Acoustic Performance Research Articles

The measurement of tire-road noise: how does standardization contribute to the development of low noise pavements in Europe

Low-noise road pavements are among the most effective solutions for reducing road traffic noise emission at the source. There was a significant international effort over the past years for developing and standardizing methods for measuring tire-road noise emission, essentially Statistical Pass-By (SPB) and Close ProXimity (CPX) methods. The dedicated Working Group of the European Committee for Standardization (CEN/TC227/WG5) recently investigated how these standards are used in practice and how they contribute to the implementation of low-noise pavements. For this, a survey was launched and 14 European countries responded on their practices. The survey showed a large diversity of use, although all refer to the measurement methods SPB, CPX. Based on these methods, some countries have developed national regulations or reference guidelines to specify and assess the acoustic performance of road surfaces. These procedures are, however, significantly different and lead to varying definitions of low-noise pavements, which prevents sharing knowledge, experience and data. This context justifies the ongoing development within CEN/TC227/WG5 of a standard procedure for the acoustic characterization of road pavements based on existing measurement methods. The paper will present and analyze the results of the survey, then will present the ongoing work in CEN.

Investigating the acoustic performance of metamaterials with internal simple expansion chamber structure

The tunable acoustic properties are possessed by acoustic metamaterials (AMMs) with internal configurable structures. Nine samples(B1-B9) were designed in SOLIDWORKS and then fabricated using 3D-printed photopolymer resin featuring an internal Simple Expansion Chamber (SEC) structure. SEC length varied from 2 to 18 mm, maintaining a constant area expansion ratio (m) of 16. Sound Absorption Coefficient (SAC) and Sound Transmission Loss (STL) were measured through the Impedance Tube Apparatus (ITA). The sample with a 4 mm SEC length exhibited a maximum SAC of 0.99 at 4.8 kHz. As SEC length increased peak SAC and peak absorption frequency linearly decreased. Across all samples, STL ranged from 1- 41 dB (0.5-2.4 kHz) and 20-36 dB (2.4-6 kHz) revealing a periodic pattern in the tested frequency range. With SEC increasing from 2 to 18 mm Peak STL decreased from 41.2 to 38.8 dB. This research contributes valuable insights into the design of acoustic materials for effective noise attenuation showcasing the potential for achieving at least a 20 dB reduction in the 2.4-6 kHz range.

Latency-free real-time auralisation in hemi-anechoic chambers

Real-time auralisation allows users to interact with a simulated acoustical room, providing a more responsive way of evaluating acoustical performance than pre- recorded auralisation. Nevertheless, real-time auralisation is computationally intensive and, therefore, susceptible to latency. This paper presents a novel latency-free real-time auralisation method that enables users to auralise a simulated acoustical event with self-excitation more accurately than current methods. The method uses a loudspeaker system inside a hemi-anechoic chamber. By exploiting the inherent floor reflection of the hemi-anechoic chamber, the impulse response can be trimmed to compensate for the total latency of the loudspeaker system. The method's validity is demonstrated with measurements presenting virtual wall reflections arriving at the correct time at the listening position. The influence of the speaker placement regarding latency is discussed. This method enables users to evaluate a given response more accurately than conventionally possible.

Acoustic behaviour and acoustic treatment strategies for the baroque church of Santuari del Miracle, Solsonès, Lleida

The church of Santuari del Miracle, located in the Catalan region of Solsonès, Lleida, is a unique barroque church in Catalonia that hosts Baroque music performances, like the festival Espurnes Barroques. However, according to the musicians and the audience, it is too reverberant to play this style of music. The objective of this work is to examine the current acoustic performance of the church and to propose acoustic treatment strategies that are respectful of this unique heritage building. Impulse response measurements are first performed following ISO 3382-1 standards, using Odeon software to assess reverberation time (T30), Early Decay Time (EDT), Clarity (C50), and Definition (D50). Simulations are next performed using Odeon. They are used to refine the smallest perceptible differences from the measured data and to examine potential treatment strategies. The proposed solution consists of elements based on variable acoustics that can be easily hidden or removed, thus preserving the original acoustics of this heritage building.

