Acoustic Treatment Research Articles

Objective and subjective assessment of PET felt recycled panels as an acoustic treatment in the meeting rooms

This study presents the performance of the PET-felt recycled panels for the room acoustic treatment. As the objective parameters, Reverberation Time (RT) and Speech Transmission Index (STI) were measured with B&K DIRAC, an omnidirectional loudspeaker, and power amplifier in the meeting room at the Department of Interior Design, Bilkent University, Ankara, Turkey, before the acoustic treatment. Following ISO 12913-2 Method A, Perceived Affective Quality (PQA), Appropriateness, and Assessment of the Acoustic Environment were measured. Fifteen participants who were occupants of the meeting room were selected for the questionnaire survey to be conducted using the snowball method. The findings showed that the reverberation time was five seconds at 1 kHz, which is insufficient, and the acoustic quality could have been better for the speech-purpose room. PET-felt recycled acoustic panels were applied to the ceiling and walls as a solution. After the acoustic treatments, all procedures were repeated with the same. The results showed that significant improvements have been provided in both objective and subjective assessments. RT was in the optimum range. The participants found the meeting room with PET-felt recycled panels more pleasant and eventful after the acoustic treatment.

Impact of surrounding environment on impinging supersonic jets resonances and their hysteretical behavior

Supersonic jets impinging on flat surface produce intense acoustic tones. Recent measurement campaigns have indicated that the surrounding environment geometry or its acoustic treatment can drastically change the observed resonance frequencies and amplitudes at identical flow regimes. For example, at supersonic speeds, a hard walled external nozzle shape leads to the existence of two main types of resonances: antisymmetric resonances (with frequencies close to the free jet screech) and axisymmetric resonances. Frequencies associated to those different resonances are very distinct. We have observed that Applying a simple non-reflective material to the outer surfaces of the nozzle suppresses the axisymmetric resonances and that antisymmetric resonances seems to be contained in the frequency range of existence of trapped acoustics modes, known to be responsible for screech resonances. Additionally, when no acoustic treatment is applied on the nozzle wall, the experiments show that the switch between different resonance regimes (symmetric - antisymmetric), induced by changes in Mach number, has an hysteretical behavior. To the authors' knowledge, this has been rarely discussed in the literature and adds to the actual complexity of the aeroacoustic behavior of such jet flows, especially when modeling is considered.

Reflectivity characterization of in-flow acoustic floor treatment for the NASA Langley 14- by 22-Foot Subsonic Tunnel

An experimental campaign was performed to assess acoustic modifications to the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Recent acoustic testing campaigns in this facility have emphasized the reduction of aerodynamic noise due to flow scrubbing across acoustically treated floor baskets. However, the measures implemented to address this noise contaminant have resulted in the installation of floor basket coverings of high acoustic reflectivity. Therefore, a controlled testing campaign was performed to identify a suitable acoustic basket configuration in terms of both acoustic absorptivity and reduced flow scrubbing noise. This testing campaign was conducted in two phases: the first in an anechoic chamber facility on a single acoustic basket panel to identify a notional configuration of acceptable absorptivity, and the second in a complete floor basket installation checkout test in the NASA Langley 14- by 22-Foot Subsonic Tunnel. Results show that the newly implemented floor treatment exhibits suitable performance in both desired categories of acoustic absorptivity and reduced flow scrubbing noise. This campaign has also validated the effectiveness and usefulness of the anechoic chamber test configuration as a means of assessing acoustic reflections at oblique angles of incidence.

Proposed project to retrofit an orchestra pit with acoustic metadiffusers

There is a pressing need for effective acoustic diffusion treatment with a minimal thickness profile, in particular for the retrofitting of orchestra pits. Sound can reach dangerously high levels in these environments, but highly absorptive boundaries in an orchestra pit are usually not desirable, among other reasons because it compromises ensemble conditions. Implementing diffusion retroactively would be difficult, as there is often little space for such treatment. Acoustic metadiffusers offer a promising solution to this, but lack real-world testing and scalable production. This paper describes this knowledge gap, with a view to ultimately creating a target sound field optimised for musician's performance and safety. This would be made possible by the inherent flexibility of metamaterial design concepts, pointing towards the future development of metadiffusers, specifically as regards to their practical implementation. The aim is to be able to soon fill this knowledge gap, contributing to advancing the understanding of acoustic diffusion treatments. An early stage study will be the assessment of the differences between near and far fields produced by such scattering surfaces in order to be sure of the suitability of ultra thin diffusers for use as retrofitted treatment.

