Octave Frequency Bands Research Articles

Assessment of hand-transmitted vibration in self propelled vertical conveyor reaper

The self propelled vertical conveyor reaper is commonly used for harvesting wheat, rice etc. It has become a main or the sole of mechanical power source on small and medium size farms in India. The operators of VCR are exposed to a high level of vibration arising from single cylinder engine during field operations. The vibration from the VCR is transmitted from handle to hands, arms and shoulders. The detrimental effect of the prolonged exposure to hand-transmitted vibration on the operators has been known for a long time. In the present study, experiments were conducted to assess the vibration extent in VCR for two operational conditions i.e. transportation on bitumen road and wheat harvesting operation. The vibrations were measured at engine speed 2200 and 2800 rpm. In this study it was found that the vibration magnitudes decreased with increase in engine speed from 2200 to 2800 rpm in both operational conditions. The highest vibration values were observed in x-direction. The maximum frequency-weighted vibration acceleration (rms) in x-direction was 18.76 and 22.8 ms-2 in transportation and wheat harvesting. One third octave band frequency spectra were also obtained. The peak acceleration appeared around 50 Hz for both transportation and wheat harvesting at engine speed 2200 and 2800 rpm. The average 8 hour exposure time for occurrence of white finger syndrome was 1.16 and 0.93 years at transportation and wheat harvesting operation.

Reduction of aerodynamic noise of single-inlet centrifugal fan with inclined volute tongue

The effect of inclined volute tongue on the aerodynamic noise and performance of a centrifugal fan was investigated by experimental test in this article. The present work highlights that the effect of both the clearance and the radius of the volute tongue has an influence on the performance and noise. The experimental tests of various models aim to obtain the aerodynamic noise and performance characteristics of several fan models. First, the experimental results of centrifugal fan performance are tested by the standard test equipment of aerodynamic performance. The experimental results of centrifugal fan aerodynamic noise are measured by the standard test equipment of experimental noise. Our experimental results mainly show that the generation of aerodynamic noise is significantly correlated with the clearance and radius of the volute tongue. Certain geometries of the volute tongue could reduce the noise of the centrifugal fan without decreasing the performance. It is experimentally demonstrated that the high A-weighted sound pressure levels mainly concentrate on a range of from 700 to 7000 Hz frequency by observing the each 1/3 octave band frequency for four fan models. The comparison of aerodynamic noise results also demonstrates that the inclined volute tongue may not only produce a deceasing of about 1.58 dB compared to that of the baseline model. We further obtain that the properly inclined volute tongue not only has positive performance features compared with the baseline model but also effectively controls the broadband frequency noise of single-inlet centrifugal fan.

Occupational noise exposure and its association with incident hyperglycaemia: a retrospective cohort study

Noise pollution is reported to be associated with diabetes, but few studies have elucidated the associations between noise frequency characteristics. We aimed to evaluate the relationships between different noise frequency components and incident hyperglycaemia. An industry-based cohort of 905 volunteers was enrolled and followed up to 2012. Octave-band frequencies of workstation noise and individual noise levels were measured in 2012 to classify subjects’ exposures retrospectively. We applied Cox regression models to estimate the relative risk (RR) of hyperglycaemia. An increased RR for hyperglycaemia of 1.80 (95% confidence interval [CI]: 1.04, 3.10) was found among subjects exposed to ≥ 85 A-weighted decibels (dBA) compared with those exposed to < 70 dBA. The high-exposure groups at frequencies of 31.5, 63, 125, 250, 500, 1000, and 2000 Hz had a significantly higher risk of hyperglycaemia (all p values < 0.050) than the low-exposure groups. A 5-dB increase in noise frequencies at 31.5, 63, 125, 250, 500 Hz, and 1000 Hz was associated with an elevated risk of hyperglycaemia (all p values < 0.050), with the highest value of 1.27 (95% CI: 1.10, 1.47) at 31.5 Hz (p = 0.001). Occupational noise exposure may be associated with an increased incidence of hyperglycaemia, with the highest risk observed at 31.5 Hz.

