Predicting sound-pressure levels in the near field and far field from radiating partitions and building elements

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One of the most common tasks of the noise control engineer is predicting sound transmission and noise reduction through structures and the sound radiation from the structures to the near and far fields. Concerning transmission loss, a large database of test data (at least from 100 to 5000 Hz), verified transmission loss theory, and practical equations for relatively simple constructions are all readily available to the noise control engineer. On the other hand, the topics of noise reduction from space to space as a function of transmission loss, and radiation patterns from partitions and building elements are rarely found in the literature or acoustical texts. A large variety of noise reduction situations arise in practice. Sound may transmit from diffuse spaces, semireverberant, or highly absorbent spaces to similar or dissimilar spaces including the outdoors. The transmission path is likely to be through the primary surface as well as windows, ventilation openings, or a combination of different wall and roof constructions. At times, the transmission from outdoors to interior spaces is the primary consideration. Often, in industrial situations, the level close to the structure is of interest for hearing conservation considerations, as is the level in the far field for community impact assessments. This paper reviews noise reduction equations as a function of transmission loss drawn from many sources for predicting sound-pressure levels in the situations discussed above. The radiation pattern from a plane wall or opening to the near and far fields is discussed. The material is presented in an orderly fashion to serve as a guide for the noise control engineer. Recommendations are given for situations in which current analytical prediction methods appear inadequate.