Time for a refresher…

The Scream

When it comes to reed-making we are mostly creatures of habit.  We are generally disinterested in thinking about the big ‘WHY’ questions.

This reluctance is easy to explain.  Reed-making is an empirically driven craft; we advance by trial and error. Struggling young bassoonists may want specific instructions from an experienced teacher, wanting clear rules to follow.  With a lesson approaching or an important concert looming…the idea of taking precious time to think about the physics of your reeds?

Uh, no thank you…

Efforts to develop an understanding of the physics underlying the reed making craft tend to get quickly subsumed. I suppose it stems from a skepticism that theoretical knowledge can actually make a difference.  Sticking to the ‘tried and true’ is a reliable strategy – provided your success rates are high enough.

Oddly, in my 50 years as a working bassoonist I rarely remain attached to a ‘tried and true’.  I guess I was always fascinated by the variables: big reeds, small reeds, wide reeds, narrow reeds, easy lips, strong lips.  I think you need to remain open to trying different paths to be true to your evolving voice.  The ultimate goal is to spend less time at your reed desk while following that path.  If you are willing to stay flexible in your thinking, it helps to define some universal principles.

Elsewhere on this website you will find a lengthy exploration of the ‘how and why’ questions. It’s a collection of essays outlining a physics-based understanding of how reeds work.  As a teaser, I thought I might offer here a brief refresher of the most basic question: what does a reed actually do?

 

Roll up your sleeve!

It all begins with a willingness to visualize the working relationship between reed and bassoon and understanding that bassoon reeds aren’t the source of sound but rather the source of energy.  It’s an important distinction.

Bassoon sound emanates from the back and forth ‘sloshing’ of longitudinal pressure waves in the tapered bore of the bassoon.  You can imagine water sloshing back and forth in a tank to help picture this. In that water tank we can see the waves.  Why?  Because water doesn’t compress, so the energy of the wave has to go somewhere.  Ups and downs, waves and troughs.  However, air does compress so the energy gets organized into waves of compression and rarefaction – oscillations between high and low pressure.  Just as the frequency of water sloshing is determined by the size of the tank and the volume of water it holds, so is the frequency of air sloshing determined by the diameter and length of the bore and the volume of air it holds.

 

You create the sloshing waves in a water tank by some form of excitation at one end.  Kicking will work in a bathtub, if you don’t mind complete disorganization. But if you’re looking to set up predictable waveforms, the experiment works better when you have a movable end wall of a tank. You can gradually set up organized ‘standing waves’ by coordinating the excitation rate with certain natural wave frequencies, determined by the volume of water.  The wave patterns that form and sustain in water are transverse waves, and clearly visible.  [Don’t fear the terminology; if you’ve been to the beach you know what a transverse wave looks like.]  The waves that form and sustain in an air column are longitudinal waves, and are invisible.  A human conga line is a good way to imagine what longitudinal waves would look like.

Just like in the water tank, sloshing pressure modes in a wind instrument become organized when the excitation frequencies are linked to the natural wave frequencies. Reeds are the excitation mechanism and the speed of their oscillation is controlled by the natural wave frequencies inside the bore.  The reed blades form an enclosure to the small end of the bore, moving along with the sloshing while at the same time delivering a constant input of energy.

I have often seen a reed described as a tuned oscillator. It’s not! Don’t confuse the peeping pitch of your reed or the more complex rattle of the crow with what transpires once you attach it to your bassoon. Those sounds are just indicators of the size and stiffness of your reed and predictors of how well the reed is likely to serve the bassoon’s resonating frequencies.  They mean different things to different players and reflect the variable shapes, profiles and embouchure preferences that go with them.

 

 

The way I see it, the bassoon plays the reed!

Our lives as bassoonists are focused on the unidirectional sensation of blowing through a reed into a bassoon, so we therefore assume that the sound comes from the reed and gets amplified and transformed by the bassoon.  In fact, it’s a bidirectional process with a controlling feedback mechanism.  The bassoon needs a reed like a violin needs a bow; horse hair does not have an inherent sound by itself and neither does arundo donax.  A bow transforms energy from the bow arm allowing the string to vibrate.  A reed transfers stored lung pressure allowing the air column to vibrate, exciting the natural resonating frequencies in the bassoon according to the air column length you have chosen.

