Daniel Bernoulli [1700 – 1782]  Heck of a guy.  Life of the party.

In Chapter 6 I showed you this little beauty: P + 1/2pv2 + pgh = constant

Just remember that when air flows next to a surface, and increases in velocity, the measurable pressure on that surface is reduced.

Bernoulli’s idea helps explain a lot in life, from carburetors to naval architecture.

Consider the miracle of flight.  Much of the lift from an airplane wing can be explained by this principle. The shape of a wing will usually include a more curved upper surface and a flatter underside.  This means that air has to travel further on the upper surface of the wing then the lower surface, so it must travel faster. Bernoulli tells us that the resulting pressure on the upper surface of the wing will be less, leading to a good deal of lift.

Blowing into the bassoon reed accelerates the flow of air, reduces the internal surface pressures and causes the blades to be drawn together.  It’s the first step in the process of converting blowing pressure into sustained bassoon tone.  Just as Bernoulli’s Principle helps us understand how an airplane gets off the ground, it also explains the process by which the reed begins its engagement with the bassoon.  That reduction of internal surface pressure brings the blades of the reed together, gives a constant ‘lift’ to the system and keeps the tone in flight.  Even on a bad day, that should lift your spirits.

Bassoon reeds are a special class of acoustical pressure valves: they initially close in response to the input of blowing pressure [from the player] and then open in response to the output of acoustical pressure [from the bassoon].  Bernoulli shows us the process, how the blades come together when we blow.  Once they are closed there’s no longer a flow of air to hold the blades together, so the natural resiliency of the cane forces the blades open.  Once open, the airflow from your lungs is readmitted, the air velocity increases, the internal pressure drops and the blades are drawn closed.  This process happens over and over and over.  Voila! We have a sustained tone.  What’s critical here is the timing, the degree of control that the acoustical pressure has on creating sustained tone.

The frequency at which this constant reengagement of the air stream occurs is determined by the change of internal pressure inside the reed.

Remember: the reed sits at the apex of the conical bore, and the interior experiences constant variations in pressure as the sound waves within the bore oscillate back and forth.   The blades of the reed will be forced open when the internal pressure begins to increase, allowing airflow to resume and reinitialize the process.  The shift of internal pressure from minimal to maximal pressure occurs as those Conga Line sound waves change direction, a process occurring at the frequency of the fundamental resonance of the bore.  If the player has chosen to play a low A, 110 times a second the pressure waves in the bore shift direction. 110 times a second the pressure at the apex of the bore [where the reed sits] alternates between rarefaction and compression.

That shift from low pressure to high pressure controls the timing of the reed valve opening.  The bore vibration harnesses the reed valve and forces it to operate at the frequency it wants.  So, at 110 Hz, repeated compression waves signal the reed to open 110 times a second.  Each time it opens, the influx of air from the player causes the valves to close and emit another pulse of energy.

Over and over, at the rate of the fundamental frequency of the note being played, the reed reengages the acoustical activity in the bore – and is at the same time controlled by it.  As a pressure controlled valve, the reed’s operational frequencies are determined by the natural resonating frequencies for the note you are playing.

It is a two way street, a bidirectional dialogue, and a complex interaction wherein the bassoon reed serves the acoustical needs of the bassoon.

In Chapter 8 I will explain more about that dialogue.

Chapter 1 – Starting Down The Path  Chapter 2 – It’s A Simple Question? 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 MyLipsChapter 15 – Resonance Chapter 16 – Corvids & Cacks Chapter 17 –   Chickens and Eggs Chapter 18 – Chiaroscuro  Chapter 19 – Donuts​ Chapter 20 – Balance Doodles & Design by Nadina

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