Validated shipping noise maps of the Northeast Atlantic

Underwater noise pollution from shipping is globally pervasive and has a range of adverse impacts on species which depend on sound, including marine mammals, sea turtles, fish, and many invertebrates. International bodies including United Nations agencies, the Arctic Council, and the European Union are beginning to address the issue at the policy level, but better evidence is needed to map levels of underwater noise pollution and the potential benefits of management measures such as ship-quieting regulations. Crucially, corroboration of noise maps with field measurements is presently lacking, which undermines confidence in their application to policymaking. We construct a computational model of underwater noise levels in the Northeast Atlantic using Automatic Identification System (AIS) ship-tracking data, wind speed data, and other environmental parameters, and validate this model against field measurements at 4 sites in the North Sea. Overall, model predictions of the median sound level were within ±3 dB for 93% of the field measurements for one-third octave frequency bands in the range 125 Hz–5 kHz. Areas with median noise levels exceeding 120 dB re 1 μPa and 20 dB above modelled natural background sound were predicted to occur in the Dover Strait, the Norwegian trench, near to several major ports, and around offshore infrastructure sites in the North Sea. To our knowledge, this is the first study to quantitatively validate large-scale modelled noise maps with field measurements at multiple sites. Further validation will increase confidence in deeper waters and during winter months. Our results highlight areas where anthropogenic pressure from shipping noise is greatest and will inform the management of shipping noise in the Northeast Atlantic. The good agreement between measurements and model gives confidence that models of shipping noise can be used to inform future policy and management decisions to address shipping noise pollution.

Graphene-based multifunctional three-port THz and long-wave infrared components.

Two graphene-based T-shaped multifunctional components for THz and long-wave infrared regions are proposed and analyzed. The first component can serve as a divider, a switch, and a dynamically controllable filter. This T-junction presents a circular graphene resonator and three graphene waveguides with surface plasmon-polariton waves connected frontally to the resonator. The resonator can be adjusted to work with dipole, quadrupole, or hexapole modes. The graphene elements are deposited on a SiO2 (silica) and Si (silicon) two-layer substrate. The dynamical control and switching of the component are provided by the electrostatic field, which defines the graphene Fermi energy. Numerical simulations show that the first component in the division regime (which is also the ON regime) has a transmission coefficient of -4.3dB at the central frequency for every two output ports, and the FWHM is 9.5%. In the OFF regime, the isolation of the two output ports from the input one is about -30dB. The second component is a T-junction without a resonator, which fulfills the function of the divider-switch in more than an octave frequency band.

Reverberation time measurements of a neonatal incubator

New-borns are exposed to high noise levels inside infant incubators. Some authors suggest that these noise levels are amplified by the reverberant nature of the materials that compose incubators. In this paper, the impulse response and the reverberation time of an incubator with standard dimensions were calculated. Two incubator configurations were evaluated, with and without mattress, under two measurements methods, impulsive, and interrupted noise method. The incubator was considered as a linear time-invariant system, and therefore the impulse response was easily obtained for each configuration and measurement method. Consequently, the impulse response for each of the six-octave bands was obtained to get the reverberation time in each band.Results show reverberation times (T30) with mattress of 0.6 s (average of all 1/8 octave band frequencies), measured in a room with controlled acoustic conditions (reverberation time of the room below 0.15 s). The longest sound persistence was obtained at low frequencies, with a reverberation time of 1.47 s in the configuration with mattress, and of 1.87 s in the one without mattress. Even if the average reverberation time is relatively reasonable for a standard room, it may be considered long and uncomfortable for such a small space. It is essential to highlight that, due to the low acoustic isolation of the incubator dome, there is a considerable influence of the reverberation time of the room in which the incubator is located.

