Sound Level Distribution Research Articles

Sound level distribution and scatter in proportionate spaces

Measurements have been conducted in two scale models of proportionate spaces each containing measures to promote a diffuse sound field. Contrary to classical statistical theory, it was found that reflected sound levels decrease with the distance from the source. Measured levels follow behavior predicted by a revised theory previously proposed for concert halls. The scatter of the measured reflected sound levels is shown consistently to exceed values predicted by Lubman/Schroeder’s theory. However, it is demonstrated that this theory does accurately predict scatter of late sound levels when the early reflections are omitted. Investigation into the scatter of reverberation times shows that it is generally well predicted by Davy’s theory.

Passive acoustic localization for Sciaenid habitat in coastal water of Taiwan

There are many Sciaenid species found in coastal water of Taiwan, and most of them can generate sound in the spawning season. However, due to overfishing, the populations of these high economic value fishes have been greatly decreased. To study and protect Sciaenid, whose habitat should be identified, seasonal protection zones should be set up. In this study, easy and low-cost measure of using passive sonar is proposed to map the habitat in the field. Measurement and analysis of Sciaenid sound were performed to investigate its acoustic characteristic, and frequency range was found to be 350 to 1500 Hz. The statistical distribution of sound levels can be built up by enough field measurement; therefore source levels can be defined in this method. In addition, the transmission loss of in-site shallow water was studied to compute the real decaying factor (TL=n*log<th>R) of the survey site. By using three sonobuoys, with known source level distribution and transmission loss, the distance of possible habitat can then be inverted. Through enough measurements, the map of coastal habitat of Sciaenid can be generated with efficiency and accuracy.

Statistical Study of the Instantaneous Values of Traffic Noise Sound Pressure Level

In environmental acoustics the knowledge of the time dependency of the sound level provides relevant information about a sound event. In this sense, it may be said that conventional sound level metres have frequently implemented programs to calculate the fractiles (percentiles) of the distribution of instantaneous sound levels; and there are several indexes to evaluate the noise pollution, based on different statistical parameters. For further analysis of sound, and to obtain the commented indexes, it is accepted that this distribution is normal or gaussian. The questions we've tried to solve in this work are the following: First of all, whether the time dependent distribution of the variable sound pressure level should be considered as Gaussian in general cases or only in some particular ones. On the other hand, we have studied how the frequency of the sampling affects the resulting distribution of a given a sound event. To these ends, a set of road traffic noise events has been evaluated. Furthermore, even in gaussian distributions of sound pressure levels, the average of the distribution will not be coincident with the equivalent sound pressure level; that is the level of the average quadratic pressure. The difference between this parameter, and its dependence on the standard deviation, is studied.

Sound level distributions on a circular ground board for wind turbine noise measurements

Sound level distributions on a circular ground board for wind turbine noise measurements

Sound levels forecasting for city-centers Part IV. Vehicles stream parameters influence on sound level distribution within a canyon street

To control an environmental noise the simulation programs are the best tools. Especially when efficiency of administration means such as introduction of limits of vehicles speed and heavy vehicles rate flows are evaluated. Here is used the computer simulation program PROP5 that allows predicting the time-average sound level within an urban system. A roadway as a noise source is represented by a sum of the sound exposures due to individual vehicles pass-by. The multi-lanes roadway and different representations of equivalent point sources for various classes of vehicles are allowed. Propagation throughout an urban system contains multi-reflections from the walls and single and double diffraction at their wedges. In the paper, the PROP5 program is used to present the sound level along façades of buildings creating a canyon street. The road of J lanes passed by two classes of vehicles: light and heavy ones is assumed. The consequence of a change in vehicle average speed treated as an independent parameter is analyzed. The vehicles speeds straight affect the sound level and by speed dependence of the equivalent sources power levels and spectra. Indirectly the change in vehicle speed limit can affect the vehicle flow rate by the interrelations of traffic. By use of calculation examples, the range of possible changes in the sound level is presented.

