How do cats purr, and how do we hear it?

Question

My cat doesn't move it's mouth at all when it purrs, yet his purr is extremely loud, and I can feel him vibrating. Why is that I can hear it then?

Answer 1

Hi there...The reason is psychological as well as physiological--the two are not mutually exclusive of one another. Cat's purr whenever they feel content, extremely frightened and some will purr when they are dying as well.

How cats purr:
One study determined that purring involves activation of nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphragm serves as a pump, pushing air in and out of the vibrating cords, thus creating a musical hum. Some veterinarians believes that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr only when they want to.

The other theory is that the sound comes more from vibrating blood vessels than in the voicebox itself. The larger the vocal chords the softer the purr whereas the smaller the louder.
Source: http://cats.about.com/cs/catmanagement101/a/why_cats_purr.htm


The Scientific Reason WHY cats purr:

Some scientists believe when cats purr the frequency of their purring will help heal damaged bones and body organs as well as help heal humans.

All the cats had purr frequencies between 20 Hz and 200 Hz. With the exception of the cheetah, which had frequencies 2 Hz from the rest, all the species had frequencies, notably 25 Hz, 50 Hz, 100 Hz, 125 Hz, and 150 Hz, that correspond exactly with the best frequencies determined by the most recent research for bone growth, fracture healing, pain relief, relief of breathlessness, and inflammation. All of the cats' purrs, including the cheetah, had frequencies 4 Hz from the entire repertoire of low frequencies known to be therapeutic for all of the ailments.

That fact that the cats in this study produced frequencies that have been proven to improve healing time, strength and mobility could explain the purr's natural selection. After a day or night of hunting, purring could be likened to an internal vibrational therapeutic system, a sort of "kitty massage" that would keep muscles and ligaments in prime condition and less prone to injury. Additionally, the purr could strengthen bone, and prevent osteodiseases. Following injury, the purr vibrations would help heal the wound or bone associated with the injury, reduce swelling, and provide a measure of pain relief during the healing process.
Source: http://www.sciam.com/askexpert_question.cfm?articleID=0005CB0D-82FC-1E31-82FC809EC5880000&catID=3&topicID=3

Answer 2

Seattle has the right and most informative answer...
my cat's purr is barely audible, but i can feel her purr when she is in my lap and i am petting her.
a friend has a cat that purrs so loudly he can be heard all over the house (and they live in a large house), i swear that animal sounds like a diesel tractor idling in the living room.
and for no bigger than he is such a big noise.... so it varies from cat to cat.

Answer 3

Cows have extra stomachs; cats have 2 voice boxes. One is for Meowing, the other for Purring. Of course, you hear the purr the same way you hear the Meow! or any other sound.

Answer 4

The sounds comes from the vibrating of teeny tiny bones all throughout their jaw. They just do it when their happy :)

Answer 5

They rumble in their chests.