Likelihood maximisation techniques for ranging gunfire over grassland

A study into acoustic parameter inversion in the presence of a non-moving, homogeneous atmosphere and grassland impedance ground is carried out using methods of likelihood maximisation. Measured frequency-dependent sound pressure level and power spectra for a blank firing pistol are used to generate simulated data with added Gaussian error to represent variations usually present in real life experiments. Inference is carried out using maximum likelihood estimation (MLE) and maximum a priori (MAP) where model parameters are either given as known or restricted to some uncertain distribution bounded by realistic conditions. The quality of inference is assessed visually and statistically as the error between the true and inferred predictions for a given propagation range. Application of a prior (MAP) greatly improves inference accuracy compared to the sole maximisation of the likelihood function (MLE). It is shown that the use of a single octave band frequency window does not improve the quality of inference, whereas combinations of several low frequency octave bands do. Exact quantification of the true values of the ground and source height are seemingly less important as range increases beyond 500m. Although the techniques presented in this paper are for military/security applications, they are readily applicable to other acoustical problems, e.g. source characterisation in engineering noise control. The methods adopted are likely to benefit from higher-dimensional models, i.e. inhomogeneous atmospheres, complex terrain or urban environments.

Ceramic Panel for Sound Insulation Application

In order to reduce noise nowadays, many researcher find different way to solve this problem. One of the ways to reduce noise is by using a sound insulation. This research has been conducted in order to produce high density sound insulation panel made from ceramic. The fabrication of ceramic panel undergo several processes which are milling, mixing, forming, drying and sintering process. The ceramic panel of different types of forming were developed as square plate 110mm x 110 mm with a constant thickness of 5 mm. Type of forming were used for this particular study are slip casting and uniaxial press. The composition used were 100 % clay and 90% + 10 % clay cement. The transmission loss were determined by using acoustic insulation test. The apparatus consists of sound level meter, portable speaker and computer. The Sound Pressure Levels (SPL) were taken at 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz which based on 1 octave frequency bands. The analysis shown that the sample 90 % + 10 % clay cement casting has the higher transmission loss in the lower frequency region, the sample 90 % + 10 % clay cement uniaxial press has the higher transmission loss in the middle frequency region and lastly the sample 100 % clay uniaxial press has the higher transmission loss in higher frequency region. The sample also were tested using Charpy impact test in order to gain their impact energy and impact strength. The tests were according to ASTM-D256. Charpy impact test can determines the amount of energy absorbed by a material during fracture. The analysis shown that the impact energy of the ceramic panel have a small percentage different. It can be concluded that uniaxial press is better than the slip casting in forming ceramic insulation panel.

Experimental study to measure the sound transmission loss and equivalent continuous sound pressure level of composite material for various disturbances

In this paper, the sound transmission loss (STL) and equivalent continuous sound pressure level (Leq) of the polypropylene/glass fiber reinforced material has been measured experimentally. The objective of the present work is to measure the sound absorption properties of the polypropylene/glass fiber reinforced composite material for various real case disturbances. The real case disturbances are harmonic sound (one-third octave band frequencies), road traffic noise, ambulance siren noise, train noise, aircraft noise, construction and machinery noise. The acoustical behavior of the composite material is then compared with the neat polypropylene and with window glass, termed as a single glass. The diameter and the thickness of the composite specimens are 152 mm and 4 mm respectively. The acoustical behavior of the composite material is experimentally measured at different fiber volume fractions. The fiber volume fraction (Vf) used in the present work is 10%, 20%, and 30%. Also, the fiber orientation, ranges from 0° to 90°, considers an important factor on the acoustical behavior of the composite material. The results are also compared with the two glasses separated with an air, termed as a double glass.

Complementary Techniques for the Accelerometric Environment Characterization of Thermodiffusion Experiments on the ISS

The accelerometric environment of IVIDIL and DCMIX experiments were successively monitored not only to identify the main disturbances that could affect the experiments but as well to ensure the correct interpretation of the experimental results. To do so, the conventional techniques used by NASA have been complemented by new tools developed and adapted to help the surveillance of the runs. A summary of these main new techniques is presented further. To show the potentiality of all these techniques, moderate and strong disturbance episodes such as berthings, dockings and reboostings were analyzed by using acceleration signals that came from three different sensors located in the Destiny, Columbus and JEM/Kibo modules, respectively. The first technique proposed is based on the Shannon entropy concept in both time (TEN) and frequency (SEN) domains. It has been found, that SEN technique is a fast and easy tool to detect the different disturbances registered throughout the experiments. The second technique suggested by the authors is based on the one-third octave frequency band RMS values and is called RMS warning map. It is a visual tool which was demonstrated to be very efficient in detecting the range of the frequencies that surpasses the ISS limits requirements, especially when a sudden disturbance occurs. Finally, in order to identify nonlinearities in the frequency domain within a signal, bispectrum and trispectrum functions have been applied. Quadratic and cubic phase couplings have been detected with these techniques only between high frequencies and especially for the signals coming from JEM/Kibo module.

