Origins of the Domino Theory. In September 1945, the Vietnamese nationalist leader Ho Chi Minh proclaimed Vietnamâs independence from France, beginning a war that pitted Hoâs communist-led Viet Minh regime in Hanoi (North Vietnam) against a French-backed regime in Saigon (South Vietnam).
The human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal.
Normal human hearing ranges from 20 hertz to 20,000 hertz. Low-frequency sounds, below 20 hertz, are referred to as âinfrasoundâ and travel farther than high-frequency sounds. Frequencies above the range of human hearing (20,000 hertz) are referred to as âultrasonic.â.