Final answer:
The voiceless fricative source is described as an articulatory constriction. It is produced by obstructing or constricting the airflow at a certain point in the vocal tract, resulting in a continuous aperiodic sound.
Step-by-step explanation:
The voiceless fricative source is described as an articulatory constriction. In human speech production, the voiceless fricative sound is created by obstructing or constricting the airflow at a certain point in the vocal tract. This produces a continuous aperiodic sound characterized by a turbulent airflow and a high-frequency spectrum of noise. Examples of voiceless fricatives include the sounds /f/ and /s/.
This constriction generates a noise source due to the turbulence, which can be modulated by the resonant properties of the vocal tract. The series of compressions and rarefactions in the air constitute the sound wave for the voiceless fricative. Overtones and intensities of the resulting sound vary with the shaping of the mouth and tongue position, but unlike voiced sounds, there is no periodic input from vocal cord vibrations.