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Showing papers in "Archives of Acoustics in 2017"


Journal ArticleDOI
TL;DR: This paper provides an example of the application of the acoustic emission (AE) method for the diagnosis of technical conditions of a three-phase on-load tap-changer (OLTC) GIII type, installed in power transformers with a capacity of 250 MVA.
Abstract: This paper provides an example of the application of the acoustic emission (AE) method for the diagnosis of technical conditions of a three-phase on-load tap-changer (OLTC) GIII type. The measurements were performed for an amount of 10 items of OLTCs, installed in power transformers with a capacity of 250 MVA. The study was conducted in two different OLTC operating conditions during the tapping process: under load and free running conditions. The analysis of the measurement results was made in both time domain and time-frequency domain. The description of the AE signals generated by the OLTC in the time domain was performed using the analysis of waveforms and determined characteristic times. Within the time-frequency domain the measured signals were described by short-time Fourier transform spectrograms.

27 citations


Journal ArticleDOI
TL;DR: The test process for unseen vibration data of the trained ANN combined with ideal output target values indicates high success rate for utomated bearing fault detection.
Abstract: Journal bearings are widely used to support the shafts in industrial machinery involving heavy loads, such as compressors, turbines and centrifugal pumps. The major problem that could arise in journal bearings is catastrophic failure due to corrosion or erosion and fatigue, which results in economic loss and creates major safety risks. Thus, it is necessary to provide suitable condition monitoring technique to detect and diagnose failures, and achieve cost savings to the industry. Therefore, this paper focuses on fault diagnosis on journal bearing using Debauchies Wavelet-02 (DB-02). Nowadays, wavelet transformation is one of the most popular technique of the time-frequency-transformations. An experimental setup was used to diagnose the faults in the journal bearing. The accelerometer is used to collect vibration data, from the journal bearing in the form of time domain. This was then used as input for a MATLAB code that could plot the time domain signal. This signal was then decomposed based on the wavelet transform. The fast Fourier transform is then used to obtain the frequency domain, which gives us the frequency having the highest amplitude. To diagnose the faults various operating conditions are used in the journal bearing such as Full oil, half loose, half oil, fault 1, fault 2, fault 3 and full loose. Then the Artificial Neural Networks (ANN) is used to classify faults. The network is trained based on data already collected and then it is tested based on random data points. ANN was able to classify the faults with the classification rate of 85.7%. Thus, the test process for unseen vibration data of the trained ANN combined with ideal output target values indicates high success rate for utomated bearing fault detection.

21 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluated acoustic comfort in open-space banks based on speech intelligibility and noise annoyance metrics, and found that speech intelligibilities in the workstations of banks were higher than the satisfactory level.
Abstract: Tasks requiring intensive concentration are more vulnerable to noise than routine tasks. Due to the high mental workload of bank employees, this study aimed to evaluate acoustic comfort in open-space banks based on speech intelligibility and noise annoyance metrics. Acoustic metrics including preferred noise criterion (PNC), speech transmission index (STI), and signal to noise ratio (SNR) were measured in seventeen banks (located in Hamadan, a western province of Iran). For subjective noise annoyance assessments, 100-point noise annoyance scales were completed by bank employees during activities. Based on STI (0.56 ± 0.09) and SNR (20.5±8.2 dB) values, it was found that speech intelligibilities in the workstations of banks were higher than the satisfactory level. However, PNC values in bank spaces were 48.2 ± 5.5 dB, which is higher than the recommended limit value for public spaces. In this regard, 95% of the employees are annoyed by background noise levels. The results show irrelevant speech is the main source of subjective noise annoyance among employees. Loss of concentration is the main consequence of background noise levels for employees. The results confirmed that acoustic properties of bank spaces provide enough speech intelligibility, while staff’s noise annoyance is not acceptable. It can be concluded that due to proximity of workstations in open-space banks, access to very short distraction distance is necessary. Therefore, increasing speech privacy can be prioritised to speech intelligibility. It is recommended that current desk screens are redesigned in order to reduce irrelevant speech between nearby workstations. Staff’s training about acoustic comfort can also manage irrelevant speech characteristics during work time.

