After washing the frog-sand very long hours, prolonged over 1000 hrs or more, we can get a new sound. If inclined slowly the acril pipe about 30 degree, the surface layer of the sand started to flow, very small scale avalanche,and some generation of a peculiar sound are observed, we can hear that just like "hea", which heared from 2-3m distance. A cat listened attentively to the wonderful sound. The sound had somewhat long , 5-10sec, duration. We named it as a hea-sound, just as it is, from we heared.
The wave forms produced by the sounds of both desert-booming and frog sands are beats. The wave forms shown below indicate this similarity between both types of sound. This similality between hea-sound and booming sand are important to study booming sand, which is difficult to meet the event.
To test the scale effect, we make a more big frog-sand set. Frog-sand confined to a 200 mm pipe produced a sound with a beat-like waveform (which resembles the waveform produced by sound from booming sand; see Fig. 1).
Fig. 1. Amplitude versus time waveforms from sound of booming sand
(left) and frog-sand (right).
Fig.2 Spectral Analysis (amplitude versus frequency) of sound produced by booming sand from the Badain-jaram desert (left) and from hii-frog sand (right).