Acoustic Treatment Research Articles

The effect of acoustical treatment on primary school children’s performance, sound perception, and influence assessment

A previous field study showed that more than 85% of Dutch children reported they were bothered by noise in the classroom. To investigate the impact of acoustical treatment on children’s phoneme identification, 335 school children (9 to 13 years old) from the previously studied schools were invited to take part in a series of tests in the acoustical chamber of the SenseLab. All the children performed two series of listening tests and evaluations in chamber A (untreated) and chamber B (acoustically treated) respectively, while at the same time one of seven background sounds (45dB or 60dB traffic noise, 45dB or 60dB children talking, 45dB or 60dB music, or no sound) were randomly played in the chambers. T-tests were conducted to compare the results of children’s phonological process tasks, sound perceptions, and influence assessments in these two chambers. Results showed a statistically significant difference in children’s sound perceptions (p=0.01). Children reported the untreated chamber A to be noisier.

Optimal cost-efficiency solution of acoustic treatment for a complex meeting room

Achieving high acoustic quality in meeting rooms is important for intelligibility therefore several measures are needed especially in reflective high volume rooms. This article tackles the method and the solution to renovate a complex enclosure. The study is divided in multiple stages: development of the 3D room model exported in ODEON acoustic software, validation of the actual condition of the room with measurements, proposing and analysing different acoustic ceiling tiles and finally selecting the optimum solution based on the cost and efficacy in reducing the reverberation time (RT). The measured RT was four times higher (3.45 sec at f=1kHz) than the recommended value (0.9 sec at f=1kHz). The numerical simulation results were in accordance with the experimental measurements with errors of less than 0.2 sec. Using the difference between the RT obtained with the acoustic measures and the optimum RT we were able to calculate an efficiency that was later on compared with the cost of the solution. As a conclusion, due to a large diversity of acoustic ceiling types with different prices and sound absorption coefficients it is important, especially for complex room geometries, to run simulations and to perform a cost-efficiency analysis.

Prospects of using extremely low doses of physical factors impact in food biotechnology

The paper deals with urgent issues of development of resource-saving methods of biotechnological processes intensification. The main purpose of the work is to show the efficiency of using extremely low doses of physical factors impact in food biotechnology. Acoustic and electric treatment was in various modes. Impact capacity did not exceed 10-4 W/kg. The duration of exposure ranged from 5 to 15 min. Barley grains enzymes and lactic acid microorganisms were subjected to treatment. Impact of vibration as a physical factor, its frequency is considered as a priority in controlling growth and biochemical processes in biological objects. Impact frequency in the range of 50–10000 Hz influences the activity of hydrolytic enzymes in bimodal way. It is presented in the article. The coincidence of the frequency ranges of the maximum activity of enzymes in the model reactions with the ones in the grain of barley under the treatment of alternating current and sound is noted. Improvement of all indexes of germinating barley and improvement of the quality of the finished malt were observed in these ranges. Low-intensity acoustic treatment at a frequency of 2000 Hz contributed to an increase in β-galactosidase activity of the CT-95 Str. thermophilus strain. Selected ST-95 Str. thermophilus strain was used in the starter composition for the experimental sample production of fermented melted milk. The fermentation process intensification was observed. The lactose content of this product is 30% less in comparison with the feedstock. The use of traditional starter without a selected strain can reduce the lactose content by an average of 7.5%. The results of biotechnological processes modification by means of the treatment of enzymes and extremely low doses of physical factors impact used in meat technologies are observed. Thus, the prospects of using low-intensity physical effects of vibration in the development of innovative food technologies are substantiated. It is also promising to use these technologies in making absolutely new food products with different qualities.