Functions for noise reduction in acoustic standards: evaluating reverberation time, mean absorption coefficient, and a novel approach

Contemporary European acoustic standards utilize dimensioning functions based on either reverberation time or mean absorption coefficient. For spaces with the primary goal of noise reduction, achieving consistent overall sound pressure level (SPL) reduction, regardless of room sizes and shapes is evidently desirable. The conditions under which reverberation time and mean absorption coefficient approaches align with the objective of consistent SPL reduction are analyzed. Generally, both approaches fall short of achieving consistency in case of varying ground surface or room shape, i.e. length, width and height relations. Additionally, in large rooms, constant or room height-dependent reverberation time functions may lead to extensive absorption areas, complicating the installation of acoustical treatments and degrading their economic efficiency. A novel dimensioning function, providing consistent SPL reduction independently of room size and shape, is derived based on diffuse field theory. The novel function is multiplied by a linear function of room height and length, to alleviate accuracy limitations of diffuse field theory in case of varying room shapes. Finally, simulations systematically varying room sizes and shapes demonstrate that the novel dimensioning function significantly outperforms existing approaches in achieving consistent SPL reduction.

Acoustic Black Hole silencers for broadband dissipation in ducted geometries

The design of novel absorbers avoiding the use of porous or fibrous materials for ventilation and air-conditioning systems constitutes a challenging issue. Recently, the development of metamaterials has provided new noise control perspectives for this problem. Traditional Acoustic Black Holes (ABHs) have been derived with close-ended configurations to achieve broadband absorption. These solutions are suitable as anechoic termination but they cannot be used as silencer as they require a mean flow going through the axis of the acoustic treatment. In this study different configurations of opened ABHs will be considered. Nominal ABHs build on straight cavities of increasing depth along the axial direction. To extend the bandwidth of acoustic performance towards the low frequencies, two different types of ABH silencers will be studied. Cavities with coiled geometries will be considered as a first instance, while the entrance of these cavities will be covered by micro-perforated consequently. The transfer matrix formulation will be adapted to these configurations and used to provide the ABH acoustical performance in terms of reflection and transmission of the silencer to find out the best configuration. These results will be validated against a Finite Element method and experiments will be carried out for the nominal configuration.

Electroacoustic Liner for tonal and broadband noise attenuation of turbofans

The new generation of Ultra-High-By-Pass-Ratio (UHBR) turbofan engine while considerably reducing fuel consumption, threatens higher noise levels at low frequencies because of its larger diameter, lower number of blades and rotational speed. This is accompanied by a shorter nacelle, leaving less available space for acoustic treatments. Therefore, alternative solutions to classic liners are required. The SALUTE H2020 project has taken up this challenge, proposing electro-active acoustic liners, made up of loudspeakers (actuators) and microphones (sensors). The electro-active means allow to program the surface impedance on the electroacoustic liner, but also to conceive alternative boundary laws. Test-rigs of gradually increasing complexities have allowed to raise the Technology Readiness Level (TRL) up to 3-4. In this paper, we illustrate the control strategies and the experimental results achieved on the Phare2 test-bench. Phare2 is a reproduction of a real turbofan (scale 1:3), available in the Laboratory of Fluid Mechanics and Acoustics in the Ecole Centrale of Lyon. The noise attenuation accomplished by the electroacoustic liner is assessed by an antenna of microphones surrounding the turbofan inlet, and two rings of microphones placed upstream and downstream the liner in the nacelle. Both broadband and tonal noise are targeted with very promising results.

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

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

Sonic restoration: acoustic stimulation enhances plant growth-promoting fungi activity.