Neural network predictions of speech levels in university classrooms

At the schematic design stage of a classroom there is a need for an expeditious and accurate method of predicting the distribution of sound levels (speech levels). The objective of this work is to investigate the possibility of developing a method of predicting the sound propagation (SP) in university classrooms, using artificial neural networks. Constructional and acoustical data for 34 randomly chosen unoccupied University of British Columbia (UBC) classrooms were used for the neural network analyses. One source position, both directional and omnidirectional sources, and a number of listener positions were chosen in each classroom making a combination of 182 cases available to train the neural networks. Assessments have been made of the method by comparing the predicted sound propagation obtained using neural networks with measured values, with predictions made using Barron's revised theory and the Hopkins–Stryker equation. The results indicate that there is a good basis for using trained neural networks to predict the distribution of sound levels in empty classrooms. The results also indicate that neural networks trained with variables which have a causal relationship to the acoustical quality of the UBC classrooms produce reliable and accurate predictions. RMS errors for Sound Propagation, in each of the frequency bands, are within the subjective difference limen for steady-state sound pressure levels, which is about 1dB (i.e. ΔE E=0.26 where E is energy density).

Sound levels forecasting for city-centers Part III: a road lane structure influence on sound level within urban canyon

The computer simulation program PROP5 for prediction of the time-average sound level within an urban system has been exploited to analyze the sound level distribution in an urban canyon. The results obtained are presented in the series of papers (Walerian E, Janczur R. Sound levels forecasting for city-centers. Part I: Sound level due to a road within urban canyon. Applied Accoustics 62(4):359–80; Walerian E, Janczur R. Sound levels forecasting for city-centers. Part II: Effect of source model parameters on sound level in built-up area. Applied Acoustics 62(5):461–92; Janczur R, Walerian E, Czechowicz M. Sound levels forecasting for city-centers. Part IV: Vehicles stream parameters influence on a sound level distribution within canyon street. Applied Acoustics, in press) and the current paper is one of them. A roadway in the PROP5 program is modeled as a sum of individual vehicle drives-by. The multi-lanes roadway and different representations of sources for various classes of vehicles are allowed. During propagation, a wave interacting with obstacles undergoes multi-reflections from their walls and single and double diffraction at their wedges. In the paper, the same equivalent point source is used to represent all the vehicles and the same vehicle stream at each lane resulting in the equal vehicles' spacing is assumed. The PROP5 program is used to present the sound level distribution along building facades creating a canyon street and the sound level value at the ground floor as a function of a canyon width, road lane number, and the outer lane distance to a building facade.

Sound levels forecasting for city-centers Part II: effect of source model parameters on sound level in built-up area

To control an environmental noise the simulation programs are the best tools. The computer simulation program PROP5, that allows predicting the time-average sound level within an urban system, contains road traffic as noise source. In the applied source model a road is represented by a sum of the sound exposures due to individual vehicle drive-by. The PROP5 allows the multi-lanes road and different representations of equivalent sources for various classes of vehicles. Propagation throughout an urban system takes into account multi-reflections from the walls and single and double diffraction at their wedges. The series of four papers devoted to sound level forecasting in city-center is presented. In the first, propagation within a canyon street is dealt with. The next three have shown how the accuracy of a road modeling affects the sound level distribution. In the second one here presented, the sound level distribution resulting from the different road models interactions with diffracting elements in the propagation space has been analyzed. In the paper, how the way, in which the sound exposure of a vehicle pass-by is calculated, affects the value of the sound level is investigated. As any object in sound field results in screening, the source parameters’ influence on the screening efficiency is presented. Appearing diffraction phenomenon is defined by the source power spectrum and its position in relation to diffracting wedge. Thus, the variation of these two parameters in the source model would be substantial for screening efficiency of occasional and planned screens in an urban system. The differences in the screening efficiency of urban elements caused by different way of a road modeling are presented. First, a road is represented by a stream of equal equivalent point sources placed at a road axis. Secondly, by two streams of vehicles, each one containing different equivalent point sources for light and heavy vehicles.

Sound level forecasting for city-centers. Part 1: sound level due to a road within an urban canyon

The computer simulation program PROP5 for prediction of the time-average sound level within an urban system has been exploited. The program contains the equivalent road model and the propagation model. A roadway modeled as a sum of individual vehicles drives-by previously investigated has been applied. The multi-lane roadway and different representations of sources for various classes of vehicles are allowed. During propagation, a wave interacting with obstacles undergoes multi-reflections from their walls and single and double diffraction at their wedges. In the paper, the PROP5 program is used to calculate sound level distribution in an urban system forming a canyon. The different degrees of accuracy in the urban canyon modeling have been tested.

