-situ end-of-chain measurements, is actively being developed. Meanwhile, standardization is evolving faster than ever, with newly published standards attempting to be more critical and informative about methods while remaining open to new techniques, as illustrated by the fundamental differences explained between diffuse-field transmission on large samples and impedance-tube transmission on small ones.

The authors close with reminders that apply across the discipline. Uncertainties in measurements are now regularly reported, improving reliability. Anisotropy remains a slowly growing research area despite its importance for fibrous materials, because it multiplies the number of parameters required as scalar quantities become tensors. Statistical approaches, particularly Bayesian methods, and machine learning algorithms are increasingly used to identify and correct errors in measurement data, aided by the commercial availability of material databases. On the acoustic side, the low-frequency parameters remain difficult to characterize even though the low-frequency range is of tremendous importance for sound-absorbing materials. On the elastic side, broadband frequency characterization remains the exception rather than the rule. The review ends with a quote from Tamas Pritz that captures the field’s philosophy: the simpler the method, the better to have reliable results, a reminder that no characterization technique is perfect and that combining complementary methods often provides the most robust and comprehensive picture of the materials that make our world quieter.

Subject of Research: Acoustics

Article Title: Characterizations of acoustical porous media: standardized methods, current trends and challenges

Article References: Jaouen, L., Bécot, F.-X., & Chevillotte, F. (2025). Characterizations of acoustical porous media: standardized methods, current trends and challenges. Frontiers in Acoustics, 3, Article 1543456. https://doi.org/10.3389/facou.2025.1543456

Image Credits: AI Generated

DOI: 10.3389/facou.2025.1543456

Keywords: acoustics, porous materials, sound absorption, impedance tube, standardization, Biot model, characterization, Characterizations, acoustical, porous, media, standardized

The core idea is deceptively simple: sound quality is not a byproduct of engineering but a design target in its own right. Perception-driven engineering, a concept first articulated by Davies in 2007, integrates human response directly into product and system design. As a structured methodology, it combines three interlocking stages—sound acquisition, sound evaluation, and design implementation—while explicitly quantifying acoustic and human factors alongside conventional engineering parameters such as mass, efficiency, and cost. The approach has gained particular traction in aircraft design, where community noise has long constrained operations, but the editorial argues that the shift to electric propulsion makes it indispensable across the entire transportation sector.

The reason is physical as much as psychological. Electric powertrains eliminate the dominant low-frequency rumble and broadband roar of combustion engines, exposing tonal whines from inverters, gear meshes, and cooling systems that were previously masked. In the air, rotor and propeller noise from unmanned aircraft introduces spectral and temporal signatures unlike anything communities have historically encountered. Conventional single-number metrics such as A-weighted sound pressure level, developed for an earlier acoustic era, struggle to capture how these new sounds are actually experienced. The editorial’s central theme is that human response emerges from a combination of acoustic and non-acoustic influences, and that engineering methods must account for these interacting factors explicitly rather than assuming loudness tells the whole story.

That principle is vividly illustrated by one of the studies gathered in the Research Topic. Woodcock and colleagues examined annoyance responses to the sound of a medical-delivery drone under varying operational and contextual conditions. Their findings reveal a layered picture: annoyance decreased as the distance between listener and drone increased, and it rose in quieter ambient environments where the aircraft stood out against the soundscape. But the most striking result concerned context. When participants were told the drone was being used for medical deliveries, their reported annoyance dropped significantly—even though the physical sound reaching their ears was identical. Perceived purpose, in other words, modulates noise response just as powerfully as acoustic mitigation does.

The implications ripple outward. The authors conclude that drone and AAM integration must be socio-acoustically informed, pairing acoustic design and operational planning with communication strategies that shape how communities interpret new sounds. For operators, this means that community engagement is not a public-relations garnish but an engineering variable with measurable effect. For regulators, it suggests that noise policy for emerging aerial mobility cannot rely on sound level limits alone; it must also consider what people are told about the vehicles overhead and how those narratives interact with the acoustic environment. A quieter drone flown without explanation may generate more complaint than a slightly louder one framed as delivering urgent medical supplies.

