Sound Peak Research Articles

Gradually perforated porous materials backed with Helmholtz resonant cavity for broadband low-frequency sound absorption

Conventional sound absorbers can hardly own the good performance of low-frequency and broadband absorption simultaneously. In order to combine these two functions into one kind of absorbers, the gradually perforated porous materials backed with Helmholtz resonant cavity are proposed. A theoretical model and a finite element (FE) model are developed to investigate the sound absorption of the proposed sound absorber. Experimental measurements are conducted to successfully verify the developed theoretical and numerical models. In the theoretical model, the gradually perforated porous material is divided into a series of thin layers and each layer is described by the double porosity theory. The backed Helmholtz resonant cavity and the connection between these thin layers are modeled by applying the transfer matrix method, so as to achieve the surface acoustic impedance of the absorber via a bottom-up approach. The FE simulations reveal the sound absorption mechanisms of the proposed absorber from the viewpoints of particle vibration velocities, sound energy flow and energy dissipation distributions. The influences of the porous material matrix and the structural parameters on the sound absorption of the proposed absorber are analyzed. Results show that the gradually perforation hole substantially improves the impedance match between the material and air to enhance broadband sound absorption. Meanwhile, the backed Helmholtz resonant cavity brings a low-frequency sound absorption peak to augment sound absorption. This proposed absorber realizes an excellent combination of low-frequency and broadband sound absorption. In addition, its easy-to-manufacture characteristics show great application potential.

Automated Heart Sound Signal Segmentation and Identification using Abrupt Changes and Peak Finding Detection

Abstract Conventionally, majority physicians used manual-based approach to determine heart sound parameters by manually printing heart sound signal waveform on the paper and trace heart sound parameters duration. Towards modern medical diagnostic technologies, this paper presents a modified framework of automated heart sound signal segmentation and parameters identification for deployment in computer aided auscultation. Envelope-based approach with reference information by abrupt changes and peak detection algorithm are proposed for PASCAL Classifying Heart Sounds Challenge database. Noted that the performance of segmentation process was measured by calculating the accuracy and F1-score while the heart sound parameters were identified by computing its mean and standard deviation. The findings yield F1-score and accuracy of proposed approach for segmentation and identification of normal heart sound signal at 95.29% and 91.0%, respectively. Heart sound parameters such as first sound, S1 duration, second sound, S2 duration, systole duration, diastole duration, heart cycle duration and ratio of systole and diastole were also determined. This proposed approach is suitable to be applied on two prominent heart sound signal peaks of S1 and S2, which continuously varies among samples due to the different auscultatory sites.

Improving the sound absorption behaviour of porous concrete using embedded resonant structures

A relatively new concept of sound absorption herein denominated as Metaporous concrete is presented, consisting of a porous concrete-based sound absorber in which different acoustic resonators are embedded. Two finite element models were implemented, using the fluid-equivalent theory to describe Metaporous concrete solutions. A Helmholtz resonator, porous concrete samples, and a Metaporous concrete prototype were built and tested through experimental techniques based on the use of an impedance tube. The fluid-equivalent complex properties were validated with comparisons between analytical predictions and experimental data. The proposed numerical tools were presented as an efficient methodology to predict the sound absorption behavior of Metaporous concrete solutions, where an excellent approach between the simulated results and experimental data is shown. The parametric study shows efficient strategies to increase the sound absorption behavior and to feature the two sound absorption coefficient peaks provided by Metaporous concrete solutions (i. e. from the acoustic resonator and the porous concrete, respectively). The denominated configuration MPCd was highlighted because of the great proximity of these two sound absorption peaks. The inclusion of non-trivial resonant structures in porous concrete, building a Metaporous concrete, can be proposed as an excellent solution to be adopted for noise control in civil engineering exterior applications.

Implications of Nonsub-Wavelength Resonator Spacing on the Sound Transmission Loss Predictions of Locally Resonant Metamaterial Partitions

Abstract Locally resonant metamaterials have recently emerged and gained attention in the field of noise control engineering. The addition of resonant structures to a flexible partition on a sub-wavelength scale enables a targeted frequency range of strongly reduced vibration and sound transmission. These structures have been widely studied and are typically analyzed using infinite periodic structure theory. The implications of nonsub-wavelength resonator spacing on the sound transmission loss of metamaterial partitions as well as on the representativeness of the infinite periodic structure modeling are, however, less well known. In this technical brief, it is shown that, although a shifted sound transmission loss peak can be predicted for partitions with nonsub-wavelength resonator spacing when using infinite periodic structure modeling, the sound transmission loss enhancement is not guaranteed for their finite structure counterparts.

