Syrinx & Airway Model

Program Description

Whatever the kind of syrinx, dual or single, bird sound starts with vibrating, fleshy membranes deep in the bird's breast. The airway above the syrinx is an important part of the vocal apparatus. The column of air in the airway vibrates, too, in the production of sound. These two vibrations interact and constrain each other.

Here we set up a simple model of a syrinx and airway: lips buzzing into a length of PVC pipe ... kind of a primitive bugle. We find that if you buzz into the pipe with a certain force and tension in your lips, you can only produce certain notes and their overtones. This is because stable vibrations in the air column have to form standing waves. And standing waves have to have wavelengths that fit a certain number of times into the length of the pipe.

The buzzing lips and the airway interact. Feedback from the air column's vibrations limits the frequencies the lips can buzz at if the buzzing is in the same range as the resonant frequencies of the pipe. Only by modifying the air column somehow, can a larger range of notes be sounded. A longer pipe allows longer wavelengths (lower notes) but still only a fixes set of tones. Putting valves on a bugle (turning it into a modern trumpet) lets players alter the length of the airway in multiple ways, alternating between several different fixed ranges of notes which together make up full scales.

Birds and humans avoid this limitation in most of their range, because the membrane generating the sound is vibrating more slowly than the resonant frequencies of the airway. The airway affects the overtone frequencies, but not the fundamental note. However, in the top of their ranges (like the upper soprano range for a human singer), the airway must be modified so that the resonant frequencies enhance instead of interfering with the note being sung.

Program & Recording Notes

Chris Tenney recorded the northern mockingbird in Salinas.

The sound of the sandhill crane is from the CD collection Bird Songs of California produced by the Cornell Laboratory of Ornithology.

The buzzing lips and the tones of the lengths of PVC pipe are from the brass acoustics page of Joe Wolfe's wonderful music acoustics website at The University of New South Wales.

I found the bugle calls on the U S Military's Bugle Signals and Calls page.

Series 3
Egg Calls
Chick ID Calls
Chicken Calls
Vocal Tract
Syrinx Styles
Airway Model
Airway Overtones
Coiled Trachea
Beak & Airway
Vowels & Airway
Tuvan Throat Singing
Whistling

Series 4
Size & Sound
Forest Soundscape
Grassland Soundscape
Bird Hearing
Local Dialects
Regional Dialects
Drumming - Woodpeckers Etc.
Bird Tongues
Bird Brains & Singing
Song Duels?
Dawn Chorus
Finale: Song Sparrow