Optimization of linear and planar array geometries for unmanned underwater vehicle acoustic imaging techniques

Unmanned underwater vehicles (UUVs) are becoming more prevalent in industrial and scientific applications. A wide range of designs is available and many platforms are highly configurable, resulting in an ever-changing acoustic profile. Changes in the UUV’s noise may affect onboard sensors and potentially disturb the environment. An acoustic source imaging process is under development to provide a detailed analysis of the UUV noise in a rapid-turnaround environment. Measurements from a hydrophone array in the geometric near field of a UUV may be input to an acoustic inverse method [e.g., generalized inverse beamforming (GINV) or statistically optimized near-field acoustical holography (SONAH)] to spatially separate noise components and ascertain their levels. However, source resolution and accuracy are highly dependent on array design. Results of a recent numerical case study are presented towards the optimization of linear and planar array geometries. The array geometry is iterated and tuned based on the resultant beamwidth, sidelobe levels, and source localization accuracy for a range of octave frequency bands and source locations. The optimization results provide insight into the critical design factors for acoustical imaging techniques, as well as a suitable array geometry for improved UUV acoustic imaging.

Small-boat source level estimates in a fjord environment

Small vessels contribute to noise in the marine environment and it is of interest to measure radiated noise levels of such. This paper presents measurements of radiated noise from small leisure boats (lengths 16 to 23 ft) conducted at a shallow water site in a fjord environment. The measurements used a bottom-deployed tripod with three hydrophones, and a laser instrument for boat range and speed estimation. Data were processed for source levels in one-third octave frequency bands from 0.1 to 1.6 kHz and using the ANSI/ASA standard for distance normalization. For boats moving at speeds 4 to 6 km, source levels varied by up to 20 dB between boat types. Estimated broadband source levels were 8 to 22 dB lower than for merchant vessels previously measured in the same environment.Small vessels contribute to noise in the marine environment and it is of interest to measure radiated noise levels of such. This paper presents measurements of radiated noise from small leisure boats (lengths 16 to 23 ft) conducted at a shallow water site in a fjord environment. The measurements used a bottom-deployed tripod with three hydrophones, and a laser instrument for boat range and speed estimation. Data were processed for source levels in one-third octave frequency bands from 0.1 to 1.6 kHz and using the ANSI/ASA standard for distance normalization. For boats moving at speeds 4 to 6 km, source levels varied by up to 20 dB between boat types. Estimated broadband source levels were 8 to 22 dB lower than for merchant vessels previously measured in the same environment.

Calibrating rhythms in L1 Japanese and Japanese accented English

Japanese and Japanese-accented English utterances produced by native Japanese speakers were classified using rhythm spectra automatically derived from the speech signals. Results of a stepwise discriminant function analysis revealed an overall classification rate of 81.9% (chance = 50%) for Japanese and 85.9% for English utterances. Two parameters extracted from the spectra emerged as the strongest predictors: normalized amplitude modulation rate above 4 Hz in the 1,000 Hz octave band frequency and normalized amplitude modulation rate between 3-6 Hz in the 4,000 Hz octave band. These results suggested that native Japanese speakers produce Japanese and English with different patterns of temporal regularities in the amplitude envelope of the speech waveform.

