Sound Characteristics Research Articles

Experimental insights on sound characteristics and psychoacoustic parameters on axial fan performance in heat pump systems

This study focuses on the computational fluid dynamics (CFD) simulations and experimental measurements of the sound power level of an axial fan used in heat pump systems. Calculations and experiments were systematically conducted for three different fan-evaporator distances. CFD results, including kinetic energy and velocity vector values, were obtained and compared with experimental sound power results. The relationships obtained were thoroughly examined in terms of their impact on psychoacoustic parameters. This study was conducted to contribute to the understanding of fan performance and sound characteristics in heat pump systems. The results provide crucial information for users aiming to reduce air-source noise and determine optimized fan-evaporator distances for acoustic comfort.

Recent investigation on VHF sound exposure sources around us

We have reported recent investigation of sound exposure sources in very-high frequency (VHF) region as the activities for research project of VHF sounds in Japan. Recently, the devices which utilize or generate VHF sounds as like rodent repelling devices, ultrasonic cleaning machines, IH cookers and corner sensors of automobile continue to increase in public space or our living environment. The VHF sounds in high level have physical or/and psychological effects for young people who can hear such sounds. So, in environment around us, we identified VHF sound sources using acoustic camera and measured the sound pressure level for such sources. In this paper, we introduce newly-discovered several VHF sounds: for example, ultrasounds from corner sensors of automobile car, VHF sounds from photovoltaic installation and VHF sounds of interior train, and so on. From both the results measured by acoustic camera and microphones show source positions and frequency characteristics of VHF sounds. However these play important role in our life environment, we need to note that these contain potential hazard for young people who can hear such VHF sounds.

Development of auditory training application for volleyball players

In various ball games, players make appropriate plays by obtaining information from their surroundings. In volleyball, players also obtain auditory information from the sound of balls being hit, people's voices, footsteps, etc. However, details such as how to use it have not been clarified. The purpose of this research is to develop a method for improving volleyball competitiveness using auditory information. The authors investigated the acoustic characteristics of good and bad sounds that athletes usually express intuitively in words, and also investigated the relationship between acoustic characteristics and athletes' subjective evaluations of the quality of the meat. We investigated the relationship. As a result, we confirmed that there are differences in the sounds that are perceived as "good" or "bad." Furthermore, we conducted acoustic measurements and acoustic analysis of serves and spikes for experienced volleyball players, and based on the analysis results, we developed an auditory training system to enable accurate discrimination of sounds during competition. In the future, we will collect logs from experiment participants who trained using the application and analyze differences in training effects due to differences in years of experience. We will also consider how to create a more efficient training system.

Development of vibration isolation system for halls and report on sound insulation and vibration experiment

Rubber and polyurethane have been widely used as vibration isolation materials in halls and studios. In this project, we have developed a floor-mounted coil spring vibration isolator with improved vibration isolation and sound insulation characteristics, while keeping the installation height equivalent or lower than rubber and polyurethane. In this paper, we evaluate the vibration isolation performance of the developed device by measuring vibration transmission loss, and confirm that the device can suppress surging, which is a weak point of metal springs, while achieving a low natural frequency. The sound transmission loss measurement also confirmed that the floating slab incorporating the device has sufficient sound insulation performance, and these results indicate that the device can be applied to acoustic spaces such as concert halls, where quietness is required.

Sound environment design using flexible wood-based sound absorbers

A sound-absorbing material made of flexible wooden boards with air permeability was developed to improve the indoor sound environment of buildings. The flexible wood-based material has sound absorbing characteristics with the Helmholtz resonator by its air permeability. In other words, various sound absorption characteristics could be realized owing to the cross-sectional shape (flat or curved) and machining conditions (cut width, cut pitch, and plate thickness). In this paper, the application of flexible wood-based sound-absorbing materials to acoustic design in actual buildings (nursery schools and a church) where acoustic considerations are required is presented. In their application to a newly built nursery school, one of the considerations was to prevent the loss of design by installing sound-absorbing materials. In their application to acoustic renovation, the sound environment improvement effect was confirmed by measuring sounds before and after the installation, and it was also confirmed that the users were able to feel the improvement effect. These results will lead to the development of sound-absorbing wooden boards as an interior material and the promotion of the use of wood in buildings to contribute to the realization of a decarbonized society.

