Acoustic Treatment Research Articles

Development of a model to assess acoustic treatments to reduce railway noise

Porous materials have recently been used in absorptive treatments around railway tracks to reduce noise emissions. To investigate the effect of porous materials, a finite element model has been developed. 2D models for porous materials have been considered either as an equivalent fluid or as a poroelastic material based on the Biot theory. The two models have been validated and compared with each other to check the effect of the skeleton vibration. The poroelastic FE model has been coupled with a 2D acoustic boundary element model for use in railway applications. The results show that it may be necessary to include the frame vibration, especially at low frequencies where a frame resonance occurs. A method for the characterization of porous materials is also discussed. From this it is shown that the elastic properties of the material determine the resonance frequency and the magnitude.

Context Specificity of the ANS Stress Response during Two Regrouping Experiments in Goats.

The aim of this study was to analyze whether the activity of the autonomic nervous system (ANS) differs between two regrouping procedures in goats, which would indicate stimulus specificity of these stressors. Applying two regrouping procedures, we evaluated heart rate and heart rate variability (RMSSD, SDNN, and RMSSD/SDNN). The two regrouping procedures were (1) introduction of individual goats into established groups (“introduction experiment”) and (2) temporary separation and subsequent reintegration of individuals from/into their group with two levels of contact during separation (“separation experiment”). In the “introduction experiment,” the heart rate of introduced goats while lying decreased continuously from an average 78 to 68 beats/min from before the introduction to the last day of the introduction period. Inversely, RMSSD increased continuously from 41 to 62 ms, which, on its own, would indicate an adaptation to the situation. During the “separation experiment,” heart rate while lying was higher when goats were separated in the “acoustic contact treatment” (82 beats/min on average) compared with the “restricted physical contact treatment” (75 beats/min on average). This difference reflected a higher level of arousal during the “acoustic contact treatment.” However, heart rate activity did not allow detecting effects of separation or reintegration. Even though it can be assumed that both the separation and introduction of goats are stressful for goats, the ANS reactions observed in this study differed between the two management procedures indicating that the ANS activation was specific to each situation. In addition, we discuss the ANS results in context with earlier findings of variables of the hypothalamic pituitary adrenal (HPA) axis (fecal cortisol metabolites) and behavior (lying and feeding). As correspondence between ANS, HPA, and behavioral reactions was limited both within and across experiments, the results of this study underline the concept that stress response patterns are context specific.

Magnetic nanoparticles-based acoustical detection and hyperthermic treatment of cancer,in vitroandin vivostudies

This paper describes a minimally invasive method for detection and growth inhibition of tumors that utilizes the unique properties of super paramagnetic nanoparticles. To demonstrate the feasibility of this method, dimercaptosuccinic acid-coated magnetite nanoparticles were successfully fabricated and used. Those nanoparticles were simultaneously used for magnetoacoustic detection of tumors and for specific hyperthermia treatment in C57BL/J mice injected with Lewis lung carcinoma cells. The in vivo acoustic signal attributed to the nanoparticles was 4.4 dB, while the single session hyperthermia treatment caused a reduction of 50% in tumor growing rate. In addition, a thermography-based method was applied to monitor the efficacy of the hyperthermia treatment. The presented method has the potential to revolutionize current cancer treatment by enabling diagnosis and treatment under real-time feedback in one session.

Assessment model of classroom acoustics criteria for enhancing speech intelligibility and learning quality

In this paper, a new classroom acoustics assessment model (CAAM) based on analytic hierarchy process (AHP) for enhancing speech intelligibility and learning quality is proposed. The model is based on five main criteria that affect the learning process and related to classrooms acoustical properties. These include classroom specifications, noise sources inside and outside the classroom, teaching style, and vocal effort. The priority and weights of these major criteria along with their alternatives are identified using the views of students, staff, education consultants, and expertise by using a developed questionnaire, and the AHP methodology. This model can be considered as a helpful framework enabling universities decision makers to take effective decisions on classroom acoustics treatment issues. It also provides colleges’ higher authorities the suitable guidelines that help for determining necessary requirements that help to raise the quality and efficiency of the educational environment; in order to reach an excellent learning environment; and hence increasing students learning outcomes.