A second strand of the Research Topic tackles a stubborn measurement problem: how to capture perception in ways that fit within practical design cycles. Münder and colleagues argue that evaluating the acoustic experience of electric vehicles requires accounting for the time-varying nature of the signals themselves. An acceleration event is not a static sound but a perceptual episode with internal structure—a sequence of tonal rises, masking shifts, and transient events that unfold over seconds. To capture this, the team employed the Continuous Evaluation Procedure (CEP), in which participants provide moment-by-moment judgments while listening to accelerating electric vehicles in an immersive simulator.

The results were revealing. CEP uncovered time-dependent patterns in perceived quality and annoyance that conventional single-value ratings simply missed—phases within an acceleration where annoyance spiked or quality dipped, invisible when the entire event is collapsed into one number. The authors recommend systematic adoption of continuous evaluation for transient acoustic events, and their work offers a practical bridge between psychoacoustics and engineering validation. For designers, this means it becomes possible to identify and control specific undesirable perceptual phases within an operational sequence—say, a jarring tonal transition two seconds into a launch—rather than tuning the vehicle against a single aggregate score.

Efficiency is the third pillar. Benghanem and colleagues addressed the need for fast, reliable prediction of perceptual attributes by developing objective models for sensory qualities and desire-to-buy judgments of recreational vehicles. Rather than deploying heavyweight machine learning, they used parsimonious multiple linear regression methods—Lasso and Elastic Net, regularization techniques that shrink and select variables to prevent overfitting. Their models were trained on combinations of standard engineering and psychoacoustic metrics together with descriptors borrowed from Music Information Retrieval (MIR) feature extraction, a field that has spent decades quantifying texture, roughness, and timbre in audio signals.

The outcome demonstrates that compact linear models can reliably represent the full set of perceptual attributes, including desire-to-buy, while relying on only a small number of physical and psychophysical predictors. This is more than a computational convenience. It reinforces a message aligned with Industry 5.0 goals: perception-driven design can link perceptual targets such as softness, aggressiveness, and perceived power to a manageable set of metrics, giving engineers actionable guidance without requiring opaque black-box models. A brand team can specify a desired character for a vehicle’s sound, and the model can trace that character back to the physical parameters that produce it.

The Research Topic also insists that perception-driven engineering operate within wider governance, health, and equity contexts, particularly as new aerial mobility vehicles introduce novel noise exposure patterns with implications for public health and fairness. Lavia and colleagues propose a transdisciplinary Sound, Noise and Health Conceptual Framework aimed at supporting fair and equitable dispersion of aircraft operations. By embedding dispersion and impact management within a structure that integrates stakeholder engagement and non-acoustic moderators, they show how perception-driven acoustics can support policy decisions—shifting the focus from narrow sound level-based optimization toward broader considerations of health, equity, and contextual response. This contribution is especially important for future AAM systems, where routing, scheduling, and operational concepts may evolve faster than community responses can be measured, leaving regulators to manage impacts they cannot yet fully quantify.

Looking ahead, the editorial identifies an emerging consensus about where the field must go. Continued expansion of electric mobility and autonomous systems will only increase the complexity of future soundscapes, and progress will depend on simplified, interpretable models that accurately link physical design parameters to perceived sound quality; advances in auralisation and psychoacoustic modelling that let designers listen to a vehicle before it exists; clearer definitions of key performance indicators to guide optimization; and evaluation methods that integrate contextual and societal factors alongside physical measurements. The stakes extend beyond technical performance. As the editorial frames it, acoustic design must ultimately serve human experience and community wellbeing—a recognition that the sound of the electric future is not something that happens to us, but something we can deliberately shape.