21 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the noise monitoring data acquired from the pilot project on the establishment of National Ambient Noise Monitoring Network (NANMN) across seven major cities in India for continuous noise monitoring throughout the year.
Abstract: The paper describes the noise monitoring data acquired from the pilot project on the establishment of National Ambient Noise Monitoring Network (NANMN) across seven major cities in India for continuous noise monitoring throughout the year. The annual average Lday (06-22h) and Lnight (22-06 h) values observed in year 2011-2014 for the 35 locations under study in which 14 locations are in commercial zone, 5 in Industrial, 7 in residential and 9 in silence zones are described. The long-term noise monitoring shows that ambient noise levels have marginally increased for 29 sites (82.9%) since past four years. The present study is focussed on evaluation and analysis of environmental noise pollution at 35 noise monitoring sites in seven major cities of India and shall be instrumental in planning for the noise abatement measures for controlling the noise pollution in these sites.

20 citations


Journal ArticleDOI
TL;DR: Whether the quality of real-time digital DAB+ broadcasted radio programs surpasses the quality offered by analog FM radio is analyzed.
Abstract: Broadcasting services seek to optimize their use of bandwidth in order to maximize user’s quality of experience. They aim to transmit high-quality digital speech and music signals at the lowest bitrate. They intend to offer the best quality under available conditions. Due to bandwidth limitations, audio quality is in conflict with the number of transmitted radio programs. This paper analyzes whether the quality of real-time digital DAB+ broadcasted radio programs surpasses the quality offered by analog FM radio. We also perform a subjective and objective quality assessment comparative study of the HE-AAC v2 audio codec used in DAB+. The subjective studies were carried out using the MOS test methodology, whereas the objective tests were realized using the ViSQOLAudio metric. These studies were followed by a questionnaire concerning the migration from analog to digital radio domain.

18 citations


Journal ArticleDOI
TL;DR: A subjective quality assessment study of the DAB and DAB+ broadcasting system is performed on a representative group of signal samples for a truly real-time and end-to-end quality evaluation.
Abstract: In the age of digital media, delivering high quality content to consumers is one of the most demanding tasks. There exist numerous broadcasting standards, with different pros and cons, and the DAB/DAB+ (Digital Audio Broadcasting) system is one of the most popular among them. From an engineer’s perspective, efficient resource management under limited bandwidth conditions has always been a challenge. In this paper a subjective quality assessment study of the DAB and DAB+ broadcasting system is performed on a representative group of signal samples. It describes the radio link, including a fully functional transmitter designed for the purpose of this test, as well as the receiver side representing a commercially available consumer device, for a truly real-time and end-to-end quality evaluation.

16 citations


Journal ArticleDOI
TL;DR: An application of signal processing and computational intelligence methods to detect presence of the wood boring insects larvae in the wooden constructions (such as the furniture of buildings) and assess the effectiveness of the old house borer’s detection by the acoustic analysis enhanced with the AI algorithm.
Abstract: The paper presents an application of signal processing and computational intelligence methods to detect presence of the wood boring insects larvae in the wooden constructions (such as the furniture of buildings). Such insects are one of the main sources of the degradation in such objects, therefore they should be detected as quickly as possible, before inflicting serious damage. The presented work involved the acoustic monitoring for detecting the presence of the larvae inside pieces of wood. An accelerometer was used to record the sound, further analyzed by a computer algorithm extracting features important for artificial-intelligence (AI) based classification employed to detect the old house borer’s (Hylotrupes bajulus L.) activity. The presented task is difficult, as the sounds made by the larvae are of relatively low amplitude and the background noise caused by people, electrical appliances or other sources may significantly degrade the accuracy of detection. The classification of sounds is needed to separate sources of noise which deteriorate the proper larva detection and should be suppressed if possible. The employed classification was based on features defined in the time domain followed by the support vector machine used as the binary classifier. The results allowed us to assess the effectiveness of the old house borer’s detection by the acoustic analysis enhanced with the AI algorithm.

15 citations


Journal ArticleDOI
TL;DR: It is found experimentally that parameters associated to some characteristic points within the MF spectrum can be used as music descriptors, thus permitting accurate discrimination of music performers.
Abstract: In this paper, we investigated the possibility to classify different performers playing the same melodies at the same manner being subjectively quite similar and very difficult to distinguish even for musically skilled persons. For resolving this problem we propose the use of multifractal (MF) analysis, which is proven as an efficient method for describing and quantifying complex natural structures, phenomena or signals. We found experimentally that parameters associated to some characteristic points within the MF spectrum can be used as music descriptors, thus permitting accurate discrimination of music performers. Our approach is tested on the dataset containing the same songs performed by music group ABBA and by actors in the movie Mamma Mia. As a classifier we used the support vector machines and the classification performance was evaluated by using the four-fold cross-validation. The results of proposed method were compared with those obtained using mel-frequency cepstral coefficients (MFCCs) as descriptors. For the considered two-class problem, the overall accuracy and F-measure higher than 98% are obtained with the MF descriptors, which was considerably better than by using the MFCC descriptors when the best results were less than 77%.

