Pressure Levels In Octave Bands Research Articles

Calculation tool NoBel for sound propagation assessment of noise from gasturbines on the ground

Gas turbine engines of aviation type are the basic element of gas-pumping stations of the pipelines around in the world. They produce harmful noise and the protection zone around the gas-pumping station must provide the safe distance to residence in its vicinity. Due to Ukrainian legal requirements for the stationary (not movable) noise sources the sound pressure levels in octave bands must be used as limits for protection of the population complementarily to equivalent and maximum sound levels at day and night periods. A new calculation tool was designed to assess the effects during sound wave propagation from stationary noise sources like gas-turbine installations, as for homogeneous atmosphere, so as for real meteorological and topographical conditions. The tool provides the possibility to predict the conditions of maximum noise exposure at point of noise control. For homogeneous atmosphere the divergence, air absorption, ground surface reflection and acoustic screens contribute to propagation effects mostly. Their formulation in accordance with current knowledge provides more accurate sound levels assessment with differences ± 2 dBA at the boundaries of protection zone in comparison with existing national legal requirements of noise protection calculations. In real atmosphere temperature and wind (in direction and speed) vary with altitude over the ground surface always. These real conditions provide the dependence of sound speed with altitude, and in consequence the refraction of sound waves. For specific conditions of positive sound refraction the tool predicts the sound levels at the receiver up to 10 dBA higher, at negative sound refraction - on 5-7 less than in homogeneous atmosphere for legal protection distances. Tool NoBel is appropriate to be used for specific airport stationary noise scenarios, like for aircraft engine run-ups after their maintenance or repair.

Acoustic Energy Harvesting in Nigeria: Prospects, Technical Problems and Socio-Economic Obstacles

Aims: To investigate the prospects or potentials of acoustic energy harvesting in Nigeria as well as highlight technical problems and socio-economic obstacles.
 Study Design: The study re-examined existing data, noise levels and noise power, from road traffic, aircraft, industrial/occupational, outdoor and indoor noise sources. Noise levels and noise power obtained from recent measurements of such noise sources were also examined and analyzed. The data were compared with values from noise sources used for electricity in other countries of the world. Technical problems and socio-economic obstacles have been highlighted.
 Place and Duration of Study: The study was carried out in Abakaliki, Ebonyi State, Nigeria. The duration was one year: April, 2019 and April, 2020.
 Methodology: Wide range noise level measurements, analysis and re-examination of existing data on road traffic, aircraft, industrial/occupational, outdoor and indoor noise were conducted, in line with the objectives of the study, in cities, industries as well as homes with different noise features. Measurements were carried out using sound level meter, SLM, (Bruel and Kjaer 2203) with – octave band filter and SLM, EXTECH 407750 with RS232, sound level recorder (B & K 7005), and noise level (statistical) analyzer (B & K 2121) to obtain noise levels and indices. Also, noise power was subsequently obtained for each of the various noise levels and indices.
 Results: Maximum noise levels, Lmax.; noise power, Wmax.; octave band pressure levels, BPLs; and other indices for the different noise sources were determined. Lmax. and Wmax for aircraft were as high as 116 dB and 0.4 W, respectively, while those for industry and road traffic ranged from 104.0 dB-131.0 dB and 67.5 dB-85.6 dB corresponding to 0.025 W-12.59 W and 0.0000056 W-0.00036 W, respectively. Spectral power of road traffic noise varied between 5.17 x 10-5 W and 9.69 x 10-3 W. Outdoor and household noise sources had Lmax. of up to 48.5 dB and 88.0 dB, that is, 0.000000071 W and 0.00063 W, for quiet and noisy periods, respectively. It was observed that road traffic noise has the highest potential for acoustic energy harvesting in Nigeria being reasonably steady over time, especially, on intra-city roads. Availability of tricycles/motorcycles in abundance and frequent use of horn by motorists support this assertion. The noise levels and noise power from these sources obtained in this investigation are higher than those that have been used as input to acoustic energy harvesters (AEHs) such as piezoelectric based and triboelectric nanogenerators (TRENGs) to achieve known efficiencies as reported elsewhere.
 Conclusion: The noise power is such that it could be used in powering microelectronic components, devices and in lighting light emitting diodes (LEDs). Power supply (PS) audio noise harvesters (ANHs) have been identified as potential noise energy sources since there is wide range use of air-conditioned by the political class, elites and government agencies in Nigeria where maximum temperature of 47.2°C is attainable. These findings show the viability of AEH in Nigeria and their addition to the existing body of knowledge in the emerging area of AEH will open a new window of research in AEH in this part of the world. Other prospects of AEH in Nigeria, technical problems and socio-economic obstacles are highlighted.