Boundary layer effects on liners for aircraft engines

The performance of acoustic treatments installed on aircraft engines is strongly influenced by the boundary layer of the grazing flow on the surface of the liner. The parametric study presented in this paper illustrates the extent of this effect and identifies when it is significant. The acoustic modes of a circular duct with flow are calculated using a finite difference method. The parameters are representative of the flow conditions, liners and sound fields found in current turbofan engines. Both the intake and bypass ducts are considered. Results show that there is a complex interplay between the boundary layer thickness, the direction of propagation and the liner impedance and that the boundary layer can have a strong impact on liner performance for typical configurations (including changes of the order of 30dB on the attenuation of modes associated with tonal fan noise). A modified impedance condition including the effect of a small but finite boundary layer thickness is considered and compared to the standard Myers condition based on an infinitely thin boundary layer. We show how this impedance condition can be implemented in a mode calculation method by introducing auxiliary variables. This condition is able to capture the trends associated with the boundary layer effects and in most cases provides improved predictions of liner performance.

Acoustic absorption of hemp-lime construction

Hemp-lime concrete is a sustainable alternative to standard wall construction materials. It boasts excellent hygrothermal properties in part deriving from its porous structure. This paper investigates the acoustic properties of hemp-lime concrete, using binders developed from hydrated lime and pozzolans as well as hydraulic and cementicious binders. To assess the acoustic absorption of hemp-lime walls, as they are commonly finished in practical construction, wall sections are rendered and the resulting impact on absorption is evaluated. Hemp-concretes with lime-pozzolan binders display superior acoustic properties relative to more hydraulic binders. These are diminished when rendered, as the open surface porosity is affected, however hemp-lime construction offers the potential to meet standard and guideline targets for spaces requiring acoustic treatment.

Acoustic Metamaterials: A Potential for Cabin Noise Control in Automobiles and Armored Vehicles

The aim of this paper is to provide an overview of the existing industrial practices used for cabin noise control in various industries such as automotive, marine, aerospace, and defense. However, emphasis is placed on automobiles and armored vehicles. Generally, automobile cabins usually constitute of thin structural panels, where the fundamental frequency typically falls below 200[Formula: see text]Hz. If a specific structural mode couples with a specific acoustic mode of the cabin, booming noise occurs. As such, discomfort may be felt by the occupants. Fundamentally, vibroacoustics problems may be minimized if the acoustic modes and the structural modes are decoupled, which is achieved usually by structural modifications or acoustical treatments. However, if excessively performed, the weight limitation of an automobile design will be exceeded; not to mention the adverse effect of increased weight on several factors such as fuel efficiency, mileage life of tires and acceleration of the vehicle. Moreover, current solutions have several drawbacks in low frequency noise control. In light of this, it is of great interest to explore the feasibility of acoustic metamaterials as an alternative with hope to improve cabin noise.

Are mussels able to distinguish underwater sounds? Assessment of the reactions of Mytilus galloprovincialis after exposure to lab-generated acoustic signals

This study examined the effects of lab-generated acoustic signals on the behaviour and biochemistry of Mediterranean mussels (Mytilus galloprovincialis). The experiment was carried out in a tank equipped with a video-recording system using six groups of five mussels exposed to five acoustic treatments (each treatment was replicated three times) for 30min. The acoustic signals, with a maximum sound pressure level of 150dB rms re 1μPa, differed in frequency range as follows: low (0.1–5kHz), mid-low (5–10kHz), mid (10–20kHz), mid-high (20–40kHz) and high (40–60kHz).The exposure to sweeps did not produce any significant changes in the mussels' behaviour. Conversely, the specimens exposed to the low frequency band treatment showed significantly higher values of the following biochemical stress parameters measured in their plasma and tissues: glucose, total proteins, total haemocyte number (THC), heat shock protein 70 (Hsp70) expression, and Acetylcholinesterase (AChE) activity.The responses observed in the mussels exposed to low frequency sweeps enable us to suppose a biological and ecological role for this sound, which contains the main frequencies produced by both shipping traffic and the acoustic emissions of fish.

