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Hearing range refers to the different frequencies that can be heard by humans or animals. The frequency that can be heard varies throughout our lifetime and a test known as an audiogram is used to measure the sounds a person can hear. There is a significant difference between the hearing range of humans and mammals which explains why humans cannot hear the noises made by certain animals.
The hearing range of humans is between 20 and 20,000 Hertz (Hz). By the time humans reach their teenage years, this upper range is significantly lower with most oral communication taking place between 200 and 8,000 Hz. Frequencies of 1,000-3,500 Hz are the most sensitive to the human ear. Ultrasound refers to sounds above the hearing range while sound below the range is known as infrasound.
An audiometer is used to test the hearing of humans. This piece of equipment allows the subject to listen to various frequencies over special headphones. A minimum audibility curve is used to compare the results of the test. This curve represents the regular hearing range.
An alternative method of discovering a person’s hearing range is a behavioral hearing test known as audiometry. This test involves a range of tones at a certain pitch and intensity. The subject raises his/her hand as an indication of having heard the sound. The tester then records the lowest intensity sound that can be heard by the subject.
Dogs have a greater range of hearing than humans. They can hear sounds between 40 and 60,000 Hz. Depending on the breed, the ears of dogs have a minimum of 18 muscles which allows them to tilt and rotate their ears to amplify the sound. Sounds that seem loud to a human frighten dogs who respond well to ultrasonic signals in training whistles. Domestic breeds are ideal guard dogs as their hearing range allows them to hear intruders clearly.
The range of hearing of mice is between 1,000 and 90,000 Hz. Although they are unable to hear the same low frequencies as people, they can communicate via sounds inaudible to a human. This is also useful when under attack. Mice are able to send warning sounds to fellow rodents without a predator hearing.
Bottlenose dolphins have a hearing range of between 250 and 150,000 Hz. Dolphins communicate differently to other marine mammals such as whales, however. While whales use signals and moans of a low frequency, dolphins use higher frequency clicks and whistles.