TABLE 16.1 Mass and acoustic data for two growling dogs Second Mass (kg) formant (Hz) formant (Hz) First Breed West Highland Terrier (Westie) 8.0 650 1950 Doberman 38 350 1050
The sounds of the human vocal system result from the interplay of two different oscillations: the oscillation of the vocal cords and the standing-wave resonances of the vocal tract. A dog’s vocalizations are based on similar principles, but the canine vocal tract is simpler than that of a human. When a dog growls or howls, the shape of the vocal tract is essentially a tube closed at the larynx and open at the lips. All dogs growl at a low pitch because the fundamental frequency of the vocal cords is quite low. But the growls of small dogs and big dogs differ because they have very different formants. The frequency of the formants is determined by the length of the vocal tract, and the vocal-tract length is a pretty good measure of the size of a dog. A larger dog has a longer vocal tract and a correspondingly lower-frequency formant, which sends an important auditory message to other dogs. The masses of two different dogs and the frequencies of their
formants are given as shown.
a. What are the approximate vocal-tract lengths of these two dogs? Assume that the speed of sound is 350 m/s at a dog’s body temperature.
b. Growls aren’t especially loud; at a distance of 1.0 m, a dog’s growl is about 60 dB—the same as normal conversation. What is the acoustic power emitted by a 60 dB growl?
c. The lower-pitched growl of the Doberman will certainly sound more menacing, but which dog’s 60 dB growl sounds louder to a human?
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