Subject of Research: Perception-driven acoustic engineering for electric mobility and advanced air mobility

Article Title: Editorial: perception-driven acoustic engineering

Article References: Torija, A. J., Krishnamurthy, S., & Merino-Martinez, R. (2026). Editorial: perception-driven acoustic engineering. Frontiers in Acoustics, 4, Article 1802446. https://doi.org/10.3389/facou.2026.1802446

Image Credits: AI Generated

DOI: 10.3389/facou.2026.1802446

Keywords: acoustics, psychoacoustics, advanced air mobility, electric vehicles, drone noise, noise annoyance, sound perception, engineering design, auralisation, noise control, soundscape, community engagement

The research team, led by Nadine Kalb and Christoph Randler, invited participants into a controlled laboratory setting where they listened to 15-second recordings of wild bird vocalizations, all taken from the widely used reference collection Die Stimmen der Vögel Europas by Bergmann and colleagues. Each participant rated the pleasantness of every sound on a five-point scale, from not very pleasant to very pleasant, without being told which species was singing. Recordings were played in randomized order through headphones at a fixed volume, and listeners could replay each clip as often as they wished before committing to a judgment. The species pool spanned the breadth of the German avifauna, from garden songbirds to owls and waterbirds, ensuring that the results reflect the acoustic diversity people actually encounter in Central European landscapes.

The ratings revealed a striking spread. The average pleasantness score across all species was 3.13 on the five-point scale, but the extremes were dramatic. The common blackbird, with its rich, fluty warbling, earned the highest mean rating of 4.52, while the barn owl, whose eerie hissing screech bears little resemblance to melodic song, received the lowest at 1.32. These extremes are more than trivia: they anchor a quantitative question about what, physically, separates a beloved dawn chorus voice from a sound many people would rather not hear at dusk.

To answer it, the researchers turned to detailed acoustic measurement. Using the bioacoustics software Raven Pro, they inspected every recording in spectrogram view and manually marked each sound element, defined as a visible trace without a temporal gap. For every element they extracted four frequency-domain parameters: the low frequency, below which the lowest 5 percent of the element’s energy falls; the high frequency, below which 95 percent of the energy is contained; the peak frequency, where spectral power is maximal; and the 90 percent bandwidth, the frequency span holding the bulk of the element’s energy. From the waveform they also derived minimum, maximum and peak amplitudes, capturing how loud each element was. Finally, they counted the total number of elements in each 15-second clip and the number of distinct element types, using the latter as an objective proxy for what psychoacoustics researchers usually measure subjectively: sound complexity.

Because seven correlated acoustic variables are unwieldy to interpret, the team ran a principal component analysis with varimax rotation, validated by a parallel analysis, which distilled the measurements into three interpretable components. The first, an amplitude component, bundled minimum, maximum and peak amplitude together. The second, a frequency component, captured low and peak frequency. The third, a bandwidth and high-frequency component, combined bandwidth with high frequency. Feeding these component scores into a multiple regression against the mean pleasantness rating of each species produced a model that explained a substantial 46.8 percent of the variance in pleasantness, with all three components emerging as significant predictors.

The direction of the effects tells a coherent psychoacoustic story. Sounds with higher low and peak frequencies were rated as more pleasant, consistent with longstanding findings that low-frequency sounds are harder to ignore, more difficult to habituate to, and often perceived as annoying or even aggressive. Conversely, sounds with lower high frequencies and narrower bandwidths scored better, which aligns with earlier work showing that the human auditory system is maximally sensitive between roughly 2.4 and 5.5 kilohertz; sounds in that range are perceived as louder and more intense, and therefore less pleasant. The most highly rated vocalizations in this study had low and high frequencies that largely avoided that uncomfortable zone. Lower amplitudes also predicted higher pleasantness, echoing previous reports that louder bird sounds are considered less restorative, although the authors urge caution here because the commercial recordings did not follow a standardized recording protocol, so amplitude differences may partly reflect recording conditions rather than the birds themselves.

Complexity added its own independent contribution. In a separate regression, the number of different element types within a vocalization significantly predicted pleasantness, whereas the sheer total number of elements did not. In other words, it is not how often a bird vocalizes but how varied its repertoire of sounds is that listeners find appealing. A follow-up model including all three acoustic components alongside complexity and element count confirmed that the complexity effect persisted independently of the spectral and amplitude characteristics, suggesting that variability in vocal output is a genuine dimension of acoustic appeal rather than a byproduct of frequency or loudness. This dovetails with earlier findings that people prefer sounds of moderate complexity and rate more complex birdsong as more restorative.

