共查询到20条相似文献,搜索用时 15 毫秒
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Dae Seung Cho 《Applied Acoustics》2008,69(3):185-195
This paper presents a new and efficient method to determine sound power levels (PWLs). PWLs, generally used for modeling outdoor sound simulations, are obtained from sounds that are emitted by various types of vehicles and cause road traffic noise. Other models, such as HARMONOISE and the ASJ Model, are also based on PWLs. However, a more efficient method is required for determining PWLs from sound pressure levels (SPLs) that typically are measured by field testing and evaluating the influence of different vehicles and road surfaces. The statistical pass-by (SPB) of ISO 11819-1 is used for SPL measurements; however, numerous SPBs must be carried out to reduce measurement uncertainty as well as to satisfy requirements related to meteorological conditions and background noise. In order to alleviate this problem and to make the determination of PWLS more efficient, a testing approach is presented that uses both the novel close proximity (NCPX) method and the pass-by method to determine PWLs. 相似文献
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Dae Seung Cho 《Applied Acoustics》2008,69(11):1120-1128
A highway traffic noise prediction model has been developed for environmental assessment in South Korea. The model is based on an outdoor sound propagation method and is fully compliant with ISO 9613 and the sound power level (PWL) estimation for a road segment, as suggested in the ASJ Model-1998 that is based on PWLs. Due to that model’s selection of two pavement types, such as asphalt or concrete pavement, an unacceptable traffic noise prediction is made in cases where the road surface is different from that on which the model is based. In order to address this problem, several road surface types are categorized, and the PWL of each surface type is determined and modeled by measuring the noise levels obtained from newly developed methods. An evaluation of the traffic noise prediction model using field measurements finds good agreement between predicted and measured noise levels. 相似文献
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The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise. 相似文献
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A detailed experimental study has been conducted to determine the effect of adding hollow ceramic-micro balloons, also known as cenospheres, on the acoustic properties of cement matrix and asphalt concrete. The motivation for this study was to explore the feasibility of using cenospheres in developing lightweight sound absorbing structural materials. Cement and asphalt concrete specimens with different volume fractions of cenospheres and varying diameter and thickness were tested to determine their acoustic characteristics over the range of frequencies (0-4000 Hz). Experimental results showed that a 40% volume fraction addition of cenospheres to cement matrix increased the Noise Reduction Coefficient by 100%. In contrast to cenosphere rich cement, the sound absorption coefficient of asphalt concrete decreased with an increase of cenosphere, volume fraction. 相似文献
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Maria Sdersten PhD Svante Granqvist Britta Hammarberg Annika Szabo 《Journal of voice》2002,16(3):356-371
Preschool teachers are at risk for developing voice problems such as vocal fatigue and vocal nodules. The purpose of this report was to study preschool teachers' voice use during work. Ten healthy female preschool teachers working at daycare centers (DCC) served as subjects. A binaural recording technique was used. Two microphones were placed on both sides of the subject's head, at equal distance from the mouth, and a portable DAT recorder was attached to the subject's waist. Recordings were made of a standard reading passage before work (baseline) and of spontaneous speech during work. The recording technique allowed separate analyses of the level of the background noise, and of the subjects' voice sound pressure level, mean fundamental frequency, and total phonation time. Among the results, mean background noise level for the ten DCCs was 76.1 dBA (range 73.0-78.2), which is more than 20 dB higher than what is recommended where speech communication is important (50-55 dBA). The subjects spoke on an average of 9.1 dB louder (p < 0.0001), and with higher mean fundamental frequency (247 Hz) during work as compared to the baseline (202 Hz) (p < 0.0001). Mean phonation time for the group was 17%, which was considered high. It was concluded that preschool teachers do have a highly vocally demanding profession. Important steps to reduce the vocal loading for this occupation would be to decrease the background noise levels and include pauses so that preschool teachers can rest their voices. 相似文献