Impact of sound levels and patient-related factors on sleep of patients in the intensive care unit: a cross-sectional cohort study

Sleep disruption is common in patients in the intensive care unit (ICU). The aim of the study was to measure sound levels during sleep-protected time in the ICU, determine sources of sound, assess the impact of sound levels and patient-related factors on duration and quality of patients' sleep. The study was performed between 2018 and 2019. A commercially available smartphone application was used to measure ambient sound levels. Sleep duration was measured using the Patient's Sleep Behaviour Observational Tool. Sleep quality was assessed using the Richards-Campbell Sleep Questionnaire (RCSQ). The study population comprised 18 (58%) men and 13 (42%) women. There were numerous sources of sound. The median duration of sleep was 5 (IQR 3.5–5.7) hours. The median score on the RCSQ was 49 (IQR 28–71) out of 100 points. Sound levels were negatively correlated with sleep duration. The cut-off peak sound level, above which sleep duration was shorter than mean sleep duration in the cohort, was 57.9 dB. Simple smartphone applications can be useful to estimate sound levels in the ICU. There are numerous sources of sound in the ICU. Individual units should identify and eliminate their own sources of sound. Sources of sound producing peak sound levels above 57.9 dB may lead to shorter sleep and should be eliminated from the ICU environment. The sound levels had no effect on sleep quality.

Optimal Design of Sound Insulation Frequency Band of Local Resonance Membrane Material

In order to broaden the sound insulation frequency band of local resonance membrane materials, established an acoustic-vibration coupling model of multilayer membrane materials, based on the derived analytical solutions of the coupling equations. Simulate the sound insulation performance of the designed single-layer membrane materials with four different mass structures. Then combine different membrane materials to analyse the changes in the sound insulation frequency band. Calculations proves that: (1) The four single-layer membrane structures have a maximum TL peak of 40.08dB and the frequency of the smallest TL peak is at 204.56Hz in the frequency range of 100-1000Hz.(2) Combination of two same structures will significantly increase the sound insulation at the sound insulation peak;(3) The combination of single-layer membrane with different structures can broaden the sound insulation frequency band and enhance the sound insulation performance.

Brighter Days May Be Ahead: Continuous Measurement of Pediatric Intensive Care Unit Light and Sound

Objective: To describe light and sound characteristics in the rooms of critically ill children.Design: Prospective observational cohort study, with continuously measured light and sound levels.Setting: Tertiary care pediatric intensive care unit (PICU), with a newly constructed expansion and an older, pre-existing section.Patients: Critically ill patients 0–18 years old, requiring respiratory or cardiovascular support. Patients with severe cognitive pre-conditions were excluded.Measurements and Main Results: One hundred patients were enrolled, totaling 602 patient-days. The twenty-four hour median illuminance was 16 (IQR 5-53) lux (lx). Daytime (07:00–21:00) median light level was 27 lx (IQR 13-82), compared with 4 lx (IQR 1-10) overnight (22:00–06:00). Peak light levels occurred midday between 11:00 and 14:00, with a median of 48 lx (IQR 24-119). Daytime median illuminance trended higher over the course of admission, whereas light levels overnight were consistent. Midday light levels were higher in newly constructed rooms: 78 lx (IQR 30-143) vs. 26 lx (IQR 20-40) in existing rooms. The twenty-four hour median equivalent sound level (LAeq) was 60 (IQR 55-64) decibels (dB). Median daytime LAeq was 62 dB (IQR 58-65) and 56 dB (IQR 52-61) overnight. On average, 35% of patients experienced at least one sound peak >80 dB every hour from 22:00 to 06:00. Overnight peaks, but not median sound levels nor daytime peaks, decreased over the course of admission. There was no difference in sound between new and pre-existing rooms.Conclusions: This study describes continuously measured light and sound in PICU rooms. Light levels were low even during daytime hours, while sound levels were consistently higher than World Health Organization hospital room recommendations of <35 dB. Given the relevance of light and sound to sleep/wake patterns, and evidence of post-intensive care syndromes, the clinical effects of light and sound on critically ill children should be further explored as potentially modifiable environmental factors.

