“You must learn to play on a fair reed, and if a good one comes along regard it as an Act of God.” – Archie Camden1
Instead of trying to explain the exact measurements and methods I use to make my own reeds, I think it would be more useful to discuss the acoustical properties of reeds in order to explain why certain measurements and adjustments give a reed the qualities they do. Many students, for example, understand that thinning the rails or clipping the tip will improve the response of the high register, but they do not necessarily understand why these adjustments affect a reed in this manner. The approach to reed making is often similar to: “I need this reed to play better in the high register, so I will thin the rails and cut the tip.” However, a bassoonist with a good understanding of the fundamental properties of reeds will approach the situation in this manner: “I need a more resistant reed to make the high range easier. There are a number of adjustments I can make—such as thinning the rails or clipping the tip—but first let me consider if any of these adjustments might negatively impact the reed qualities I already have.” This second line of thinking allows for a much more self-sufficient approach to reeds, and gives a student the tools to problem-solve their own reed issues.
Of course, finer adjustments that affect very specific qualities (even down to specific notes) are still necessary, but these adjustments should be focused on after the student has formed a solid grasp of the general adjustments that can and should be made. Teaching finer adjustments before a student is ready would be akin to teaching a student how to perform vibrato before proper breath support. Much of my own knowledge of bassoon reeds and their role in sound production comes from two excellent sources: “Physical Forces at Work in Bassoon Reeds” by James Kopp,2 and Reed Design for Early Woodwinds, by David Hogan Smith.3 Most of my discussion here will focus on simplified versions of the concepts discussed by these two authors, and I highly urge bassoonists to read their original writings for much more comprehensive explanations.
First, we must understand the acoustical function a reed performs in relation to the instrument it is attached to—in this case the bassoon. The bassoon has a conical bore that extends from its widest radius at the bell to its narrowest radius at the tip of the bocal, and if we were to unfold the bore it would look similar to a very long and narrow cheerleader’s megaphone. However, because the bore has been cut off at the tip (the end of the bocal), the cone is missing part of its volume—in essence, the cone is acoustically “incomplete.” It is therefore the reed’s job to fill this missing apical portion of the cone, and we measure its effectiveness in terms of what’s called equivalent volume.
The most important thing to understand about bassoon reeds is that a great reed replaces 100% of this missing equivalent volume. But how is this even possible? If the conical bore of the bassoon had not been cut off at the end of the bocal, it would extend on for almost another foot; yet a bassoon reed measures less than a quarter of this length! The key is to remember that actual size is not the same as acoustical size, so instead of measuring the equivalent volume of a reed in terms of its actual static size, we measure it in terms of a reed’s vibrational size.
There are a number of properties that directly contribute to a reed’s vibrational size—the length of the reed, the thickness of the blades, and the ratio of the tip to the throat, to name a few. A reed’s vibrational size is directly related to each property we adjust when we work on our reeds, and in this way we can think of all our measuring and scraping as an attempt to get our reeds closer to replacing 100% of the missing equivalent volume. To help us in our quest, Kopp provides us with a basic yet very useful equation:
Vibrational size of a reed = Static size + Compliance
This simple equation is perhaps the closest thing we have to a “theory of relativity” for reed making, and through it we can better understand exactly why specific adjustments lead to certain results. The term “compliance” refers to the amount of resistance a reed has—a reed with lower compliance has more resistance, while a reed with higher compliance has less resistance. Reeds with lower compliance produce a darker tone and are much easier to play in the high register, while reeds with higher compliance are freer blowing with a brighter tone and are easier to play in the lower range. We can use the above equation to discover the adjustments necessary to make a reed more or less compliant:
For Increased Compliance (Lower Frequency)
- Increase blade length
- Make the ratio of tip width to tube width greater (more flare)
- Make the ratio of tip thickness to back thickness greater
- Make the ratio of rail thickness to heart thickness smaller (thicker rails)
- Flatten the tube
For Decreased Compliance (Higher Frequency)
- Shorten blade length
- Make the ratio of tip width to tube width smaller (less flare)
- Make the ratio of tip thickness to back thickness smaller
- Make the ratio of rail thickness to heart thickness greater (thinner rails)
- Round the tube
We can explain the vibrational frequency of a bassoon reed using what is known as the clamped-free bar model. One common example of a clamped-free bar is a diving board from a swimming pool, so examining the way it vibrates can help us better understand the way a bassoon reed vibrates. When a diver jumps off of a longer diving board, the frequency of the board’s movement will be lower than if the same diver jumps off a shorter diving board. The same is true for the blades of a bassoon reed—the longer the blades are, the lower their vibrational frequency will be, while the shorter the blades are, the higher their vibrational frequency will be.4
The clamped-free bar model also explains the changes that occur in a reed when we alter the thickness or width of its blades. Returning to the diving board, we can see that if a person begins jumping near the end of the board, it will move up and down at a lower frequency than if the same person begins jumping near the point where it is attached to the concrete. In other words, the point where the weight is placed on the diving board directly corresponds to the frequency it will bounce (i.e., vibrate). Likewise, if we leave more weight (thickness) at the tip of the blades compared to the back, the reed will vibrate at a lower frequency; if we leave more weight at the back compared to the tip, the reed will vibrate at a higher frequency.
These properties of weight balance also apply to the width of the reed tip, since increasing the tip’s width compared to the tube is yet another way of adding mass to the end of the blade. Just imagine the side view of a vibrating diving board as the top-down view of a bassoon reed—the farther the board bounces up and down (i.e., the lower the frequency), the wider the tip of the reed.
Since the tip aperture is held under tension by the deformation of the cane and wires, we can also see certain properties of vibrating membranes in the reed. This primarily concerns us in terms of the roundness or flatness of the tube, which we can alter by adjusting the roundness or flatness of the wires. Flattening the first wire will close the tip aperture, while flattening the second wire will actually open the tip aperture; the opposite results are true when rounding each. Because adjusting these two wires has converse actions, flattening each will flatten the entire tube while keeping the tip aperture constant (making the reed more compliant), while rounding both will round the tube while also keeping the tip aperture constant (making the reed less compliant).
1 Camden, 36.
2 James Kopp, “Physical Forces at Work in Bassoon Reeds,” http://koppreeds.com/physicalforces.html (accessed April 30, 2012).
3 David Hogan Smith, Reed Design for Early Woodwinds (Bloomington: Indiana University Press, 1992).
4 Out of all the properties discussed, it is this property (blade length) that has the greatest influence on vibration frequency.