HYGIENIC ASSESSMENT OF INTERVENTIONS FOR REDUCING EXCESSIVE ACOUSTIC IMPACT ON RESIDENTIAL AREAS

Introduction. The most important external sources of excessive noise levels on the territories of residential development are transportation sources (road, rail, aviation). The aim of the present study is the hygienic assessment of the acoustic situation in the areas in the zone of influence of traffic flows and currently used measures to reduce the excess acoustic impact on residential premises. Material and methods. The studies were carried out on the territories along the roads and Railways, with different intensity of traffic flows in accordance with GOST 23337-2014 Noise. Methods of noise measurement in residential areas and in the premises of residential and public buildings, MUK 4.3.2194-07 “Methods of noise measurement in residential areas and in the premises of residential and public buildings.” Experimental studies of materials used for the construction of acoustic screens were carried out. Here were investigated window units were used to reduce external noise in the house. Sound pressure levels in octave bands (dB) and sound levels (dBA) in the sound-measuring reverberation chamber were measured in accordance with GOST 27296-2012. Results. Exceeding the permissible equivalent noise levels at a distance from 2 to 7.5 m from the roadway of vehicles in the daytime reaches 25-32 dBA. Noise from railway transport at a distance of 25 m from the source in terms of the equivalent sound level for freight transport is of 77 dBA, maximum - 83 dBA; for cargo transport, Sapsan, Lastochka, Allegro identical data were obtained; for passenger trains, the equivalent sound level accounted for 71 dBA, for electric trains - 66-69 dBA. Exceeding the standards for octave frequencies were most often observed at low frequencies from 31.5 to 500 Hz. The air noise insulation index (dB) is higher for the concrete and wood chips material, i.e. the material with higher density. The study of the parameters of the window blocks allowed us to establish all the studied samples to provide a reduction in the equivalent noise level by more than 20 dBA, but differ in the spectral characteristics of noise damping. Conclusion. Traffic flows create excessive noise levels in urban and rural settlements and impair the quality of life of the population. The effectiveness of existing measures aimed to mitigating noise in the source of generation by both road and rail transport has been exhausted. Acoustic screens in high-rise buildings have very limited efficiency. An option to reduce the adverse impact of external noise on public health is the construction of buildings protected from noise. Placement of buildings along the linear objects of road and rail transport should be provided at the stage of planning of quarters, the construction of such buildings should be carried out on special projects. When designing and building, special attention should be paid to the window units used and the quality of their installation. Window blocks should be selected on the basis of frequency characteristics of noise attenuation.

A study of classroom acoustics: Verification of perception responses according to time-variant sound exposure

In educational contexts, learning processes focus on stimulation and development of students’ cognitive abilities, which, in turn, will improve their learning capacity. Cognition refers to the mental activity of the process and uses information in judgment. Based on that, this study investigates how acoustic perception responses can differ according to sound exposure inside a classroom for different time spans. To achieve this aim, students and lecturers were asked to answer a survey about classroom comfort, which included acoustic perception questions, at a controlled environment classroom from the Free University Bozen-Bolzano. Perception responses could be given at any moment of the lecture, but it was recommended to answer the survey after the lecture. Additionally, two data collection campaigns were considered for this investigation: (1) without absorbers and (2) with fake absorbers. Sound pressure levels in octave bands were collected using a microphone array during the lectures period. The post-treatment of this data consisted of calculating sound pressure level averages for two different time spans: the whole lecture period and for the moment which the participants answered the survey. Room acoustic measurements were carried out to characterize the environment on different scenarios.

Analysis of noise from reusable solid rocket motor firings

As part of investigations into the design of next-generation launch vehicles, near and far-field data were collected during horizontal static firings of reusable solid rocket motors. In addition to spectral analysis at individual microphone locations, the spatial variation of overall and one-third octave band pressure levels at sideline and polar arc arrays is considered. Analysis of the probability density functions reveals positively skewed pressure waveforms, but extreme skewness in the first-order estimate of the time derivative because of the presence of significant acoustic shocks.