The study also probed the listeners themselves. Age, gender and, perhaps surprisingly, birding specialization had no significant effect on pleasantness ratings, indicating that appreciating a beautiful birdsong does not require expert knowledge or years spent in the field. What did matter was how much participants valued birds in general. Those who agreed more strongly with statements such as liking birds because they are beautiful to look at, pleasant to listen to, or helpful for feeling good rated the vocalizations as more pleasant overall, with a positive correlation between the two measures. The authors suggest that people who spend more time in nature-related activities accumulate positive associations and memories with bird sounds, which color their perception. Notably, the pleasantness ratings from this German sample correlated positively with the Perceived Restorative Potential scores reported for 21 overlapping species in earlier research by Ratcliffe and colleagues, hinting that pleasantness and restorativeness are related, though not identical, constructs.

The implications reach beyond the laboratory. If not all bird vocalizations contribute equally to human well-being, then soundscape quality in urban parks and green spaces may depend not just on how many birds are present but on which species. Management practices that support acoustically pleasant species, those with higher low frequencies, moderate loudness, narrow bandwidths and varied repertoires, could enhance the restorative value of recreational areas. The authors also raise the provocative idea that acoustic pleasantness represents an additional dimension of wildlife charisma. Conservation programs have long relied on visually appealing flagship species to rally public support; incorporating how a species sounds into that calculus might strengthen conservation communication and deepen human connection to nature.

The authors are careful to note the limits of their findings. The participant pool was modest and skewed toward women, the ratings come from a single cultural context, and individual differences in perception were not explicitly modeled, leaving room for future work with larger, more balanced samples and mixed-effects approaches. Still, the core message stands: the pleasure we take in birdsong is not mysterious. It can be traced, element by element, to measurable properties of sound, and understanding those properties gives planners, conservationists and anyone who loves a dawn chorus a new tool for protecting the acoustic richness that makes natural spaces restorative in the first place.

Subject of Research: Acoustic parameters of bird vocalizations and their perceived pleasantness by human listeners

Article Title: Analyzing the acoustic parameters of bird vocalizations and their perceived pleasantness by humans

Article References: Kalb, N., von Lücken, G., Lukanowski, J., Dechant, F., & Randler, C. (2026). Analyzing the acoustic parameters of bird vocalizations and their perceived pleasantness by humans. Frontiers in Bird Science, 5, Article 1794594. https://doi.org/10.3389/fbirs.2026.1794594

Image Credits: AI Generated

DOI: 10.3389/fbirs.2026.1794594

Keywords: birdsong, acoustics, psychoacoustics, sound pleasantness, restoration, birding, soundscape, conservation, frequency, amplitude, complexity, human perception

The human vocal tract is a remarkably variable structure. The tissues of the head and neck differ in size and shape from person to person, and even when two speakers produce what listeners perceive as the same sound, they may achieve it by shaping their anatomy in noticeably different ways. On top of this biological variation, developmental and cultural factors sculpt the way people speak, from the accents of their communities to the habits formed over a lifetime of conversation. The central question the researchers posed was deceptively simple: how much of the variation in the way people sound is rooted in the physical machinery of speech itself?

To answer it, the team turned to a rich source of data: the USC 75-Speaker Speech MRI Database, an open-source collection of real-time magnetic resonance imaging recordings made while people spoke. From this resource, the researchers analyzed 32 speakers, 16 male and 16 female, focusing on five American English vowels: the sounds written in the International Phonetic Alphabet as [i], [e], [a], [o] and [u]. Real-time MRI is a powerful tool for speech science because it captures the moving articulators—the tongue, jaw, lips and other structures—in action, allowing researchers to see not just the end product of speech but the dynamic configurations that produce it.

The results revealed striking diversity. The subjects had widely different vocal tracts, and they used very different ranges of motion within those tracts to produce the very same vowel sounds. In other words, two speakers aiming at the same target sound did not simply scale a single template of tongue and jaw positions to fit their anatomy; they each found their own articulatory solution. These individual ranges of motion were a direct consequence of each person’s specific vocal anatomy, and they produced two things at once: the correct, recognizable sound, and a subtle but systematic acoustic signature that distinguished one speaker from another.