Effects of Ultrasound Assistance on Dehydration Processes and Bioactive Component Retention of Osmo‐Dried Sour Cherries

Despite having numerous health benefits, dried sour cherries have proven to be more acceptable to consumers when infused with sugar or other sweeteners to enhance their flavor, which, in turn, leads to serious anthocyanin losses. For this reason, a consideration was made for the application of ultrasound to accelerate solid gain and shorten drying time, thus favoring bioactive component retention. To determine the usefulness of ultrasound as a tool for sour cherry osmotic infusion enhancement, the effect of sonication time on dehydration effectiveness, as well as the stability of bioactive components during osmotic treatment and consecutive convective drying, was investigated. Fruits were osmo-dehydrated using a 60% sucrose solution for 120 min (40 °C), during which, ultrasound of 25 kHz (0.4 W/cm(2) ), was applied for 0, 30, 60, 90, and 120 min, after which, the fruits were convectively dried. In the range of the applied ultrasound energy no significant effect of sonication on mass transfer intensification was observed; moreover, longer acoustic treatment seemed to retard moisture removal during subsequent convective drying, which can be related to the breakdown of the parenchyma cell walls caused by the prolonged ultrasound (US) action. It was concluded that although US assistance could be considered neutral for bioactive component retention, excessive sonication time can lead to some anthocyanin deterioration. According to high-performance liquid chromatography analysis, the particular anthocyanin alterations, both during dehydration and final drying, occurred in a similar way. Sonication time prolongation caused approximately 10% more bioactive compound deterioration, than earlier, shorter trials.

Active membrane-based silencer and its acoustic characteristics

Abstract A membrane-based silencer using dielectric elastomer absorbers (DEAs) was developed and explored in the present study. Dielectric elastomer, a soft smart material, was used to fabricate this actuator. It has the characteristic of lightweight, high elastic energy density and large deformation under external direct current (DC) or alternating current (AC) voltages. The typical acoustic performances of this membrane-based silencer were experimentally identified using a transmission loss (TL) duct acoustic measurement system. It was found that the resonance peaks of this membrane-based silencer could be controlled by applying different external voltages, a maximum resonance frequency shift of 59.5 Hz for the resonance peaks was achieved which indicated that this membrane-based silencer could be adjusted to absorb the target noise without any addition mechanical part. Furthermore, the resonance shift and multiple resonances mechanisms using DEAs were proposed and discussed which was aiming to achieve multi-peaks noise reduction. The present results also provide insight into the appropriateness of the absorber for possible use as an acoustic treatment to replace the traditional acoustic treatment in the noise reduction technology.

A field measurement study on the acoustic environment of primary and secondary schools in Southwestern China

A number of studies over the past 30 years have shown that the environmental and classroom noise have detrimental impacts on children’s academic performance. This paper presents the field measurement results of the acoustic environment in 15 typical primary and secondary schools in Southwestern China. RT and three different background noise levels (outdoor, indoor with and without fan) were taken into account for all the 30 classrooms (two rooms per school). Compared with UK’s schools, Chinese classrooms are normally bigger, with the average volume of 180 m3. Both RT and background levels at most of the measured schools largely exceeded the suggested values, as guided by the relevant Chinese standard. RT ranged from 0.62 s to 2.63 s, whereas the maximum background noise levels were as high as 74 dBA. A possible reason might be the lack of appropriate acoustic treatments in those selected schools.

