Sound Peak Research Articles

Predicting Lightweight Powders with Useful Sound Absorption Characteristics from Their Specifications

Powders that absorb sound by longitudinal vibration have either a gentle or sharp sound absorption curve at the first absorption peak frequency. Experiments were performed to investigate the conditions under which longitudinal vibration occurs in powders of various grain sizes and bulk densities. The sound absorption characteristics of the powders were then classified according to their specifications, and the sound absorption coefficients predicted by derived empirical equations were compared with the measured sound absorption coefficients. A threshold value for the areal density per grain layer was identified where lightweight powders at 0.0006 g/cm2 or less demonstrated useful sound absorption characteristics via longitudinal vibration. Powders with smooth (i.e., useful) and sharp (i.e., not useful) sound absorption curves could be further identified by the half-width value at 0.0974 < log f2 − log f1 < 0.119 decade. The bulk density can also be used to identify powders with useful sound absorption characteristics at 0.0868 < ρ < 0.124 g/cm3. A regression analysis was performed to obtain empirical equations expressing the relationship between the areal density per grain layer and first sound absorption peak frequency normalized by the layer thickness.

Efficient and broadband sound absorption properties of slotted aluminum foam

To enhance the sound absorption performance of aluminum foam, a slotted structure was developed. Firstly, the theoretical model of sound absorption for the slotted aluminum foam was established by the transfer matrix method. Secondly, the finite element model was established using COMSOL software to predict the sound absorption coefficient. The reliability of the theoretical and finite element models was validated through impedance tube experiments. The sound absorption mechanism is investigated by analyzing the internal sound field. Finally, the sound absorption properties of aluminum foam with other slot patterns are investigated. Additionally, the factors that influence sound absorption properties are investigated. The results indicate that the slots alter the sound pressure distribution within the material, inducing a pressure diffusion effect. When sound waves enter the interior of the material through the narrow slots, they are absorbed and dissipated by the matrix material on the sides of the slots. The sound absorption coefficient can be improved by increasing the thickness, slot scale, and slot depth of the slotted aluminum foam. Specifically, when the slot depth is 15 mm, and the slot width is 5 mm, the average sound absorption coefficient of incompletely slotted aluminum foam in the frequency range of 1000 ∼ 6300 Hz is 0.86, which can realize broadband sound absorption. With the increase of slot depth, the sound absorption peak becomes more pronounced.

Numerical study of acoustic metamaterial made of Helmholtz resonators with complex necks for low frequencies noise attenuation

In this paper, an acoustic metamaterial consisting of Helmholtz resonators with complex necks is proposed for low frequency noise reduction. The resonators are made of a cavity and a complex neck, which is a periodic succession of necks with small and large diameters. The acoustic attenuation performance of the proposed metamaterial design is demonstrated using finite element method. For such a shaped neck, the sound absorption coefficient presents multiple peaks. With a succession of N small and (N - 1) large neck diameters, N peaks in the sound absorption coefficient are obtained. By increasing the number of successions, the number of peaks increases. At the peaks, the surface acoustic impedance of the metamaterial nearly matches with the characteristic impedance of the air. This makes the sound absorption coefficient being nearly 100%. Keeping the same cavity volume, we increase the number of sound absorption peaks by the complex shape of the neck, while the classic Helmholtz resonator presents only one peak.

Centrifugal pump impeller wheel inspired acoustic metamaterial for low frequency sound absorption

Addressing low-frequency noise is a significant concern within the realm of acoustics and noise management. Labyrinthine channel based acoustic metamaterials have been proved to control low frequency noise using local resonance effect and thermoviscous dissipations. Drawing inspiration from centrifugal pump impeller wheel, an acoustic metamaterial absorber has been devised. The design incorporates impeller vanes to create a channel with variable widths and a micro-perforate panel through which sound wave propagates to the channels. Numerical simulations using COMSOL Multiphysics and experimental analysis are conducted employing Two microphone impedance tube method. Acoustic pressure and acoustic particle velocity distribution plots from numerical simulation study are used to comprehend the sound absorption mechanism. Sound absorption coefficient results reveal that this design offers a tunable sound absorption peak in low frequency regime. Furthermore, this paper discusses the influence of various geometric parameters such as, number of vanes, panel thickness and micro-hole diameter. The subwavelength dimensions of the design contribute to noise control in machineries with space constraints.