This distinction matters because it separates intelligibility from identity. Speakers compensate for their anatomical differences in order to remain mutually intelligible—listeners must be able to understand one another for language to function. Yet the compensation is never perfect in the acoustic sense. Each vocal tract leaves its own imprint on the sound waves that emerge from the mouth. The study’s imaging data made these imprints visible at their source, showing how the same phonetic goal is reached through different physical means and with measurably different acoustic outcomes.

The next step took the researchers beyond English. By combining their real-time MRI results with multilingual speech data, they examined whether the pattern of individual variation they observed was peculiar to American English speakers or something more general. The comparison included languages such as Basque and Hindi, which belong to entirely different language families and occupy very different linguistic and geographic worlds. The amount of variation within those languages turned out to be similar to the variation present in American English, suggesting that within each language there exists a basic level of speaker variation that arises from vocal tract anatomy itself, independent of the particular language being spoken.

Building on these observations, the authors propose a biocultural model of how spoken sounds might vary and diversify between peoples. In this model, the variation of pronunciation within a group feeds into the development of language differences between groups. Over time, as communities separate and pronunciation habits drift, those small anatomically grounded differences can accumulate until two groups eventually produce speech systems that are no longer mutually intelligible. In this view, the biological diversity of human populations is not merely a constraint that languages must work around; it is an active ingredient in the process by which languages split apart and diversify.

The authors are careful to acknowledge the limits of the study. The sample of vocal tracts was small, and the comparison spanned only a few language families, so the conclusions remain a proposal rather than a settled account. Even so, the researchers argue that the work offers something linguistics has lacked: a null model for studying the phonetic evolution of spoken languages. If some of the differences between the world’s languages reflect variation already present in the anatomical differences between speakers, scientists now have a baseline against which they can identify the sociocultural or historical factors that have driven language diversification beyond that biological starting point.

The implications reach into how linguists interpret everyday data. As the authors note, differences in pronunciation between speakers of a language are often treated as noise to be normalized away in linguistic analysis. The results of this study suggest the opposite: that variation between individuals may be an important source of information for understanding the evolution of spoken languages. Rather than filtering out the acoustic fingerprints of individual anatomy, researchers may need to study them directly, because those fingerprints could reveal the mechanisms by which phonetic systems change over generations.

Perhaps the most striking idea in the study is that the seeds of phonetic difference between languages are already present in the variation between individual speakers alive today. Spoken language evolution, in this account, is driven jointly by the biological diversity within populations and the sociocultural forces that shape how languages change. The Tower of Babel, long a metaphor for the mysterious multiplicity of human tongues, may have a partial explanation written into our own bodies: the same anatomical variation that makes every voice instantly recognizable to those who know it may also have nudged whole communities of speakers down different phonetic paths, one small acoustic signature at a time.

Subject of Research: The influence of interindividual vocal tract anatomy on phonetic variation and language diversification

Article Title: Variations in the human vocal tract could have influenced our language diversity

Article References: Variations in the human vocal tract could have influenced our language diversity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: vocal tract, phonetics, language diversity, speech MRI, PLOS Biology, biocultural model, linguistic evolution, vowels, articulation, acoustics, anatomical variation, language evolution

The study, published in the journal Sports Engineering, was led by Thomas Daney of Sorbonne Université and the Arts et Metiers Institute of Technology, together with Delphine Chadefaux, Jean-Loïc Le Carrou and Arthur Paté, spanning laboratories in Paris and Lille that specialize in acoustics, musical instrument making and human biomechanics. The group set out with a deceptively simple question: if a highly skilled player perceives two rackets as behaving differently under vibration, can physics find the fingerprint of that difference? Rather than testing rackets in isolation on a bench, the team chose to measure them in the messiest possible setting, a real padel court, with a real player hitting real forehands.

