Effects of diffraction for acoustic loads on building structures

Acoustic loads on building structures from external noise are influenced by acoustic diffraction of the incident wave front. An experimental study by Wyle Labs of diffraction consisted of measurements on a solid ground-mounted cubical obstacle insonified by approximately plane waves. The diffraction effect is equal to the sound level at various positions on the cube relative to the free field sound level. The former was measured with a microphone mounted flush with the surface of the cube. As expected, the diffraction effect varied systematically with the ratio of the cube side to wavelength and is portrayed by contours of equal diffraction correction. The maximum correction was equal to or more than the expected 6 dB near the center of the side facing the source but also exceeded 6 dB near the center of the back (shadow) side of the cube when the ratio of cube side to wavelength is close to 1. This positive diffraction correction may not normally be considered in assessment of noise on the shadow side of...