Ecosystem restoration interventions often utilize visible elements to restore an ecosystem (e.g. replanting native plant communities and reintroducing lost species). However, using acoustic stimulation to help restore ecosystems and promote plant growth has received little attention. Our study aimed to assess the effect of acoustic stimulation on the growth rate and sporulation of the plant growth-promoting fungus Trichoderma harzianum Rifai, 1969. We played a monotone acoustic stimulus (80 dB sound pressure level (SPL) at a peak frequency of 8 kHz and a bandwidth at -10 dB from the peak of 6819 Hz-parameters determined via review and pilot research) over 5 days to T. harzianum to assess whether acoustic stimulation affected the growth rate and sporulation of this fungus (control samples received only ambient sound stimulation less than 30 dB). We show that the acoustic stimulation treatments resulted in increased fungal biomass and enhanced T. harzianum conidia (spore) activity compared to controls. These results indicate that acoustic stimulation influences plant growth-promoting fungal growth and potentially facilitates their functioning (e.g. stimulating sporulation). The mechanism responsible for this phenomenon may be fungal mechanoreceptor stimulation and/or potentially a piezoelectric effect; however, further research is required to confirm this hypothesis. Our novel study highlights the potential of acoustic stimulation to alter important fungal attributes, which could, with further development, be harnessed to aid ecosystem restoration and sustainable agriculture.

The Influence of Acoustic Treatment on the Activity of Amylases of the Microbial Enzyme Preparation

The Influence of Acoustic Treatment on the Activity of Amylases of the Microbial Enzyme Preparation

Sustained acoustic medicine treatment of discogenic chronic low back pain: A randomized, multisite, double-blind, placebo-controlled trial.

Sustained acoustic medicine (SAM) is a noninvasive long-term treatment that provides essential mechanical and thermal stimulus to accelerate soft tissue healing, alleviate pain, and improve physical activity. SAM increases localized deep tissue temperature, blood flow, cellular proliferation, migration, and nutrition exchange, resulting in reduced inflammation and an increased rate of tissue regeneration. To assess the efficacy of SAM treatment of discogenic back pain in the lower spinal column to reduce pain, improve quality of life, and lower pharmacotherapy use. Sixty-five subjects with chronic low back pain were randomly assigned to SAM (N= 33) or placebo (N= 32) groups. Subjects self-applied SAM device bilaterality on the lower lumbar region for 4 hours daily for 8 weeks and completed daily pain diaries before, during, and after treatment. Subjects recorded pain reduction using a numeric rating scale (NRS), medication use, and physical activity using the Global Rating of Change (GROC) and Oswestry Disability Index (ODI). SAM treatment significantly reduced chronic lower back pain from baseline relative to placebo treatment (p< 0.0001). SAM treated subjects reported significantly lower back pain at 4 weeks, with the highest pain reduction (-2.58 points NRS, p< 0.0001) reported at 8 weeks. Similar trends were observed in improved physical activity (3.48 GROC, p< 0.0001, 69-88% ODI, p< 0.0001) and 22.5% (15.2 morphine milligram equivalent) reduction in the use of opioid medication from baseline to 8 weeks. Daily, home-use SAM treatment significantly improves the clinical symptoms of chronic lower back pain, improves physical mobility, and reduces daily medication use. SAM treatment is well-tolerated by patients and may be considered a safe, non-invasive treatment option for chronic discogenic, lower back pain.

Beyond silence: evolving ultrasound strategies in the battle against cardiovascular thrombotic challenges.

Cardiovascular thrombotic events have long been a perplexing factor in clinical settings, influencing patient prognoses significantly. Ultrasound-mediated acoustic therapy, an innovative thrombolytic treatment method known for its high efficiency, non-invasiveness, safety, and convenience, has demonstrated promising potential for clinical applications and has gradually become a focal point in cardiovascular thrombotic disease research. The current challenge lies in the technical complexities of preparing ultrasound-responsive carriers with thrombus-targeting capabilities and high thrombolytic efficiency. Additionally, optimizing the corresponding acoustic treatment mode is crucial to markedly enhance the thrombolytic effectiveness of ultrasound-mediated acoustic therapy. In light of the current status, this article provides a comprehensive review of the research progress in innovative ultrasound-mediated acoustic therapy for cardiovascular thrombotic diseases. It explores the impact of technical methods, therapeutic mechanisms, and influencing factors on the thrombolytic efficiency and clinical potential of ultrasound-mediated acoustic therapy. The review places particular emphasis on identifying solutions and key considerations in addressing the challenges associated with this cutting-edge therapeutic approach.

Recovery rate after acute acoustic trauma: a case series and meta-analysis.

