Abstract
The effects of soft (grass) and hard (asphalt) horizontal reflecting planes on the measurement of the sound pressure level have been determined as a function of source‐receiver distance for 15 one‐third octave bands of noise from 250 to 6300 Hz and for several combinations of heights of the source and receiver relative to the reflecting surfaces. Comparisons are made between these measurements (semifree field) and measurements made in a free field (anechoic chamber). It is found that interference effects, characterized by the ratio of the difference between the distances of the direct and bounce paths to the wavelength, tend to dominate the semifree‐field data and show strong noise‐band dependency. Computed A‐weighted sound pressure levels are compared for the various semifree‐field and free‐field source‐receiver combinations. A second and more complicated configuration consisting of two orthogonal intersecting planes has also been studied. Again, comparisons to the free‐field data have been made.
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