Thermal effects on sound velocity peak and conformality in isospin QCD

We study thermal effects on equations of state (EOS) in isospin QCD, utilizing a quark-meson model coupled to a Polyakov loop. The quark-meson model is analyzed at one-loop that is the minimal order to include quark substructure constraints on pions which condense at finite isospin density. In the previous study we showed that the quark-meson model at zero temperature produces the sound velocity peak and the negative trace anomaly in the domain between the chiral effective theory regime at low density and the perturbative QCD regime at high density, in reasonable agreement with lattice simulations. We now include thermal effects from quarks in the Polyakov loop background and examine EOS, especially the sound velocity and trace anomaly along isentropic trajectories. At large isospin density, there are three temperature windows; (i) the pion condensed region with almost vanishing Polyakov loops, (ii) the pion condensed region with finite Polyakov loops, and (iii) the quark gas without pion condensates. In the domain (i), the gap associated with the pion condensate strongly quenches thermal excitations. As the system approaches the domain (ii), thermal quarks, which behave as nonrelativistic particles, add energy density but little pressure, substantially reducing the sound velocity to the value less than the conformal value while increasing the trace anomaly toward the positive value. Approaching the domain (iii), thermal quarks become more relativistic as pion condensates melt, increasing sound velocity toward the conformal limit. Corrections from thermal pions are also briefly discussed. Published by the American Physical Society 2024

Assessing textural changes of breaded deep‐fat fried chicken nuggets during post‐frying holdings under infrared heat‐lamp using acoustic‐mechanical techniques

SummaryTexture is a multi‐parameter attribute and one of the prime quality attributes of fried products. This study examined the influence of post‐frying holdings under a heat lamp on the texture of breaded fried chicken nuggets. Chicken nuggets were deep‐fat fried (2, 4, 6, and 8 min) in canola oil at 180 °C. The fried samples were kept under an infrared heat lamp for up to 1 h, and the textural characteristics were compared with samples not exposed to post‐frying holdings. Textural characteristics were analysed through mechanical‐acoustic approach. The mechanical‐acoustic parameters related to crispiness analysed included maximum force (Fmax, N), number of force peaks (NFP), the area under force‐deformation curves (AF, N.sec), sound pressure level (SPL, dB), number of sound peaks (AUX) and the area under the amplitude‐time plots (AS, dB.sec). The mechanical parameters (Fmax: 19.11–48.96 N; NFP: 5–40; AF: 43–135 N.sec) of chicken nuggets increased with frying time, and these attributes were decreased during post‐frying holding. Similarly, acoustic parameters (SPL: 64.75–90.67 dB; AUX: 180–795; AS: 63–98 dB.sec) of chicken nuggets increased with frying time, and these attributes were decreased during post‐frying holding. Considering the studied parameters, 6 min of frying was found as optimal frying time. However, the post‐frying infrared heat lamp treatment affected the mechanical textural parametres more than the acoustic parameters. Findings from this study will be useful to food industries in optimising textural retention during post‐frying heat lamp holdings of fried products.

Conditions for sound absorption caused by longitudinal vibration of lightweight powder

It has been reported that powder layers composed of powder materials with a grain diameter of several tens of micrometers exhibit significant sound absorption capabilities in the low-frequency range when the bulk powder density is low. In a previous study, a model considered factors like “powder vibration” and “sound wave attenuation due to gaps between powders.” The remaining challenge lies in the unknown conditions under which a powder with a high sound absorption coefficient is formed through the attenuation of acoustic energy due to the longitudinal vibrations of the powder. In this study, we aimed to estimate these conditions based on the grain size and bulk density. The relationship between the “areal density per grain layer,” expressed as “grain diameter X bulk density,” and the first-order sound absorption peak value revealed that the sound absorption coefficient increases as the areal density per grain layer decreases.

An improved evaluation method of industrial noise based on level of noise pollution and kurtosis-weighted cumulative noise exposure

While industry development has improved people's lives, industrial noise has also caused negative impacts. Industrial noise cannot be avoided in industrial environments. It is essential to accurately evaluate industrial noise. Most existing industrial noise evaluation methods consider the factors of industrial noise but ignore the factors of human perception and cannot accurately reflect the subjective auditory perception of humans. The paper proposes an industrial noise evaluation method, LCINE, based on level of noise pollution (LNP) and kurtosis-weighted cumulative noise exposure. First, statistical regression is used to determine the LNP constant based on improved Robinson's method. The consideration of both industrial noise and individual worker in improved method makes the constant suitable for evaluating industrial noise. Second, the improved LNP is combined with kurtosis to determine the intensity evaluation item. Kurtosis is used to capture the extremity of outliers and amplitude variations effectively in statistics, so kurtosis accurately reflects sound peaks and intensity here. Then, the exposure time evaluation item is determined by combining kurtosis with exposure time. Finally, the normalization method is used to allocate theweights of the intensity evaluation item and the exposure time evaluation item, which can unify the measurement units and reduce the adverse effects caused by extreme data. The superiority of LCINE is verified through methods including correlation test, paired-samples t test, partial regression sum of squares test, and subjective evaluation. The results indicate that the method LCINE can more accurately evaluate industrial noise and is more consistent with the subjective auditory perception of humans.