Steroids given systemically, locally, or both are the mainstay of treatment for acute acoustic trauma (AAT). The overall recovery rate (full, partial, and none) is undetermined. Original case series and systematic literature review. Case series of a tertiary referral center and a systematic literature review. Cases of AAT between 2012 and 2022 were retrospectively analyzed for demographics, acoustic trauma characteristics, treatment modality and delay and prognosis. This case series was added to the series identified by a systematic literature review. This review included "Medline" via "PubMed", "EMBASE", and "Google scholar". All series were pooled for meta-analysis defining prognosis following steroidal treatment for AAT patients. The pooled analyses included 662 ears, out of which 250 underwent complete recovery of hearing (overall proportion = 0.2809, 95%confidence interval [CI] = 0.1611-0.4178). Any recovery was recorded for 477 ears (overall proportion = 0.7185, 95% CI = 0.5671-0.8493) and no recovery was documented for 185 ears (overall proportion = 0.2815, 95% CI = 0.1507-0.4329). The rate of overall recovery for AAT is around 70%, and around 30% for full recovery when steroids are initiated within the first 2 weeks following the insult.

Selecting Measurement Locations for Inverse Pellicular Modes Analysis

Inverse pellicular mode analysis is an approach to reconstruct an acoustic source from measurements in the sound field. After a source is reconstructed, the simulation can be used to predict the sound pressure level at some distance from the source. The method is especially useful for considering acoustic treatments such as partial enclosures and barriers. Pellicular modes are generated by assuming a thin acoustic layer around the source boundary and determining the acoustic modes. These acoustic modes are then used as structural modes and serve as basis functions for the inverse calculation. However, the quality of the reconstruction depends greatly on the selection of measurement locations. In this research, inverse pellicular mode analysis is used to reconstruct the normal boundary velocity on a small generator set. Different measurement set locations are considered and sound pressure levels in the field are calculated and compared to direct measurement to assess the quality of the reconstructed source. The reconstructed source is then utilized to predict the insertion loss of a partial enclosure.

Evaluating an Additive Manufactured Acoustic Metamaterial Using the Advanced Noise Control Fan

This paper examines the performance of a 3D printed acoustic metamaterial as an acoustic treatment for aircraft engine nacelles in the Advanced Noise Control Fan. As the level of air travel continues to increase, so too does the demand for better noise-reduction technologies for aircraft. Engines are one of the two main sources of noise generated by aircraft, with fan noise, in particular, being of concern due to its broadband and tonal contributions. Small and lightweight methods of addressing both broadband and tonal noise are necessary due to the limitations presented by the current engine design. Presented in this paper is a novel acoustic metamaterial that has undergone design optimization for broadband noise reduction. The final design was produced using 3D printing and tested using the Advanced Noise Control Fan at the University of Notre Dame. It was found that the material is capable of reducing the first harmonic of the blade passing frequency by up to 18.5 dB, with an overall noise reduction of 3.7 dB.

Optimizing Sound Quality and Immersion of a Proposed Cinema in Victoria Island, Nigeria

Enhancing sound quality and immersion is vital for an enriched cinematic journey. This study is centered on the proposed cinema in Victoria Island, Nigeria, aiming to tackle challenges and opportunities in this realm. It explores the current landscape of cinema sound technology, focusing on innovations like Dolby Atmos and DTS:X, renowned for transforming global audio experiences. Through thorough analysis, the research aims to offer comprehensive recommendations for augmenting sound quality and immersion in the proposed cinema. It scrutinizes acoustic aspects, employing acoustic treatments and advanced audio processing technologies, alongside immersive audio solutions. Cultural nuances specific to Nigeria are factored in to ensure resonance with local audiences. Ultimately, the research seeks to establish new benchmarks for cinematic audio experiences in Nigeria.

Recent advances on the fabrication and application of sound absorption coating-based textile composites

Noise pollution has been considered as a serious threat to the health of humans. The application of sound absorption materials is an effective noise reduction approach. Fibrous materials exhibit the unique micro-structures including small diameter, large specific surface area, and high porosity, which has been widely developed for sound absorption. Recently, rapid growth has been observed in the coating treatment of fibrous based materials and composites for acoustic applications, which can be attributed to the advantages of a facile production process, cost-effectiveness, and good sound absorption capability. This review aims to provide a brief overview on different coating layers of fibrous materials for improved sound absorption properties. The details of various factors affecting the acoustic behavior of coating materials are described. Among them, polymer coating is a widely used acoustic treatment method, adding particles and nanofiber materials to the polymer matrix, and carrying out structural design, which can further improve the sound absorption performance of textile materials. According to the different needs of the application field, different coating treatment methods have their own advantages. In summary, coating materials are promising to be used in buildings and interiors for efficient noise reduction and control.