Research the influence of acoustical treatment of concrete on its water absorption

Research the influence of acoustical treatment of concrete on its water absorption

Effets du traitement acoustique d’une salle de dialyse sur la qualité de vie des patients

The impairment of quality of life experienced by patients treated with chronic hemodialysis results from many factors, including the care environment. Current regulations have significantly improved reception and treatment conditions for patients, but perhaps insufficient attention has been paid to the noise nuisance associated with dialysis equipment. We therefore found it useful to conduct a study on acoustic parameters in the dialysis room, and to evaluate the effects on perceived quality of life of an acoustic treatment intended to reduce the level of ambient noise. After measurements carried out under standard conditions, adapted noise absorption (devices panels and trellis) were installed in a treatment room of 8 posts hosting 32 volunteer patients, and their effects evaluated by a quality of life questionnaire administered 3 times (before, at the end of one week, and after the removal of the devices), each patient being his own witness. Measurements of ambient noise during dialysis periods and numerical modeling of the room were performed in parallel in order to search for correlations between the subjective changes expressed by the patients and the quantitative noise criteria. The results show that such devices can significantly reduce the perceived acoustic discomfort and their consequences (headaches), and suggest that these improvements are due to the frequential homogenization of the reverberation time in the room and the reduction of the low frequency components induced by the different sources of noise identified.

Acoustic barriers as an acoustic deterrent for native potamodromous migratory fish species.

This study focused on the use of sound playbacks as acoustic deterrents to direct native potamodromous migratory species away from all kind of traps. The effects of two acoustic treatments, a repeated sine sweep up to 2 kHz (sweep-up stimulus) and an intermittent 140 Hz tone, were tested in three fish species native to Iberia: Salmo trutta, Pseudochondrostoma duriense and Luciobarbus bocagei. In contrast with S. trutta, the endemic cyprinids P. duriense and L. bocagei exhibited a strong repulse reaction to the frequency sweep-up sound. The 140 Hz stimulus did not seem to alter significantly the behaviour of any of the studied species. These results highlight the potential of acoustic stimuli as fish behavioural barriers and their application to in situ conservation measures of native Iberian fish populations, to protect them from hydropower dams. In addition, this study shows that acoustic deterrents can be used selectively on target species.

Optimum acoustic impedance in circular ducts with inviscid sheared flow: Application to turbofan engine intake

Acoustic liners are widely employed in turbofan aero-engines as acoustic treatment. Their performance is determined by its acoustic impedance in the presence of flow. In recent years, much effort has been devoted to find the “optimum impedance” i.e. the impedance that results in the maximum attenuation. Although such analysis can be carried out by means of numerical simulations, analytical expressions can also be derived in order to predict the optimum impedance based on exceptional points i.e. when two modes coalesce, resulting in a maximum modal decay rate. Previous works focus on the optimum impedance of higher order modes in rectangular ducts with uniform flow. In this work, the analysis is expanded to circular ducts for both uniform and sheared inviscid flows. Typical turbofan engine intake geometry and flight conditions are considered, corresponding to certification points: sideline, cut-back and approach. It is shown that, for sideline and cut-back conditions, the optimum impedance and the maximum attenuation are affected even by the presence of a small boundary layer. For approach condition, uniform and shear flows lead to essentially the same results. Limitations of the analytical expression in the presence of multi-modal propagation is also discussed.

The identification of minimum-weight sound packages

Generally, heavier noise control treatments are favored over lighter treatments since heavier acoustical materials generally insulate (block) noise sources more effectively than do lighter materials. In automotive applications, however, heavier materials cannot always be adopted because of concerns about the total weight of the vehicle. Thus, it would be useful to identify lightweight acoustical treatments that can mitigate vehicle interior noise. Automotive sound packages have both absorption and transmission characteristics, and there is inevitably a trade-off between these two. Therefore, it is important to study the exchange between the absorption and transmission of acoustical materials particularly as it pertains to weight. Here, we describe a procedure, based on plane wave analysis, that can be used to identify weight reduction opportunities by adjusting the acoustical properties of a generic sound package, consisting of a fibrous layer and a flexible microperforated panel surface treatment, so that it meets a target sound pressure level in a downstream interior space. It has been found for the configuration studied here that there are lightweight sound package configurations that can maintain acoustical performance equivalent to that of heavier noise treatments, and further, it has been found that the lightest treatments tend to favor barrier performance rather than absorption. Further, the impact of acoustical leaks is considered, and it has been found that even very small leaks can result in a very substantial weight penalty if a specified level of acoustical performance is to be ensured.

