|Giancoli, Douglas C. Physics: Principles with Applications. USA: Prentice-Hall, 2002.||"Many animals can hear ultrasonic frequencies; dogs, for example, can hear sounds as high as 50,000 Hz, and bats can detect frequencies as high as 100,000 Hz."||< 50 kHz|
|Hearing Range in Animals. MSN Learning and Research. Microsoft Corporation. June 2003.||30 Hz–40 kHz|
|Wegler, Monika. Dogs: How to Take Care of Them and Understand Them. New York: Barrons Educational Series, 1996.||"Dogs hear high tones in particular much better than humans do. Humans can pick up an average of 20,000 acoustic vibrations per second (kHz), whereas a dog is able to perceive between 40,000 and 100,000 vibrations."||< 40–100 kHz|
|Strain, George M. Hearing frequency ranges for dogs & other species? Lousiana State University. 3 June 2003.||Species - Dog; Approximate Range (Hz) - 67–45,000||67 Hz–45 kHz|
|Budiansky, Stephen. The Truth about Dogs. New York: Penguin Group, 2000.||"Dogs can hear sounds up to about 65,000 Hz, or cycles per second."||< 65 Hz|
Humans can hear sounds approximately within the frequencies of 20 Hz and 20,000 Hz. Anything below 20 Hz, typically cannot be heard although it can be felt. This can be experienced to when you feel the bass of a song. Likewise humans normally cannot hear any sounds above the frequency of 20,000 Hz. Although human hearing is limited to this frequency range, many animals have a wider range of sounds of which they can hear, like dogs for example.
The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz, of course depending on the breed of dog as well as its age. Like humans, dogs can begin to go deaf as they become older. In some breeds of dogs it is natural for them to go completely deaf in their old age.
When dogs become aware of a sound they've heard their ears will prick up and move around. Part of the reason why dogs can hear better than humans is that their ears have more mobility which enable it to maximize its ability to ear. The shape of a dog's ear also helps it hear more proficiently. As we cup our ears, some dogs ears are already in that position. A German Shepherd, for example, has upright curved ears which helps it to maximize sound.
As an animal that hears higher sounds than humans, a dog has a different perception of the world as opposed to humans. One example of this is the dog whistle, which is above human hearing, will catch the ear of any well hearing dog. A vacuum cleaner, which merely sounds loud to us, can produce a high frequency sound which may scare dogs away.
Timothy Condon -- 2003