Arc welding noise assessment from the measured ultrasound pressure levels. Part II: Pulsed and double pulsed metal active gas welding

The assessment method of the total and A-weighting-filtered sound pressure levels from the sound pressure levels in selected bands of ultrasonic frequencies, suggested in Part I of this work, was verified on the basis of 226 sets of measurement results of acoustic emission during welding. The pulsed and double pulsed metal active gas welding (MAG-P and MAG-DP) was studied, that constituted a continuation of research on MAG methods. It was shown that the total sound pressure levels due to welding could be reasonably assessed from the sound pressure levels in the octave band with center frequency of 31.5 kHz using a simple empirical equation. The assessment uncertainty was estimated for ±1 dB, which was equal to that attainable in direct measurements with class 1 meter in the field. The assessments of A-weighting-filtered sound pressure levels were based on the measurement results in the 1/3 octave frequency bands with center frequencies of 40 kHz and 20 kHz for MAG-P and MAG-DP weldings, respectively. Although the uncertainty was slightly worse, it was still acceptable taking into account potential practical application of the method: measurements in work environment, especially in places where the acoustic background is not stable. A simple rule for proper selection of the frequency band suitable for this purpose was suggested, refined in comparison with that reported previously.

Automatic determination of a speaker’s gender based on the Cauchy distribution in the octave frequency band

Algorithms for recognition of a speaker’s gender based on the use of the Cauchy distribution in the octave frequency band with a geometric mean frequency of 125 Hz are obtained. Classifiers based on the maximum logarithm of the likelihood function are constructed. The algorithm for determining the speaker’s gender is considered, where not only the logarithm of the Cauchy distribution in the octave frequency band is taken into account, but also estimates of the average value of the formant frequencies and the antiformant frequencies. Studies of the probability of correct recognition of the speaker's gender determination algorithms are carried out

Application of land-use regression models to estimate sound pressure levels and frequency components of road traffic noise in Taichung, Taiwan

Few studies have applied land-use regression to predict road traffic noise exposure, and there are few predictive models for different frequencies. This study aimed to measure 24-h average road traffic noise levels and to analyze the frequency components over one year to establish land-use regression models of noise exposure. Fifty monitoring stations were set up to conduct 3 measurements for A-weighted equivalent sound pressure levels over 24 h (Leq,24h) and night equivalent sound pressure levels (Lnight), as well as octave-band analyses, during the 2013–2014 period. Noise measurements were integrated with land-use types, road and traffic information, meteorological data and geographic information systems to construct land-use regression models. Leave-one-out cross-validation was performed to test the validity of the predictive models. The annual means of Leq,24h and Lnight were 66.4 ± 4.7 A-weighed decibels (dBA) and 62.1 ± 6.0 dBA, respectively. Octave-band frequency analyses revealed that the highest means over 24 h and at night were 61.4 ± 5.3 decibels (dB) and 56.7 ± 6.6 dB (both at 1000 Hz), respectively. The model-explained variance (R2) of the full-frequency noise was 0.83 for Leq,24h and 0.79 for Lnight. The R2 values for octave-band-frequency noise ranged from 0.67 to 0.88 for Leq,24h and 0.65 to 0.85 for Lnight, with the highest R2 at 250 Hz for Leq,24h and at 125 Hz for Lnight. The differences between the model R2 and the leave-one-out cross-validation R2 ranged from 5% to 15% for both Leq,24h and Lnight at all frequencies. In the validation, the root mean squared error was 2.09 dBA and 2.80 dBA for the full-frequency Leq,24 and Lnight, respectively, and ranged from 1.89 to 2.62 dB and from 2.51 to 3.28 dB for the octave-band-frequency Leq,24h and Lnight, respectively. This study observed that the annual means of the measured Leq,24h and Lnight in Taichung were both above 60 dBA and had the highest level at 1000 Hz. The developed land-use regression models of Leq,24 and Lnight both had good predictive capacity for the full frequency spectrum and within octave bands and can therefore be applied for epidemiological studies.