A Time Distribution of Equivalent Sound Level and Percentile Level (L50) in Residential Area

A Time Distribution of Equivalent Sound Level and Percentile Level (L50) in Residential Area

Audible noise of transmission lines caused by the corona effect: Analysis, modelling, prediction

The paper presents the results of investigations of audible noise of high voltage transmission lines of alternating current (a.c. UHV) caused by the corona effect. The investigation results concern the 400 kV lines in two basic layouts existing in Poland: single horizontal and double vertical. Environmental investigations in real conditions were executed in a whole year cycle with the short-term method. Apart from the results of the environmental investigations the paper contains also the laboratory investigation results. The influence of constructional design and environmental parameters on the sound level distribution along a span was analysed. The influence of the conductor surface state and weather conditions on the level and shape of the emitted audible noise spectrum was particularly taken into account. The evaluation of the influence of the line audible noise on the acoustic climate of the environment was carried out. The analysis of possibilities of the application of well known computational procedures to the prediction of the line audible noise caused by the corona effect in Polish conditions was executed and an original form of a line acoustic model with the audible noise prediction possibility as a function of rainfall was presented.

Objective measures of listener envelopment

This paper reports the results of subjective studies to determine objective predictors of perceived listener envelopment in concert halls. Subjects, seated in an anechoic room, were exposed to simulated sound fields that were expected to have varied listener envelopment. As independent variables: the reverberation time, the early-to-late sound ratio, the overall sound level, and the angular distribution of the late-arriving sound levels were varied. All of these factors had statistically significant effects on perceived listener envelopment. The results indicate, however, that the angular distribution of the late arriving sound and the overall level would have the largest effects in real concert halls. Thus listener envelopment depends on having strong lateral reflections arriving at the listener 80 ms or more after the direct sound. Several objective measures correlated significantly with listener envelopment. However, a new measure, the late lateral sound level, as measured using a figure-of-eight microphone, was found to be both conceptually simple and a very good predictor of the perceived listener envelopment of the sound fields in this experiment.

Nonoccupational noise exposures and estimated daily Leq values for attendance at college basketball games and shopping centers

Noise exposure data were collected during 1988–1989 home basketball games at North Carolina State University. Thirteen exposure samples averaging 2 h in duration were collected utilizing Larson–Davis 700 noise dosimeters. Measured noise level results were as follows: average unweighted peak pressure was 133.1 dB, average maximum sound level (LA) was 115.2 dB, and average LAeq2 h was 97.1 dBA. The equivalent 40-h exposure level LAeq40 h was 84 dBA. As another example of nonoccupational noise exposure, between 1982 and 1994 seven shopping malls in four different cities were visited to establish the sound level distributions. Over 800 noise level samples were obtained. When the data were restricted to malls with at least 500 000 sq ft, it was determined that measured noise levels LA could be approximated utilizing the following equations (where N is the number of shoppers within a radius of 7.6 m of the measurement location): LA=61+10 log(N0.55), for N≤10, and LA=54+10 log(N1.20), for N≳10.

Nonoccupational noise exposures and their estimated daily L (eqs.) for general commercial air travel and local bars, restaurants, discos, and socialization establishments

Over a period of several years the authors have collected noise exposure data (N≳150 samples) during normal commercial air travel. The data were collected utilizing noise dosimeters, and an octave-band analyzer. The resulting noise exposures for air passengers will be presented, including the distribution of the measured A-weighted sound pressure levels. In addition, as part of regular class assignments, the students of the first author’s Effects Of Noise And Vibration graduate class have collected sound exposure data over several years at popular bars, restaurants, discos, and socialization establishments in the Raleigh, NC area. The noise exposures and sound level distributions from these surveys will also be presented.

Distribution of sound levels for consonants and vowels within individual frequency bands

While it has been long known that vowels are, in general, more intense than consonants in naturally spoken speech, this statement is based upon the overall sound levels of the phonemes. The purpose of the present study was to determine the sound levels of consonants and vowels within individual frequency bands, with potential application to the provision of consonant audibility to hearing-impaired patients via amplification. The NST speech materials were digitized and subjected to 1/3 octave-band analysis in contiguous 23-ms samples. The samples were then classified as vowels or consonants, based upon waveform and spectral analysis. A large majority of the samples were vowels, reflecting their greater duration. The long-term consonant spectrum was flat, in contrast to the more familiar low-pass shape of the traditional speech spectrum. In the higher-frequency bands, consonant levels were in many cases more intense than the vowels. [Work supported by NIDCD Grant No. 00377.]

