Almost all of us have studied about the role of nose and lungs in the respiratory system and the function of mouth in the digestive system, most of us do not know much about the role of these very organs in speech. Although numerous complex effects are produced by the human voice, the inner system that makes the sounds (which make up the speech) is extremely simple in its nature. This system can be compared to an organ pipe, a comparison that enables us to explain what happens inside.
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. This puts 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 resulting sound depends upon various sizes of the producing parts. If the tube is long, the sound will have a low pitch. If the tube is short, the sound will be high. You can alter the pitch by stopping the end of the pipe or by leaving it open. 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, you will hear a louder note. If the air is under little pressure, a soft note will be heard.
Now let’s compare this with our inner system, the system in our body which produces voices. The bellows can be compared to our 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 required during ordinary breathing. However, our lungs can also force air out with tremendous power that is sufficient to carry a sound over hundreds of yards. In ordinary repose, the outward-moving breath does not produce any sound, because it does not meet any obstructions in its passage.
At the upper end of the windpipe is a triangular chamber, the front angle of which forms the Adam’s apple where the vocal cords are located. These cords are two tapes of membrane which can be brought closely together, and by muscular tension stretched until passing air causes them to vibrate. As a result, they cause vibration in the air above them, like the air in an organ pipe vibrates. Hence, a tone is produced.