Optimal scheduling to minimize noise exposure in an oil and gas field

Noise analysis with different scenarios has been conducted for an oil and gas field to determine whether workers during sandblasting operations were fully protected from high noise to prevent ear injuries and downtime. The main purpose is to minimize noise doses affecting workers through an optimal scheduling algorithm. Data collected from a noise meter was fully evaluated and analyzed in terms of LAeq—A-weighted average energy equivalent sound pressure levels—and Lpk energy peak, in the audible range from 12.5 Hz to 20 kHz based on the one-third octave band frequencies. All noise results were found above the maximum permissible exposure limit 85 dB(A). Another important feature is the sharp rise observed in all weighted levels up to a mean value of 67 dB at low frequency of 80 Hz. A sharp decrease in the high frequency noise levels beyond 8 kHz is also observed. Comparisons between different scenarios are also presented. Additional noise sources such as compressors and air coolers add up an important fraction of the workers’ noise exposure dose and highly contribute to the hearing loss. Finally, a fair scheduling algorithm to optimize noise exposure time by minimizing the noise dose is proposed.

Analytical modeling of antisymmetric split-ring resonators coupled with transmission line

AbstractCoupled-mode theory is applied to obtain an analytic form of scattering parameters for a class of transmission line metamaterials with antisymmetric split-rings. The same structure is modeled with equivalent circuit, which includes electric and magnetic coupling with the line and inter-resonator coupling. Modified even/odd analysis is used to obtain scattering parameters from the equivalent circuit. These two methods are shown to be equivalent in a narrow band, and their constants related. The obtained results are compared with full-wave simulations and measurements, and it is shown that both methods give accurate approximation in one octave frequency band. The derived analytic expressions are suitable for study of resonant phenomena, with potential practical applications for filters, phase shifters, delay lines, and sensors.

DETERMINATION OF THE MAIN SOURCE OF EXTERNAL NOISE CAUSED BY THE ENTERPRISE ENGINEERING AND TECHNOLOGICAL EQUIPMENT IN THE RESIDENTIAL DEVELOPMENT AREA

The article considers two approaches to solving the problem of searching sources that make the greatest contribution to noise levels in the residential area caused by the enterprise engineering and technological equipment operation. The first approach is based on the analysis of the sound pressure levels in 1/3 octave frequency bands, the second one – of the levels of its narrow-band spectrum. It is determined that the results obtained using narrow-band analysis (Δf=1 Hz) provide more accurate results.

Occupational Noise Exposure and Its Association with Incident Hyperglycemia: A Retrospective Cohort Study

Background: Few studies have reported the relationship between noise exposure and fasting blood glucose, which are risk factors of cardiovascular disease. This study investigated the association between occupational noise exposure and incident hyperglycemia. Methods: An industry-based cohort of 905 volunteers was enrolled and followed-up during 1973-2012. Personal noise levels and environmental octave-band frequency components were measured systematically in 2012 to classify subjects' exposure retrospectively. Cox regression models were used to estimate the relative risk (RR) of hyperglycemia by continuous and categorical noise-exposure and frequency-component levels, adjusting for potential confounders. Findings: Participants exposed to ≥80 A-weighted decibels (dBA) had an increased RR for hyperglycemia of 1·78 (95% confidence interval [CI]: 1·11, 2·84) compared with those exposed to <70 dBA. The high-exposure groups (noise levels ≥ median values) at frequencies of 31·5, 63, 125, 250, 500, 1000, and 2000 Hz had a significantly higher risk of hyperglycemia (all p < 0·05) than did the low-exposure groups, and those exposed at 31·5 Hz had the highest risk (Adjusted RR=1·97, 95% CI: 1·23, 3·16). Per 5-dBA increase in noise frequencies at 31·5, 63, 125, 250, 500 Hz, and 1000 Hz were associated with an elevated incidence of hyperglycemia (all p < 0·05), with the highest risk of 1·27 (95% CI: 1·10, 1·47) at 31·5 Hz (p = 0·001). Interpretation: Occupational noise exposure may be associated with an increased incidence of hyperglycemia, with the highest risk observed at 31·5 Hz, providing a possible link between noise exposure and cardio-metabolic disease. Funding Statement: National Science Council, Taiwan. Declaration of Interests: The authors state: None exist. Ethics Approval Statement: This study was reviewed and approved by the Institutional Review Board of the School of Public Health, China Medical University. Written informed consent was acquired from each participant.