Study on the influence of geometric characteristics of micro-periodic structures with slits on sound absorption properties

In recent years, there has been considerable interest in acoustic metamaterial technology that leverages sub-wavelength scale microperiodic structures to control the behavior of sound waves for sound absorption material development. This technology offers high design flexibility in unit shapes and holds promise for the development of sound absorption materials with diverse characteristics. However, the field remains in its foundational exploration phase, with the detailed relationship between geometric shapes and sound absorption properties yet to be fully elucidated. To address this gap, we conducted a thorough investigation focusing on their relationship by examining the transport parameters of the Johnson-Champoux-Allard-Lafarge-Pride (JCALP) model, which are closely associated with sound absorption properties. We designed a cubic lattice with slits on the incident surface of the unit shape as a microperiodic structure and examined the normal incident sound absorption characteristics using the finite element method. Our results indicate that manipulation of slit partition numbers and slit widths allows for control of transport parameters, suggesting the potential to achieve various sound absorption properties.

Comparative analysis of acoustic testing methods of a multi-layered material: uncovering the membrane effect

This paper presents a comprehensive investigation into the differences observed when evaluating the acoustic properties of a multi-layered material using different standardized methods. The primary focus is on the membrane effect of the upper aluminum layer, which has been shown to contribute to the overall acoustic absorption. This phenomenon, crucial for applications requiring enhanced acoustic performance at lower frequencies, is observed in tests conducted with large sample sizes but remains undetected in impedance tube measurements. Through a series of experiments, including reverberant chamber, impedance tube, and in-situ absorption measurements, this study investigates the complexities of accurately estimating sound absorption characteristics in multi-layered materials. Additionally, 2D colormaps to visualize the spatial distribution of sound absorption across different samples are examined, offering deeper insights into the uneven absorption patterns that standard testing methods may overlook. The experimental findings highlight the importance of selecting an appropriate evaluation technique for multi-layered materials, particularly in applications where acoustic performance is critical at lower frequencies.

A study on a micro perforated panel applied luggage board design for road noise reduction

The automotive industry is on the age of rapid transformation from internal combustion engine vehicles to electric vehicles powered by motors. The main source of noise in conventional internal combustion engine vehicles is the engine, while electric vehicles are mainly affected by road and wind noise. A road noise in the medium and low frequency bands, caused by friction between tires and road surfaces, can be improved by increasing the thickness and weight of the insulation material. Still, this countermeasure causes other challenges that related to driving efficiency decrease because of limitations space and weight. As a new method to reduce road noise, therefore, the study introduces the luggage board which applied the micro-perforated panel system. This system utilizes a resonance-type sound absorbing material with excellent sound absorption characteristics at specific frequencies so that a tire pattern noise within the 800-1,000 Hz could be reduced. Because the thickness of the luggage board is partially limited, the study set a number of variations such as changing the porosity, perforated diameter in the perforated panel system. As a result, the study confirmed 2% improvement A.I. (Articulation Index) in the interior with installation of the designed luggage board on the vehicle.

Sound absorption of slit resonator with embedded aperture in linear and nonlinear regimes

This paper presents a slit resonator with embedded aperture (SREA) by embedding the slit-type neck into the cavity, and investigates its sound absorption characteristics in linear and nonlinear regimes. The theoretical acoustic impedance model of the SREA is established through transfer matrix method. The theoretical, simulation and experimental results demonstrate that the SREA enhances oscillating mass without altering acoustic capacity through the embedded slit-type neck, enabling it to achieve quasi-perfect absorption at lower frequencies with the same external geometry as traditional slit resonator. The formation and shielding of acoustic vortex caused by the high sound intensity increase the normalized acoustic resistance and decreases the acoustic reactance, causing the peak sound absorption coefficient to decline. This paper introduces a nonlinear correction expression for the normalized acoustic resistance of SREA by analogy with cylindrical neck.

Estimation and experiment on acoustic properties of rice straw (estimation of sound absorption coefficient based on CT image)

The sound absorption characteristics of rice straw were estimated using micro-CT scan images and theoretical analysis. Since it is difficult to express the structure and dimensions of rice straw in a regular manner, the voids in the straw were approximated as clearance between two parallel planes based on the micro-CT scan images. Using the surface area of the straw and the volume of the voids, a theoretical estimation of the sound absorption coefficient of the straw was made. Propagation constants, characteristic impedance, and normal incident sound absorption coefficient were obtained for the derived clearance. Since the rice straw is tubular, the sound absorption coefficient was also obtained assuming that an arbitrary CT scan image is continuous in the thickness direction. In addition, the sound absorption coefficient was estimated from ordinary photographs taken of the sample incident surface. In the experiments, the sound absorption coefficient was measured using a two-microphone impedance tube. The theoretical values were close to the experimental value.