Optimizing the signal to noise ratio in classrooms using passive acoustics

Adults with normal hearing require a roughly 0 dB signal-to-noise ratio (SNR) for good speech intelligibility in classrooms and lecture halls. However, values in excess of 15 dB are needed to compensate for neurological immaturity, sensorineural and conductive hearing losses, language proficiency, and excessive reverberation. ANSI 12.60 addresses ways to lower the noise interference due to background levels and reverberation time. However, simply reducing the mid-high frequency reverberation time is not sufficient and may lead to masking of the high frequency consonant information, needed for speech intelligibility, with lower frequency vowel sounds. Research has shown that increasing the signal by including early reflections is also needed. This presentation will discuss a classroom design, along with several potential acoustical treatments, which aims to passively increase the SNR and improve speech intelligibility. These acoustic tools include a multi-layer, broad bandwidth absorptive panel, a hybrid diffusive/absorptive panel, an absorptive wood system simultaneously offering early reflections and mid-low frequency sound absorption and an LED lighting fixture system that simultaneously provides light and sound diffusion, as well as variable color and intensity for task lighting that has been shown to improve reading speed, increase test scores, and reduce hyperactivity.

A case of classroom acoustic treatment in Tsinghua University

Room 114 is an 100 audience classroom located in the Architecture Department Hall of Tsinghua University with unsatisfactory acoustic effects. This paper briefly introduces the whole process of acoustic design for this classroom which included document survey, acoustic test, acoustic simulation analysis, scale model test, auralization simulation, etc. After weighing both the acoustic and visual effects of three designs, the executives determined the final one to put into effect. This case suggests that technology has been able to well solve the problem of the sound quality of the classroom in universities, but how to persuade managers adopt these technologies, maybe more difficult in classroom acoustics which need further studies.

Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time

Abstract The increasing presence of low frequency sources and the lack of acoustic standard measurement procedures make the extension of reverberation time measurements to frequencies below 100 Hz necessary. In typical ordinary rooms with volumes between 30 m 3 and 200 m 3 the sound field is non-diffuse at such low frequencies, entailing inhomogeneities in space and frequency domains. Presence of standing waves is also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays caused by room modes, a new approach based on reverberation time measurements of single resonant frequencies (the modal reverberation time) has been introduced. From background theory, due to the intrinsic relation between modal decays and half bandwidth of resonant frequencies, two measurement methods have been proposed together with proper measurement procedures: a direct method based on interrupted source signal method, and an indirect method based on half bandwidth measurements. With microphones placed at corners of rectangular rooms in order to detect all modes and maximize SNRs, different source signals were tested. Anti-resonant sine waves and sweep signal turned out to be the most suitable for direct and indirect measurement methods respectively. From spatial measurements in an empty rectangular test room, comparison between direct and indirect methods showed good and significant agreements. This is the first experimental validation of the relation between resonant half bandwidth and modal reverberation time. Furthermore, comparisons between means and standard deviations of modal reverberation times and standard reverberation times in third octave bands confirm the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach. Modal reverberation time measurements applied to furnished ordinary rooms confirm previous results in the limit of modal sound field: for highly damped modes due to furniture or acoustic treatment, the indirect method is not applicable due to strong suppression of modes and the consequent deviation of the acoustic field from a non-diffuse condition to a damped modal condition, while standard reverberation times align with direct method values. In the future, further investigations will be necessary in different rooms to improve uncertainty evaluation.

Transformation of acoustic pulses into electromagnetic response in stratified and damaged structures

The article gives the results of simulated propagation of electromagnetic signals in stratified and damaged dielectric solid model structures exposed to pulsed acoustic treatment. It is shown that the acoustoelectric transformations in such structures result in transition of energy of acoustic pulses to energy of electromagnetic responses in double electric layers. The amplitude–frequency parameters of electromagnetic signals are connected with the characteristics of the determinate acoustic effects and with the charge state of the stratified and damaged structures.

Evaluation of the acoustic performance of a modular construction system: Case study

The aim of this technical note is to characterize the value of acoustic treatments applied to sustainable buildings. The technique is not common in Brazilian construction, but the market needs construction techniques like the ones that will be showed here. At the end of the article, a comparison between masonry with concrete blocks and the industrialized system (built in steel framing) is presented. The simplified method of measuring acoustics was chosen, to be as close as possible to the regular engineering method. The tested buildings have been classified accordingly. This project made use of the Brazilian law and some European laws.