14 citations


Journal ArticleDOI
TL;DR: The article presents the results of the analysis of vibrations generated by the high power transformer in which a defect was found on the basis of tests of oil carried out using the chromatography tests and it was stated that the increased level of vibrations is a consequence of the loss of rigidity of the mechanical structure of its core.
Abstract: This article presents the results of research connected with the development and industrial use of vibroacoustic methods for the evaluation of the technical condition of the active part of transformers. The article presents the results of the analysis of vibrations generated by the high power transformer in which a defect was found on the basis of tests of oil carried out using the chromatography tests. In order to confirm the damage of the active part of this transformer, vibroacoustic measurements were performed in three states of its operation. The measurement using the classical vibroacoustic method included the registration of vibrations at the idle speed and during the load operation of the transformer. The original diagnostic method, so-called the modified vibroacoustic method, was also used during the measurement. The analysis of signals recorded using the classical vibroacoustic method was carried out in the frequency domain by indicating the amplitude of even harmonic vibrations. However, the analysis of signals measured during the commissioning of the transformer was conducted in the time-frequency domain using the short-time Fourier transform (STFT), continuous wavelet transform (CWT), and discrete wavelet transform (DWT). On the basis of the analysis of the results obtained it was stated that the increased level of vibrations of this transformer is a consequence of the loss of rigidity of the mechanical structure of its core.

13 citations


Journal ArticleDOI
TL;DR: The first extensive investigation on the Lombard effect with Polish speech has been performed as discussed by the authors, where the authors investigated the effect in a task involving real communication, solving a Sudoku puzzle.
Abstract: The first extensive investigation on the Lombard effect with Polish speech has been performed. Characteristic parameters of Lombard speech were measured: intensity, fundamental frequency, spectral tilt, duration of words, duration of pauses and duration of vowels. The effect was investigated in a task involving real communication – solving a Sudoku puzzle. The speakers produced speech in quiet and in three different backgrounds: competing speech, speech-shaped noise and speech-modulated noise. The experimental conditions were held as close as possible to those in the study by Cooke and Lu (2010) so that conclusions could be drawn whether differences between the Lombard effect in Polish speech and English speech existed. Most of the findings on the Lombard effect known from the literature have been confirmed with Polish speech. In three parameters, Polish speakers were more sensitive to modulated backgrounds while English speakers were more sensitive to a stationary background. In both languages, the modulated backgrounds induced speakers to extend pauses in the communication tasks.

13 citations


Journal ArticleDOI
TL;DR: In this article, a specific 3D locally resonant phononic crystal (LRPC) with alternating elastic and fluid matrices is proposed, whose resonance and Bragg gaps are already close in frequency.
Abstract: Three-dimensional (3D) locally resonant phononic crystals (LRPCs) are studied with the aim of optimising the sub-wavelength band gaps of such composites. By analysing their effective acoustic properties, it has been found that the effective acoustic speed of the composite will drop to zero when local resonance arise, and will increase monotonically when Bragg scattering effects occur. Moreover, if the matrix is a low-shear-speed medium, local resonators can significantly reduce the effective acoustic speed of the composite and, therefore, lower the frequency where Bragg scattering effects occur. Hence, a specific LRPC with alternating elastic and fluid matrices is proposed, whose resonance and Bragg gaps are already close in frequency. The fluid matrix behaves as a wave filter, which prevents the shear waves from propagating in the composite. By using the layer-multiple-scattering theory, the coupling behaviour of local resonance and Bragg scattering band gaps has been investigated. Both gaps are enhanced when they move closer to each other. Finally, a gap-coupled case is obtained that displays a broad sub-wavelength band gap. Such proposal excels at the application of underwater acoustic materials since the arrangement of structure can be handily adjusted for tuning the frequency of coupled gap.

