Abstracts of Technical Articles from Bell System Sources (01 October 1933)

Tested is built into an opening between two adjacent but structurally isolated rooms. A loud speaker acts as a source of sound in one room and a portion of the sound energy is transmitted into the second room through the test partition. The transmission loss is taken as TL = L 1 - U - 0 logio (at/A), where L and £2 are the intensity levels in the source and test room respectively, expressed in db, at is the absorption in the test room and A is the area of the partition. The levels L and L 2 are measured and plotted with a moving coil microphone and an automatic level recorder, and a beat frequency oscillator is used as a source of tone so that the frequency m a y be varied continuously. Measurements with a continuous variation in frequency enable resonances in the partition to be much more easily and quickly detected than is possible when measurements are made at discrete frequency intervals. 

Both pure and frequency modulated tones have been used for the measurements. Results of measurements on a few partitions are given. The Optical Behavior of the Ground for Short Radio Waves.3 C. B. FELDMAN. The role of the ground in radio transmission is first considered generally. In short-wave propagation taking place via the Kennelly-Heaviside layer only the ground in the vicinity of the antennas is involved, and its effect may be included in antenna directivity. The utility of so ascribing the ground effect exclusively to the terminals of a radio circuit rests on the applicability of simple wave reflection theory in which the distance between the terminals does not appear.