Unravelling the nexus between structure, texture, and acoustic traits of fried chicken nuggets

SummaryTexture is a multi‐parameter attribute and one of the prime quality attributes of fried products. This study explored the nexus between microstructure and texture of fried breaded chicken nuggets. Chicken nuggets were deep‐fat fried (2, 4, 6, and 8 min) in canola oil at different frying temperature (170, 180, and 190 °C). Microstructure and texture of fried samples were assessed by scanning electron microscopy (SEM) and acoustic‐mechanical texture analyser, respectively. Maximum force (Fmax), number of force peaks (NFP), area under force‐deformation plots (FA), sound pressure level (SPL), number of sound peaks (AUX), and area under amplitude‐time curves (SA) were used to describe the textural parameters. Microstructural indices (porosity, number of pores, average pore area, polydispersity index, and average shape factor) were estimated from the SEM images. Results revealed that, both the frying time and temperature were positively correlated with the mechanical (Fmax: 25–55 N, NFP: 05–74 N, FA: 6500–15 000 N.sec) and acoustic (SPL: 88–97 dB, AUX: 650–810 dB, SA: 380–405 dB.sec) parameters. Frying time and temperature significantly (P < 0.05) impacted the formation of micropores in fried chicken nuggets. Crust microporosity showed strong positive correlations (r = 0.82) with the AUX value. The NFP, SPL, and SA of the fried nuggets were significantly (P < 0.05) impacted by the crust microporosity. Crust porosity (10–30%), number of pores (8–400), average pore area (10–4000 μm2), polydispersity index (0.05–0.2), and average shape factor (0.8–1.1) of fried nuggets were significantly (P < 0.05) influenced by both the frying time and temperature. Findings from this study would be useful in quality improvement and process monitoring including modelling of coated fried products.

Sound velocity peak induced by the chiral partner in dense two-color QCD

Recently, the peak structure of the sound velocity was observed in the lattice simulation of two-color and two-flavor QCD at the finite quark chemical potential. The comparison with the chiral perturbation theory (ChPT) result was undertaken; however, the ChPT failed in reproducing the peak structure. In this study, to extend the ChPT framework, we incorporate contributions of the σ meson, that is identified as the chiral partner of pions, on top of the low-energy pion dynamics by using the linear sigma model (LSM). Based on the LSM, we derive analytic expressions of the thermodynamic quantities as well as the sound velocity within a mean-field approximation. As a result, we find that those quantities are provided by sums of the ChPT results and corrections, where the latter is characterized by a mass difference between the chiral partners, the σ meson and pion. The chiral partner contributions are found to yield a peak in the sound velocity successfully. We furthermore show that the sound velocity peak emerges only when mσ>3mπ and μq>mπ, with mσ(π) and μq being the σ meson (pion) mass and the quark chemical potential, respectively. The correlation between the sound velocity peak and the sign of the trace anomaly is also addressed. Published by the American Physical Society 2024

Enhancing sound insulation performance with active constrained layer damping plates at low frequencies

In this paper, the normal incident sound transmission loss characteristics of active constrained layer damping (ACLD) plates are investigated numerically and experimentally. The sound insulation performance of the ACLD plate configuration with a centrally positioned 30 mm × 30 mm patch is initially examined in both passive and active control states. The analog feedback control strategy is employed to physically demonstrate that the ACLD treatment can effectively improve airborne sound insulation performance at low frequencies. To enhance control efficiency and mitigate control spillover effects, an edge-enhanced ACLD (EACLD) plate configuration is proposed, which enables a direct electrical connection between the PZT layer and base plate. Control mechanism is further analyzed from the perspectives of mean quadratic normal velocity and deformed modal shapes. Results show that, in the passive state, the formation of sound insulation peaks of the ACLD and EACLD plate configurations are attributed to structural anti-resonance effects. By applying active control, the shear deformation degree of the viscoelastic layer can be further increased, and the advantages of active and passive hybrid damping are formed. Therefore, the sound insulation performance of the EACLD plate configuration in the first-order resonance region around 190 Hz can be enhanced by approximately 20 dB. The proposed EACLD plate configuration demonstrates a broad low-frequency sound insulation bandwidth and holds strong potential for engineering applications.