Journal ArticleDOI
TL;DR: The paper presents the application of Artificial Neural Networks in predicting sound insulation through multi-layered sandwich gypsum partition panels through back-propagation algorithm and shows a prediction error of ±3 dB or points with a confidence level higher than 95%.
Abstract: The paper presents the application of Artificial Neural Networks (ANN) in predicting sound insulation through multi-layered sandwich gypsum partition panels. The objective of the work is to develop an Artificial Neural Network (ANN) model to estimate the $R_w$ and STC value of sandwich gypsum constructions. The experimental results reported by National Research Council, Canada for Gypsum board walls (Halliwell et al., 1998) were utilized to develop the model. A multilayer feed-forward approach comprising of 13 input parameters was developed for predicting the $R_w$ and STC value of sandwich gypsum constructions. The Levenberg-Marquardt optimization technique has been used to update the weights in back-propagation algorithm. The presented approach could be very useful for design and optimization of acoustic performance of new sandwich partition panels providing higher sound insulation. The developed ANN model shows a prediction error of ±3 dB or points with a confidence level higher than 95%.

Journal ArticleDOI
TL;DR: In this article, the authors presented a general description of the constructed measuring system 8AE-PD, the results of calibration of this system by the Hsu-Nielsen method as well as the testing of the measuring system during recording signals generated by HsuNielsen sources in a steel plate and a modeled partial discharge (PD) source.
Abstract: In the paper, there are presented a general description of the constructed measuring system 8AE-PD, the results of calibration of this system by the Hsu-Nielsen method as well as the testing of the measuring system during recording signals generated by Hsu-Nielsen sources in a steel plate and a modeled partial discharge (PD) source. There is also presented the methodology of investigations by the calibrated acoustic emission method. The results of analyses of PD signals coming from the modeled sources are given. In particular, there are described the properties of acoustic emission (AE) signals generated by the PDs as well as the dependencies of the peak-to-peak voltage $U_{mm}$, the RMS voltage $U_{rms}$ and the descriptors of acronyms ADP and ADC on the apparent charge Q introduced by the modeled PD source. There are determined the limit values of the apparent charge Q introduced by the modeled PD source for which the recorded signal is identified as originating from the PDS.

Journal ArticleDOI
TL;DR: In this article, the authors quantify the existing A-weighted time-average sound level (LAeq, T ) in the study area to probe its effects on the human dwellings and noise sensitive areas with the probability of future development of the mines, roads, and industrial and commercial zone.
Abstract: Noise mapping is a well-established practice among the European nations, and it has been follow for almost two decades. Recently, as per guidelines of the Directorate General of Mines Safety (DGMS), India, noise mapping has been made mandatory in the mining expanses. This study is an effort to map the noise levels in nearby areas of mines in the northern Keonjhar district. The motive of this study is to quantify the existing A-weighted time-average sound level (LAeq, T ) in the study area to probe its effects on the human dwellings and noise sensitive areas with the probability of future development of the mines, roads, and industrial and commercial zone. The LAeq, T was measured at 39 identified locations, including industrial, commercial, residential, and sensitive zones, 15 open cast mines, 3 major highways, and 3 haulage roads. With the utilisation of Predictor LimA Software and other GIS tools, the worked out data is mapped and noise contours are developed for the visualisation and identification of the extent and distribution of sound levels across the study area. This investigation discloses that the present noise level at 60% of the locations in silence and residential zone exposed to significantly high noise levels surpasses the prescribed limit of Central Pollution Control Board (CPCB), India. The observed day and night time $L_{Aeq, T}$ level of both zones ranged between 43.2–62.2 dB(A) and 30.5–53.4 dB(A), respectively, whereas, the average $L_{dn}$ values vary between 32.7 and 51.2 dB(A). The extensive mobility of heavy vehicles adjoining the sensitive areas and a nearby plethora of open cast mines is the leading cause of exceeded noise levels. The study divulges that the delicate establishments like schools and hospitals are susceptible to high noise levels throughout the day and night. A correlation between observed and software predicted values gives $R^2$ of 0.605 for $L_d$, 0.217 for $L_n$, and 0.524 for $L_dn$. Finally, the mitigation measure is proposed and demonstrated using a contour map showing a significant reduction in the noise levels by 0–5.3 dB(A).

Journal ArticleDOI
TL;DR: A neural network that estimates the appropriateness of HRTF datasets based on input vectors of anthropometric measurements is proposed and produces a much more reliable HRTF selection than previously used methods.
Abstract: In binaural audio systems, for an optimal virtual acoustic space a set of head-related transfer functions (HRTFs) should be used that closely matches the listener’s ones. This study aims to select the most appropriate HRTF dataset from a large database for users without the need for extensive listening tests. Currently, there is no way to reliably reduce the number of datasets to a smaller, more manageable number without risking discarding potentially good matches. A neural network that estimates the appropriateness of HRTF datasets based on input vectors of anthropometric measurements is proposed. The shapes and sizes of listeners’ heads and pinnas were measured using digital photography; the measured anthropometric parameters form the feature vectors used by the neural network. A graphical user interface (GUI) was developed for participants to listen to music transformed using different HRTFs and to evaluate the fitness of each HRTF dataset. The listening scores recorded were the target outputs used to train the neural networks. The aim was to learn a mapping between anthropometric parameters and listener’s perception scores. Experimental validations were performed on 30 subjects. It is demonstrated that the proposed system produces a much more reliable HRTF selection than previously used methods.

