The Bassoon Reed As a Little Instrument
My former teacher, K. David VanHoesen used to treat the reed like a miniature instrument. He worked with us to find the point on the reed blade for lip placement that made each note on the bassoon most resonant. There were different places for different registers.
He would encourage us to play pitches on the reed alone to develop this skill. I still use this in my first lessons with a new student. You should be able to get about an octave's range of pitches on the reed. The position for the lowest note may be similar to what you use when playing low Bb on the bassoon, the highest for high D or E. When playing scales on the bassoon a subtle use of this skill is helpful for tuning and finding resonance.
Let's think of the reed as a small musical instrument that can be tuned and adjusted for maximum benefit.
Here is a chart of the reed's vibrating frequencies:
For a note in the second octave (the notes above open F) lips, air speed and fingering combine to close the tip a bit, helping the reed and air column to select the first harmonic and not the fundamental. Using the fingering alone (half hole or no whisper key) is not sufficient to produce the correct pitch. Try using a very loose embouchure and slow air speed to play a C above the bass clef staff and you'll get the lower octave.
Anyway, the tip must be closed down a bit. The smaller opening helps increase the speed of the air rushing into the reed, allowing the faster vibrating frequency needed for the first harmonic.
Notice that the sides and part of the edges of the tip are in contact with each other. While in contact they do not vibrate. This is called damping.
You are in effect making the vibrating surface of the reed more narrow. The reed will vibrate faster and select out the fundamental, choosing instead, the first harmonic when the player plays a note in the second octave (the notes just above open F).
String players do this by changing to a different string. Each string is different in thickness and length. Bassoonists "change strings" by selecting differing amounts of reed for vibration with their lips!
It is as though we need three or four different reeds to play on. A large fat one for low notes, a medium one for middle register and a small narrow one for high notes.
Speaking of high notes, here's what a reed tip would look like while someone is playing a high note:
Since bassoon cane vibrates both with and across the grain, I'm over-simplifying some of this argument. What I'm going to say next is true, but an even greater simplification.
Let's go back to the reed spectrum chart:
Assuming that only parts of the reed blade that are open in the static phase can be made to vibrate we can deduce from observation where the lows, middle range and highs in a particular sound can be found.
I credit the late L. Hugh Cooper for imparting his knowledge of the acoustic properties of reeds for this information. Cooper was Professor of Bassoon at the University of Michigan for over 50 years and taught a class in acoustics there as well. I had the honor of working with him during a sabbatical from Michigan State University about 15 years ago.
It has been universally observed that certain tip openings impart certain tone qualities. Below are two extremes:
Most bassoon players can just look at these two shapes and start to feel lip muscles adjust to the openings!
In the first one, the sides are heavily dampened. They are not vibrating. This reed has a covered, dark sound.
In the second, the sides of the reed are open and available for vibration. Hugh Cooper identified the buzz or edge in a bright reed's tone as coming from a preponderance of lows in the sound. He believed that these vibrations came when the areas near the corners were open and available for vibration.
From this we can deduce that that is where the lows in the reed's sound lie. By the lows, I mean the resonance from the fundamental and first few harmonics.
Following the color photos of reed tip openings above, you can then discover where the mid range and highs in the sound lie on the reed.
You can play a low Bb with a loose embouchure that allows all of the reed to vibrate. You can also play it with a very tight embouchure.
What happens? You will either get a very sharp and dark low Bb or the octave above that Bb will sound. By adopting a tight embouchure you close the reed tip, selecting out the lows in the reed's tonal spectrum and allowing only the highs and mid range to vibrate. This raises the pitch and/or cuts out the fundamental.
Thus, it must be the case that the highs in the sound (the upper partials in a particular tone) exist in the spine or middle of the bassoon reed blade, since that's the only area vibrating with a more closed tip.
That leaves the mid-range, which, by process of elimination is found in the channels or the section between the spine and the rails.
So the big question in all of this is: How do you adjust a reed to enhance one or more of these parts of its tone?
This is where the artistry in bassoon reed making is found. Adjusting for enhancement of the lows, mid-range or highs in a sound is like adjusting the controls on a playback system. Perhaps another analogy for the bassoon reed would be a stereo system!
I'll need another post to elaborate on the topic of adjustment.