A study on the multi layers of automotive interior trim parts to improve the acoustic performance with microfiber applied to the surface layer

As the world joins environmental regulations, there is an increasing demand for the production of eco-friendly cars. As a result, the driving method of the vehicle was changed from the engine to the electric motor, and the main noise source was changed. In case of existing internal combustion engines (ICE), the low-frequency sound range, which is the engine's main noise, is the main source of sound. As it is converted into an eco-friendly car, the noise that was hidden by the engine combustion sound and the high-frequency noise of the motor are being highlightened. PP meltblown generally has a lower denier than other fibers, so it is effective in improving sound absorption performance because the surfaces of the fibers are large compared to the same weight of another fibers. In conclusion, by applying this PP meltblown fibers to the structure of Dash Insulation, sound absorption performance is improved and resulting in lightweighten effect of Dash Insulation

Random incidence absorption characteristics and parameterized design of micro-perforated panel absorbers with parallel-arranged backing cavities at different depths

Micro-perforated panel absorbers (MPAs) are recognized as efficient and environmentally friendly materials for sound absorption, prompting significant research efforts to expand their frequency ranges. This study investigates the acoustic performance of MPAs with parallel-arranged backing cavities at different depths (PCD) under random incidence conditions. Initially, an analytical model is proposed to predict the acoustic performance of PCD-MPA. The model exhibits significant consistency with finite element simulations and experimental measurements, validating its reliability in calculating absorption coefficients within the primary frequency band of concern (500~4000 Hz) in architectural acoustics applications. Subsequently, a thorough discussion of the key parameters, including the depth sequence and perforation parameters, which influence the random incidence absorption characteristics of PCD-MPA is presented based on the proposed model. These discussions lead to the development of an enhanced parameterized design method aimed at improving the absorption performance of PCD-MPA, enabling precise modulation of parameter combinations to meet specific application requirements and design nearly perfect absorbers.

The effect of temperature difference on the acoustic performance of Helmholtz resonator

Passive control devices such as liners and Helmholtz resonators (HRs) are commonly employed in practical applications to mitigate thermoacoustic instabilities. To safeguard the HR from being corroded by the invasion of hot flow from the combustor, a cooling flow with significantly lower temperature than that in the combustor is injected from the rear of the HR cavity. However, this results in a dynamic mixing of cold bias and hot grazing flows in the combustor, which may generate an entropy wave downstream of the HR, thereby affecting its sound absorption performance. Unfortunately, these effects are often neglected when modelling such systems. In this context, an acoustic model is derived for a one-dimensional combustor duct with distinct temperature compared to that of the attached HR. The model offers physical insights into the underlying mechanisms of the impact of HR on the acoustic fields. It considers not only the mean temperature difference between the cooling bias flow and the main flow in the combustor, but also the mean temperature difference between the up- and downstream sides of the combustor across the HR. The effect of both temperature differences on the HR’s performance will be discussed.

Iterative eigenvalue method coupled with RSM for structural acoustic analysis and optimization of the CLD-damped orthotropic steel deck

