In the first part of this work we studied several oral signals suitable for human echolocation. Palatal clicks were proven to be optimal pulses for this task. In the second part of this series, we analyze, from a physical and psychoacoustical point of view, the sounds produced by hand clapping and finger snapping. One additional sound is studied: a loud sound made by clapping one finger against the vacuum space between fingers near the knuckles. The results of our experiments show that these sounds are fairly good for echolocation. The best one is the knuckle vacuum pulse, due to its extraordinary acoustical properties. This sound has many of the good characteristics of palatal clicks with an even richer content in the high frequency part of the spectrum. Besides, this sound exhibits an interesting symmetry in the ultrasound range, which palatal clicks do not have. Experimenters noticed that, in spite of their sound quality, hand and finger produced pulses were inferior to palatal clicks, mainly due to difficulties in the relative orientation between the head and the hands, without sight clues, lack of reproducibility and muscle fatigue during long sessions. Some people with basic echolocation skills, however, found these sounds useful for distant sources, because they were able to make such pulses louder than palatal clicks.
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