Brains and Membranes

Bassoon Reed Making by Christopher Millard

Chapter 17 – LIFT

If you have managed to navigate the previous 16 chapters of this project, you might now be longing for some practical information rather than the fanciful analogies about conga lines and trampolines. Sorry, I have one more fanciful – and perhaps silly concept – to present. It’s one that helps me analyze what I feel and hear in the initial trim.

Bi-plane, flight factors, bassoon reed

Little Bassoonist would love to fly as much as she would love to master the bassoon. She dreams of soaring above the clouds while solveging 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 imagines herself immaculately garbed as an airline pilot, flying a 300 an Airbus, or during those passive-aggressive days – she’d happily pilot a stealth fighter! Anything to get up in the sky.

Everything you read from here on you might take with a grain of salt.  It’s all whimsical.

Reeds and airplanes are tied by a gossamer common thread.  Obviously, they’re both dependent on airflow and 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 gradually narrowing V shape of a bassoon reed also causes some acceleration of airflow; we have discussed how this behaviour leads to decreased pressure on the insides of the blades, pulling them together and initiating vibration.  

Thinking about different sizes of planes is a bit analogous to thinking about different sized reeds. Ultralight planes have tiny engines and don’t weight much – something like those effortless Baby Bear reeds I discussed in Chapter 12. Lightweight designs allow us to glide with nuance and ease in the third octave. A single engine Cessna is a bit heavier still nimble and efficient in the air.  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. Does that have anything to do with making your reeds better? Well, meditating on these factors will at least help you get your head away from dial indicators, refresh your thinking and get you up off the ground…

4 flight factors, thrust, drag, weight, lift, bi-plane

The factors shown here represent the forces on a plane moving forward through the air. With a little imagination we can see some analogies with how air moves through a reed (below).

The challenge in writing this ‘philosophical’ blog about reed making is finding concepts and ideas that are inclusive for a broad range of bassoonists. I’m always searching for images and analogies that might illuminate highly divergent individual techniques. Fifty years of reed making has taught me that a very broad range of profiles and measurements can still be brought to the service of the specific tonal and performing preferences of an individual. In other words, I believe that we will always tend to produce the sound we want no matter how we vary our reed designs. We can use a Papa Bear reed or a Baby Bear reed and still achieve our preferred sound.

It’s worth investigating whether these four principle factors in flight have corollaries in the bassoon reed.  

Here are the loose counterparts in the dynamics of a bassoon reed.

1. Thrust represents propulsive energy. No problem there – that’s your air supply.

2. Lift represents how a plane leverages airflow to create reduced pressure on the upper surfaces of its wings. In a reed, Bernoulli ‘suction’ continually converts airflow by repeatedly pulling the blade membranes together.

3. Weight is the airplane plus its contents – pilots, passengers and cargo. If we define ‘mass’ as a measure of a body’s inertia, then we can think of the static mass of the whole reed as resistance to vibration.  Mass is about size and thickness mostly.

4. Drag measures how efficiently the airplane’s external shapes cut through the atmosphere. In a reed this might be a measure of the inconsistencies in cane structure, profiling asymmetry as well as embouchure dampening.

Sit back and relax

Let’s focus on how a pilot might evaluate the crow of a bassoon reed! 

Little Bassoonist is dreaming of her cockpit. Her 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 panel indicators 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 her teacher has supplied. She has an expensive dial indicator!  It seems that the reed in her hands matches all the assigned measurements. Unfortunately for LB, her reed is not a precision piece of aeronautical technology; it’s just flimsy wood. Careful measuring may not assure her of a successful take off. But like an experienced pilot, LB can certainly 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 blowing ‘thrust’ sufficient to initiate vibration? If not, she intuitively increases her air supply until the reed responds by overcoming its inertia, at which point she can start listening for peeping pitch, crow behaviour and additional overblown harmonics. [See Chapter 16]

This testing stage with just a reed is 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 might offer a refreshing viewpoint. 

  • 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, as well as the resulting effect on wind resistance.

I know this is a stretch…but a bassoon reed suggests some analogies.

  • No matter the contours and dimensions, reeds with too much mass will resist the Bernoulli process. They are too stiff to allow to allow the thrust of air to overcome the inertia. 
  • 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 elasticity in the cane as well as the effect of embouchure dampening.

 

cane, bi-plane

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.

I think removing cane is an often-misunderstood process. Always ask, “When I scrape cane in a specific spot will I increase or decrease vibration?” For example, removing cane at the center point of the tip increases amplitude because it ‘leverages’ the prime area for mechanical response to air. But removing cane at the tip corners will usually weaken the membrane and reduce potential vibration. The outcome depends on whether the adjustment primarily enhances the ‘aerodynamics’ of internal flow or weakens the structural integrity of the membrane as a whole.

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.

Flight Cane 2

Cane Plane (from the Archives of the Imagination)

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

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