Functionalized Anatomical Models for Computational Life Sciences.

The advent of detailed computational anatomical models has opened new avenues for computational life sciences (CLS). To date, static models representing the anatomical environment have been used in many applications but are insufficient when the dynamics of the body prevents separation of anatomical geometrical variability from physics and physiology. Obvious examples include the assessment of thermal risks in magnetic resonance imaging and planning for radiofrequency and acoustic cancer treatment, where posture and physiology-related changes in shape (e.g., breathing) or tissue behavior (e.g., thermoregulation) affect the impact. Advanced functionalized anatomical models can overcome these limitations and dramatically broaden the applicability of CLS in basic research, the development of novel devices/therapies, and the assessment of their safety and efficacy. Various forms of functionalization are discussed in this paper: (i) shape parametrization (e.g., heartbeat, population variability), (ii) physical property distributions (e.g., image-based inhomogeneity), (iii) physiological dynamics (e.g., tissue and organ behavior), and (iv) integration of simulation/measurement data (e.g., exposure conditions, “validation evidence” supporting model tuning and validation). Although current model functionalization may only represent a small part of the physiology, it already facilitates the next level of realism by (i) driving consistency among anatomy and different functionalization layers and highlighting dependencies, (ii) enabling third-party use of validated functionalization layers as established simulation tools, and (iii) therefore facilitating their application as building blocks in network or multi-scale computational models. Integration in functionalized anatomical models thus leverages and potentiates the value of sub-models and simulation/measurement data toward ever-increasing simulation realism. In our o2S2PARC platform, we propose to expand the concept of functionalized anatomical models to establish an integration and sharing service for heterogeneous computational models, ranging from the molecular to the organ level. The objective of o2S2PARC is to integrate all models developed within the National Institutes of Health SPARC initiative in a unified anatomical and computational environment, to study the role of the peripheral nervous system in controlling organ physiology. The functionalization concept, as outlined for the o2S2PARC platform, could form the basis for many other application areas of CLS. The relationship to other ongoing initiatives, such as the Physiome Project, is also presented.

Research the influence of acoustical treatment of concrete on its water absorption

The problem of the influence of the technological seam of concreting on the performance of reinforced concrete structures was studied. The requirements of the current regulatory documents on the construction of the working seam of concreting and the existing proposals on increasing the adhesion of “new” and “old” concrete in Russian and foreign sources are considered. The methodology of carrying out and the results of an experimental study of the effect of acoustic treatment of concrete on its moisture absorption in combination with the following technological factors are presented: the type and pH of the medium (penetrating composition), the orientation of the layers of “old” concrete with respect to the plane of moisture absorption. In the course of this study, the frequency of free vibrations of the structural elements of concrete samples was calculated. The conclusions are formulated that will serve as the basis for drawing up technological maps for the organization of the working seam of concrete structures.