Efficient modeling of flat and homogeneous acoustic treatments for vibroacoustic finite element analysis. Direct field formulations

This paper is concerned with the development of a simplified model for noise control treatments to speed up finite element analysis in vibroacoustic applications. The methodology relies on the assumption that the acoustic treatment is flat and homogeneous. Moreover, its finite lateral extent is neglected. This hypothesis is justified by short wavelength and large dissipation, which suggest that the reflected field emanating from the acoustic treatment lateral boundaries does not substantially affect its dynamic response. Under these circumstances, the response of the noise control treatment can be formally obtained by means of convolution integrals involving simple analytical kernels (i.e. Green functions). Such fundamental solutions can be computed efficiently by the transfer matrix method. However, some arbitrariness arises in the formulation of the mathematical model, resulting in different baffling conditions at the two ends of the treatment to be considered. Thus, the paper investigates the possibility of different formulations (i.e. baffling conditions) within the same hybrid finite element-transfer matrix framework, seeking for the best strategy in terms of tradeoff between efficiency and accuracy. Numerical examples are provided to show strengths and limitations of the proposed methodology.

Laboratory Experimental Verification of the Effectiveness of Acoustical Treatment of Façade Element Frame Profiles

Development of modular transparent elemental façade. Laboratory experimental verification of a façade panel and optimization of its acoustic parameters. Measured samples. Laboratory equipment. Methodology of measurement. Results and conclusions of laboratory experiment.

Acoustic Intervention in a Cultural Heritage: The Chapel of the Royal Palace in Caserta, Italy

The modern use of ancient heritage sites can be, to say the least, challenging from an acoustical perspective. In fact, modern needs may require acoustical interventions in contrast with the preservation issues of the cultural heritage. This paper deals with this topic in an UNESCO designated world heritage site, the Palatine Chapel of the Royal Palace in Caserta, Italy. Since this chapel is currently being used for meetings and music chamber concerts, the acoustical characteristics of the chapel, originally used for religious purposes, are investigated. Field measurements were undertaken to evaluate the acoustical performance of the empty chapel. The measurements were then used to calibrate and validate a computer simulation model. Different acoustical treatments are then considered and simulations are used to determine the related acoustical improvements. Finally, the benefits of different acoustical treatments which are respectful of the aesthetic and historical value of this cultural heritage are discussed.

Multiparameter evaluation of in vivo gene delivery using ultrasound-guided, microbubble-enhanced sonoporation

More than 1800 gene therapy clinical trials worldwide have targeted a wide range of conditions including cancer, cardiovascular diseases, and monogenic diseases. Biological (i.e. viral), chemical, and physical approaches have been developed to deliver nucleic acids into cells. Although viral vectors offer the greatest efficiency, they also raise major safety concerns including carcinogenesis and immunogenicity. The goal of microbubble-mediated sonoporation is to enhance the uptake of drugs and nucleic acids. Insonation of microbubbles is thought to facilitate two mechanisms for enhanced uptake: first, deflection of the cell membrane inducing endocytotic uptake, and second, microbubble jetting inducing the formation of pores in the cell membrane. We hypothesized that ultrasound could be used to guide local microbubble-enhanced sonoporation of plasmid DNA. With the aim of optimizing delivery efficiency, we used nonlinear ultrasound and bioluminescence imaging to optimize the acoustic pressure, microbubble concentration, treatment duration, DNA dosage, and number of treatments required for in vivo Luciferase gene expression in a mouse thigh muscle model. We found that mice injected with 50μg luciferase plasmid DNA and 5×105 microbubbles followed by ultrasound treatment at 1.4MHz, 200kPa, 100-cycle pulse length, and 540 Hz pulse repetition frequency (PRF) for 2min exhibited superior transgene expression compared to all other treatment groups. The bioluminescent signal measured for these mice on Day 4 post-treatment was 100-fold higher (p<0.0001, n=5 or 6) than the signals for controls treated with DNA injection alone, DNA and microbubble injection, or DNA injection and ultrasound treatment. Our results indicate that these conditions result in efficient gene delivery and prolonged gene expression (up to 21days) with no evidence of tissue damage or off-target delivery. We believe that these promising results bear great promise for the development of microbubble-enhanced sonoporation–induced gene therapies.