Padel, a sport played on an enclosed court with solid-faced rackets perforated with holes, has exploded in popularity across Spain, France, Latin America and beyond. Unlike stringed tennis rackets, padel rackets are composite slabs, typically of carbon or fiberglass faces bonded to a foam core, and their dynamic behavior during impact is far less documented in the scientific literature. The sport also carries a real injury burden. Epidemiological studies cited by the authors report substantial rates of elbow, wrist and shoulder complaints among both professional and amateur players, which makes understanding how impact vibrations travel from the racket into the human arm more than an academic curiosity.

The experimental design was elegantly economical. Two rackets were selected specifically because a single, highly skilled player judged them to exhibit clearly different vibratory behaviors, a perceptual judgment that served as the hypothesis to be tested. The player then performed twenty routine forehand strokes on a padel court, giving the researchers a set of repeated, ecologically valid impacts rather than the artificial strikes of a pendulum or robot rig. Accelerometers were mounted on each racket and on the player’s body, capturing the shock-induced vibration at the wrist and elbow joints and in the soft tissues of the upper limb. Simultaneously, a microphone recorded the sound radiated by each ball-racket impact, the sharp percussive crack that fills a padel court with every shot.

The technical challenge of measuring vibration in playing conditions should not be underestimated. Previous work on tennis has shown that a player’s grip itself alters the dynamic behavior of a racket, damping and shifting its modes of oscillation, and that muscle activity in the forearm can actively tune the vibrations that reach the hand. The French team built on this lineage, drawing on methods developed for tennis serves, golf shots and baseball bats, where researchers have long known that the perception of a good shot is a multisensory experience combining vibrotactile feedback through the hand with acoustic feedback through the ear. Studies in psychoacoustics have established that human listeners are exquisitely sensitive to the frequency content, loudness and decay of impact sounds, and that these cues shape judgments of equipment quality even when players cannot articulate why.

To translate raw sensor data into perceptually meaningful terms, the researchers analyzed both the vibration and the sound using classical descriptors known to have correlates in human perception. In the time domain, these included peak amplitude, the maximum excursion of the signal, and RMS level, a measure of overall energy, along with decay time, which captures how quickly the ringing of the impact dies away. In the frequency domain, the team examined the spectral content of each signal and the spectral centroid, essentially the balance point of the spectrum, which psychoacoustic research links to the perceived brightness or dullness of a sound. These are the same tools used to characterize the timbre of musical instruments, a fitting choice given that one of the contributing laboratories, the Lutheries-Acoustique-Musique team at the Institut Jean Le Rond d’Alembert, spends its days studying violins and guitars.

The results vindicated the expert player’s ear and hand. Across the twenty strokes, the analysis revealed statistically significant differences between the two rackets in several of these descriptors, in both the time and frequency domains, differences that the authors say highlight genuinely distinct vibratory behaviors. In other words, the vague impression that one racket feels different from another was anchored in objective, repeatable physical measurements taken under authentic playing conditions. The combination of racket-mounted and body-mounted sensors meant the team could trace not only how each racket rang after impact but also how those vibrations were transmitted into the wrist, elbow and soft tissues of the player’s arm, the pathway most relevant to both comfort and injury risk.

The study was not without its measurement compromises, which the authors report transparently. For one muscle location on the forearm, electromyography data proved unusable while inertial measurement data remained valid; for another location, the situation was reversed. Such is the reality of embedded sensing on a moving, sweating athlete, and the team’s willingness to work within these constraints underscores the value of their approach: laboratory rigs produce cleaner signals, but only playing conditions produce signals that actually matter to players. The statistical analysis applied multiple-comparison corrections, using procedures designed to control false discovery rates across the many descriptors tested, lending rigor to the claimed differences.

Why does this matter beyond the padel court? For manufacturers, the findings suggest a concrete route to designing rackets with targeted feel. If specific acoustic and vibratory descriptors, such as decay time or spectral centroid, reliably encode the perceptual differences that players notice, then engineers can tune foam cores, face laminates and hole patterns with those descriptors in mind, much as guitar makers tune bracing patterns for tone. For sports medicine, quantifying how different rackets channel vibration into the joints of the upper limb could inform equipment recommendations for players prone to overuse injuries, a question that has been studied extensively in tennis but barely at all in padel. And for the science of perception, the work adds another sport to the growing evidence that what athletes call feel is a genuine, measurable, multisensory construct rather than marketing mystique.

