When air moves past the vocal folds to make sound, the folds vibrate side to side and up and down, stretching and shearing the folds properties the researchers tested.
First, they attached lion and tiger vocal folds to levers that measured force and distance as the tissue was stretched "like the strings of guitar," says Riede.
Next, the researchers put small circular disks of vocal fold tissue between plates and twisted one plate by a few degrees, slowly and quickly, while measuring the force needed to do that. That shows how well the material withstood shearing during roaring.
The scientists then used these measurements of tension and shear strength of big cat vocal folds to predict the lung pressures and "fundamental frequency" range at which the animals roar the range of rates at which the vocal folds are able to vibrate.
They came up with 10 to 430 hertz, or cycles per second, which is consistent with known roaring frequencies of 40 to 200 hertz in lions and 83 to 246 hertz in tigers, Riede says. Men speak at 100 to 120 hertz and women at a higher 200 to 250 hertz, but big cats are much louder because they more efficiently convert lung pressure into acoustic energy.
It makes sense that lions' and tigers' frequency when roaring is a function of the mechanical properties of their vocal folds, not the mass or weight. After all, elk have similarly sized vocal folds, yet they have a high-pitch bugle not a low roar, Titze says.
"It is confirmation that the frequencies of phonation are described by mechanical properties of the vocal folds and not by nerve impulses from the brain," he adds.
A lion's or tiger's roar can reach 114 decibels to someone standing a few feet away, which "is about 25 times as loud as a gas lawn mower," Titze says. And roars aren't delivered one at a time; instead, lions roar about 50 times in 90-second bouts.'/>"/>
|Contact: Lee Siegel|
University of Utah