The acoustic principles formulated in the previous chapters provide a sufficient basis for a consideration of the acoustics of speech but, as we said earlier on, the sound waves of speech are among the most complex to be found in nature, particularly in the sense that extreme changes in sound quality follow each other with great rapidity. It follows from this that the speech mechanism viewed as a generator of sounds must work in a very complicated way and must indeed be capable of operating in a wide variety of ways. In this chapter we shall examine the basic properties of the speech mechanism in order to see what its principal modes of operation are and what kinds of sound they give rise to.

The musical instruments already used as examples consist essentially of a vibrating source of sound coupled to a resonating system and the speech mechanism is best considered in the same way. For a great deal of the time in speech the larynx is the source and the air column from the larynx to the lips, that is the vocal tract is the system. We know, however, that no sound can be produced without a supply of force or energy, so the first thing to establish is the nature of the energy supply for speech.

The energy supply in speech

Speech sounds may issue from a speaker in a continuous stream for quite an appreciable time and it is clear that the necessary force is not applied in one brief moment, as it is when a tuning fork is set in motion.