The average frequency range for human speech varies from 80 to 260 Hertz. The vocal speech frequency of an adult male ranges from 85 to 180 Hertz, while the frequency of an adult female ranges from 165 to 255 Hertz.
According to Wikipedia, the fundamental frequency of speech falls between this bandwidth. Unified Over IP explains that human speech is created using several distinct sounds that include plosive, voiced sound and unvoiced sound. Variations in these specific types of sound can produce higher-than-average and lower-than-average speech frequencies. These frequencies range from 50 to 500 Hertz. This causes the sound and frequency range of human speech to differ from person to person.