Bipedal bugles
Via Eurekalert, an interesting finding with an overstated headline.

Headline: Birds' surprising sound source

Well, the syrinx itself isn't the surprise. The surprise is a beautifully simple explanation of why the syrinx is so flexible and effective.

Now, a team that brings together physics, biology, computation and engineering finds that the syrinx confers an advantage: by sitting so low in the airway, the syrinx can produce sound with very high efficiency.

"I'm always excited when something is counter-intuitive," says Ingo Titze, director of the National Center for Voice and Speech at the University of Utah and a co-author of the study. "Most people would say 'Put the sound source right by the mouth or the beak, and you'll get the sound to the listener.' But that's not what we're finding."

"In the old days we used to think that the sound source just produces the sound and the airway just modifies the sound," says Titze. "Our research has shown that there is strong dependence on both the tube, or airway, and the sound source. Where the sound source is in the tube makes a difference, whether it's in the middle, front or back."

Ingo Titze has been around a long time, and has always been an original thinker who doesn't fall into orthodox traps.

The main point is simple: Putting the 'reed' down near the lungs gives the bird a long resonator. A long resonator makes it possible to tune a wide range of frequencies. A trumpet mouthpiece on its own sounds like an untuned fart. A trumpet mouthpiece coupled to a long tube produces strong and tuneful sound because the resonator phase-locks the vibrator. With the tube connected, the trumpeter's lips are forced to vibrate at harmonics of the tube.

This may partially answer a question I've been asking. Why do birds and humans share the ability to remember and produce music, while other mammals don't share the ability? I wondered if upright bipedal position was relevant. The partial answer is Yes.

Here's a suggestive picture.



Default mammals, with spine and head horizontal, have very little resonance. The larynx is immediately followed by the mouth, which is typically** open on both sides. There's no cavity or tube or column after the larynx.

Humans, with spine and head vertical, are built like a pipe organ or train whistle. The pharynx is a closed Helmholtz resonator above the larynx, with the mouth branching off and providing another closed resonator.

Birds, as per Titze's finding, are bugles. The mouthpiece or reed is at the bottom of a long resonator with muscular control. The beak is open on both sides like a cat, but the beak isn't needed as a resonator.

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** Typically, but when a dog wants to make a long-distance signal, he closes the sides of his mouth and howls. You can hear harmonic phase-locking in a howl.

Labels: Asked and partly answered, Entertainment, Grand Blueprint

  ¶ 7:27 AM