In the present work, an iterative eigenvalue method (IEM) is proposed and combined with the boundary element method (BEM) to perform the structural acoustical analysis of the orthotropic steel deck (OSD) damped with constrained layer damping (CLD), through which the frequency-dependent properties of the viscoelastic core can be accurately considered. Then, a series of hammer tests are carried out in a semi-anechoic chamber to verify the acoustic prediction method. It shows that the simulated structural noises basically agree with the test results, and the overall deviations at the field points M2 and M8 are merely 2.4 and 2.3 dB, respectively. Subsequently, taking the thicknesses of the damping layer and the constraining layer, as well as the material properties of the constraining layer as design variables, a central composite experiment is designed and combined with response surface methodology (RSM) to fit the relationship between analysis objectives and design variables. With the objective of minimizing the acoustic radiation power, a program for finding the optimal values of design variables is developed based on the interior penalty function method. Through iterative computations, the optimal points are numerically determined as t 1 = 2.3 mm and t 2 = 0.3 mm for the thicknesses of the damping layer and the constraining layer, respectively. Steel alloy is found to be the optimal material for the constraining layer. After optimizing CLD treatment, the overall acoustical power level can be reduced from 97.7 dB to 93.1 dB and the overall sound pressure levels (SPLs) at the field points M2 and M8 can be reduced from 89.2 dB to 83.5 and 76.9 dB to 70.3 dB, respectively, indicating that the optimization of CLD design parameters can significantly improve acoustic performance of the CLD-damped structures.

Effect of Sound Absorption on Noise Reduction in the Automotive Industry

Industrial noise is one of the most common physical factors that cause annoyance and damage to workers' health in the long term. Precautions should be taken to reduce noise and to improve acoustic performance in industrial working environments. This paper aims to analyze the acoustic performance of the automotive industry contributes to the global outcomes of sustainability and develop strategies for improving the quality of the working environment through improvement scenarios. For this purpose, the automotive industry in Türkiye was examined as a case study. In-situ acoustic measurements were made in the seat manufacturing unit of an automotive factory, and the current situation was transferred to the simulation program. The effects of acoustic improvements on A-weighted sound pressure level and reverberation time at mid-frequencies (500, 1000, 2000 Hz) were investigated through three scenarios. In the investigations, noise distributions were carried out through noise mapping. The A-weighted sound pressure levels in the automotive industry were reduced by approximately 15 dB. As a result of the study, suggestions for noise control precautions and their effects on the automotive industry seat manufacturing unit are presented.

Effect of SAW-IDT Electrodes Composed of Aluminum-Nickel Composite Thin Films on the Acoustic Performance of SAW Devices

Effect of SAW-IDT Electrodes Composed of Aluminum-Nickel Composite Thin Films on the Acoustic Performance of SAW Devices

Material Design and Performance Study of a Porous Sound-Absorbing Sound Barrier

A new type of porous sound-absorbing sound barrier was developed with quartz sand and self-developed polysiloxane resin. The forming process of the material was studied. The test specimens of the porous sound-absorbing sound barrier were prepared with different mesh numbers of quartz sand and different proportions of resin, and the void properties, compressive strength, durability, and acoustic performance were investigated. Based on the mix design results, it is suggested that 20-mesh quartz sand and a 10:1 mass ratio of quartz sand are used to prepare the porous sound-absorbing sound barrier. The durability study showed that the porous sound-absorbing sound-barrier material had good salt and alkali resistance, poor acid resistance, good water stability, and freeze–thaw stability. The laboratory acoustic test and practical engineering application results showed that the porous sound-absorbing sound barrier had excellent acoustic performance and good noise-reduction effects.

Viscoelastic material enhancement of underwater sound absorption in higher-order resonators: From low-frequency to ultra-broadband

Underwater noise control is crucial for improving the marine acoustic environment. This study introduces a novel underwater acoustic absorber design that integrates viscoelastic materials with higher-order resonance structures to enhance the absorption efficiency of low-frequency sound waves. By embedding a thin layer of rubber within a conventional second-order Helmholtz resonator, the rubber's viscoelastic and damping properties significantly improve this structure's underwater low-frequency acoustic performance. Theoretical and simulation calculations have shown that the structure has two perfect absorption peaks in the low-frequency range. The simulation results show that in the frequency range of 415–1848 Hz (Simulation), only four units are needed to effectively absorb up to 90 % of noise energy, and the total volume is only. Moreover, the absorber maintains excellent absorption performance over a wide range of incidence angles from 0 to 60 degrees. This work is helpful to design ultra-thin low-frequency underwater absorbers.