Sources of Sound Exposure in Pediatric Critical Care.

Sound levels in the pediatric intensive care unit (PICU) are often above recommended levels, but few researchers have identified the sound sources contributing to high levels. To identify sources of PICU sound exposure. This was a secondary analysis of continuous bedside video and dosimeter data (n = 220.7 hours). A reliable coding scheme developed to identify sound sources in the adult ICU was modified for pediatrics. Proportions of sound sources were compared between times of high (≥45 dB) and low (<45 dB) sound, during day (7 AM to 6:59 PM) and night (7 PM to 6:59 AM) shifts, and during sound peaks (≥70 dB). Overall, family vocalizations (38% of observation time, n = 83.9 hours), clinician vocalizations (32%, n = 70.6 hours), and child nonverbal vocalizations (29.4%, n = 64.9 hours) were the main human sound sources. Media sounds (57.7%, n = 127.3 hours), general activity (40.7%, n = 89.8 hours), and medical equipment (31.3%, n = 69.1 hours) were the main environmental sound sources. Media sounds occurred in more than half of video hours. Child nonverbal (71.6%, n = 10.2 hours) and family vocalizations (63.2%, n = 9 hours) were highly prevalent during sound peaks. General activity (32.1%, n = 33.2 hours), clinician vocalizations (22.5%, n = 23.3 hours), and medical equipment sounds (20.6, n = 21.3 hours) were prevalent during night shifts. Clinicians should partner with families to limit nighttime PICU noise pollution. Large-scale studies using this reliable coding scheme are needed to understand the PICU sound environment.

Sound velocity peak and conformality in isospin QCD

We study zero temperature equations of state (EOS) in isospin QCD within a quark-meson model which is renormalizable and hence eliminates high density artifacts in models with the ultraviolet cutoff (e.g., Nambu-Jona-Lasinio type models models). The model exhibits a crossover transition of pion condensations from the Bose-Einstein-Condensation regime at low density to the Bardeen-Cooper-Schrieffer regime at high density. The EOS stiffens quickly and approaches the quark matter regime at density significantly less than the density for pions to spatially overlap. The squared sound velocity cs2 develops a peak in the crossover region, and then gradually relaxes to the conformal value 1/3 from above, in contrast to the perturbative QCD results which predicts the approach from below. In the context of QCD computations, this opposite trend is in part due to the lack of gluon exchanges in our model, and also due to the nonperturbative power corrections arising from the condensates. We argue that with large power corrections the trace anomaly can be negative. Our EOS reproduces the qualitative trend of the lattice results from the BEC to the BCS regime, implying that the quark-meson model captures relevant effective degrees of freedom. The BCS gap in our model is Δ≃300 MeV in the quark matter domain, and naive application of the BCS relation for the critical temperature Tc≃0.57Δ yields the estimate Tc≃170 MeV, in good agreement with the lattice data. Published by the American Physical Society 2024

Sound absorption analysis of a metamaterial based on parallel dual Helmholtz resonators

In this paper, a sound absorbing material consisting of four parallel dual Helmholtz resonators is proposed and its sound absorption coefficient is studied using finite element method. The dual Helmholtz resonator is made of neck-cavity-neck-cavity where each neck extends into each cavity. The sound absorption coefficient of the dual resonator presents two resonant peaks. It is demonstrated that when the radius of the first or the second neck increases, the two resonant frequencies of the sound absorption increase while they decrease when the length of the first or the second neck increases. The proposed material design, which combines four parallel dual Helmholtz resonators, presents eight sound absorption peaks and these eight resonant frequencies can be tuned to specific frequencies by adjusting the parameters of the necks. It is a compact sound absorber, which can help to attenuate the noise simultaneously at eight different frequencies in several engineering applications.

