Brains and Membranes

Bassoon Reed Making by Christopher Millard

Chapter 14 – Reed My Lips

As our Little Bassoonist climbed the ladders into the high register she found herself thinking about the adaptations she makes in the upper register. Her teacher often reminds her to increase air support as she ascend; scaling ladders and scaling registers both demand effort. We usually think supplying faster air or more ample air is an important part of ‘holding up’ the pitch of the upper registers. I’m going to present a slightly different take on all this.

Balance, Bassoon Reed Physics

Unless our reeds are too sharp [Baby Bear!] and stuffy, it’s usually not a problem to get a lot of sound in the lower fundamental register. In fact, most reeds with optimal compliance produce more sonority at the lower end and less at the top. The bassoon is a bottom-heavy instrument. Flutists, who struggle with the bottom octave, are frequently jealous of the ease with which we can honk out low Bbs, though flutists have a relative advantage in the upper octaves.

LB’s teacher demands she practice her scales with a bit of crescendo in the ascent and a corresponding diminuendo in the descent. This guidance isn’t because ascending phrases always require expressive growth or descending phrases always require diminishing tone, although that is frequently appropriate. Rather, the habit of adding more support in an ascending passage is a strategy to correct the imbalance inherent to bassoons: loud and edgy at the bottom and squeezed at the top.

Chapter 13 examined the acoustical reasons for this diminishing sound profile.Each step to a higher register is achieved by eliminating a strong lower harmonic; sonority can suffer as we optimize the remaining higher frequency resonances. Increased embouchure damping reduces the richness of sound by reducing the cumulative energy of these remaining harmonics. Even modest damping changes the contours of the membranes and thereby increases inertia. As we move to higher frequencies, the slight closure of the reed not only alters the MCA value but changes how the blades respond to the Bernoulli effect. Tenor register pitches in particular become less responsive to nuance and articulation.

How does our little bassoonist respond to this? By increasing air supply. Mimicking a crescendo during an ascending scale compensates for the reduced amplitude of the reed membranes. If we must lose the 1st and 2nd harmonics and all their energy, we need to rebalance input air supply simply to maintain the impression of even dynamics.

 

LB is sometimes confused by these discussions. The balance between air support and embouchure can be minefields in the pedagogy of both playing and reed making. She aspires to play in the third octave by moving the air faster, but she sometimes expects too much. Most reeds required a bit of help from the lips.

I think we can take some reassurance from the laddered acoustics that I outlined in Chapter 13. Ascending the registers demands a certain amount of embouchure damping which needs an increase in air supply to compensate. I’ve seen many young players get into throat and upper body tensions by over-reliance on air as the only tactic for holding up the upper register. I’m not necessarily advocating for larger MCA value reeds – effortless reeds are deeply appealing!! But embouchure serves a critical role in climbing the ladders. Reed making demands adaptation to the changing conditions of cane, weather, repertoire, performing environments and our emotional state. Respecting the physics will lead to better strategies in solving our reed challenges.

laddered bassoon accoustics

Chapter 10 saw our little bassoon character inside a huge, imaginary reed.

Climbing back inside, LB observes in slow motion the blades flexing. There are changes in the overall shape of the membranes as the player moves from low register to high register. In addition to an observable reduction in the aperture gap, she sees a reduction in the flapping motions in the wings. This concave collapse of the wings results from increased embouchure pressure, which transfers into these wider, thinner areas of the membranes. When blades are held a bit tighter, larger motions are restricted and help dampen the lower harmonics as well as move the reed into a Mama Bear or even Baby Bear dimension.

 

 

Wider flexing motions feed the lower harmonic standing waves for any bore length. Our typical reed profiles encourage functional concavity in the wings, reducing the amplitude of lower frequency vibration. Damping those wider motions reduces the lower harmonics in the dialogue. This strategy of damping the lowest available modes helps the reed more efficiently supply energy when we are utilizing higher bore resonances. As we climb the ladder past the 2nd harmonic area and up into the tenor range the embouchure, plus the manipulation of half-holes, vents and cross fingerings, helps eliminate the 1st and 2nd bore harmonics and allow for control in the upper range of the bassoon. My Chapter 12 assignment demonstrates this behaviour with all but the most extremely light reeds. You played the reed with your lips over the 1st wire and observed what happens as you climb the ladders. The pitches may continue to operate up into C4, but you will almost certainly find the bassoon reverting to its lower modes and sounding like a dying porpoise.

If you go back to the lips over wire exercise I suggested in Chapter 12, you will no doubt realize that if you blow REALLY hard, you can indeed extend the operation of the bassoon well up into the top of the third octave. It just takes a heck of a lot of air.

Repeating the experiment with lips on the reed but with only enough embouchure to seal the air will have taken you a little bit further – depending on how light your reeds are. But rather instinctively, we tend to dampen the embouchure and increase air support as we ascend.

But….

LB remains slightly confused. Surely, she thinks, accelerated air supply must have an effect on pitch!? And indeed, it does.

Air speed

This is a very confusing phenomenon, because in other instruments excessive volume tends to lower pitch. We see this flattening effect in the clarinet when it’s overblown. However, the bassoon will usually sharpen with increased air flow. We see this in vibrato production when the intermittent acceleration of air several times a second not only causes repetitive increases in volume but also in pitch. Sufficient air flow into a bassoon reed will also sharpen the upper bore resonances, and at an exaggerated rate! In fact, the intonation effects of embouchure and air increase substantially as we move into higher bore resonances. That’s why vibrato is so hard to temper up high, and pitch bending in the high register can be so extreme. The physics are elusive, but we presume that increased air velocity through the aperture must raise the natural frequencies of the membrane ‘shell’ as well as cause greater inward displacement of the blades and decrease that theoretical missing conical aperture. So, there’s absolutely real physical reasons why air speed might sustain both register and pitch. The evidence is with us constantly.

Next week, in Chapter 15, we are going to explore Resonance. It may not be what you think…

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 Doodles & Design by Nadina

 

 

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