摘要:

Use of solid walls and earth berms as highway noise barriers is becoming more widespread. A survey of the methods generally accepted for use in acoustical evaluation and prediction of barrier performance indicates the following: First, most methods are based on the theory of Maekawa (diffraction by a semi‐infinite screen). Second, the methods are either too complex to use except for final design evaluation, or they are too simplified for use except in preliminary design stage. This paper describes a method developed to bridge this gap. The method is based on the results of Maekawa and involves the analysis of a single truck pass‐by. The vehicle is modeled as three incoherent noise sources representing stack, engine, and tire noise. The attenuation for each octave band is determined; then the octave bands are combined to give anA‐weighted sound level. Evaluation of the effectiveness of the sound wall is done by comparing the noise signature with and without a barrier present. The method is simple enough to allow comparison of many barriers in a short period of time, but complete enough to be considered as accurate as the Maekawa results it is based on. Results from use of the method in the design and analysis of several projects are presented.

ISSN:0001-4966    

DOI:10.1121/1.3438042

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Measurements of absorptionAand sound powerW0have been made at various audio frequencies in the 425‐m3reverberation chamber of the Bureau. The modulated source of sound power was electroacoustical—an array of four loudspeakers having their audio input voltage waveforms amplitude‐modulated at frequenciesF= 0.1 to 0.4 Hz. The sound pressure |p2| was measured with an array of four microphones. A trihedral vane rotated at the center of the chamber. The phase φ was obtained by means of an analog computer (phase‐meter) based on a least‐squares principle of design. The results for the absorption cross sectionAare compared with cross sections obtained by the ASTM standard method of test based on the time decay of sound energy in a reverberation chamber. The recording phase meter displayed φ as a running function of time. From the recordings we obtained also (a) the influence of the vanes on diffusion, (b) the interaction between the loudspeaker source and the sound energy in the chamber, and (c) the relative effects of bands of noise and frequency modulation at various audio frequencies.

ISSN:0001-4966    

DOI:10.1121/1.3438045

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Using the theory of linear systems and stochastic processes, a model of the flat acoustic absorber was devised. By cross‐correlating the system input and output, the cross‐correlogram is shown to consist of the input autocorrelation function plus the input autocorrelation function convolved with the impulse response of the absorbing material. Proper truncation of the cross‐correlogram, coupled with the standard frequency transform/system relations, makes possible the calculation of the frequency response functionH(f). For white‐noise inputs, the magnitude ofH(f) is shown to have a simple relationship to the reflection coefficient, and hence enables the calculation of α, the absorption coefficient. Using a digital correlator whose correlation functions were Fourier transformed on the computer, system response functions for several common building materials were measured in an anechoic chamber. From these data, the reflection and absorption coefficients were calculated. Although the method is generally applicable to any angle, data are only presented for normal incidence. Measurements were also made in more complicated acoustic environments to test the general engineering applicability of the method.

ISSN:0001-4966    

DOI:10.1121/1.3438050

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Statistical energy analysis (SEA) has been recently used to predict the sound transmission loss of single and double partitions [Price and Crocker, J. Acoust. Soc. Am.47, 683 (1970)]. The present authors have applied a similar SEA technique to the problem of sound transmission between two adjacent rooms whose walls, floor, and ceiling are all structurally coupled. The model examined consisted of a rectangular box separated into two cavities by a dividing partition. The SEA model therefore consisted of five coupled resonant elements: the source room, the source and receiving room common sidewalls (assumed to be identical in each of the two rooms), the dividing partition, and the receiving room. The theory considers the effects of the material thickness and damping of both the dividing partition and the coupled sidewalls. Wave interaction at the structural junctions of the partition and the sidewalls was also examined and used to predict the required structural coupling loss coefficients. The theory was found to produce good agreement from 500 to 16 000 Hz (±2 dB) with experimental data obtained from a pair of model rooms. It is shown that by careful selection of system parameters, the effects of structure‐borne flanking can be minimized.

ISSN:0001-4966    

DOI:10.1121/1.3438052

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP