Generally, the lowest frequency of sound the human ear can hear is 20 Hz. Sounds below this frequency are referred to as infrasound. Some people, however, have extra sensitivity and are capable of detecting sounds as low as 15Hz in the infrasonic range.
It is common for people to experience slight hearing loss as the age. This is caused by changes in the inner ear. An average middle-aged person can detect a maximum frequency of 12,000 Hz to 15,000Hz. Some animals have wider frequency ranges. For instance, dogs have an average frequency range of 67 to 45,000 Hz, and dolphins have a maximum frequency range of up to 100,000 Hz.