Comparison of Simple Room Acoustic Models Used for Industrial Spaces

In order to select the most cost-effective noise control solution, the influence of the noise control measures on noise level should be reliably predicted. Reasonably accurate commercial ray-tracing, image source and finite element method modeling programs are available. However, the creation of a model and sometimes the calculations are time-consuming and their use in preliminary room acoustic design is not always cost-effective. These sophisticated room acoustic modeling programs demand special expertise which limits their use in practice. Several simple room acoustic models have been developed for noise control but information on their usability and prediction accuracy is rather hard to find. The purpose of this study was to examine simple room acoustic models developed for predicting noise levels and reverberation times in octave bands. Seven simple sound pressure level models, seven simple reverberation time models and a validated ray-tracing program (ODEON 3.1) were tested in four industrial workplaces, in which major noise control measures were implemented. The prediction results were compared to measurement results which were performed using an omni-directional sound source before and after the implementation of noise control measures. Accuracies of predicted sound pressure levels were determined as differences between measured and predicted sound pressure levels in octave bands of 125―4000 Hz. Accuracies of predicted reverberation times were similarly determined. The accuracy of the ray-tracing model was the most acceptable, as expected. The accuracy of simple sound pressure level models developed by Kuttruff, Osipov et al., and Thompson et al. was comparable to the accuracy of the ray-tracing models. The accuracy of the simple reverberation time model developed by Heerema and Hodgson was almost comparable to the accuracy of the ray-tracing model. The above-mentioned simple sound pressure level models provided sufficient accuracy for predicting average insertion loss, e.g. by using acoustic tiles or sound-absorbing materials. For more detailed or complex room acoustic design, sophisticated room acoustic modeling programs are recommended.

Levels And Spectra Of Aircraft Noise And People\'s Reactions In Some Nigerian Cities

A study of sound levels and spectral distribution as well as people\'s reactions to aircraft noise in three Nigerian international airports have been conducted. The study comprised physical measurements and social survey. Results show that maximum octave band pressure levels (BPLs) for Margaret Ekpo, Port Harcourt and Murtala Mohammed International Airports were 88 dB(A), 94 dB(A) and 99 dB(A), respectively with corresponding the deafening levels recorded as 102.5dB(A), 122.5 dB (A) and 123.5 dB(A). Maximum sound level (L) wasas high as 116 dB(A) in each case. The Day-night level (L), weighted equivalent continuous perceived noise level (WECPNL), noise and number index (NNI), noise exposure forecast (NEF), A-weighted sound level (L), and noise pollution level (L) were also obtained based on acoustical data generated at the airports under study, and were found to exceed the recommended doses of 55, 60, 20, 24, 45 and 60dB (A), respectively. From these results it is clear that octave band pressure levels exceed the recommended 85 dB(A). Octave band pressure levels obtained tend to be Gaussian and the spectra were flat. Percentage responses correlated well with NNI with power law relationships between it and the latter in all the cases considered. Results clearly show that people resident near Nigerian airports are exposed to psychological and physiological damage as a result of excessive aircraft noise with serious activity interference. Keywords: Noise levels, spectra, aircraft noise, damage risk and activity interference.Nigerian Journal of Physics Vol. 19 (2) 2007: pp. 223-227

Relationships between arithmetic averages of sound pressure level calculated in octave bands and Zwicker’s loudness level

Previously it has been found through a series of psychoacoustical experiments that the arithmetic average of sound pressure level calculated in octave bands is a good estimator of loudness for various kinds of environmental noise. Remarkably, the arithmetic average of sound pressure level in octave bands from 63 Hz to 4 kHz, L m,1/1 (63–4k), strongly correlates with the loudness level specified in ISO 532B, LL( Z), as well as with loudness assessment. To investigate this relationship further, a numerical study has been carried out based on Zwicker’s loudness model. As a result, practical expressions to estimate the loudness levels of general environmental noises from the sound pressure levels in octave bands from 63 Hz or 125 Hz to 4 kHz are proposed.

床衝撃音レベルの評価指標及び主観評価との対応に関する研究

We experimented rating of impact sound pressure level by hearing impression with floor impact sound including life sound. And we select the best evaluation index that has a high correlation in hearing impression. As the result, it is shown that maximum A-weighted impact sound pressure level LA,Fmax is better for heavy impact source than L-Number, and arithmetic average of sound pressure levels in octave bands L (63-4k) is better for light impact source than L-Number. Next, we examined the correspondence of LA, Fmax, L (63-4k) and hearing impression.

Validity of arithmetic average of sound pressure levels in octave bands as a loudness index.

In order to examine the method of estimating loudness on general noises in living en-vironments, two steps of subjective experiments were performed using artificial sounds. The results of Experiment 1 suggested that arithmetic average of sound pressure levels in octave bands is an appropriate loudness index for various kinds of sound with broad band spectra as well as the precise index such as the Loudness Level proposed by Zwicker. In order to further examine this fact, Experiment 2 was conducted using test sounds with discrete prominent spectral components. As a result, it has been clarified that the arithmetic average can no longer be applicable to such kinds of sound. In addition to these experimental studies, the relationships among representative noise indices were examined by numerical investigation on various sounds general in living environments. As a result, it has been confirmed that the arithmetic average of SPLs in octave bands from 125 Hz to 4kHz is highly correlated to Loudness Level by Zwicker for general sounds without tonal components.

