Why some cats' purrs sound deeper than others

Dear Cathy,

I’m curious about the purring of cats. I’ve read that their purr can range from about 25 hertz up to 150 hertz. My calico and brown tabby are the same age, yet the calico has a low, deep purr while the tabby’s is much higher. I understand what causes cats to purr, but I can’t find an explanation for the wide difference in sound. Could it have anything to do with their early upbringing? The calico was feral during her first year, while the tabby was nurtured and socialized from an early age. Can you comment on this?

Sue C.

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Dear Sue,

I have to say you’re an excellent listener. Not everyone pays close enough attention to notice the difference between one cat’s purr and another’s. That kind of observation often leads to the most interesting questions — and yours is one science has only partially answered.

Researchers report that most domestic cats purr within the 25-50 hertz range — the deep, steady vibration we’re all familiar with. Interestingly, studies in human medicine have shown that low-frequency vibrations in this same range can stimulate bone repair and tissue healing. While this doesn’t prove that cats purr to heal themselves, some experts believe the overlap may help explain why cats purr not only when content, but also when injured, frightened or in pain, possibly as a form of self-soothing.

When scientists study purring more closely, they sometimes detect higher frequencies mixed into the sound. The core vibration usually remains in the 25-50 hertz range, but lighter tones closer to 150 hertz have also been recorded, similar to faint overtones in a musical note.

Purring itself is mechanical. Small muscles in the larynx rhythmically contract and relax, causing the vocal folds to open and close rapidly during breathing. That repeated motion creates the continuous, low vibration we recognize as a purr.

What we don’t know is why one cat’s purr sounds deeper than another’s. The most likely explanation is anatomy. Just as people have different voice pitches, cats vary in the size and tension of their vocal folds, the shape of their throat, and how sound resonates through the chest. Even cats of similar age and size can sound different because of subtle physiological differences.

Personality may also play a small role. Some studies suggest cats can slightly modify their purr to a higher pitch when communicating with humans. If you’ve ever had a cat summon you at dinnertime, you know how effective that can be.

As for early upbringing, there’s no evidence that being feral changes the pitch of a cat’s purr, though it may influence when and how readily she purrs. A cat who grew up outdoors may be slower to relax and more guarded about expressing that level of comfort, particularly with people.

In short, your calico’s lower purr and your tabby’s higher one are most likely individual vocal differences — simply two distinct feline voices shaped by their anatomy.

Send your pet questions, tips and stories to cathy@petpundit.com. You can follow her on Twitter at @cathymrosenthal.