Reactive acoustic liner design

Acoustic treatment to reduce fan noise levels in a wind tunnel circuit consists of fibrous materials such as fibreglass or rockwool. Open cell foam materials are also used as acoustic treatments. The acoustic treatments are conventionally applied at fan tail cone regions, tunnel walls along fan diffuser section, cross-legs, test section diffuser, and nozzle contraction areas. However, conventional treatments are not possible in cryogenic wind tunnels, since bulk absorber materials with required resistivity, when operating at cryogenic temperatures, are not available. One possible solution is to design reactive silencers tuned to dominant frequencies. One such approach was used as noise control technique so as to satisfy test section noise specifications. The sound power spectrum of the compressor at different speeds were evaluated. The estimated test section sound pressure levels showed noise reduction at two dominant frequencies were required. The acoustic treatment, therefore, resulted in a double layer reactive design tuned to the two dominant frequencies. The design process will be highlighted in the presentation. The final treatment details will also be presented.Acoustic treatment to reduce fan noise levels in a wind tunnel circuit consists of fibrous materials such as fibreglass or rockwool. Open cell foam materials are also used as acoustic treatments. The acoustic treatments are conventionally applied at fan tail cone regions, tunnel walls along fan diffuser section, cross-legs, test section diffuser, and nozzle contraction areas. However, conventional treatments are not possible in cryogenic wind tunnels, since bulk absorber materials with required resistivity, when operating at cryogenic temperatures, are not available. One possible solution is to design reactive silencers tuned to dominant frequencies. One such approach was used as noise control technique so as to satisfy test section noise specifications. The sound power spectrum of the compressor at different speeds were evaluated. The estimated test section sound pressure levels showed noise reduction at two dominant frequencies were required. The acoustic treatment, therefore, resulted in a double layer...

Optimization of the acoustic treatments in order to achieve the Italian minimum environmental criteria (CAM) for classrooms

A recent Italian legislation has established the Minimum Environmental Criteria (CAM) for working environments. With regard to schools, adequate acoustic comfort targets are required in terms of noise control and acoustic quality. Schools must comply with the UNI 11532 for their reverberation (T), clarity (C50) and speech intelligibility (STI). In classrooms, the following values are required: T 0dB and STI>0.6. In sports facilities such as gyms or swimming pools, the requirements are T -2 dB and STI>0.5. To achieve these objectives, the insertion of acoustic treatments is often unavoidable. Acousticians commonly use the perfectly diffused theory to calculate the amount of need sound-absorbing material to comply with current legislation. The purpose of this work is to evaluate the optimal position in which to place the minimum amount of sound-absorbing treatments to reach CAM. Some university classrooms are used. These classrooms have a marble floor and plastered walls and, at 1.0 kHz, have T values between 2.5s and 4.5s, C50 between 3 dB and -0.5 dB, and ST between 0.34 and 0.47. Using an acoustic software, it was possible to estimate the minimum quantity and the optimal placement of the sound-absorbing panels to insert to reach the CAM of these classrooms.

Variables governing the initial stages of the synergisms of ultrasonic treatment of biochar in water with dissolved CO2

The objectives of a series of our researches are to determine the feasibility of applying ultrasonic pretreatment prior to biochar gasification. As per the initial results, the heating value (HV) of biochar significantly increased after acoustic treatment in water with dissolved CO2 (AIChE Journal, 2014;60:1054–1065). Accordingly, emphasis of the current work is placed on the parameters governing the HV of biochar in the early stage of the treatment. Switchgrass and miscanthus biochars were treated under different conditions. The reactant ratio, biochar:water:CO2, exhibited profound impacts on the synergism. The highest (but not yet systematically optimized) ratio of HV increase (or HV Gain, HG) to ultrasound energy supplied (ES) takes place when biochar-to-water ratio, or BC:W, equals 0.06 g/ml. The observed HG/ES is about 10, suggesting that the energy consumption is only a fraction of the acoustic energy supplied. Miscanthus biochar’s HV increases by up to 4.6% after treatment at 5% amplitude for 135 s (HG = 33 cal/g). For the same run, miscanthus biochar's H content increased by 42.7%. Changes in HV can be mediated by mineral leaching, C or H fixation, or O content loss. Mineral leaching is influenced by pH and CO2 concentration. CO2 and water are the sole contributors to C and H gains, respectively. CO2 concentration in the solution during the treatment is also affected by mass transfer limitations, ultrasound power, and design of the three-phase reactor. Increasing the BC:W ratio initially enhances the cavitation nuclei on the fluid/solid surface, and therefore sonolysis. The subsequent decrease in HV with increasing BC:W may be due to the limitation in ultrasound penetration and H supply from water. Carbon and hydrogen fixation may be connected to the formation of H2, CO, formic acid, formaldehyde, and associated radicals during sonolysis of aqueous CO2.