Journal ArticleDOI
TL;DR: In this paper, experimental modal analysis of a resonance and non-resonance spruce wood (Picea abies L.) is presented, where the modal parameters (modal frequency, modal damping and mode shapes) of the wood samples were determined for the samples of 8 mm in thickness.
Abstract: Results of experimental modal analysis of a resonance and non-resonance spruce wood (Picea abies L.) are presented. The resonance wood came from a tree from Poland and Bosnia and Herzegovina, while the non-resonance wood came from the vicinity of Olsztyn from the north-eastern Poland. The modal parameters (modal frequency, modal damping and mode shapes) of the wood samples were determined for the samples of 8 mm in thickness. Modal analysis was made by pulse excitation. The resonance and non-resonance wood differ in the fundamental modal parameters as well as in the number of potential modes. Additionally, calculated values of damping factor are presented. The values are much bigger for a non-resonance wood than for good quality resonance spruce.

Journal ArticleDOI
TL;DR: In this article, the authors reported the results of an experimental study of the acoustic and articulatory features of the gemination in Modern Arabic language, pronounced by Algerian speakers, and carried out an acoustic analysis by computing the values of frequency formants, energy and durations of the consonants and subsequent vowels in the various [VCV] and [VCgV] utterances (Cg: geminate consonant).
Abstract: In this paper, we report the results of an experimental study of the acoustic and articulatory features of the gemination in Modern Arabic language, pronounced by Algerian speakers. To extract the feature characteristics, we have carried out an acoustic analysis by computing the values of frequency formants, energy and durations of the consonants and subsequent vowels in the various [VCV] and [VCgV] utterances (Cg: geminate consonant). For the articulatory analysis, a range of kinematics parameters were analyzed from the phoneme productions including movement trajectories, distance, velocity, and duration of tongue movements. Among the most important results, we note a longer duration of the vowel following a geminate consonant, a decreasing in levels of F1 and F2 formants and a rising in level of F3 formant of this vowel.

Journal ArticleDOI
TL;DR: In this paper, the results of numerical experiments for evaluating the capability of capturing the tonal airborne noise by using an advanced, yet low computationally demanding, unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence model augmented with a transitional model to account for the laminar to turbulent transition.
Abstract: Tonal airborne noise of aerofoils appears in a limited range of moderate Reynolds numbers and angles of attack. In these specific conditions, the aerofoil is characterised by a large region of laminar flow over the aerodynamic surface, typically resulting in two-dimensional laminar instabilities in the boundary layer, generating one or more acoustic tones. The numerical simulation of such phenomenon requires, beside an accurate prediction of the unsteady flow field, a proper modelling of the laminar to turbulent transition of the boundary layer, which generally imposes the use of highly CPU demanding approaches such as large eddy simulation (LES) or direct numerical simulation (DNS). This paper aims at presenting the results of numerical experiments for evaluating the capability of capturing the tonal airborne noise by using an advanced, yet low computationally demanding, unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence model augmented with a transitional model to account for the laminar to turbulent transition. This approach, coupled with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, is adopted for predicting the far-field acoustic sound pressure of a NACA 0012 aerofoil with Reynolds number ranging from $0.39 · 10^6$ to $1.09 · 10^6$. The results show a main tone located approximately at 1.6–1.8 kHz for a Reynolds number equal to $0.62 · 10^6$, increasing to 2.4 kHz at Reynolds number equal to $0.85 · 10^6$ and 3.4 kHz at $1.09 · 10^6$, while no main tones are observed at $0.39 · 10^6$. The computed spectra confirm that the acoustic emission of the aerofoil is dominated by tonal structures and that the frequency of the main tone depends on the Reynolds number consistently with the ladder-like tonal structure suggested by Paterson et al. Moreover, in specific conditions, the acoustic spectra exhibit a multi-tonal structure visible in narrowband spectra, in line with the findings of Arbey and Bataille. The presented results demonstrate the capability of the numerical model of predicting the physics of the tonal airborne noise generation.