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Integrated noise model (INM) is the most internationally used software to calculate noise levels near airports. Take off, landing or pass by operations can be modeled by INM, but it does not consider aircrafts taxiing, which, in some cases, can be important to accurately evaluate and reduce airports’ noise assessment.Aircraft taxiing noise emission can be predicted using other prediction tools based on standards that describe sound attenuation during propagation outdoors. But these tools require data inputs that are not known: directivity and sound power levels emitted by aircraft during taxiing.This paper describes methods used to calculate directivity indexes and sound power levels, based on field measurements made in Madrid-Barajas Airport (Spain). Obtained results can be used as inputs for general purpose outdoor sound prediction software, which will be able to evaluate noise at airports vicinity as industrial noise.Directivity and sound power levels have been estimated in octave and third octave band terms, for several aircraft families. 相似文献
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During ultrasound-induced cavitation in liquids, acoustic emissions at fundamental and harmonic frequencies can be detected. The effect of acoustic emissions at harmonic frequencies on the sonochemical and sonophysical activities has not been explored, especially in large-scale sonoreactors. In this study, the acoustic emissions in the range, 0-250 kHz in a 36 kHz sonoreactor with varying liquid heights were studied and compared with the sonochemical activities. The acoustic pressures at both fundamental and harmonics decreased drastically as the liquid height was increased due to the attenuation of sound energy. It was observed that the increase in input power resulted in only an increase in the acoustic emissions at derivative frequencies such as, harmonics and subharmonics. The sonochemical activity, evaluated in terms of sonochemiluminescence and H2O2 yield, was not significantly enhanced at higher input power levels. This suggests that at higher power levels, the “extra” acoustic energy is not effectively used to generate primary cavitation activity; rather it is converted to generate acoustic emissions at harmonic and subharmonic frequencies. This is an important observation for the design of energy efficiency large-scale sonochemical reactors. 相似文献
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Dae Seung Cho 《Applied Acoustics》2008,69(9):833-843
The effects of vehicles and pavement surface types on noise have been investigated at the Korea Highway Corporation’s Test Road along the southbound side of the Jungbu Inland Expressway, South Korea. The study was conducted in 2005 and 2006 through field measurements at nine surface sections of asphalt concrete and Portland cement concrete pavements using eleven vehicles. For the road noise analysis, the sound power levels (PWLs) of combined noise (e.g., tire/pavement interaction noise and power-train noise together) and tire/pavement interaction noise using various vehicles were calculated based on the novel close proximity (NCPX) and pass-by methods. Then, the characteristics of the PWLs were evaluated according to surface type, vehicle type, and vehicle speed. The results show that the PWLs of vehicles are diversely affected by vehicle speed and the condition of the road surface. 相似文献
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The phased beam tracing method (PBTM) was suggested as a medium-frequency simulation technique for the calculation of impulse response, although main assumptions of geometric acoustics still hold. The phased method needs the reflection coefficient for characterizing the acoustic property of a surface and the complex wave number for describing the propagation characteristics. In this study, two types of approximate real reflection coefficients derived from the measured absorption coefficient were tested for a practical applicability. As a test example, pressure impulse responses and energy impulse responses computed from the PBTM were compared with those from the measurement and the ordinary beam tracing method. The PBTM employing the approximate reflection coefficients greatly increased the accuracy of the prediction compared to the ordinary beam tracing method, in particular at the medium-frequency range in octave bands above the Schroeder cutoff frequency. A comparison was made between angle-dependent and angle-independent reflection coefficients in the calculation of acoustic measures. Although the angle-dependent reflection coefficient yielded best matched results with measured data, but the simple angle-independent reflection coefficient can be also used with a reasonably good precision. 相似文献
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A.A. Al-Ghamdi Shamshad A. Khan A. Nagat M.S. Abd El-Sadek 《Optics & Laser Technology》2010,42(8):1181-1186