An experimental study of the flow structure and acoustics of jets: Implications for volcano infrasound

Aeroacoustic jet noise theory describes the relationship between acoustic signals and jet operating parameters. Based on empirical aeroacoustic relationships, a link between peak frequency and amplitude and jet diameter and velocity has been used by volcano acousticians to return the operating parameters of column generating volcanic eruptions. There are however significant differences between the nozzle geometries and structures of flows studied in the aeroacoustic literature and flows emitted from volcanic vents. These differences raise questions as to the validity of applying engineering relationships to volcanic eruptions. Combining particle image velocimetry and acoustic data we investigated the flow structures, acoustic signals and dominant source locations of jet flows emitted from three simple nozzle geometries (convergent, straight and divergent). Flows from the straight and divergent nozzles exited in a more developed flow regime than those emitted from convergent nozzles. While for the convergent nozzles dominant sound sources were located within the jet flow, the dominant signals from the straight and divergent nozzles were located in the region of the nozzle exit. Consequently, for the straight and divergent nozzles it was not possible to differentiate between signals generated by the jet flow and those generated by internal sound sources without beamforming analysis. In order to better replicate the volcanic case and in contrast to studies for industrial applications, our experimental test section was not engineered to minimise internal noise. Without acoustic treatment such as screens, choke plates and paddles, jet noise signals were contaminated by signals generated within the test rig and so, even for the convergent nozzles, the aeroacoustic relationships derived from engineering studies could not be used to retrieve the jet operating parameters. Our results indicate that in the volcanic case, the raw acoustic spectra will contain signals generated by both in-conduit and above-vent processes. Therefore inversions for volcanic jet parameters such as mass eruption rate from standard aeroacoustic relationships may be unreliable.

Evaluation of acoustic performance open-plan office at Jawa Pos building based on ISO 3382-3

The acoustic performance of open-plan office has become an important topic for discussion along with the development of office centers in major cities in Indonesia, including in Surabaya. Acoustic problems at open plan office often arise, such as background noise and speech privacy. Based on ISO 3382-3 2012, an open plan office must meet certain standards to keep productivity and concentration. These parameters are Average A-Weighted Background Noise (Lp, A, B), A-Weighted SPL of Speech at 4 m (Lp, A, s, 4m), Spatial Decay Rate of A-Weighted SPL of Speech (D2,s), Distraction Distance (rD), Privacy Distance (rP). From measurement and calculation did to an office building in Surabaya obtained a value of Lp, A, B equal to 52 dBA, Lp, A, s, 4m 52 dBA, D2, S 4,19 dBA, rD 11,75 m, rP 23, 8 m, and STI at the nearest table 0.78. These results indicate that further acoustic treatment is required to meet the standards specified by ISO.

The development of acoustic environment simulator for passenger’s train soundscape

The study of soundscape in laboratory usually conducted by reproducing acoustic environment recording or simulated acoustic environment. Different method has been developed to understand the soundscape in the laboratory using acoustic environment composition. The soundscape composition has been validated and implemented for outdoor urban soundscape but not the indoor soundscape. The previous soundscape simulator only considers the behaviour of sound sources (movement, and position in space) without considering the sound reflection. This study tries to develop an acoustic environment simulator for passenger train soundscape study. In the passenger train, there are some annoying sound source that cannot be removed such as the sound of bogie or the sound of buffers and chain coupler. The soundscape composition concept using acoustic environment simulator can be implemented to understand the existing soundscape, to fix the soundscape (by selecting different sound source for masking and adjust the sound level), and to evaluate the effect of the acoustic treatment inside the passenger train. The simulator can reproduce realistic acoustic environment using ambisonic reproduction concept. Furthermore, the reflection inside the passenger train simulated by using the concept of auralization.