The research, funded through a doctoral grant from the French National Center for Scientific Research’s network on sports and physical activities, was approved by an ethics committee and relied on the generous commitment of a single expert player, whose twenty forehands formed the entire dataset. The authors acknowledge that broader panels of players and additional stroke types will be needed to generalize the findings, and the data are available upon reasonable request for other teams to build on. But the conceptual leap is already in place: the percussive crack of a padel rally, the buzz in a player’s wrist and the ringing in the racket’s frame are not separate phenomena but one coupled system, and by measuring that system where it lives, on the court, mid-rally, researchers have begun to give the word feel its physics. For a sport played by millions and heard in every point, that is a sound worth decoding.

Subject of Research: Vibration and acoustic analysis of ball-racket impacts in padel under playing conditions

Article Title: Vibration and sound of two padel rackets compared in playing conditions

Article References: Daney, T., Chadefaux, D., Carrou, J.-L. L., & Paté, A. (2026). Vibration and sound of two padel rackets compared in playing conditions. Sports Engineering, 29(2), Article 35. https://doi.org/10.1007/s12283-026-00565-4

Image Credits: AI Generated

DOI: 10.1007/s12283-026-00565-4

Keywords: padel, racket vibration, acoustics, ball impact, biomechanics, psychoacoustics, spectral centroid, decay time, sports engineering, injury prevention, embedded sensors, perception

The fundamental obstacle is the stiffness of air itself. When sound compresses the air inside a resonator cavity, the trapped air behaves like a stiff spring, and this stiffness grows as the cavity shrinks. A compact device therefore has a very stiff air cavity, and to push its resonance down to useful low frequencies, engineers must add a large acoustic mass. The result is a sharp, narrow absorption peak that misses most of the noise spectrum. Passive approaches such as porous materials help by converting the compression of air from an isentropic process into an isothermal one, which lowers the effective stiffness by a factor equal to the ratio of specific heats for air, roughly 7/5. But even this so-called thermodynamic limit demands cavity depths on the order of one-eighth of a wavelength, which at 100 hertz means tens of centimeters of depth per absorber.

The key insight behind the new work is that instead of adding mass, one should reduce stiffness, and the most powerful way to do that is with negative stiffness. A structure exhibits negative stiffness when, upon being displaced from equilibrium, it generates a force in the same direction as the displacement, producing a negative slope in its force-displacement curve. Because magnetic attraction and repulsion scale with the inverse square of distance, magnets are a natural source of such behavior. The idea of using magnetic negative stiffness against the positive stiffness of an air cavity was first explored theoretically in 2000, but subsequent experimental attempts ran into two recurring failure modes: initial force imbalance and rotational instability of the moving magnetic element, both of which introduced parasitic stiffness that canceled the intended benefit.

The new device, called the Acoustic Resonator with Magnetic Bearing, or aRMB, solves these problems with an elegant arrangement. A fixed outer ring magnet faces a moving inner magnetic disk across a fixed radial air gap, so the negative stiffness arises from repulsive forces rather than attraction. The inner disk is attached to a rigid steel rod that slides in a linear ball bearing, which constrains the angular motion that plagued earlier designs while allowing nearly friction-free axial movement. Radial stability comes for free from the magnet geometry itself: displace the disk sideways and the magnetic forces push it back to center, so the magnetic pair functions as a contactless bearing. Calculations show this configuration delivers 1.96 times the negative stiffness of a comparable attraction-based design for the same magnet volume, and shrinking the radial gap can boost the effect further.