Prediction of flanking sound transmission through cross-laminated timber junctions with resilient interlayers

While the low weight and high bending stiffness of cross-laminated timber (CLT) are key to its popularity, these properties also contribute to poor acoustic performance. Notably flanking sound transmission is a critical factor, driving the need for vibration reduction solutions such as resilient interlayers in the junction design. However, due to the complex material behavior of CLT and resilient interlayers, the improvement related to these solutions is difficult to predict. In this research, an analytical model with low computational cost is developed to evaluate the vibration reduction index Kij for CLT junctions with resilient interlayers. The CLT panels are considered as thin orthotropic plates with homogenized material properties. Three potential material models are proposed for the interlayer: it is considered as a thin plate, a thick flexible layer with out-of-plane motion governed by shear or distributed springs. The prediction model is experimentally validated for junctions consisting of CLT panels, with and without resilient interlayers. For junctions without interlayers, the predicted and experimentally determined vibration reduction index Kij correspond most closely when the junction is realized with stiff connectors. In this case, the predictions are moderately accurate with deviations below 5 dB in 1/3 octave bands up to approximately 2000 Hz for both corner and coplanar transmission paths. For junctions with resilient interlayers, the shear interlayer model exhibits the best performance with deviations of less than 5 dB in most 1/3 octave bands. For frequencies below 1000 Hz, the accuracy of the simplified spring model is comparable to that of the thick layer model. Simulations with equivalent isotropic material parameters yield slightly inferior predictions than for orthotropic parameters if the degree of orthotropy of the panels is high.

Growth of Al-Cu Thin Films on LiNbO3 Substrates for Surface Acoustic Wave Devices Based on Combinatorial Radio Frequency Magnetron Sputtering

Al-Cu thin films were fabricated by RF magnetron sputtering from aluminum (Al) and copper (Cu) metal targets to improve the acoustic performance of SAW devices on LiNbO3 substrates. To optimize the electrode material for SAW devices, Al-Cu films with various compositions were fabricated and their electrical, mechanical, and acoustic properties were comprehensively evaluated. The Al-Cu films exhibited a gradual decrease in resistivity with increasing Al content. The double-electrode SAW devices composed of Al-Cu films demonstrated a resonant frequency of 70 MHz and an average insertion loss of −16.1 dB, which was significantly lower than that of devices made with traditional Au or Al electrodes. Additionally, the SAW devices showed an increase in the FWHM values of the resonant frequency and a decrease in the insertion loss as the Al content in the IDT electrode decreased. These findings indicate that improving the performance of SAW devices can be achieved by reducing the density of the IDT electrodes, rather than focusing solely on their electrical characteristics.

Sound absorption performance of honeycomb metamaterials Inspired by Mortise-and-Tenon structures

To address the limitations of traditional honeycomb sandwich structures in attenuating mid to low-frequency sounds, particularly in configurations with minimal thickness and weight, this study introduces an innovative honeycomb acoustic metamaterial incorporating the traditional Chinese mortise-and-tenon joint. We systematically investigate the acoustic absorption characteristics of the modified honeycomb structure through theoretical analysis, empirical validation, and numerical simulations. Our experimental setup maintained consistent geometric parameters across all trials and demonstrated that the resonance frequency of the modified honeycomb structure decreased by 10 % relative to its conventional counterpart. We conducted detailed analyses on the influence of micropore positioning, tenon geometric dimensions, and micropore diameters on the acoustic performance. Notably, elongating the tenon from 2 mm to 6 mm resulted in a 15 % reduction in resonance frequency, whereas increasing the micropore-to-tenon distance from 0 mm to 4 mm led to a 30 % increase. The integration of the mortise-and-tenon joint significantly enhances the mid to low-frequency sound absorption performance of the honeycomb panels. This improvement is achieved while preserving the structural benefits of low panel thickness and shallow cavity depth, alongside simplified processing of micropores. Our findings elucidate a promising approach to augmenting the acoustic properties of lightweight structural materials, thereby extending their application potential in noise control engineering. This study not only contributes a novel perspective to the design and optimization of acoustic metamaterials but also highlights the potential for integrating traditional architectural techniques with modern material science to enhance noise control solutions.