Comparison of different in situ measurements techniques of intelligibility in an open-plan office

Acoustic comfort in open-plan offices is a relatively recent research topic and some practices have not yet been consolidated. The goal in these spaces is to achieve good speech privacy at every workstation, reaching a high value of spatial decay of the sound pressure level. In case of refurbishment, a proper measurement of intelligibility criteria is needed, for example, in order to properly calibrate a numerical model or to plan acoustic treatments. This work compares different measurement techniques to evaluate the spatial distribution of intelligibility criteria. In situ measurements were done in an open-plan office used as a case study. Both omnidirectional and directional sound sources with different sound power levels were used, according, respectively, to ISO 3382-3:2012 and ITU-T P.51:1996. Furthermore, compensation algorithms were used in impulse response measurements in presence of Heating, Ventilation and Air Conditioning noise. The study shows, in a preliminary way, how different techniques and equipment can influence intelligibility criteria used in the open-plan office characterization. Results show that the indirect method of measuring Speech Transmission Index could not be used when the background level is high as the case study while the direct method returns good results.

An image-based method for non-contact and dynamic room acoustics analysis

Noise is defined as “unwanted” sound and the workers in industrial workroom are often exposed to noise. Acoustics analysis helps to evaluate and improve noise absorption of the reflecting surfaces. Acoustics treatment aims to control sound reflections within the room. This study investigated a method of dynamic room acoustics analysis in industrial workrooms which was developed using image processing and MATLAB software. This method can be used for collecting data and calculating the noise absorption surface area, and may help to identify the acoustics index of buildings more accurately on the basis of the existing conditions.The proposed method was compared with the classical method through 82 dimensional measurements. The required tools including camera, targets, and checkerboard were installed in the site of experiment. Taking into account the distance between the camera and the fittings of interest, the required data were gathered along the two directions of the hall in order to calculate the length, width, and the height of the fittings. The captured photos in jpg format were saved on a computer and processed using suitable algorithms. To collect the data via the classical method, the data collection stage was repeated using a Laser distance meter Tajima Model F02.Based on the results obtained from dimensional analysis in the Industrial settings, the average sound absorption index measured using the new and the classical method, respectively, was 4.15 and 4.39 Sabin·m2. The intra class correlation coefficient between these two methods was 0.989 (R2 = 0.994).The proposed method as a measurement and monitoring instrument was accurate enough to be used for acoustic analysis of buildings and can be considered as an alternative for the classical method. This method requires less time to be performed and provides more accurate calculations, thus, it can be used to make the right decision regarding the building acoustic condition; moreover, as it is a non-contact analysis method, it can significantly protect evaluator person against the risk of accidents caused by industrial machinery.

Dynamic acoustic shell with diffusers in the acoustical treatment of Carolina Coronado Theatre, Almendralejo (Badajoz, Spain)

Carolina Coronado Theatre was inaugurated in 1916. Its original design resembles a classical opera theatre, having a traditional horseshoe form, used throughout 19th century. Before the renovation its volume-number of seats ratio and its reverberation time with audience, were far away from some recommended values. Its renovation was done respecting faithfully the original appearance of the hall, without changes in the raised stage, seating area or walls and only including a new concept of acoustic dynamic shell based in diffusers, above the stage, that can create different acoustical ambiences. This acoustic configuration was slightly helped by covering lateral walls with acoustic panels. The results were obtained from the simulations in the software ODEON and “in situ” measurements.

On the use of a stress-impedance model to describe sound propagation in a lined duct with grazing flow.

With flow, the acoustic effect of a locally reacting lined wall cannot be described by a single quantity independent of the incident wave, such as a wall impedance. At least two quantities, intrinsic to the liner and to the flow, are required to describe the effect of the lined wall regardless of the incident wave. In addition to the impedance, the unsteady tangential force exerted by the wall on the flow has to be taken into account. This force is due either to viscous effects or to the unsteady transfer of axial momentum from the flow into the lined wall. This paper describes a stress-impedance model, where the two variables used are the impedance and the friction factor that links the pressure to a tangential stress at the wall. The use of a wall stress helps to better understand the mechanisms of momentum transfer between the flow and the wall in the vicinity of an acoustic treatment.