Sound quality evaluation and quantification for power seat operating noise

In recent years, vehicle interior condition at running has been quiet due to progress of noise reduction technology. On the other hand, quietness is not required only at running condition but also at parking where slight operating noise is generated by various devices. In this study, we then focused on an operating noise during power seat operation as one of the devices radiated noise in cabin. The impression to power seat operating noise were investigated through subjective evaluation test. For the test, power seat radiated noise at various operating modes and seat types were recorded binaurally and presented in the subjective evaluation test. Participants evaluated the presented sound quality in several evaluation terms such as "loudness," "pitch," and "discomfort." As the results, representative power seat operating mode, in which sound impression varies widely among presented sounds, was found out and suitable evaluation terms for describing the sound quality characteristics well were also extracted. In addition, the representative sound quality tendency was attempted to be evaluated quantitatively using psychoacoustic metrics from recorded sound pressure signal of the power seat.

Experimental investigation of the sound absorption characteristics of unconsolidated granular materials

In the context of a wider research project investigating the use of Granular Material (GM) within floor and wall structures to increase their sound insulation, this study presents the sound absorption coefficient (SAC) measurements of different thicknesses for a range of GM. A primary aim has been to extend the understanding of the behaviour of GM layers in absorbing the propagated incident sound wave. Equally important has been an assessment of what GM could be sourced from waste and be acceptable for use in buildings from the point of view of fire insulation, handleability, economy, etc. Samples of GM were placed in an 88mm diameter vertical impedance tube and SACs measured up to 2kHz. The results show the effect GM's different structure (size and shape), bulk volume, and mechanical characteristics have on the range and value of the SAC. These determine the extent to which GM could be a replacement for traditional sound absorption materials.

Determination of the acoustic characteristics of a gabion noise barrier

In recent road construction projects in NL more and more stone gabions are used as noise reducing measure. First measurements on noise characteristics on gabions using EN 1793-5 showed peculiar results for sound absorption. This was thought to be an effect of the thickness of the gabion and due to scattering of the sound on the non-flat surface. A new investigation was done on stone gabion NRD's and on a regular reflective and absorptive NRD. Focus was on the applicability of EN 1793-5 for determination of the sound reflection characteristics of gabion NRD's. This paper shows the results of measurements on gabion and "regular" NRD's, and of model simulation of these measurements to understand the results, and give guidance on modeling a gabion NRD in a general TNM.

The crossover frequency of acoustic simulation for small-scale enclosures by wave and statistic based methods

In the field of room acoustic simulation, wave-based and statistical numerical methods are pivotal for acquiring sound field characteristics. Although the Schroeder Frequency has been utilized to deduce the suitable frequency range of these methods in large enclosures, the crossover frequency warrants further investigation for the small-scale enclosures with complicated inner structures, such as car cabins. This work aims to explore the applicable frequency range of these acoustic simulation methods for a small-scale model, which means identifying the crossover frequency between wave-based Finite Element Method (FEM) and statistical Ray Tracing Method (RTM). First, the crossover frequency was analyzed by the Schroder Frequency equation and modal density estimated from the room transfer functions (RTFs) in a simplified car model, which considering the interior with and without seat occlusion. Further, the crossover frequency was validated by comparing the magnitude spectra of RTFs simulated by FEM and RTM. This work provides a foundational frequency reference for applying statistical acoustic methods in small-scale enclosures.

A basic study on sound insulation characteristics of Triply Periodic Minimal Surface by using the finite element method

Triply periodic minimal surfaces (TPMS) have garnered attention in the field of natural science. For example, these structures are observed in insect wing scales, where their intricate periodic structures create structural colors via the reflection and interference of certain wavelengths of light. The objective of this study is to utilize the acoustic analogy of such photonic properties for sound insulation. In a previous report, it was found that the bandgap of G-surface, which is one of TPMS, enabled us to insulate sound effectively at specific frequencies. Furthermore, it was suggested that sound insulation performance can be improved by compressing the structure along the incident direction while maintaining its thickness. In this paper, we focus on the P-surface, which is a typical TPMS other than the G-surface. The sound insulation properties were calculated by numerical analysis and compared with those of the G-surface. As a result, it is found that P- and G-surfaces are effective structures for different frequency bands. In addition, compression of the P-surface along the incident direction in the same manner as in the previous study improves the sound insulation performance without increasing the thickness, as well as G-surface.

A fundamental investigation on the sound absorption characteristics of acoustic meta-surface type baseboards

The sound of footsteps generated in corridors propagates into surrounding spaces, sometimes becoming a problem of noise pollution. Therefore, the aim of this study is to reduce footstep noise by incorporating sound absorption mechanisms into the baseboard of corridors. We focus on the acoustic metasurface that has gained significant attention in recent years in order to absorb a relatively wide range of frequencies. In this study, we proposed acoustic metasurface type baseboards by utilizing multiple resonators with different resonance frequencies. The proposed models feature parallel arrangement of multiple resonators with straight or inclined slits. The absorption performance of these models is evaluated through theoretical analysis, numerical simulations, and experiments. Results suggest that acoustic metasurface type baseboards is found to be able to absorb the dominant frequencies in the sound of footsteps. In addition, increasing the number of resonators and incorporating slanted perforations in the neck contribute to improved absorption performance. Furthermore, the possibility of thinning the models through slanted perforations is also suggested.

Heavy-weight impact sound insulation characteristics related with vibrational properties of Korean domestic CLT slabs with different species and joint types

Korea has the world's most strict inter-floor noise regulations. In order to build an apartment house with more than 30 units, it must meet the minimum requirement of impact sound level, single number quantities of 49 dB. These regulations make it hard to expand residential tall wood building in Korea. For making quality satisfied CLT floors, as the preliminary investigations, the effects of wood species and CLT panel joints on the vibration and sound insulation performance of CLT were analyzed. The natural frequency range of the CLT slabs is from 20 Hz to 22 Hz. There were no significant differences depending on wood species and CLT panel joint type. As the stiffness of the slabs increased, the floor impact sound insulation performance also improved. The deflection model for CLT slabs was developed and validated with the actual deflection derived by acceleration spectrum. The measured value was 62 ~ 87% of the predicted value.

Sound quality characteristics of reciprocating hermetic refrigeration compressors

In recent years, sound quality (SQ) has become an increasingly important factor in the home appliance industry, enhancing the customer experience and comfort. Manufacturers that prioritize SQ in their designs can gain a competitive advantage in the market and increase customer satisfaction. The compressor is one of the main sources of noise in a refrigerator. While manufacturers typically provide refrigerator sound quality and noise labels, research that specifically evaluates the compressor sound quality metrics at a component level is not common. Therefore, this study aims to isolate the compressor from the refrigerator to investigate SQ metrics for hermetic refrigeration compressors. To achieve this, compressors with different capacities are operated and recorded at different working speeds for different thermal conditions. Objective parameters are calculated and tested using time domain signals and analyzed with spectral analysis methods. In addition to the objective parameters, subjective results are obtained through jury tests consisting of 75 people of different genders and age ranges. By considering objective parameters of sound quality as input and sound quality evaluation values as output, a regression model is established. It is found that Loudness, Sharpness, and Degree of Modulation play an important role in compressor sound quality evaluations consider.

Acoustic characterization of porous windscreens for sound pressure and particle velocity sensors

Acoustic measurements of ground vehicles, wind turbines or aircrafts are often performed outdoors in presence of wind. Air movement around an acoustic sensor may significantly disturb the measured signals due to flow-induced vibrations and turbulence. This is specially relevant for pressure-gradient and particle-velocity based acoustic transducers which are more sensitive to these perturbations. To attenuate this effect and improve measurement quality, the sensors are typically covered with windscreens made of porous materials. However, designing an appropriate windscreen poses a challenging task, demanding a deep understanding of sound transmission characteristics. This study works towards quantifying acoustic properties of rigid-frame porous materials through in-situ measurements and fitting a parametric fluid-equivalent model to find optimal model parameters. The parameters are subsequently investigated by comparing windscreen insertion loss through finite-element numerical simulations and measurements on a sound intensity PU probe.

A deep learning approach to predicting UAV sound affect

The most prevalent method by which the impact of an acoustic environment upon people is assessed is the `environmental noise' approach, in which the sounds are quantified based entirely on their recorded weighted sound pressure levels. This does not account, however, for the character of sounds outside of their loudness. Objective metrics such as psychoacoustic annoyance have been developed to attempt to rectify this, however this is still heavily weighted towards loudness as the most important factor and may not provide a good estimate for subjective perceived annoyance for all sound sources, including unconventional aircraft such as unmanned aerial vehicles (UAVs). Here we present a novel method using a convolutional neural network (CNN) to predict perceived annoyance directly from mel-spectrograms derived from recorded audio featuring both traditional and unconventional aircraft sources. The network is trained and tested using data collated from five separate listening tests, and is shown to outperform conventional regression models based on psychoacoustic annoyance as a predictor of perceived annoyance. The time-frequency resolution of the calculated mel-spectrograms is shown to be a key factor in performance.