To quantify progress, the researchers introduced a stiffness ratio kappa, defined as the sum of the magnetic negative stiffness and any parasitic positive stiffness, divided by the original stiffness of the pure air cavity. A value of zero means the negative stiffness has exactly canceled all parasitic stiffness, matching the thermodynamic baseline of a plain air cavity. A value of minus 2/7 corresponds to the limit achieved by filling the cavity with porous material. Values between minus 1 and zero represent genuinely effective negative stiffness that beats the thermodynamic limit, while dynamic stability requires the ratio to stay above minus 1. Fitting their model to previously published data, the team found that earlier magnetic and buckling-plate devices never actually reached this effective regime; their fitted stiffness ratios remained stubbornly positive, meaning parasitic effects had swallowed the benefit.

Experimentally, the team tested the aRMB in an impedance tube using the standard two-microphone transfer function method. The moving assembly, a piston of about 20.6 grams, oscillates against a 90-millimeter-deep cavity. With no magnets, the resonance sat at 79.1 hertz and the stiffness ratio measured a positive 0.22, matching theory. As progressively stronger magnet types were installed, the ratio fell to minus 0.01, minus 0.25, and finally minus 0.35, driving the resonance down to 57.8 hertz while the acoustic mass stayed constant. Crucially, the strictest comparison, against the bare air-cavity stiffness without any suspension, showed the total stiffness reduced by a factor of 1.57, which the authors identify as the first demonstrated breakthrough of magnetic negative stiffness over classic resonator designs.

The head-to-head comparison with the classic approach is striking. At a 70-millimeter cavity depth, the magnet-enhanced resonator shifted its resonance from 85.6 to 62.8 hertz and reached a stiffness ratio of minus 0.40, already beyond the porous-material thermodynamic limit of minus 0.286. Tuned against an optimized perforated-panel design targeting the same frequency and damping, the aRMB delivered 1.57 times the total low-frequency absorption and a bandwidth 65 percent wider over the two lowest octaves from 31 to 125 hertz. The device also proved robust: absorption curves were essentially identical at sound pressure levels from 95 to 105 decibels, and simulations indicate stable linear operation up to about 125 decibels, near the threshold of pain, beyond which the magnet displacement exceeds a critical point of no return.

The potential goes further still. By narrowing the magnet air gap from 3.5 to 2.5 millimeters and replacing the acrylic plate with a lightweight conical diaphragm inspired by loudspeaker construction, simulations show the stiffness ratio could reach minus 0.80, equivalent to making the effective cavity five times deeper. Under those conditions, the total absorption over the 31-to-125-hertz range would rise 3.21-fold relative to the best classic design, with an effective bandwidth five times broader. The authors caution that these advanced configurations pose real manufacturing challenges, since tighter tolerances make the system sensitive to misalignment and an imperfect diaphragm can excite unwanted higher-order modes. But these are engineering hurdles, not barriers of principle.

What makes the work compelling is its decoupling of acoustic performance from physical size. For decades, the pursuit of deep subwavelength metamaterial absorbers has often produced complicated structures whose added mass exceeds the optimum and whose stiffness is left untouched or even increased. By contrast, stiffness tuning with magnetic negative stiffness lowers the optimal mass as well, compounding the broadband benefit. The researchers suggest their platform could seed a new class of acoustic metamaterials for aerospace, transportation, and consumer electronics, wherever miniaturization and low-frequency performance collide. If the manufacturing challenges can be mastered, the humble resonator, reinvented with a magnetic bearing, may finally bring compact, broadband silence within reach.

Subject of Research: Magnetic negative stiffness in compact acoustic resonators for broadband low-frequency sound absorption

Article Title: Absorption of Broadband Low‐Frequency Sound Beyond the Thermodynamics Limit: An Acoustic Resonator With Magnetic Bearing

Article References: Hu, Y., Zhang, Z., Huang, B., Han, X., Kilcoyne, H. B., & Huang, L. (2026). Absorption of Broadband Low‐Frequency Sound Beyond the Thermodynamics Limit: An Acoustic Resonator With Magnetic Bearing. Advanced Science, 13(56), Article e76584. https://doi.org/10.1002/advs.76584

Image Credits: AI Generated

DOI: 10.1002/advs.76584

Keywords: acoustics, negative stiffness, magnetic bearing, sound absorption, low-frequency noise, acoustic resonator, acoustic metamaterials, thermodynamic limit, impedance tube, noise control, aerospace, stiffness tuning