Loudness Summation and Weightings for Loudness and Environmental Noise Assessment

A stationary loudness model has been built up on the basis of the former ISO 226: 1987 concerning equal-loudness-level contours. The loudness and loudness level expressions derived in the study include the same parameters as used when determining the equal-loudness-level contours of the former ISO standard. However, as an additional main idea, a loudness summation rule has been proposed in the study. Moreover, the loudness expressions have been normalised to give the same values for people who have a similar sense of hearing. It has also been found that the loudness expressions include basically two different weightings. The first weighting is a conservative frequency weighting in the domain of sound pressure level, and the second weighting consists of coefficients applied to the weighted sound pressure levels. The latter have the greatest effect on the very low-frequency range. Finally, the paper includes a new way to use the A-weighting which takes into account the compressed character of the equal-loudness-level contours at the low frequency range. This method remarkably transforms the character of the A-weighting as a measure for low-frequency environmental noise.

Improved Methods for In-situ Measurement Railway Noise Barrier Insertion Loss

Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments.However,there are no universally acknowledged receiver positions for the evaluation of the barrier performance,a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers.In terms of the descriptor of the barrier performance,the general recommendation is the A-weighted sound pressure level,although the latter is considered to underestimate low frequencies for railway noise barrier.Thus,in this study,the comparison of receiver positions and the descriptors among existing Chinese,ISO and European standards were investigated.Based upon a combination of diffraction theory and standards,a rearrangement of receiver positions and one-third-octave-band analysis were proposed.In addition,in line with improved methods,an in-situ measurement of insertion loss for a 1.5 mhigh railway noise barrier was designed and conducted.The results of the experiment validate as effective and applicable the new receiver positions.These results also suggest that one-third-octave-band analysis is indispensable.

A Survey of Noise Pollution in Ado-Ekiti Metropolis Using Mobile Phone

Noise is considered as the most pervasive pollutant, it constitutes the most disturbing among the city pollutants and is a serious urban crisis in Ado Ekiti metropolis. Noise pollution was monitored at five different locations in Ado-Ekiti, the capital town of Ekiti State of Nigeria. The study was done using a Virtual Instrument;a Sound Pressure Level mobile application installed on a mobile phone. The equivalent noise level using A-weighting was taken every fifteen minutes in each location between 6:00 am and 9:00 pm and the LAeq,T of each location was calculated. Maximum LAeq,6h of 105.40 dB was obtained in marketplace between 6:00 am and 12:00 pm while the minimum value of LAeq,6h obtained for a residential area in the same period is 69.51 dBA. The residents are exposed to average noise levels of 75 - 98 dB (A) or more every day which is higher than the recommended value of 60 dBA by WHO. This is very dangerous to the health of the people in these areas, and the results obtained in this study are useful as reference and guideline for future regulations on noise limit to be implemented for urban areas in Nigeria.

Interpreting Dose-Response Relation for Exposure to Multiple Sound Impulses in the Framework of Immunity

Hearing loss is a common military health problem and it is closely related to exposures to impulse noises from blast explosions and weapon firings. In a study based on test data of chinchillas and scaled to humans (Military Medicine, 181: 59-69), an empirical injury model was constructed for exposure to multiple sound impulses of equal intensity. Building upon the empirical injury model, we conduct a mathematical study of the hearing loss injury caused by multiple impulses of non-uniform intensities. We adopt the theoretical framework of viewing individual sound exposures as separate injury causing events, and in that framework, we examine synergy for causing injury (fatigue) or negative synergy (immunity) or independence among a sequence of doses. Starting with the empirical logistic dose-response relation and the empirical dose combination rule, we show that for causing injury, a sequence of sound exposure events are not independent of each other. The phenomenological effect of a preceding event on the subsequent event is always immunity. We extend the empirical dose combination rule, which is applicable only in the case of homogeneous impulses of equal intensity, to accommodate the general case of multiple heterogeneous sound exposures with non-uniform intensities. In addition to studying and extending the empirical dose combination rule, we also explore the dose combination rule for the hypothetical case of independent events, and compare it with the empirical one. We measure the effect of immunity quantitatively using the immunity factor defined as the percentage of decrease in injury probability attributed to the sound exposure in the preceding event. Our main findings on the immunity factor are: 1) the immunity factor is primarily a function of the difference in SELA (A- weighted sound exposure level) between the two sound exposure events;it is virtually independent of the magnitude of the two SELA values as long as the difference is fixed;2) the immunity factor increases monotonically from 0 to 100% as the first dose is varied from being significantly below the second dose, to being moderately above the second dose. The extended dose-response formulation developed in this study provides a theoretical framework for assessing the injury risk in realistic situations.

Urban Noise in a Metropolitan Towns

This study is aimed at bringing out the salient aspects of urban noise and its study and control aspects, at different location of a metropolitans town. Field measurements at different points of times a day have also been recorded at a number of high-traffic-intensity locations on main roads of towns. The data obtained are analyzed using SPSS package for calculation through ANOVA technique and the findings of these studies have been recorded. The variation of SPL considering the time of the day has been studied and illustrated through graphical plots. It shows that the peak early morning max sound pressure levels observed over the recommended limiting value. In some places, the low frequency noise predominates in the early morning hours, noise levels are significant among and within the 15 groups. The variation of sound pressure (Maximum, Minimum and L equivalent readings) levels as shown in the graphical plots, the Maximum and L equivalent levels exceeded the recommended noise level. Important conclusions of this work have been drawn subsequently.

Analysis of Road Traffic Noise Pollution around a University in Binzhou

The number of automobiles in the urban area of Binzhou City continues to increase,and traffic noise pollution is increasingly serious. In this study,noise pollution on Huanghe 5 Road near the south gate of Binzhou University was monitored. The results showed that the road noise pollution on Huanghe 5 Road was relatively serious on the whole,especially in the peak periods of traffic flow in the morning and afternoon,because the increase in the number of pedestrians brought inconvenience to traffic,thereby resulting in an increase in car whistle.