Journal ArticleDOI
TL;DR: Experiments on flat panel loudspeakers with optimized force actuator array layouts show that each of the panel modes within a selected frequency band may be addressed independently and that the inter-modal crosstalk is typically −30 dB or less with non-ideal drivers.
Abstract: The recently demonstrated ‘modal crossover network’ method for flat panel loudspeaker tuning employs an array of force drivers to selectively excite one or more panel bending modes from a spectrum of panel bending modes. A regularly spaced grid of drivers is a logical configuration for a two-dimensional driver array, and although this can be effective for exciting multiple panel modes it will not necessarily exhibit strong coupling to all of the modes within a given band of frequencies. In this paper a method is described to find optimal force driver array layouts to enable control of all the panel bending modes within a given frequency band. The optimization is carried out both for dynamic force actuators, treated as point forces, and for piezoelectric patch actuators. The optimized array layouts achieve similar maximum mode coupling efficiencies in comparison with regularly spaced driver arrays; however, in the optimized arrays all of the modes within a specified frequency band may be independently addressed, which is important for achieving a desired loudspeaker frequency response. Experiments on flat panel loudspeakers with optimized force actuator array layouts show that each of the panel modes within a selected frequency band may be addressed independently and that the inter-modal crosstalk is typically −30 dB or less with non-ideal drivers.

Journal ArticleDOI
TL;DR: The spectrogram magnitude of a mixed signal has been factorised with the help of NMF with consideration of sparseness of speech signals and shows an improvement in the separation capability using the proposed model as compared with an existing one in terms of correlation between separated and original signals.
Abstract: Application of wavelet decomposition is described to speed up the mixed speech signal separation with the help of non-negative matrix factorisation (NMF). It is assumed that the basis vectors of training data of individual speakers had been recorded. In this paper, the spectrogram magnitude of a mixed signal has been factorised with the help of NMF with consideration of sparseness of speech signals. The high frequency components of signal contain very small amount of signal energy. By rejecting the high frequency components, the size of input signal is reduced, which reduces the computational time of matrix factorisation. The signal of lower energy has been separated by using wavelet decomposition. The present work is done for wideband microphone speech signal and standard audio signal from digital video equipment. This shows an improvement in the separation capability using the proposed model as compared with an existing one in terms of correlation between separated and original signals. Obtained signal to distortion ratio (SDR) and signal to interference ratio (SIR) are also larger as compare of the existing model. The proposed model also shows a reduction in omputational time, which results in faster operation.

Journal ArticleDOI
TL;DR: The results of measurements and assessments of noise emitted by the wind turbines Vestas V80-2.0 MW show that noise does not constitute health hazard for wind farm workers as discussed by the authors.
Abstract: Dynamic development of wind power should take into account requirements resulting from environmental protection and human health. However in the case of occupational exposure to noise emitted by wind turbines (workplaces of wind turbine operation personnel, including persons performing maintenance) there are no documented data in literature in this regard. An example of pilot assessments of noise and infrasonic noise at workplaces in a wind farm is presented in the paper. The results of measurements and assessments of noise emitted by the wind turbines Vestas V80-2.0 MW show that noise does not constitute health hazard for wind farm workers. Furthermore infrasonic noise emitted by the wind turbines Vestas V80-2.0 MW is not an annoyance agent for wind farm workers.

Journal ArticleDOI
TL;DR: The paper presents basic legal conditions, applicable to the calculation of cumulative noise levels in the environment with indication mainly on lack of detailed regulations both in formal and methodological approach for evaluating those levels.
Abstract: The paper presents basic legal conditions, applicable to the calculation of cumulative noise levels in the environment with indication mainly on lack of detailed regulations both in formal and methodological approach for evaluating those levels. The paper is focused on methodological approach with the emphasis on analysis of existing case studies in the industry. The main subject of the analysis is the cumulation of industrial noise sources: newly designed and existing ones, together with a proposal of accumulate other types of the noise. Evaluation of cumulative noise levels for new (designed) objects is realised by computational methods, and for existing objects, by measurements or by combination of measurement and computational methods. It is assumed that the cumulative level is an energetic sum of the rating levels for all installations and it will not exceed the limit value in a given place. For the cumulation of different noise sources, the weighting for criterion values of these sources will be applied in aggregation.

