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The present study agrees with earlier ones that the binaural absolute threshold is about 3 dB lower than the monaural. It also finds that reversing the interaural phase of the signal lowers the threshold still further.The findings are shown to indiacate the likelihood that so-called absolute thresholds are really masked thresholds, with the masking noise present internally and exhibiting a small positive correlation. The close relation of our results to the earlier work of Hirsh on binaural masking phenomena is discussed. A NUMBER of earlier workers (see Hirsh's I andLicklider's •' reviews, but also Pollack a) have found that when subjects have equal monaural thresholds, or where experimental adjustments are made to compensate for differences, the binaural absolute thresholds are in general about 3 dB lower than the monaural. This difference has been taken as suggesting a power summation at the two ears. Since, at least at threshold levels, sound at one ear will not summate acoustically with sound at the other, something else must be responsible. The first thought that comes to mind is that there is some sort of neural summation. Lorente de N64 found evidence for what is calledRedistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 141.218.1.105 On: Mon

Problems in acquisition, storage, and analysis of delphinid echolocation signals are described and illustrated. It is shown that adequate bandwidth is the prime requisite for validity in measurement. However, idiosyncracies of the detector and recorder may alter the signal and, therefore, its derived characteristics. Uncertainty about the signal leads to ambiguous results in analysis.

Experimental measurements of the velocity and the rate of decay of circumferential waves traveling within the shells of thin-walled air-filled metallic cylinders in water have been made. Outside diameters of 3.5, 5.5, 8.5, and 12 in. were studied. Ratios of d (shell thickness) to λ (wavelength) of 0.01 to 0.97 were obtained over a frequency range of 80 to 300 kc. The measured velocities are compared with the theoretical velocities for the longitudinal and flexural modes in infinite plates. The agreement obtained defines the nature of the waves measured and supports the analogy of an infinite plate applied to the cylindrical surfaces. Empirical relations describing the decay measurements are given.

Measurements of the target strength of a single fish, species Ictiobus bubalus, over the frequency range from 50 to 470 kHz are presented and compared with estimated values calculated using an empirical relation recently derived by Love. The present measurements reveal an optimum frequency for detecting this fish. The measured target strength at this frequency is 17 dB greater than the value estimated using Love's equation.