From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10−6 Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index (n) and extinction coefficient (k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size. 相似文献
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The impact of shipping noise on marine life and quality of marine mammal habitats in oceans and coastal environments has become a major concern worldwide. Background noise can also limits detection of marine mammal sounds in passive acoustic monitoring (PAM) systems. Characterisation of this noise over long time periods and estimates of the exposure of the different marine mammal groups are still very fragmentary and limited to only a few locations. This paper presents such observations for a part of a busy seaway of North America, the St. Lawrence Seaway, which cuts through the Gulf of St. Lawrence and crosses several cetaceans and pinnipeds feeding areas. Noise was continuously recorded for a 5-month period in summer 2005 by an AURAL autonomous hydrophone deployed close to the bottom in the 300-m deep seaway. The maximum received noise level in the 20 Hz-0.9 kHz band reached 136 dB re 1 μParms. The median level of 112 dB re 1 μParms was exceeded 50% of the time due to transiting merchant ships. Median spectral level tracks the reference curve for heavy traffic in oceans and 50% of the noise is within a ±6 dB envelope around it. Strong spectral lines were common at low frequencies and in the 400-800 Hz band. M-weighting functions applied for the three groups of cetaceans and pinnipeds indicate wideband median levels varying from 106 to 112 dB-M re 1 μParms surrounded by a ±5 dB two-quartile interval. Higher values are expected for animals frequenting the sound channel at intermediate depths. As expected, the highest M-weighting levels correspond to low-frequency specialists and pinnipeds. Criteria for assessing the behavioural and physiological impacts of long term exposure of marine mammals to such shipping noise levels need to be worked out. 相似文献
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The fundamental frequency (F0) for the habitual pitch (F0HAB), F0 for the lowest physiological tone (F0L), F0 for the highest physiological tone (F0H), F0 range of phonation (F0 Rg), sound pressure level (SPL) for habitual loudness (SPLHAB), SPL for the softest tone (SPLS), SPL for the loudest tone (SPLL), and SPL range of phonation (SPL Rg) were measured in 40 normal adult subjects and 1,563 voice patients with varying diseases. F0H, F0 Rg, SPLL, and SPL Rg were decreased in many disease groups. F0HAB and F0L varied. SPLHAB and SPLS were increased in some disease groups. F0-related parameters reflected effects of treatments in the cases with polyp, Reinke's edema, epithelial hyperplasia, carcinoma, and paralysis. Effects of treatments were manifested in SPL-related parameters in the cases with nodule, polyp, carcinoma, and paralysis. 相似文献
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This paper presents an evaluation method for measuring the sound pressure level and mode shapes of tire cavity resonance by using a multi-microphone system. Two commercial tires were evaluated to compare abilities of noise suppression by means of this method in the range of the first resonance from 200 to 260 Hz. One tire was a special tire that suppresses tire cavity resonance with polyurethane foam mounted on the tire’s inner liner. The other tire was a normal tire with no polyurethane foam. The mode shape change from vertical to horizontal direction in both tires. However, the sound pressure level of the special tire was lower than the normal tire at all frequencies. 相似文献
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Acoustic and aerodynamic design and characterization of a small-scale aeroacoustic wind tunnel 总被引:1,自引:0,他引:1
The aeroacoustic wind tunnel at Brandenburg University of Technology at Cottbus is a newly commissioned research facility for the experimental study of sound generation from bodies immersed in a fluid flow. The paper discusses the design criteria for the open jet wind tunnel that provides a maximum wind speed of 72 m/s at continuous operation and may be operated with nozzles of different dimension between 35 cm diameter (circular nozzle) and 12 cm by 14.7 cm (rectangular nozzle). Experiments may be performed either in a reverberant or in an anechoic environment. Both the aerodynamic and the acoustic design of the wind tunnel components are discussed in detail. Background noise measurements in the completed facility revealed very low levels comparable to other wind tunnels. The results of aerodynamic wind tunnel calibration confirmed a uniform flow quality in the jet and a very low axial turbulence intensity which is less than 0.2% for the 35 cm nozzle and less than 0.1% for the other nozzles. A final benchmark is provided by results of successful trailing edge noise measurements on an SD7003 airfoil that are presented and compared to results from the literature. 相似文献