But wait!! Why are we always testing peeps and crows?  Don’t they play a part in the sound?  Well, yes – the reed does ‘kickstart’ each note with some of its own oscillations [these are indicated in its peep/crow].  But it very quickly becomes a responsive servant of the natural frequencies within the air column. The reed’s oscillation frequencies are controlled by the pressure variations experienced between the blades.  Though we can control the loudness of the sound by delivering more blowing energy, we cannot control the primary frequency of the note produced.  At least, only to a relatively small degree.

Of course you can influence both pitch [frequency] and colour [harmonic content] by changing things in the reed. Size and stiffness are the major factors for both pitch and response. The pitch effects are simple: anything that makes the bore effectively shorter will cause sharpness, and anything that makes the bore effectively longer will cause flatness.  And yes, the bassoon will ‘allow’ pitch adjustments up or down – but will do so grudgingly at the cost of tone [harmonic complexity] and flexibility [physical efficiency].

I like to define reeds as pressure-controlled valves that convert steady air pressure from your lungs into very fast pulses of air, but delivered at precise frequencies. This definition can be confusing until you understand how we use the word pressure in the term ‘pressure-controlled’.  It does not refer to your blowing pressure! Rather, it’s the bassoon’s oscillating internal acoustical pressure which is ‘felt’ at the start of the bore within the blades of the reed.  Those oscillations – natural alternation between high and low pressure – are caused by the longitudinal sloshing behaviour of sound waves in the bore. Their frequency is defined by the design of the bassoon, not by your reed.

Understanding all this begins with respecting the instrument’s almost complete control over frequency behaviour.  When you choose to finger a middle octave ‘A’ the air column within your bassoon really wants to vibrate at a frequency of A=220.  It’s true that the bassoon can be persuaded to play a bit sharper or a bit flatter by changing your embouchure or your air pressure.

Let’s dig into this a bit. High A on a bassoon operates at 440 hz, [pressure waves sloshing back and forth 440 per second].  To sustain this natural resonating frequency, the reed must supply energy pulses 440 times a second.  If we finger high Bb, the reed needs to increase the frequency of its energy inputs to 466 times per second.  You can make those internal pressure waves slosh back and forth fairly well from 438 to 445 hz, but asking for anything outside of this range is asking for trouble. If your reed design forces the system to operate at too high a frequency both your tonal richness and your response will suffer.  Playing sharp is not pleasant for your colleagues, but it’s equally unpleasant for the bassoon, which is designed to maximize harmonic complexity within narrow frequency ranges. I’ll explain…

Bassoons manifest a complex array of harmonics at every moment.  You can think of harmonics as overlapping sloshing modes; frequencies that live in the air column in addition to the ‘fundamental’ oscillation.  For example, if you play the lowest A on your bassoon, you will activate a basic fundamental frequency of 110hz.  But the air column will also setup additional sloshing frequencies at 220hz, 330hz, 440hz, 550hz, 660hz, etc.  These overtones are part of that low A, and include the octave higher  A, 12th E natural, the two octave higher A, C#, E, G natural and so on. This is one of nature’s marvels and makes acoustical instruments so rich and varied.  It’s a beautifully organized – though complex – stew of harmonics.

Each note will have variable amounts of those harmonics at any given time. Some notes will have a strong fundamental while others will show stronger second or third harmonics. Every note must include the  participation of these higher components, but with huge variation in the relative strengths of the harmonics from note to note. These inconsistencies are part of the charm and character of the bassoon.

The pitch effects are simple to categorize. A point made above is worth repeating…Anything that makes the bore effectively shorter will cause sharpness and anything that makes the bore effectively longer will cause flatness. You all know this.  But remember there is a limited range to this flexibility, for while the bassoon will ‘allow’ pitch adjustments up or down it is always at the cost of sound and efficiency. It’s important to ask not what you want from a reed but what your bassoon needs!  The bassoon is asking for constant reinforcement of its harmonically complex bore vibrations.  The qualities we are seeking sit on the precipice between what we think we want and what is ideal for the bassoon.

 

I hope that didn’t hurt…

© The Council of Canadian Bassoonists. Website by Mighty Sparrow Design.

Contact Us

  • Are you a bassoonist of any age looking for help?
  • Do you wish to donate reeds, music or even a bassoon?
  • Do you have a bassoon event to publicize?
  • Do you have ideas, questions or comments about our website content?

COCB Footer Contact Form