Model study of sound propagation over ground of finite impedance

Experimental results are presented for the sound level distribution at different distances from the source when the sound waves propagate over ground with finite impedance. The measurements have been carried out in an anechoic chamber using a point source and using materials that can be used to model both reflecting and absorbing surfaces. The results from the measurements are compared with the theoretically calculated ones. The latter are obtained making use of a one-parameter ground model to allow for the presence of the finite impedance of the ground.

Noise radiation of (rectangular) plane sources

In this paper an analytical equation of the sound level distribution caused by a rectangular noise source is derived. It is assumed that the area elements of the noise source radiate the sound incoherently as point sources with (cosine) radiation characteristics. Hence the whole rectangular noise source has (more or less) cosine radiation characteristics. Analytical equations are used to calculate the sound level distribution in a chosen receiver area, for example perpendicular and parallel to the noise radiating area. The sound level reduction per doubling of the distance for a rectangular noise source parallel to the receiver area is found to be constant. The analytical equations are used to calculate the noise level produced by industrial sound sources in planes which are perpendicular and parallel to the noise radiating area. Scale model measurements of the sound level outside a continuous line of open windows are compared with calculations based on the derived equations.

Acoustic Conditions for Speech Communication in Classrooms

The purpose of this study was to measure reverberation times, background noise levels and Rapid Speech Transmission Index (RASTI) values in occupied and in unoccupied classrooms. Probability distributions of sound levels were also measured during classroom instruction. The reverberation time was measured according to the ISO 3382-1975 standard and RASTI according to IEC 268-16. In one-third of the classrooms the reverberation times were found to be longer than 0.9 s. at one or more frequencies ranging from 250 to 2,000 Hz. In most of the unoccupied classrooms, the background noise level was 35 dB(A) or less. During classroom instruction the background noise levels (L90) were high, ranging from 40 to 58 dB(A). The equivalent continuous sound levels (LAeq) were also high, from 58 to 79 dB(A), indicating that teachers increase their vocal effort while speaking. Most classrooms had RASTI values that reflected fair intelligibility, but very few classrooms had RASTI values indicating excellent intelligibility. The acoustic design of classrooms should be based on achieving the highest possible degree of speech intelligibility for all the pupils.

Determination of vehicle noise source levels

In 1974 the Florida Department of Transportation participated in a study sponsored by the Federal Highway Administration to determine vehicle source levels. This paper reports the findings of a second study designed to extend the range of the operating speeds of the vehicles in question down to 20 mph (32 kph). A total of 11 sites were included in the study with vehicles operating between 20 to 61 mph. The subsequent data were analyzed to provide distributions of maximum passby sound levels and reference energy mean emission levels as a function of speed for automobiles, medium trucks, and heavy trucks. The data were analyzed over the entire speed range and on the basis of 5 mph speed band to provide empirical relations for use in predictive models. Of particular interest was the extent to which the choice of these formats influenced the noise source relationships and, of more significance, the extent to which the introduction of low-speed data which were not previously available influenced source level relationships. [Work supported by the Florida Department of Transportation.]

Two probabilistic evaluation methods for single and double walls type sound insulation systems with arbitrary random noise excitation.

In the practical engineering field of noise control, it is as important as the sound source countermeasure to improve the sound propagation characteristics by newly setting a sound insulation system. On the other hand, the noise statistics like an Lx (x=5, 10, 50, 90, ) defined as a (100 -x) percentage point of the sound level distribution are very important as well as the lower order energy moment statistics like an Leq in the actual noise evaluation and regulation problems. In this paper, two kinds of probabilistic evaluation methods for sound insulation systems are theoretically proposed from typically different points of view for the probability distribution of the transmitted sound intensity, when a general stationary random noise having an arbitrary distributionform and frequency characteristics is insulated by a wall. To evaluate its sound transmission coefficient, a somewhat modified statistical energy analysis method has been used.The validity of the theoretical results is experimentally confirmed by applying it to the actually observed data on the output response fluctuation of single and double walls type insulation systems inserted between two reverberation rooms.