This is the 2007 version. Click here for the 2017 chapter 04 table of contents.

Sensitivity of Human Hearing

A human with perfect hearing can detect sounds from about 20-20,000 cycles per second (Hertz). Above about 15,000 Hz, sounds are difficult to hear as isolated tones, but people can often detect a difference between two sound sources if one includes frequencies above 15,000 Hz and the other does not. The recording with more high frequencies will sound brighter and have more presence. In other wrods, it will sound more like somebody is actually in front of you, playing the music. However, music can still be enjoyable with the very highest frequencies missing. FM radio stations do not transmit sound information above 15,000 Hz.

Dogs can hear ultrasonic sounds, frequencies higher than humans can normally detect. That is why dog whistles can be silent to humans. Cats hear sounds up to 50,000 Hz, porpoises up to 80,000, and bats-the champions-hear sounds up to 98,000 Hz. Bats use extremely high-frequency sounds as a navigational sonar, bouncing sound waves off objects in the dark to avoid obstacles and detect insects.

What is the normal frequency range for adult human hearing? Can fleas hear ultrasonic flea collars?

Dog and cat owners may be interested to learn that ultrasonic flea collars sold in many catalogs apparently do not work. A veterinary research team at Purdue University tested two different brands of ultrasonic flea collars on a pair of cats. The researchers found that 49 of 50 fleas were still on cats after 7 days of wearing the ultrasonic flea collars. The researchers said this did not surprise them, because "there is no evidence that fleas can either hear or produce ultrasonic signals." (Holden, 1990)

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