Taken from:
http://friedbeef.blogspot.com
This distinction between the sensorial and physical meaning of the sound gives a form to respond us to the old philosophical question: a tree falls in the forest and there is nobody hears it, was there sound. The answer is no, in terms of the sensorial ear and if in terms of the physical waves, the answer depends on how the sound is defined. The definition of sonorous waves covers three aspects: the origin, the means of propagation (in the longitudinal sonorous waveform), and its detector, that must be the ear)."