What do frog calls tell us about males? The advertisement call of Physalaemus albifrons (Amphibia: Leptodactylidae) in the Brazilian semiarid region does not reflect either gonadal investment or energy storage

ABSTRACT Anuran advertisement calls can provide accurate information on the reproductive quality of the male callers, thus providing females with indicators for the selection of mates. Body size is generally correlated with the dominant frequency of male advertisement calls. However, it is unclear whether and to what extent call parameters are associated with gonadal investment and the energy reserves of the males. Given that in tropical seasonally dry environments the wet season is very short, gathering information about gonadal investment and energy reserves of mates should be particularly important. In the present study, we evaluated the relationship between acoustic performance, gonadal condition, and fat storage in the Neotropical frog Physalaemus albifrons from the Brazilian semiarid region, testing the hypothesis that the advertisement call (repetition rate, call duration, and fundamental and dominant frequencies) would be a good predictor of male quality in terms of gonadal investment (testicle length) and energy reserves (mass of fat bodies). Contrary to our predictions, neither testicle length nor the mass of fat bodies was related to any of the acoustic parameters of the advertisement calls of P. albifrons. These results indicate that the advertisement call of P. albifrons does not provide reliable information on gonadal investment or energy storage of males. Possibly, in habitats with little and unpredictable rainfall, males of P. albifrons should present small variation in gonadal and fat storage conditions during its short reproductive window. Our findings contribute to the understanding of anuran reproductive strategies in seasonally dry environments.

Renewable insulation panels made with Cynodon dactylon grass for building applications: Physical, mechanical, acoustic, and thermal properties

This paper presents a pilot study investigating the manufacturing process and properties of novel bio-based materials intended for insulation in building walls. Panels with a thickness of 20mm were fabricated by mixing grass, water, and potato starch, followed by pressing and heating. Various combinations of coarse, medium, and fine Cynodon dactylon particles, along with three starch-to-water ratios (1:3, 1:4, and 1:5), were explored. The panels underwent characterization in terms of density, quasi-static compressive behavior, quasi-static flexural strength, high-strain compressive strength, sound absorption coefficient, thermal conductivity, and degradation under external environmental conditions. Results indicate that density is influenced by particle size and micro-structure arrangement, while static compressive stiffness is affected by both particle size and starch-to-water ratio. The panels exhibit low damage and effective dissipation under compressive high-strain deformation. The sound absorption test reveals superior capabilities (Class III of ISO 11654:1997) due to the porous structure. Thermal conductivity values ranging from 0.075 to 0.092 Wm−1K−1 support the application as a thermal insulation material. Furthermore, the study demonstrates that reducing particle size and increasing starch-to-water ratio enhance mechanical properties while slightly diminishing acoustic and thermal performance. Under external environmental conditions, the panels lasted more than 1 months, demonstrating acceptable resistance to rain and humidity. Comparative analysis with other natural bio-based materials shows that Cynodon dactylon-starch panels possess similar or superior physical, mechanical, acoustic, and thermal characteristics. These findings suggest that these panels could serve as environmentally friendly alternatives in the insulation materials sector within the building industry.