Properties and mechanism of a novel metallic‐hollow‐spheres/polyurethane acoustic composite

AbstractIn this article, 316L stainless steel hollow spheres (316L HS) and polyurethane (PU) resins were used to prepare a novel metallic‐hollow‐sphere/polyurethane (MHSP) acoustic composite by casting. The acoustic experimental results of this composite revealed that compared to monolithic PU, the sound transmission loss of the composites increased and the maximum sound absorption peak shifted to lower frequency with the change of acoustic impedance and resonance frequency. When the surface of metallic hollow sphere used in MHSP composite was modified by silane coupling agent, the sound insulation and sound absorption performance of MHSP composites were further improved. This is related to the addition of the molecular layer of coupling agent between MHSP matrix. In addition, the addition of silane coupling agent creates PU foaming in matrix, resulting in a large number of pores and gaps that can increase the sound waves energy loss through air friction and heat exchange.

Acoustic Properties of 316L Stainless Steel Hollow Sphere Composites Fabricated by Pressure Casting

In this study, we prepared metal hollow sphere composites (MHSCs) using metal hollow spheres (MHSs) by pressure casting under vacuum conditions, and investigated the acoustic properties. The density of the MHSCs was measured using the mass to volume ratio, the microstructure of the MHSCs was observed using a scanning electron microscope, and the acoustic properties of the MHSCs were tested using an impedance tube. The measured MHSCs showed that the densities of the MHSCs with the random distribution of MHSs with diameter ~3.28 mm (1.74 g/cm3 to 1.77 g/cm3) (MHSC-3.28) were nearly equal to that of the MHSCs with the random distribution of MHSs with diameter ~5.76 mm (1.74 g/cm3 to 1.76 g/cm3) (MHSC-5.76), and lower than that of the MHSCs with the layered structure of MHSs with diameter ~3.28 mm (1.93 g/cm3 to 1.97 g/cm3) (MHSC-LS). Microstructural observations confirmed that the interface region between the MHSs and matrix demonstrated a simple physical combination pattern with pores. The acoustic properties of the MHSCs showed that the sound absorption coefficient of MHSC-LS was lower than that of MHSC-3.28 and higher than that of MHSC-5.76 at off-resonance. The sound absorption coefficient peak value of MHSC-3.28 was higher than that of MHSC-LS, and lower than that of MHSC-5.76 at resonance. The sound transmission loss of MHSC-3.28 was lower than that of MHSC-5.76, which shows the rules are independent from the resonance. The sound transmission loss of MHSC-LS was higher than that of MHSC-5.76 at resonance, but lower than that of MHSC-3.28 at off-resonance. In addition, we discuss the propagation mechanism of the sound waves in the MHSC, which is mainly determined by the distribution of the MHSs in the MHSC.

The sound absorption performance of the highly porous silica ceramics prepared using freeze casting method

AbstractHighly porous silica ceramics with unidirectional pores were prepared using the freeze casting method. By adjusting the solid content and freezing temperature, the porosity of the ceramics was tailored in the range of 78.20%‐84.59% and pore size in the range of 8.4‐71.4 μm, respectively. Sound absorption properties of porous silica ceramics was studied and the effect of structural factors was systematically investigated. The results showed that higher porosity and smaller pores of the porous ceramics favored the sound absorption in the entire sound wave frequency. By backing the sample with small pore size porous ceramics, the sound absorption property was enhanced, particularly in the low and medium frequency range, thus the sound absorption peak shifted towards lower frequency. The presence of air gap in the back would also favor sound absorption in low and medium frequency range. The as‐fabricated porous silica ceramics owed excellent sound absorption properties due to their unidirectional pores and low flow resistances.

Improving sound insulation in low frequencies by multiple band-gaps in plate-type acoustic metamaterials

According to the mass law, low-frequency sound attenuation is very difficult in engineering because the mass and space of structures are usually limited. In this paper, we propose a plate-type acoustic metamaterial with good sound insulation in low-frequency ranges. By attaching multilayered rubber and metal cylinders on a thin plate, multiple flexural wave band-gaps at low-frequency ranges are obtained. The band structures and eigenmodes are elucidated by finite element calculations. Both the flexural wave transmission spectra and the sound transmission loss are investigated. The results show that the obtained multiple band-gaps lead to more than one sound insulation peak at low frequencies. The geometrical parameter effects on the band-gap frequencies are discussed. By combining cells with different geometrical parameters, the formed supercell can improve the low-frequency sound insulation efficiency and introduce much more variety. The results in this paper will be useful for sound and vibration control in engineering applications.