Journal ArticleDOI
TL;DR: It is suggested that differences in the hearing threshold (at high frequencies) in analyzed groups may be due to differences in spectral composition of noise and show the need to continue the undertaken studies.
Abstract: The aim of the study was to assess the hearing threshold levels (HTLs) in employees exposed to noise generated by low-frequency ultrasonic technological equipment in comparison with the HTLs of workers exposed to audible noise at the similar A-weighted equivalent-continuous sound pressure level. The study includes measurements of ultrasonic and audible noise at workplaces and hearing tests, i.e. conventional pure-tone audiometry and extended high-frequency audiometry. The study group comprised 90 workers, aged 41.4±10.0 years (mean±SD), exposed for 17.3±9.8 years to noise generated by ultrasonic devices at mean daily noise exposure level ( ) of 80.6±2.9 dB. The reference group consists of 156 subjects, exposed to industrial noise (without ultrasonic components) at similar A-weighted equivalent-continuous sound pressure level ( = 81.8±2.7 dB), adjusted according to age (39.8±7.7 years), gender and job seniority (14.0±7.0 years). This group was selected from database collected in the Nofer Institute of Occupational Medicine. Audiometric hearing threshold levels in the frequency range of 0.5–6 kHz were similar in both groups, but in the frequency range of 8–12.5 kHz they were higher in the group of employees exposed to ultrasonic noise. The findings suggest that differences in the hearing threshold (at high frequencies) in analyzed groups may be due to differences in spectral composition of noise and show the need to continue the undertaken studies.

Journal ArticleDOI
TL;DR: In this article, the authors used the residual minimization method to work out a suitable correction to be applied for classrooms, which is the most commonly applied formula in the designing process of room acoustics with the use of analytical methods.
Abstract: The objective of the residual minimization method is to determine a coefficient correcting the Sabine’s model. The Sabine’s equation is the most commonly applied formula in the designing process of room acoustics with the use of analytical methods. The correction of this model is indispensable for its application in rooms having non-diffusive acoustic field. The authors of the present paper will be using the residual minimization method to work out a suitable correction to be applied for classrooms. For this purpose, five different poorly dampened classrooms were selected, in which the measurements of reverberation time were carried out, and for which reverberation time was calculated with the use of theoretical methods. Three of the selected classrooms had the cubic volume of 258.5 m3 and the remaining two had the cubic volume of 190.8 m3. It was sufficient to estimate the correction for the Sabine’s equation. To verify the results, three other classrooms were selected, in which also the measurements of reverberation time were carried out. The results were verified by means of real measurements of reverberation time and by means of computer simulations in the program ODEON.

Journal ArticleDOI
TL;DR: In this article, an effective optimization approach was proposed to improve acoustical behaviors of PU foams by using Taguchi methods and incorporating bamboo chips as fillers to improve the sound absorption coefficient and transmission loss.
Abstract: In this study, an effective optimization approach was proposed to improve acoustical behaviors of PU foams. The important parameters of PU foams: content of water, silicone oil and catalyst A1 were chosen and their effects on sound absorption coefficient and transmission loss of PU foams were studied by using Taguchi methods. In addition, bamboo chips were incorporated into PU foams as fillers to improve the acoustical properties of PU foams. Four controlled factors: the content of water, silicone oil, catalyst A1 and bamboo chips with three levels for each factor were chosen and Taguchi method based on orthogonal array L9(34) was employed to conduct the experiments. Based on the results of Taguchi’s orthogonal array L9(34), signal-to noise (S/N) analysis was used and developed to determine an optimal formulation of PU-bamboo-chips foam composites.

Journal ArticleDOI
TL;DR: The need of investigations to recognise the 24-hour noise load of a human, with taking into account various forms of their activity and the need of rest is indicated.
Abstract: The civilisation progress has caused noise to become one of essential pathogenic and life comfort decreasing factors. There are several legal regulations aimed at controlling the noise influence on humans. Assessment of the twenty-four-hour influence of noises in various environments constitutes an essential problem. The answer can be supplied by 24-hour monitoring of the sound pressure. This paper is an attempt to learn the real loading of humans by noises. A personal noise indicator was used in measurements. The human 24-hour activity was divided into cycles allowing to model noise hazards. The collected data, even though they did not signal exceeding of individual standards, in the 24-hour period indicated the essential noise influence. These results indicate the need of investigations to recognise the 24-hour noise load of a human, with taking into account various forms of their activity and the need of rest.

