Brains and Membranes

Bassoon Reed Making by Christopher Millard

Chapter 17 – LIFT

Those of you who have patiently followed this blog for several months might be longing for some practical information rather than the fanciful analogies about conga lines and trampolines. Sorry, I have one more holistic concept to impart. It’s one that helps me analyze what I feel and hear in the initial trim.

Little Bassoonist  would love to fly as much as she would love to master the bassoon. She dreams of soaring above the clouds and humming Jolivet. She’s not particular about what kind of plane. A glider will do, or maybe a compact Cessna for those weekend flights. Sometimes she sees herself immaculately garbed as an airline pilot, flying a 300 tonne Airbus, and on those passive-aggressive days – she’d happily pilot a stealth fighter!

Anything to get up in the sky.

Reeds and airplanes are bound by a common thread because they are both dependent on airflow, especially the relationship between air velocity and surface pressure as expressed in the Bernoulli theorem. The typical curved top/flat bottom shape of an airplane wing produces accelerated air flow and reduction in surface pressure on the top wing. The V shape of a bassoon reed causes acceleration of airflow and a continual tendency to pull the blades together.

Thinking about different kinds of planes is a bit analogous to thinking about reeds. Ultralight planes have tiny engines and low mass -something like those effortless Baby Bear reeds that allow us to float with nuance and ease in the third octave. A single engine Cessna is heavier, but it’s still nimble and efficient in the air, like a good flexible Momma Bear recital reed. On the other hand, that big Airbus requires 50,000 HP engines to get off the ground. But they can carry huge loads and go long distances – like the requirement to project a solo passage in a 90 player orchestra.

What are the primary factors to consider in achieving flight? The plane needs enough lift and thrust to overcome the weight of the plane and the drag caused by friction during forward motion. What’s this have to do with reed making? Well, meditating on these factors might help you get your head away from dial indicators, refresh your thinking and get you up off the ground…

The factors shown here represent the forces on a plane moving forward through the air. By shifting perspective a bit we can see similar force when air is moving forward through a reed (below).

In Chapter 16, I described the acoustical behaviour of reeds unattached to bocal and bassoon. As we begin adjusting our reeds, it can help to visualize each of these four interacting factors.

So, let’s examine the crow from a pilot’s point of view!

Little Bassoonist is dreaming of her cockpit. She is reviewing the manual. This small plane requires her engine to run at 1700 RPM for takeoff and with a normal load she will become airborne at 60 mph. The instruments deliver precise information for a safe and predictable flight. But what would she do without an instrument panel? I expect an experienced pilot might remember the sound of the engine at 1700 RPM and have a visual memory of what 60 mph looks like.

Back at her reed desk, LB is reviewing all the recommended measurements from the manual her teacher has supplied. She has an expensive dial indicator and a sharp profiler blade! The blank in her hands precisely matches all the assigned measurements. Unfortunately for LB, her reed is not a precision piece of technology; it’s wood. No amount of measuring is going to assure her of a good take off. But like that experienced pilot, LB can remember what appropriate air flow feels like.

With the blank in her mouth for the first time, she gently tests out this ‘remembered’ air flow. Is the ‘thrust’ sufficient to initiate vibration? If not, she intuitively increases her air supply until the reed responds, at which point she can start listening for peeping pitch, crow behaviour and additional overblown harmonics. [See Chapter 16]

This a moment fraught with uncertainty for young reed makers, and it’s when all the individual approaches diverge. For example:

• Is the crow loud and raucous with excessive low frequency components?
• Is it a tight and sharp peep, unwilling to open into the complexity of a crow?
• Does it feel strong, resilient and vibrant?
• Is it stiff like a popsicle stick with very little available vibration?
• Is the overall challenge to encourage more vibration or to tame too much vibration?

The Weight/Lift/Thrust/Drag model offers possibilities.

• No matter how efficient its wings or engine, a plane with too much cargo will not get airborne.
• The aerodynamics of the plane are designed to operate within the parameters of the other three forces. Lift is modified by weight, thrust and drag.
• Thrust is determined by the power of the engines, which exert forward momentum via the structure of the fuselage. That thrust is attenuated by the weight [mass] of the plane and by the aerodynamics of the wings.
• Drag is determined by the profile of the body and wings and the resulting effect on wind resistance.

In a bassoon reed we see some analogies.

•  No matter the contours and dimensions,, reeds with too much mass will resist the Bernoulli process. They are too stiff to allow lift.
• The profile of a reed is designed to balance structural stiffness with flexible response to air flow and to permit natural embouchure damping.
• The driving thrust of airflow is controlled by the blowing preferences of the player in any given musical circumstance. The response to airflow is attenuated by thickness [mass] and the aerodynamics of the profile.
• Drag is associated with lack of plasticity in the cane as well as the effect of embouchure dampening.

