How Cats Purr
"How cats purr is thought to happen when a cat vibrates the vocal chords. The purring is thought to signal contentment, communicate with kittens and warn of injury. The purring sound may actually help improve bone density and healing."
The way cats purr is believed to caused by muscles that control the vocal chords. The internal laryngeal muscles are responsible for the opening and closing of the space between the vocal chords called the glottis. The separation of the vocal chords as they vibrate is believed to cause the purring sounds. This is confirmed by cats that can't purr because of a complete loss of strength in the laryngeal muscles (called paralysis).
Purring happens when your cat is inhaling and exhaling. It is not vocalization like meowing and hissing which are made only during the exhale.
Your cat’s purr may sound like an idling diesel engine. That’s because it’s roughly the same velocity, approximately 26 cycles per second. Cats can purr for several hours at a time. The purring is at a consistent pattern and frequency between 25 and 150 Hertz. Research has shown that sound at these frequencies can promote healing and improve bone density.
Other members of the Felidae or cat family purr including the bobcat, cheetah, lynx, and puma. Large cats like lions, tigers, leopards, and jaguars (members of the Patherinae subfamily) can make a short burst of sound that is similar to a purr, but they don’t truly purr.
Kittens learn to purr when they are just a few days old. It is believed that they purr while nursing in order to signal to their mother that they are getting enough milk and that they are doing well.