Journal ArticleDOI
TL;DR: In this article, a smoothed finite element/boundary element coupling procedure (SFEM/BEM) is extended to analyze the structural-acoustic problem consisting of a shell structure interacting with the cavity.
Abstract: Nowadays, the finite element method (FEM) – boundary element method (BEM) is used to predict the performance of structural-acoustic problem, i.e. the frequency response analysis, modal analysis. The accuracy of conventional FEM/BEM for structural-acoustic problems strongly depends on the size of the mesh, element quality, etc. As element size gets greater and distortion gets severer, the deviation of high frequency problem is also clear. In order to improve the accuracy of structural-acoustic problem, a smoothed finite-element/boundary-element coupling procedure (SFEM/BEM) is extended to analyze the structural-acoustic problem consisting of a shell structure interacting with the cavity in this paper, in which the SFEM and boundary element method (BEM) models are used to simulate the structure and the fluid, respectively. The governing equations of the structural-acoustic problems are established by coupling the SFEM for the structure and the BEM for the fluid. The solutions of SFEM are often found to be much more accurate than those of the FEM model. Based on its attractive features, it was decided in the present work to extend SFEM further for use in structural-acoustic analysis by coupling it with BEM, the present SFEM/BEM is implemented to predict the vehicle structure-acoustic frequency response analysis, and two numerical experiments results show that the present method can provide more accurate results compared with the standard FEM/BEM using the same mesh. It indicates that the present SFEM/BEM can be widely applied to solving many engineering noise, vibration and harshness (NVH) problems with more accurate solutions.

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TL;DR: In this article, the transient vibroacoustic response suppression of a piezo-coupled sandwich circular plate backed by a rigid-walled cylindrical acoustic enclosure is investigated.
Abstract: The transient vibroacoustic response suppression of a piezo-coupled sandwich circular plate backed by a rigid-walled cylindrical acoustic enclosure is investigated. Problem formulation is based on the linear acoustic wave theory, Kirchhoff thin plate model, fluid/structure compatibility relations, Rayleigh integral formula, and active damping control (ADC) strategy. Matlab’s Genetic Algorithm (GA) is utilized to identify and optimize the feedback controller gain parameter based on a multi-objective performance index function. Durbin’s numerical Laplace inversion scheme is then used to calculate the key acousto-structural response parameters due to a transverse impulsive shock force for selected cavity depths. Numerical simulations demonstrate satisfactory performance of adopted control methodology in effective suppression of panel displacement response and radiated external sound pressure for enclosures of shallow and moderate depths. Limiting cases are considered and accuracy of the proposed model is rigorously verified.

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TL;DR: In this article, three different reverberation time (RT) conditions were obtained by room acoustical simulation, and the working memory span scores (WMSSs) were obtained under the different RTs and SNRs conditions.
Abstract: Three different reverberation time (RT) conditions were obtained by room acoustical simulation. The working memory span of grades 3 (8 to 9 years old) and 6 children (11 to 12 years old) was tested under these reverberation conditions with different signal-to-noise ratio (SNR) by headphone reproduction in a quiet classroom. The working memory span scores (WMSSs) were obtained under the different RTs and SNRs conditions. The results demonstrated that children’s age, RT and SNR had significant effect on children’s WMSSs. With the increase of SNR and the decrease of RT, the WMSSs increased gradually. Under the same SNR and RT condition, the children’s WMSSs were increased with the increase of their age. Multiple linear regression analysis shows that children’s WMSSs are related to age, RT and SNR, and the correlation coefficient is 0.99.

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TL;DR: The experiment results show that the SPL of the optimized speaker box with a passive radiator is improved by 5 dB at 200 Hz compared with the one without a radiator, and the analysis results also matched the experiment results.
Abstract: With the rapid development of multimedia devices such as smart phones and tablet PCs, microspeakers have been recently increasingly used for audio equipment. Improving the acoustic performance of a microspeaker is always a main concern, especially in the low frequency range. To avoid sound cancelation, a microspeaker unit is usually inserted into a speaker box. A passive radiator is also used in speaker boxes to improve the sound performance in the loudspeaker system. However, passive radiators have not been applied into microspeaker system. In this study, a speaker box with a passive radiator was analyzed and optimized to achieve a higher Sound Pressure Level (SPL) in a microspeaker system. The Finite Element Method (FEM), two-degree-of-freedom (DOF) vibration theory, and a plane circular piston sound source were used to study the electromagnetic, vibration, and acoustic characteristics, respectively. Optimization was conducted by changing the mass, stiffness, and size of the passive radiator. Based on the optimized parameters, a new sample was manufactured. The experiment results show that the SPL of the optimized speaker box with a passive radiator is improved by 5 dB at 200 Hz compared with the one without a radiator. The analysis results also matched the experiment results.