NOISE PROPAGATION IN URBAN AND INDUSTRIAL AREAS

STUDIES ARE BEING MADE OF NOISE PROPAGATION IN AREAS WITH COMPLICATED GEOMETRIES REPRESENTING TYPICAL URBAN AND INDUSTRIAL APPLICATIONS. THE STUDIES COVER THREE AREAS: ACOUSTIC REFLECTION FROM ROUGH SURFACES, INCLUDING BOTH PERIODIC RECTANGULAR CORRUGATIONS AND RANDOM ROUGHNESS; NOISE PROGAGATION IN CORRIDORS WITH ROUGH WALLS; AND NOISE PROGAGATION IN ARRAYS OF STREETS. THE STUDIES INCLUDE BOTH ANALYTICAL AND EXPERIMENTAL WORK. HIGH AND LOW FREQUENCY APPROXIMATIONS ARE BEING OBTAINED TO DESCRIBE THE REFLECTION OF SOUND FROM RECTANGULAR CORRUGATION. MANY BUILDING SURFACES CAN BE DESCRIBED BY THE MODEL; THE CORRUGATIONS REPRESENT, FOR EXAMPLE, BUTTRESSES OR WINDOW RECESSES. AT LOW FREQUENCIES, OF COURSE, THE CORRUGATIONS CAUSE ONLY A SMALL DEPARTURE FROM SPECULAR REFLECTION. AT HIGH FREQUENCIES A LARGE FRACTION OF THE INCIDENT SOUND IS SCATTERED RATHER THAN SPECULARLY REFLECTED. EXPERIMENTS AT MODEL SCALE USING THE SPARK SOURCE SUGGEST THAT WHEN THE ACOUSTIC WAVELENGTH IS MUCH LESS THAN THE DIMENSIONS OF THE CORRUGATIONS, THE SPECULARLY REFLECTED WAVE MAY BE AS MUCH AS 4 DB LESS THAN THAT REFLECTED FROM A SMOOTH SURFACE. EXAMINATION OF THE MEAN-SQUARE PRESSURE OF THE REFLECTED WAVE VERSUS TIME PRVIDES INFORMATION ON BOTH THE SPECULARLY REFLECTED AND THE SCATTERED FIELDS. THE EFFECT OF SCATTERING ON THE FIELD REFLECTED FROM A ROUGH SURFACE MAY NOT BE GREAT EXCEPT AT HIGH FREQUENCIES. HOWEVER, SINCE NOISE PROPAGATION IN STREETS AND CORRIDORS TYPICALLY INVOLVES MULTIPLE REFLECTIONS, THE CUMULATIVE EFFECT OF THE SCATTERING OR THE NOISE DISTRIBUTION ALONG THE STREET MAY BE QUITE PRONOUNCED. STUDY IS CURRENTLY BEING MADE OF THE PROPAGATION OF NOISE IN A STREET WITH ROUGH WALLS TO DETERMINE HOW IMPORTANT ARE THE PRECISE DETAILS OF THE SCATTERED FIELD. IT IS EXPECTED THAT A REASONALBLE PREDICTION OF THE NOISE PROPAGATION CAN BE OBRAINED BY KNOWING ONLY GROSS FEATURES OF THE REFLECTION, FOR EXAMPLE, THE RELATIVE PROPORTION OF SCATTERED AND SPECULARLY REFLECTED SOUND. THE THIRD ASPECT OF THE NOISE PROPAGATION STUDIES INVOLVES THE PROPAGATION OF NOISE IN ARRAYS OF STREETS. EXPRESSIONS ARE NOW REQUIRED FOR THE PROPAGATION OF NOISE AROUND CORNERS AND THROUGH INTERSECTIONS. ANALYTIC STUDIES OF THIS ARE UNDER WAY. SOME EXPERIMENTAL VERIFICATION OF RESULTS IS AVAILABLE FROM OTHER WORK. THE PRESENT APPROACH IS TO CONSIDER ONLY THE FLOW OF ACOUSTIC ENERGY FROM, FOR EXAMPLE, A STREET TO A SIDE STREET. SUBSEQUENTLY, EITHER A FORM OF NETWORK ANALYSIS, OR POSSIBLY STATISTICAL ENERGY ANALYSIS WILL BE USED TO DESCRIBE THE NOISE PROPAGATION IN ARRAYS OF MANY STREETS.

  • Corporate Authors:

    Massachusetts Institute of Technology

    Department of Civil Engineering, 77 Massachusetts Avenue
    Cambridge, MA  USA  02139
  • Authors:
    • Lyon, R H
  • Publication Date: 1974-3

Media Info

  • Pagination: 5 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00224565
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jun 19 1974 12:00AM