0734 Does Noise Masking Improve Sleep Consolidation In Patients Weaning From Prolonged Mechanical Ventilation?

Abstract Introduction Sound masking is a noise reduction strategy that adds a mixed-frequency blend of ambient sound to the environment and may improve sleep. Critically ill patients often cite noise as one of the main factors preventing sleep while they are cared for in an intensive care unit (ICU). The effect of sound masking on sleep in patients weaning from prolonged mechanical ventilation is unknown. Methods 12-hour overnight polysomnography was obtained in eight patients undergoing weaning from prolonged mechanical ventilation. None had hearing impairment, delirium, sedation or agitation. In random order, patients were exposed to sound masking half of the recording time. Noise events were defined a 10dB increase from baseline or any sound peak over 75dB. Arousals or awakenings were attributed to noise if they occurred within 5 seconds of the noise event. Results Environmental sound was 61.7± 0.9 dB (mean±SE) during sound masking and 55.9±1.4 dB during no sound masking. During sound masking, there were fewer sound events per hour of sleep when compared to no sound masking (4.1/hr vs 9.3/hr p=0.03). The percentage of sound events leading to a subsequent arousal or awakening with sound masking was less than during no sound masking:11% vs 22% (p=0.04). Arousal index and fragmentation index (arousal and awakenings/hr of sleep) were similar between the two conditions. In a post-study survey, five patients reported improved sleep quality with sound masking while the remaining three reported no difference. Conclusion Sound masking decreases sound-induced arousal from sleep in patients being weaned from prolonged mechanical ventilation. Support Veterans Administration Research Service

Multi-mass synergetic coupling perforated bi-layer plate-type acoustic metamaterials for sound insulation

Thin plate-type acoustic metamaterials have the advantages of lightweight, high rigidity and adjustable parameters, showing great practical application values in sound wave control. In this paper, a type of perforated bi-layer plate-type acoustic metamaterials (PBPAM) is designed for low-frequency noise control. The sound insulation peaks can be increased by combining the perforated plate and synergetic masses, making the sound insulation performance close to the mass law at the resonant frequency. Compared to the results predicted by the mass law, a better performance of sound insulation is achieved based on the PBPAM. The effects of the structural parameters are investigated in this study. Based on the impedance tube experiments, the measured results have a good agreement with the simulated ones. This work can provide a reference for low-frequency and broadband sound insulation based on plate-type acoustic metamaterials in practical engineering.

Decision making in the face of a deadly predator: high-amplitude behavioural thresholds can be adaptive for rainforest crickets under high background noise levels.

Many insect families have evolved ears that are adapted to detect ultrasonic calls of bats. The acoustic sensory cues indicating the presence of a bat are then used to initiate bat avoidance behaviours. Background noise, in particular at ultrasonic frequencies, complicates these decisions, since a response to the background may result in costly false alarms. Here, we quantify bat avoidance responses of small rainforest crickets (Gryllidae, Trigoniinae), which live under conditions of high levels of ultrasonic background noise. Their bat avoidance behaviour exhibits markedly higher thresholds than most other studied eared insects. Their responses do not qualitatively differ at suprathreshold amplitudes up to sound pressure levels of 105 dB. Moreover, they also exhibit evasive responses to single, high-frequency events and do not require the repetitive sequence of ultrasonic calls typical for the search phase of bat echolocation calls. Analysis of bat and katydid sound amplitudes and peak frequencies in the crickets' rainforest habitat revealed that the cricket's behavioural threshold would successfully reject the katydid background noise. Using measurements of the crickets' echo target strength for bat predators, we calculated the detection distances for both predators and prey. Despite their high behavioural threshold, the cricket prey still has a significant detection advantage at frequencies between 20 and 40 kHz. The low-amplitude bat calls they ignore are no predation threat because even much louder calls would be detected before the bat would hear the cricket echo. This leaves ample time for evasive actions. Thus, a simple decision criterion based on a high-amplitude behavioural threshold can be adaptive under the high background noise levels in nocturnal rainforests, in avoiding false alarms and only missing detection for bat calls too far away to pose a risk. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

Partial microperforated panel and its acoustic siphon effect

Partial microperforated panel (MPP) structures have been proposed for MPP with low sound absorption properties. Its purpose is to improve the sound absorption performance of the MPP in certain frequency bands. The structure was studied by the transfer matrix method, finite element simulation and experimental test. The results show that the three kinds of curves, that is, theoretical and simulation and experimental curves, are in good agreement. In the parallel structure of partial MPP and the cavity, the MPP structure occupying three-quarters of the total area makes perfect sound absorption at 1076 Hz. The sound absorption peak of the MPP structure which occupies half of the total area is 0.89 at 980 Hz. The theory of calculating the partial MPP, which is accurate for fast prediction of sound absorption peaks, is proposed. The sound absorption performance of the multi-partial MPP structure has also been theoretically verified. The acoustic siphon phenomenon of partial MPP is discussed. On this basis, a multi-Helmholtz resonance structure is designed to achieve high sound absorption effect. The sound absorption coefficient is greater than 0.87 at 488–712 Hz.

Effect of casing on sound absorption characteristics of fine spherical granular material

To determine sound absorption coefficients of fine granular materials, the materials must be cased to suppress their flowability. In this study, effects of casing on the sound absorption coefficients of fine granular materials were investigated. The normal incidence sound absorption coefficients of cased hollow glass beads were measured using cylindrical impedance tubes. The measurement results demonstrated that the hollow glass beads present a sound absorption peak, which was attributed to the vibration of a particle frame, in the frequency range of 180 to 700 Hz for sample thickness in the range of 20 to 550 mm. With an increase in the material thickness or diameter of the casing, the first peak of the sound absorption coefficients shifted to a lower frequency. The sound absorption coefficients were calculated using an elastic frame model for porous materials. The effects of friction between the lateral wall of the case and the particle frame were incorporated in the bulk modulus and bulk density of the particle frame in the model. The model predicts correctly the frequency at which the first sound absorption peak occurs with an uncertainty of 10%.

The effect of inattention and cognitive load on unpleasantness judgments of environmental sounds

Evaluations of our acoustical environment depend on sound characteristics as well as on factors attributable to the person and situation. The aim of the study was to investigate the role of the listener’s attentional state and cognitive load, temporal characteristics of environmental sounds, and potential interaction effects on overall retrospective sound evaluations. Sixty-three test participants were presented six two-minute recordings of environmental sounds, whereby the temporal position of one occurring sound peak or valley was varied. The experimental group was distracted from the test sounds and cognitively loaded by performing the Stroop Test during the sound presentation and retrospectively rated the sounds in terms of loudness and pleasantness. In contrast, the control group attentively listened to the sounds and rated them during and after listening. Results showed that participants in the experimental group rated the sounds on average as 6.7% more pleasant than the participants of the control group. Moreover, previous findings on the influence of the peak position on the retrospective judgments (recency effect) were replicated; however, no effect of the temporal position of sound valleys was found. Retrospective judgments in the control group could further be predicted by the averaged momentary judgment, the linear trend over time as well as the momentary judgment during the peak and the end. Findings thus emphasize the need of taking into account human (in)attention and memory processes when assessing complex environmental sounds.

Highly porous silica foams prepared via direct foaming with mixed surfactants and their sound absorption characteristics

The highly porous silica ceramics were fabricated by direct foaming with mixed surfactants and the influence of silicon nitride addition and solid content on the microstructures and properties were investigated. The results showed that silicon nitride can impede the formation of cristobalite and facilitates the sintering of silica ceramics. When the addition of silicon nitride powders reached 15 wt%, the highest compressive strength of silica ceramic foams could be obtained. The porosity of silica ceramic foams was tailored in the range of 84.61%–91.35% by adjusting the solid content, and the compressive strength of the obtained ceramic foams ranged from 5.89 MPa to 0.94 MPa. Sound absorption characteristics of silica ceramics foams were investigated. With the porosity of ceramic foams increased from 84.61% to 91.35%, the sound absorption coefficients in the entire sound wave frequency were enhanced due to the reduction of flow resistances, besides, the sound absorption peak varied from 4200 Hz to 2300 Hz, and became more intense and sharper.

Broadband low frequency sound absorption using a monostable acoustic metamaterial.

This Letter presents a monostable acoustic metamaterial that has the potential to implement broadband sound absorption in low frequencies. The proposed metamaterial is realized by placing a flexible panel with a magnetic proof mass in a symmetric magnetic field. A theoretical model of the metamaterial is established and experimentally validated. Predictions and measurements demonstrate that the sound absorption peak frequency significantly shifts downwards with the increasing magnetic field. The relative bandwidth of the metamaterial is also broadened with the increasing magnetic field due to its inverse proportionality to the absorption peak frequency.

A double porosity material for low frequency sound absorption

This work designs a double porosity material (DPM) composed of two types of pores, i.e., the micro-pore from the porous layer and the meso-pore made by the labyrinthine channel. The both loss mechanisms of two different pores are combined to explore the low frequency sound absorption. All theoretical, numerical and experimental results show that the DPM possesses much lower frequency sound absorption than that of homogenous porous material (HPM) under the same thickness. Both the pressure and particle velocity distributions reveal that the sound absorption peaks are induced by the resonances of the labyrinthine channel and the hybrid resonance between the porous layer and labyrinthine channel respectively. Moreover, unconventional features such as negative bulk modulus and slow sound speed are observed around the resonant frequencies of the DPM. Finally, the absorption tailoring of the DPM with different strategies is investigated.