Mitigating Intensive Care Unit Noise: Design-Led Modeling Solutions, Calculated Acoustic Outcomes, and Cost Implications.

The study aimed to decrease noise levels in the ICU, anticipated to have adverse effects on both patients and staff, by implementing enhancements in acoustic design. Recognizing ICU noise as a significant disruptor of sleep and a potential hindrance to patient recovery, this study was conducted at a 40-bed ICU in Fiona Stanley Hospital in Perth, Australia. A comprehensive mixed-methods approach was employed, encompassing surveys, site analysis, and acoustic measurements. Survey data highlighted the importance of patient sleep quality, emphasizing the negative impact of noise on work performance, patient connection, and job satisfaction. Room acoustics analysis revealed noise levels ranging from 60 to 90 dB(A) in the presence of patients, surpassing sleep disruption criteria. Utilizing an iterative 3D design modeling process, the study simulated significant acoustic treatment upgrades. The design integrated effective acoustic treatments within patient rooms, aiming to reduce noise levels and minimize transmission to adjacent areas. Rigorous evaluation using industry-standard acoustic software highlights the design's efficacy in reducing noise transmission in particular. Additionally, cost implications were examined, comparing standard ICU construction with acoustically treated options for new construction and refurbishment projects. This study provides valuable insights into design-based solutions for addressing noise-related challenges in the ICU. While the focus is on improving the acoustic environment by reducing noise levels and minimizing transmission to adjacent areas. It is important to clarify that direct measurements of patient outcomes were not conducted. The potential impact of these solutions on health outcomes, particularly sleep quality, remains a crucial aspect for consideration.

Evaluating the Effects of Building Characteristics of Worship Auditoriums on Speech Intelligibility in Makurdi Metropolis

To enjoy the comfort of the indoor environment of any enclosed space, it is important to have a reasonable measure of understanding of any spoken word in the room. In line with the above this study assessed the characteristics of worship auditoriums with regards to speech intelligibility in Makurdi metropolis with the view to identifying building characteristics that affect speech intelligibility worship auditoriums. The study was carried out through the employment of walkthrough survey and physical observation; a well structured checklist was employed for the study. Measurements of lengths, widths and heights were carried out, from which the room volume was obtained to have an insight of the space under consideration. The auditoriums of ten worship centres in Makurdi Metropolis were studied. The findings that showed all the auditoriums were rectangular in shape. It was found that there was use of inappropriate application of materials for surface finishes in the auditoriums. In terms of room volume, it was found that G recorded the highest volume with 17064.00m3 while E recorded the lowest volume of 756.00m3 . The mean volume of the auditoriums was calculated to be 517.64m3 , the Standard Deviation (SD) was 4733.44 and the Coefficient of Variation (CV) was found to be 81.36%. The study recommended that proper selection and application of surface finish materials be ensured during construction of worship centres. Also, that acoustic treatment is applied in auditoriums where defects are identified, with the aim of effectively enhancing speech intelligibility in worship auditoriums in Makurdi Metropolis.

A machine learning approach for predicting the Johnson-Champoux-Allard parameters of a fibrous porous material

Porous fibrous materials have been widely used as acoustic treatments for noise attenuation. Their acoustic properties are typically characterized by Johnson-Champoux-Allard (JCA) model, which includes five dominant parameters, i.e., open porosity, flow resistivity, tortuosity, viscous characteristic length, and thermal characteristic length. The JCA parameters depend on the microstructure configuration of the material, which can be attained by experimental measurements or numerically analyzing the flow field inside the microstructure, but significant efforts to predict the parameters are typically required. This study proposes a machine learning approach based on an artificial neural network (ANN) for predicting the JCA parameters of a fibrous material. Two geometric parameters that can characterize the fibrous material, i.e., the radius of the fiber and the equivalent throat size between neighbouring fibers, are set as inputs for the prediction model, while the five JCA parameters are set as outputs. The datasets for the network are prepared from finite element simulations. Results confirm that the trained model can predict the JCA parameters accurately and reliably based on the micro-structural geometric parameters. Finally, the model is further validated by the measured acoustic characteristics of a metal-based fibrous material in an impedance tube. The machine learning model opens up possibilities to facilitate the design of advanced porous materials.