In length and diameter, the pipe is proper to the tone produced: a short pipe of small diameter for the high tones, and a long, wide pipe for the bass tones.
The short vibrations of the high tones are perceived by the ear as affecting the air only, while the tones of the lowest bass pipes shake the solid foundations as well as the superstructure.

So with the human voice.

The coarser tissues cannot answer to the short vibrations of the upper tones, because they cannot move so quickly, while they can, and do, respond to the vibrations of the low tones.

This may cause some difference in degree, but not in kind.

With all tones focused alike, the low tones of the human organ may be regarded as head tones plus the vibrations of the coarser tissues.
It has been said of registers that they are "acoustic illusions which disappear in the perfectly trained voice." As soon as the singer has learned to use his voice normally all these defective changes disappear.
TWO CASES The following incident illustrates the fact that registers are an artificial creation: A young lady who had been a patient of the author since her childhood studied elocution in a metropolitan city, and to improve her voice took vocal music lessons of a teacher of more than local repute.