William J. Strong
Dept. Phys. and Astron., Brigham Young Univ., Provo, UT 84602
A resonator is something that responds to and enhances some frequencies with respect to other frequencies. In the simplest case of voiced speech production, an air-filled tract acts as a resonator that selectively enhances certain frequencies of the periodic glottal airflow as it passes from one end to the other end of the tract. As a simple example for demonstrating the effect of a resonator, the tract is represented by a cylindrical tube closed at the ``glottal'' end and open at the ``mouth'' end. The resonance frequencies of the tube---those frequencies of the airflow that will be enhanced as the air passes through the tube---can be determined easily from the tube's length and end conditions. The resonance frequencies---formant frequencies in the terminology of speech science---are verified by clapping a cylindrical tube to produce a tube spectrum. The tube is then driven with an artificial larynx as a source to produce a ``voiced'' sound. The spectrum of the sound is seen to be the sum of the source spectrum and the tube spectrum (when expressed in terms of sound levels). The production of ``vowel'' sounds by this method will be demonstrated.