|Fauna Communications Research Institute.Wounded cats purr to heal. 2001.||"Fauna Communication Research Institute in North Caroline has determined that the frequency at which cats purr is 27-44 hertz."||27-44Hz|
|Syufy, Fran. Why and how do cats purr? May 6, 2005.||"It seems that the measurable hertz of a cat's purr lies between 25-150Hz"||25-150Hz|
|Stewart, Jack. Purring cats. April 2005.||"Cats purr at a range of between 20 and 50Hz."||20-50Hz|
|Peterson, Paula. Secret sounds that heal. September 2002.||"Cat's purr falls well i the 20-50 hertz anabolic range."||20-50Hz|
Cats are one of the most sought pet to have in a home. Domestic cats are very amicable and express themselves through a fascinating way; purring. But why and how does a cat purr? Purring in cats consists of alternative impulses of sound, arising in the larynx. Each individual sound is caused by rapid variation of air pressure after left and right voice ligaments are separated. Larynx muscles are stimulated by nerve impulses coming from twenty to thirty times a second. With this, voice ligaments close up and air pressure rises. When this stimulation of muscle stops, voice ligaments move apart and make the released air to produce a sound. This sound is the purr that we hear from the cat. Purring is heard from a cat when the cat is injured, anxious, or just showing signs of contentment. A purr is first heard in a kitten who is suckling milk from his mother.
Small cats are able to easily produce the purr, but so can some big cats. Lions, tigers, leopards, and cheetah are able to purr. Jaguars on the other hand aren't able to purr due to the difference in how the nerves stimulate the larynx. Whoever the big cats that are able to purr can only produce it during exhalation and in a less common vocalization than in the domestic cat.
The frequency of the cat's purr falls within the range of 27–44 Hz but can extend up to 150 Hz.
Lev Mazniker -- 2006