THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

316 12. Walls, Enclosures, and Barrierswhere b ′ = 0 for a wall and b ′ = 1 for a berm. The correction factor b ′ allowsfor the experimentally determined fact that berms tend to produce 3 dB moreattenuation than walls of the same height. The above set of equations apply onlyto barriers that are perpendicular to a line between the source and the receiver. Adetailed discussion of attenuation through scattering and diffraction is given byPierce (1981).ReferencesBarry, T. M., and Reagan. J. A. December 1978. FHWA Highway Noise Prediction Model.U.S. Department of Transportation Report FHWA-RD-77-108.Beranek, Leo L. 1971. Noise and Vibration Control. New York: McGraw-Hill: 566–568.Brüel & Kjær. 1980. Measurements in Building Acoustics. Nærum, Denmark: 19.Crèmer, L. 1961. Statistische Raumakustik. Chapter 29. Stuttgart: Hitzel Verlag:.Moreland, J. B., and Musa, R. S. 1972. International Conference on Noise Control Engineering,October 4–6, 1972, Proceedings: 95–104.Pallett, D. Wehrli, Kilmer, R. R., and Quindry, T. 1978. Design Guide for Reducing TransportationNoise in and around Buildings. Washington, DC: U.S. National Bureau ofStandards.Pierce, A. D. 1981. Acoustics, An Introduction to its Physical Principles and Applications.New York: McGraw-Hill.Reynolds, D. D. 1981. Engineering Principles of Acoustics. Boston: Allyn and Bacon.Ver, I. L. 1973. Reduction of noise by acoustic enclosure. Isolation of Mechanical Vibration,Impact, and Noise (J. C. Snowdon, and E. E. Ungar, eds), AMD-Vol. 1, ASMEDesign Engineering Conference,: 192–220.Ver, I. L. and Homer, C. I. 1971. Interaction of sound waves with solid structures. NoiseControl (Beranek, L. L., ed.). New York: McGraw-Hill, 270–361.Problems for Chapter 121. A room is subdivided in its middle by a concrete wall with a transmission lossof 52 dB. The room is 4 m high, and the division occurs across the entire widthof 12.5 m. In the middle of the dividing wall there is a door 2.5 m high × 1.0 mwide. The door’s rated transmission loss is 28 dB. There is a crack underneaththe door that extends across the door’s width and it is 2.5 cm high.(a) Determine the effective transmission loss of this structure.(b) If you could reduce the crack to 0.30 cm (by lengthening the door) whatwill be the change in the overall transmission loss?2. A 5.8 ft 2 sample of a building material is being tested by being placed in awindow between a receiving room and a source room. There is no appreciablesound transmission except that through the sample. Average sound levels inthe 1-kHz octave band are 93 dB in the source room and 68 dB in the receivingroom. The equivalent absorption area of the receiving rooms is 18 ft 2 . Estimatethe transmission loss (TL) and the transmission coefficient (TC) for the sampleat 1 kHz.