Sound attenuation performance at high sound pressure level of micro-perforated panel sound absorber with embedded resistive screen

In this paper, a composite sound absorber made of a micro-perforated panel (MPP), an air cavity with embedded resistive screen and a rigid back plate is investigated at high sound pressure level (SPL). The sound absorption coefficient predicted theoretically is compared with the experimental measurement at 150 dB and a good agreement is obtained. It is demonstrated that the incorporation of resistive screen within the air cavity improves significantly the sound absorption that presents a large frequency band and remains almost identical with respect to the SPL compared to a classical MPP absorber whose sound absorption peak varies with the SPL. The MPP absorber with the resistive screen glued on the MPP is studied and different resistive screens are compared at 150 dB and it is observed that the sound absorption coefficient increases with a large frequency band, which depends on the airflow resistivity of the screen. A sensitivity analysis shows that the resistance per unit area of the screen affects the acoustic properties of the absorber at low SPL while at high SPL, the acoustic properties are mainly controlled by the perforation ratio of the MPP and the acoustic orifice Mach number.

Inverse design of laminated plate-type acoustic metamaterials for sound insulation based on deep learning

The laminated plate-type acoustic metamaterial (LPAM) has designable low-frequency sound insulation performance and ultrathin and ultralight characteristics. However, the complexity of LPAM design increases significantly as the number of layers increases. An inverse design method is proposed to determine the topology and design parameters of LPAM based on deep learning. To train the deep learning model, the finite element and analytic models are combined to generate sufficient training data. The experimental validation of the finite element model and the acoustic impedance model are carried out to reduce the deviation between the experiments and simulations. The LPAM design system contains the pre-processing, inverse design and post-processing modules. The pre-processing module can produce candidate targets based on the required sound-insulation design target. For each candidate target, the inverse design module utilizes convolutional neural networks to autonomously design topology and parameters of LPAM. Finally, the pre-processing and post-processing modules are combined to choose the optional LPAMs meeting the sound-insulation target. To verify effectiveness of the LPAM design system, typical cases, involving the sound insulation targets of one and two sound insulation peaks, and uniform sound insulation in a broadband from 50 Hz to 600 Hz, are designed successfully and efficiently.

Sound insulation performance of membrane-type acoustic metamaterial based on defect state structure

Although conventional Membrane-type Acoustic Metamaterial(MAM) has good sound insulation performance in low frequency bands, the sound insulation performance in middle and high frequency bands is not as good as conventional sound insulation materials with the same quality. This problem still persists by using the double-layer MAM structures. To solve this problem, the defect state is introduced into the double-layer MAM structure. Although the ideal periodic structure is destroyed, the sound insulation performance will also change greatly, and it has a strong creativity. In this paper, the sound insulation performance of MAM with defect states is studied. Firstly, the theoretical model of sound insulation of double-layer membrane-type acoustic metamaterial with eccentric composite mass block (MAMEM) structure is calculated by using modal superposition method and transfer matrix method. Secondly, the influence of different defect locations on the sound insulation of membrane-type acoustic metamaterial with eccentric composite mass block(MAMECM) structure is discussed. The results show that the sound insulation peaks of the angular defect structure appear at 300 Hz, 320 Hz, 1040 Hz and 1410 Hz. The average sound insulation in the whole study frequency band of the angular defect structure is 4.23 dB higher than the non-defect structure. In addition, the experiment verifies the accuracy of the results. Thirdly, based on genetic algorithm, the area enclosed by the sound translation loss (STL) curve of the double-layer MAMECM structure above the mass law curve is taken as the optimization target to optimize the structure topology. The results show that the optimal structure not only has good sound insulation performance in the low frequency band, but also reaches the sound insulation peak at 1230 Hz, 1300 Hz, 1430 Hz and 1450 Hz. Besides, the optimal structure heaviness is reduced by 12%.

Determination of the sound level during different management measures in piglet rearing related to animal welfare and human health and safety

