7 FEBRUARY 2008
The sound of sax
Once you get over the newbie's inevitable squeaks and squawks, learning the saxophone can be pretty easy -- for the first two octaves or so. But once you reach the "altissimo"range, you'll run out of the keys that you used to raise the horn's pitch.
In that difficult range, you must adapt your mouth and throat (your "vocal tract") to control the horn.
One reason the sax sounds so much like a human voice is the role played by the larynx and mouth in shaping the sound. Notice the muscular activity around Stu Reynolds' vocal tract? Courtesy Stu Reynolds.
Many sax players have long contended that the shape of the throat was critical to getting a good sound, especially for the highest notes. Now some acoustic researchers from Down Under have confirmed part of that wisdom -- by analyzing the physics of the vocal tract while a sax is played.
The researchers rigged up a sax mouthpiece with sensors and had amateurs and pros play while they measured how air vibrates in the mouth.
Musical instrument or foghorn! An amateur plays G correctly, then plays the fingering for A sharp, more than one octave above. Because he does fails to tune the vocal tract, the instrument plays at its strongest impedance peak, a much lower note that sounds rather like a ship lost at sea!
An amateur begins a scale, but fingering the correct keys is not enough: without appropriate vocal tract tuning, the instrument plays at one of the lower impedance peaks, swerving badly off pitch. Ouch!
A professional plays comfortably over the normal and altissimo ranges of the tenor sax. Notice the fluidity and purity of the notes. There is no bleating, no honking, but plenty of control.
First, an itty-bitty dose of acoustics. Every column of air has a characteristic distribution of acoustic impedance, which tells us how easily that air can vibrate at various frequencies; in other words, how the chamber resonates.
Impedance controls the saxophone reed, which vibrates at frequencies near the peaks of impedance. In fact, the horn is covered with holes that players can open and close because this adjusts the peak of acoustic impedance.
With all holes closed, the tenor sax can play its lowest note: B-flat (which equates to A-flat on a piano). But if you blow harder, and/or adjust the shape of your vocal tract, you can cause the note to jump one octave or more. Without moving your fingers, you can reach pitches called "overtones."
In other words, it's not just fingering that determines the pitch played on a sax.
Pitch perfect
Nonetheless, there has been disagreement about the role of the vocal tract in wind instrument performance, says Jer-Ming Chen, a graduate student in acoustics at the University of New South Wales in Sydney, Australia. "Some acousticians and musicians claim its contribution is negligible, while others say the vocal tract is vital for every note sounded. One side says that thevocal tract had to be adjusted for each note played, while the other maintains that" the 
vocal tract is isolated from the instrument and therefore is irrelevant.
Monterey, California sax teacher Stu Reynolds stands firmly on the throat side of the argument. "Most saxophonists don't understand about throat control, and at the beginning, you don't want to be concerned with that. But when you want to refine your sound and increase your control, it's important to train the throat. By using the larynx, you can control the horn in the throat, and it becomes like singing."
The experimental rig: The speaker makes sounds that are reflected by the vocal tract (red), all the way to the glottis, in the larynx. The reflections are picked up by the microphone, to allow an analysis of the acoustics of the vocal tract. Adapted image from original, courtesy Jer Ming Chen, John Smith and John Wolfe.
To explore the role of the vocal tract, the Australian researchers cobbled together a sax mouthpiece with a specially adapted loudspeaker and a microphone, says Chen. "With the special mouthpiece, we can unobtrusively introduce a carefully adjusted sound signal into the player's mouth while the built-in microphone picks up the signal reflected from within the throat while the saxophonist plays normally. Because we know the signal we put in, and can measure the signal coming back, we can do some math and work out the acoustic resonance of the player's vocal tract."
The acoustic impedance of the vocal tract plays a major role in determining the pitch of the sax, at least in the higher ranges. Graphic: NIH
Altering altissimo
What they found does not completely jibe with the sax teacher's viewpoint, but it does confirm the importance of the vocal tract in the hard-to-hit altissimo range. The altissimo is the highest playing range on the saxophone, reaching up into the third and fourth octaves, and is notoriously tricky to sound.
When professionals played altissimo, the resonance of their throat was typically many times stronger than the resonance of the saxophone -- suggesting that controlling the throat is as important as controlling the fingers in that range.
This saxophone "plays" the player, Col Loughnan, saxophonist and teacher at the Sydney (Australia) Conservatorium of Music. A pipe in the mouthpiece injects 224 pure sounds into the player's vocal tract, a microphone measures the resulting sonic reflections from the vocal tract. Image courtesy Jer Ming Chen, John Smith and John Wolfe.
"The sax teacher has some bits of that right," says Chen. "We found that to play in the altissimo range, you have to adjust the throat in a certain way to make its resonance frequency match the saxophone's for those notes to possibly sound."
And why would the throat play such a special role in altissimo? "For most of its playing range, the sax's own resonance is quite strong, so the notes sound naturally," says Chen. "When you try to play higher up, the resonances begin to fall away," and that's where the throat plays a crucial role.
The conical shape and broad bell of the sax, which were designed to make it easy to play and, well, LOUD, unfortunately also make the higher pitches harder to sound. "This is where the vocal tract comes in," Chen says. "By adding a strong and appropriately tuned vocal tract resonance to the sax, you can then sound the higher notes."
Musicians are way ahead of the acousticians on this one, says Reynolds, who points to jazz saxophonist Dave Liebman as an example. "He has so much control, he can start very high on the horn and run his fingers up and down, and lock on the pitch, completely overriding the horn; he can override the hardware completely."
- David "Tenorman" Tenenbaum
Related Why Files
• The Music of Sound
• Music & Speech
• Fiddling Physics
Bibliography
• Experienced Saxophonists Learn to Tune Their Vocal Tracts, J.M. Chen, J. Smith, and J. Wolfe, Science, 8 Feb. 2008.
• Background from the researchers