Organs of Speech
Although the effects produced by the human voice are myriad in their complexity, the apparatus involved in making the sounds which constitute speech is extremely simple. In construction it has been usually compared to an organ pipe, a comparison justifiable for imparting a non-technical understanding of its operation.
An organ pipe is a tube in which a current of air passing over the edge of a piece of metal causes it to vibrate, thus putting into motion the column of air in the pipe which then produces a note. The operating air is forced across the sounding piece of metal from a bellows. The tube in which the thin sounding plate and the column of air vibrate acts as a resonator.
"...the apparatus involved in making the sounds which constitute speech is extremely simple"
The resulting sound depends upon various sizes of the producing parts. If the tube is quite long the sound is low in pitch. If the tube is short the sound is high. Stopping the end of the pipe or leaving it open alters the pitch. A stopped pipe gives a note an octave lower than an open pipe of the same length. The amount of the vibrating plate which is allowed to move also determines the pitch of a note. If the air is under great pressure the note is loud. If the air is under little pressure the note is soft.
It is quite easy to transfer this explanation to the voice-producing apparatus in the human body.
To the bellows correspond the lungs from which the expelled air is forced upwards through the windpipe. The lungs are able to expel air regularly and gently, with no more expense of energy than ordinary breathing requires. But the lungs can also force air out with tremendous power—power enough to carry sound over hundreds of yards. In ordinary repose the outward moving breath produces no sound whatever, for it meets in its passage no obstruction.