As we begin trimming, we are faced with the decision of how much to take from the front, sides, middle or back. Many bassoonists start with thinning the tip and then move on to the wings. This technique produces thinner cane in the area where the Bernoulli sucking force is most pronounced – where the membranes in their static position are closest together. The typical thin tip/weak wings/heavier heart profile serves the aerodynamic efficiency for air entering the reed.

Aeronautical engineers are skilled at creating strength while reducing mass. Metallurgical advances have produced metal composites that optimize balance between rigidity and flex. Millions of years of evolutionary advances have produced in Arundo donax sufficient longitudinal and radial strength to grow 20 ft tall and withstand all weather. But the cane would much rather be in the field than stuck on a bassoon!

• Longitudinal strength in an airplane fuselage is essential to staying aloft.
• Longitudinal strength in a reed is essential to staying up to pitch.

Regrettably for us, at the granular level cane is highly inconsistent. We typically find areas of mushiness unevenly distributed between the strong vascular bundles that give the blades rigidity. Softer materials vibrate with less resiliency and at slower frequencies, so they correlate to ‘drag’.

Bernoulli-initiated lift is not the only force that allows airplanes to fly, but it’s the one that seems to apply to bassoon reeds. Here are some points of comparison:

• Reduced pressure on the upper surface of a wing lifts the entire plane. That force depends on sufficiently stable connections where wings meet fuselage.
• The big variable in the operation of an airplane is the weight of passengers and cargo.
• Reeds with too much wood in the back are analogous to an overloaded plane; they’re both going to require increased thrust to compensate for weight.
• Reeds with too much wood in the tip – front loaded – are like airplanes with poor aerodynamic design in the wings requiring extra airflow.
• Commercial aircraft have to be careful about the distribution of load. If a half full plane seats all the passengers in the front row the plane will keep its nose down, require more power to lift off and present more drag.
• Reeds need care in the distribution of load. Too much cane in the tip inhibits Bernoulli lift, lowers the pitch [especially in the higher operational modes] and will be a drag to play…
• The backbone of a plane is the airframe within the fuselage. It requires a careful balance between strength, weight and flexibility.
• The backbone of a reed, though often presumed to be the ‘spine’, is a more complicated balance between the longitudinal resilience of the fibres, the cellular structure [at the molecular level], the original radius of the plant and the leverage exerted on these factors by the structure of the tube.
• Flaps and flexible wings are necessary to manage changes in speed and altitude. Flight efficiency is a dynamic process as conditions evolve.
• Flapping, flexible wings in reeds are necessary to manage changes in musical dynamics and registers.
• Airplanes don’t fly at fixed altitudes. They must be capable of more thrust and lift at takeoff, and then find cruising altitudes that are more efficient and economical. Pilots adjust wing shapes [flaps] to adapt to these differences.
• Bassoon reeds don’t operate in single notes or registers. They must be capable of more lift during attacks and be able to climb the ladders from fundamental to register to 2nd harmonic notes, 3rd harmonic tenor register and on up into the wild blue yonder of the altissimo register. Bassoonists constantly adjust membrane shapes to adapt to these differences.

So, what’s the point of all these comparisons?

I like to think of the two blades of the bassoon reed, interacting in reasonably balanced fashion, as small airfoils. Stretched and extended over lengths approaching 30 mm and maximum widths of 15 mm, these singular membranes are profiled to deliver aerodynamic response unique to the preferences of each player. All of these analogies to flight are a way to focus our attention on the ‘input response’ behaviour outlined in my earlier blog chapters, just as my trampoline analogy focuses on the ‘output response’ to standing waves within the bore.

As you think about whether these unusual models have any relevance to your reed making, I’d ask you to begin considering a really important question which I’ll take up in the next chapter. “Should we adapt our profile preferences to match our shapes or match our shapes to suit our inherent profile preferences?”

Chapter 18 – Chickens and Eggs

Read more about Christopher Millard. Chapter 1 – The Craftsman Chapter 2 – Can you explain how a bassoon reed works? Chapter 3 – Surf’s up! Chapter 4 – The Physicist’s Viewpoint Chapter 5 – The Big :Picture Chapter 6 – We’ll huff and we’ll puff… Chapter 7 – Look Both Ways Chapter 8 – Dialogue Chapter 9 – The Big Bounce Chapter 10 – The Incredible Shrinking Bassoonist Chapter 11 – A Useful Equation  Chapter 12 – Goldilocks’ Dilemma Chapter 13 – Stairway to Heaven  Chapter 14 – Reed MyLips Chapter 15 – Resonance Chapter 16 – Corvids & Cacks Chapter 17 – Lift  Chapter 18 – Chickens and Eggs Chapter 19 – Chiaroscuro  Chapter 20 – Donuts Part One / Donuts Part Two Doodles & Design by Nadina