Study of Sound Insulation of Control Cabins in Industry in the Low Frequency Range

The number of control cabins installed in industry has increased considerably during the last few years. Most cabins installed nowadays show a satisfactory noise reduction in the frequency range above 500 Hz. The effect of noise damping however shows a gradual decrease for lower frequencies. The present paper is a description of the distribution of low frequency noise in different types of control cabins installed in typical low frequency noise environments in steel plants and the machine building industry. Measurements were made in 20 control cabins, constructed of metal and stone Measurements of sound pressure levels in octave bands were made inside and outside the cabins. The sound pressure level in octave bands in the low frequency range (4–31.5 Hz) inside the cabins was high and varied between 60–108 dB. This is probably due to the insufficient noise reduction for lower frequencies. In some control cabins there was an increased level of low frequency noise inside the cabin compared to the outside. In these control cabins sound pressure levels exceed the admissible values according to Polish standards. The increase of noise level within the low frequency range is considered to be based on resonances.

Subjective assessment of indoor noises—Basic experiments with artificial sounds

To investigate appropriate measures for assessing loudness of various noises in buildings, two kinds of psycho-acoustical experiments were conducted. In these experiments, noises which have dominant spectral components in the low frequency range were electronically synthesized and loudness-matching tests were performed in an anechoic room using loudspeaker sources. As a result of these tests, it has been reconfirmed that the precise noise measurements, like the Loudness Levels proposed by Zwicker and Stevens, are valid. In addition, it has been found that the arithmetic mean value of sound pressure levels in octave bands is also a good measure for loudness estimation of low frequency noises. Regarding the evaluation of sound insulation efficiency of building walls, various assessment measures were compared and it has been suggested that the arithmetic mean value of sound insulation indices in octave bands is an appropriate single-number index from the psycho-acoustical viewpoint.

Loudness evaluation of sounds transmitted through walls—basic experiment with artificial sounds

A basic psycho-acoustic experiment was performed in order to establish a reliable method for evaluating insulation properties of building walls against airborne sound. Eleven models were used to represent actual sound insulation characteristics and three models used for incident noises on walls. Results of a four-step hearing test were arranged according to five well-known measures for noise assessment, and Perceived Level ( PL) was found to be the best among them for assessing the loudness of the sound transmitted through walls. In addition, arithmetic mean values of the sound pressure levels in octave bands from 63 Hz or 125 Hz to 4 kHz were examined. It was found that such simple measures have an unexpectedly high correlation with the loudness, surpassing even the PL. This suggests that the arithmetic mean value of the sound transmission losses in octave bands is a good single-number measure for rating the airborne sound insulation performance of walls.

A comparison of the noise environment in open‐plan and traditional single family dwellings

The noise environment within two single family dwellings was investigated using a sound power source and sound level meter. The dwellings have three levels and are roughly the same size. One of the dwellings is an open‐plan design, both within and between levels, and the other is a traditional multilevel design. Both dwellings are representative of common residential construction and neither incorporate special noise control features. Octave band pressure levels from 125 Hz to 8 kHz were measured at eight locations in each dwelling for each of three source locations. Average NC values in living areas of the traditional dwelling were found to be 7 dB less than in the open‐plan dwelling. In bedroom areas, the average NC values were more than 20 dB lower in the conventional dwelling. These results are in good agreement with those of a previous study [D. K. Holger and M. S. Pickett, J. Acoust. Soc. Am. Suppl. 1 72, S91 (1982)] which concluded that boundary absorption is very important in open‐plan residential design. [Work supported by the Engineering Research Institute.]

Noise Produced on the Ground by Jet Aircraft in Flight

Several types of jet aircraft with one and two engines were flown at specified altitudes and subsonic speeds directly over a recording microphone on the ground, and continuous recordings of the noise were made. The ranges of altitudes, speeds, and engine operating conditions included those normally used by jet aircraft operating within a few miles of air bases. From the recordings, sound pressure levels in octave bands of frequency were determined as a function of time. Typical results are presented, and comparisons are made between measurements of the noise generated by aircraft running up on the ground and by the same aircraft in flight. The effects of aircraft speed and altitude on the sound pressure levels and on the time patterns and spectra of the noise are evaluated, and some interpretation of the data is given. [This work was supported by the U. S. Air Force.]

A Survey of Noise Environments in Industry

A survey has been made of steady-state noise in various manufacturing industries. Pressure levels in octave bands and corresponding loudness values are classified according to type of industry. Measurements are further sub-divided into “machine levels” taken close to the principal noise sources, and “area levels” taken at greater distances where a larger number of workers is affected. In the noisiest industries about 50 percent of the machine levels were between 95 and 115 db with a loudness between 50 and 500 sones. The area levels in some of the quiet industries were between 77 and 81 db with a loudness around eight to ten sones. A correlation between over-all level and total loudness indicated a range of about 9 db for noises of different character having the same total loudness. The noise spectra of several typical machines will be presented also. Median, quartile, and extreme values are used to specify the range of values encountered.