The resonant behavior of airborne standing-wave acoustic levitators based on arrays of ultrasonic transducers

Recently airborne standing-wave acoustic levitation has seen great advances, and its applicability has been broadened due to the development of cavities constructed with arrays of compact ultrasonic sources. Yet, the numerical methods employed to study and predict the pressure distributions inside these cavities do not consider the effect of multiple reflections on the boundaries, hiding their resonant effects. This work presents an analytical, numerical, and experimental study of the effect of multiple reflections inside ultrasonic cavities based on arrays of transducers exhibiting their influence on the pressure amplitudes of focused standing waves. Our numerical results come from a modified version of the Matrix Method to numerically compute the multiple wave reflections of cavities constructed by two opposite arrays of multiple compact sources as boundaries. The correlation between numerical and experimental results reveals that intra-cavity reflections are relevant in focused axisymmetric cavities based on two arrays of multiple ultrasonic sources having a considerable impact on the amplitude of the standing waves and consequently, on the acoustic levitation performance. Thus, intra-cavity reflections must be considered for optimal cavity designs.

An experimental investigation on the influence of pore foaming agent particle size on cell morphology, hydrophobicity, and acoustic performance of open cell poly (vinylidene fluoride) polymeric foams

Abstract Globally, the development of porous structured materials has been receiving incredible responses for various high-performance engineering applications. Piezoelectric cellular foams have recently attracted the attention of researchers to emerging applications of acoustic sensors, low-frequency hydrophones, and energy-harvesting devices. As pore morphology is closely related to the shape and the size of the pore-foaming agent, it is necessary to address the influence of particle size of the foaming agent on cell morphology to expand their application area. Hence, this research article establishes the impact of particle size of pore foaming agents on pore morphology, hydrophobicity, and acoustic characteristics of open-cell polyvinylidene fluoride (PVDF) based piezoelectric cellular composites. Open-cell PVDF cellular composites have been fabricated using the template removal method with sodium chloride (NaCl) as a sacrificial templating agent in three different particle sizes: larger, medium, and finer. Based on the experimental results, it can be stated that the particle size of the templating agents dramatically influences the pore morphology, hydrophobicity, and acoustics performance of the PVDF foam samples. The PVDF foams possessing medium pore size have exhibited a maximum sound absorption coefficient of 0.89 at a frequency range of 1,000–1,500 Hz, indicating that PVDF foams have great potential for noise-controlling applications.

Simulation Analysis of Influence Laws of Sound Barrier Acoustic Performance When Using Ceramic as Sound-absorbing Materials

Abstract The excellent sound absorption performance of Sound Barrier which using Ceramic as Sound-absorbing Materials can be attributed to their corrosion resistance, lightweight nature, small particle size, and internal microporous structure. As a result, the application of new ceramic-based sound absorption materials in sound barriers is becoming increasingly widespread. To address the challenging issue of predicting the sound absorption and isolation performance of ceramic sound barriers and understanding the influencing factors on acoustic parameters, a simulation analysis method was employed for analyzing and studying various factors affecting the acoustic performance of these barriers. The calculation results demonstrate that increasing the thickness of both the sound absorption material and air layer behind exhibits similar effects on enhancing the sound absorption and isolation performance of ceramic acoustic barriers. Specifically, increasing either parameter leads to improved sound absorption performance by significantly increasing the sound absorption coefficient at 125Hz and 250Hz while decreasing it at 500Hz. However, in high-frequency bands above 1000Hz, structural parameters have minimal overall influence. Moreover, when keeping the thickness of ceramic sound absorption plates constant, every additional 20mm increase in air layer thickness behind results in a weighted increase in sound isolation by approximately 1dB; notable improvements are observed when this air layer thickness is below 1600Hz. When the thickness of the air layer behind is kept constant, an increase in the thickness of the sound absorption material by 10mm results in a 1dB increment in weighted sound isolation. However, when maintaining a total thickness of the sound barrier at 140mm, increasing the material’s thickness leads to a reduction in air layer thickness. Consequently, there is a slight enhancement in the sound absorption coefficient at frequencies of 125Hz and 250Hz while a minor decrease occurs at frequencies of 500Hz and 1000Hz. The impact on other frequency bands and overall sound absorption performance remains inconspicuous. Moreover, variations in weighted sound insulation quantity have minimal influence on sound insulation characteristics.