Brains and Membranes

Chapter 2 

“Can you explain how a bassoon reed works?” 

 This is the first question I ask of a student reed maker. It’s an incredibly difficult question, as it implies some knowledge of acoustical physics.  Have you noticed how few music schools offer acoustical physics as required courses? The answer to this question reveals a whole lot about the student’s ability to visualize and verbalize.

The first response is always a look of consternation. After a few moments of helpless uncertainty  the tentative answer might include:

• “It produces the sound, right?”
• “It vibrates, but I’m not completely sure what that means.”
• “Well, it makes a crow, so I guess the bassoon transforms that crow to produce the different frequencies and the quality of sound.”

From the very first day we hold a bassoon in our hands, we experience the reed as the primary connection between body and bassoon. We feel its vibration with our lips – it’s a very personal and interactive relationship.  We can even taste it!

As we try to master the basics of the instrument, we are painfully aware that reeds seem to determine response, intonation, articulation and sound quality – as well as our emotional state! We develop a largely subjective vocabulary about reeds:  resistant, unresponsive, hard, bright, dark, buzzy, muffled, tubby, flat, harsh, sharp or simply bad. Considering how much time we devote to reed making, it’s alarming how little we understand. Most remarkably, we can become quite expert at producing good reeds and still not understand them.

It’s logical to conclude that because the reed sits at the tip of the bocal [and is the source of so much grief] it must be the actual source of the sound itself. Bassoonists tend to think of their reeds as independent sound generators that are adjustable in all sorts of subtle ways to deliver either a beautiful or a horrible tone, good or bad intonation and flexible or inflexible response. We nurture a unidirectional view – where sound comes out of the reed into the bassoon – a one way flow of energy. The reed makes noise and the bassoon transforms this into tone and pitches.

Unfortunately, it’s not an accurate description. To find a better model, let’s consider sound production in other instruments.

The sound of a violin comes from the vibration of the string amplified and modified by the body.  Vibration occurs when the string is displaced from its resting position.  The energy of this motion is transferred to the violin body, which enriches the complex modes of the string’s vibration and excites the air molecules both inside and outside the violin.  This excitation occurs at specific frequencies, made sonorous by complex overtones.  The top and the bottom of the violin are actively vibrating, as is the air enclosed within the body.  These vibrations cause compression waves to move outward into the room and eventually engage our eardrums.

Nature gives a stretched violin string a natural tendency to move back and forth at frequencies dependent on tensile strength, elasticity and length.  The most basic motion of a string is a simple displacement from end to end.  Strings also exhibit more complicated modes of displacement; while the string moves back and forth in its whole length, it also experiences motions in smaller segments.  These modes always act in a very predictable way, with the string dividing into halves, thirds, quarters, etc.  Each of these vibrations happens at different frequencies, all of which are related in a simple mathematical ratio.  We call the extra vibrational modes that reach our ears – harmonics.   It’s an extraordinary fact of nature that the string vibrates in multiple modes of displacement simultaneously.  We’ll come back to this subject in future chapters.  For now, just remember that musical instruments produce very complex vibrations.

 The simple way to get a violin string to vibrate is to pluck it.  Pizzicato is a great musical tool, but because it involves a single act of energy input (one finger plucking), it can’t produce a sustained tone.  Guitars, with their very large bodies, extend the duration of their plucking significantly, but violinists need a better way of sustaining the sound.  By dragging stretched horsehairs across the string, the movement of the bow continually excites the natural frequencies of the string and we achieve a sustained tone.  It’s like thousands of pizzicato per second.

Violinists will pay a great deal of money for a good bow – and are meticulous about the condition and tension of the bow hairs – but I don’t imagine they ever think of the wood of the bow or even the horsehair itself as containing sound.  Rather, they understand a violin achieves a singing sound through the interaction of bow hair and string.  Notwithstanding the fact that well designed bows offer significant performance improvements, when a violinist says that “this bow sounds better”, she means “this bow produces a better sound” meaning “this bow gives me a more responsive interaction with the violin.”  Violinists implicitly understand that the basic tonal character comes from the violin; the bow is the means of supplying energy to those very expensive boxes.

Here is the big picture: the food that the violinist eats for breakfast is converted to stored potential energy in the body; the movement of the bow arm transfers this energy into the mechanical interaction of bow to violin, producing the acoustical energy we call tone.

Head to Chapter 3 to see how this translates into bassoon!