In the present study, sound level measurements were taken during management measures with expected high noise exposure on three German pig farms in order to quantify the noise level for pigs and farm staff. The sound level was measured during different activities, such as teeth grinding and tail docking of piglets, vaccination, castration with anaesthesia, stabling and rehousing the pigs. The equivalent continuous sound level (LAeq) was measured as well as the actual sound level (LAF) and the peak sound pressure level (LCPKmax). The latter two were assigned to specific sound events during the individual measures, such as piglet screams or using the pig paddle. Rehousing the pigs at the end of the nursery period resulted in the highest continuous sound levels (LAeq= 83.3 ± 4.9 dB(A)), followed by anaesthesia before castration (LAeq = 78.1 ± 7.4 dB(A)) and teeth grinding and tail docking of piglets (LAeq = 77.5 ± 3.6 dB(A)). The peak sound pressure level LCPKmax was more than 100 dB(A) for all measures with an absolute maximum of 129.7 dB(A) when pigs were being moved out of the nursery compartment. Furthermore, the human pain threshold of 120 dB(A) was exceeded in isolated cases when nursery pigs were being moved to the stable (LCPKmax = 121 dB(A)) and during anaesthesia before castration (LCPKmax = 125.2 dB(A)). During the individual measures, particularly high sound levels were generated when using a pig paddle (LAF = 92.1 ± 7.8 dBA)), when pigs ran over a loading ramp of a transporter (LAF = 93.8 ± 1.4 dB(A)) or when piglets screamed (LAF = 87.9 ± 7.5 dB(A)). The piglets’ screams were particularly loud during anaesthesia before castration (LAF = 90.0 ± 9.2 dB(A)), during vaccination (LAF = 89.6 ± 6.5 dB(A)) and during teeth grinding and tail docking (LAF = 89.5 ± 5.9 dB(A)).Even if the LAeq was always below 85 dB(A), i. e. the limit specified in European legislation (EU Directive 2008/120/EC) for continuous noise in piggeries, there were brief sound peaks that exceeded the pain threshold of 120 dB(A). In the interest of animal welfare and human health, noise should be reduced by a gentle handling of pigs. The use of the pig paddle should be restricted whenever possible. Additionally, farm staff should wear hearing protection when carrying out those measures that were identified as particularly noise-intensive in this study.

Pulsed Vibro-Acoustic Analysis Technique for Monitoring Bone Health in Preterm Infants: A Pilot Study.

Despite advances in neonatal care, metabolic bone disease of prematurity (MBDP) remains a common problem in preterm infants. The development of non-invasive and affordable diagnostic approaches can be highly beneficial in the diagnosis and management of preterm infants at risk of MBDP. In this study, we present an ultrasound method called pulsed vibro-acoustic analysis to investigate the progression of bone mineralization in infants over time versus weight and postmenstrual age. The proposed pulsed vibro-acoustic analysis method is used to evaluate the vibrational characteristics of the bone. This method uses the acoustic radiation force of ultrasound to vibrate the bone. The generated acoustic waves are detected using a hydrophone placed on the skin over the tibia. The frequency of vibration and the speeds of received acoustic waves have information regarding the material property of the bone. We examined the feasibility of this method through an in vivo study consisting of 25 preterm and 10 full term infants. The pulsed vibro-acoustic data were acquired longitudinally in preterm infants with multiple visits and at a single visit in full term infants. Speed of sound and mean peak frequency of slow and fast sound waves recorded by hydrophone were used to analyze bone mineralization progress. Linear mixed model was used for statistical analysis in characterizing the mineralization progress in preterm infants compared to data from full term subjects. Significance changes in wave parameters (speed of sound and mean peak frequency) with respect to the postmenstrual age and weight in preterm infants were observed with p-values less than 0.05. Statistical significances in speed of sound measurement for both fast and slow waves were observed between preterm and full term infants, with p-values of <0.01 and 0.02, respectively. The results of this pilot study indicate the potential use of vibro-acoustic analysis for monitoring the progression of bone mineralization in preterm infants.

In-depth investigations into symmetrical labyrinthine acoustic metamaterial with two micro-slit entries for low-frequency sound absorption.

Sound absorption below 1000 Hz has been extremely difficult through traditional barriers and absorbers, but it is required for noise control of appliances and machineries. Existing passive acoustic metamaterials attenuate low-frequency noise but with narrow bandwidths and bulky sizes. Hence, this paper proposes an acoustic metamaterial with enclosed symmetrical labyrinthine air channels and two micro-slits (configuration 1, identical slits; configuration 2, unequal length slits) at the end channels. Its theoretical model is established by acoustic impedance analysis using electro-acoustic analogy and validated numerically and experimentally. Sound absorption is found to happen as a result of impedance matching, Fabry-Perot-like labyrinthine resonances, and thermo-viscous losses in micro-slits. Parametric investigations reveal that increase in the number of channels, channel length, total height, and outer panel thickness shifts sound absorption peak to lower frequency but also decreases the magnitude and frequency range of absorption. Decreasing the channel width and slit width increases the sound absorption magnitude without changing absorption frequencies. Interestingly, unequal slit lengths perform better than equal slits by giving a lower frequency sound absorption with increased magnitude and frequency range, which is unlike that in existing labyrinthine metamaterials. Therefore, the proposed unequal slit metamaterial has enhanced low-frequency sound absorption and can be applied to appliances and machineries.