A Cruise Down the Bore River! Part 1

Think of all the hours you have spent mastering the complex technical challenges of the bassoon.  All those strange fingerings, the weird combination of open holes and linked keys, the mysterious boot joint.  And yet…most of us get to this point without much understanding of the layout of the bore and tone holes.  So, let’s take a voyage down that long bore from reed to bell.  You can pretend I’m your tour guide!

Welcome to all our guests.  I hope you’re vaccinated…

Our cruise follows the gradual enlargement of the bore from the bocal tip to the bell.   On the way, we’ll stop at each tone hole opening. Remember, this is not an examination of the bassoon mechanism; I presume you already know all about that. Instead, it’s a look from the inside out. I’m hoping that visualizing how the bassoon is organized acoustically might give you a better idea of how to organize your own tuning and voicing.

Our itinerary includes passage through the bocal and wing in Part 1, then on to the boot in Part 2, and concluding with the long joint in Part 3.

Put on your life jacket!

To make your journey more meaningful…

From the beginning of our journey down the bassoon, we see the bore around us enlarge at a very steady rate; the bassoon is uniformly conical.  Over the whole 250 cm length of its length, the bore undergoes a steady expansion from an initial diameter of @ 4 mm at the bocal tip to @ 40 mm at the end of the bell.  [We calculate this as a .41° taper.]  When we increase the length of the bore by closing tone holes, the overall volume increases, and the wavelengths increase, so the sounding pitches get lower.  Tone hole sizing works differently.  Enlarging the volume of a tone hole makes the pitch go up because a larger tone hole effectively shortens the bore at the position of the hole.  Bassoon makers balance placement, angle, and length to control for pitch, overtones, and stability.

So, longer and/or smaller diameter tone holes lower the pitch; shorter and/or larger diameter holes will raise the pitch. Many of you have stubborn notes on your bassoons.  For example, if your open F is sharp the solution is to make the diameter of the hole – and thus its volume – smaller.  Or perhaps your C#3 is always flat, in which case enlarging the hole will make it sharper, though often at the expense of its tonal richness and stability.

We’ll embark at the tip of the bocal with our first stop at the 29 cm mark…

‘Whisper’ vent – this little hole was added to the bassoon in the late 19th Century to allow sustained playing in the 2nd, 3rd and 4th registers.  It creates a little leak that weakens the lowest harmonic[s] for whatever length of bore you have chosen.  For example, our second octave A natural [A3=220hz] can be hard to start because the 1st harmonic low A [A2=110hz] desperately wants to sound.  This little leak at the whisper vent robs that fundamental 1st harmonic of enough energy that it allows the next harmonic at the octave [A3] to dominate. Most of the notes above Ab3 work best with that vent open, although there are a couple of exceptions.

Our journey really gets moving as we start sailing down the rubber-lined bore of the wing joint.  Our next stop…just 6 cm downriver…

High D vent – because the frequency of this note [D5= 587hz] is so high, the bore must be very short, so we need an especially high position for this vent. It’s not absolutely necessary to have this little hole. High D keys were not common in the middle of the last century; many of us learned to play high D with only a C vent. The D vent is not the primary ‘source’ of D5; instead, it adds a helpful leak in the complex fingering and discourages a lower harmonic from taking over. This hole typically has a diameter of about 1.8 mm, which is all the venting necessary for such a high frequency.

High C vent – travelling down the bore another 4 cm brings us to an almost identically sized little vent. Though the high D will usually speak without a D vent, C5 [523hz] really needs this vent to make the high C happen.  And, like the D vent, we use this for helping to make our mid-range articulations clearer.  These little leaks help establish those high notes with less of a ‘split’ attack, because they weaken the lower bore resonances that would otherwise sound.

High A vent – just down river another 5 cm brings us to the larger vent that makes A4 [440hz] possible. As you can see, the hole has a diameter of about 3.5 mm.  Although its primary function is for the high A, we use this as a speaker key for the middle octave A.  More expensive bassoons often have an ‘A bridge’ which connects to the whisper key and causes the bocal vent to close on a sustained A3. When both vents are open, the A3 can be a bit sharp, the sound a bit unfocused, and the diminuendo a little more challenging.

woodwind acoustics bassoon wings

Before we continue our downstream passage, let’s have a little refresher about the relationship between bore length, tone hole placement and tone hole size.

  •  the longer the bore, the lower the frequency
  • as the bore gets longer the tone holes get larger and further apart.

These are features of all conical bore woodwinds and explain much of the bassoon’s extended and complicated mechanisms. We typically designate the bocal, wing joint and small side of the boot as the “down-bore”; the large side of the boot, the long joint and the bell, are the upbore.  These terms refer to the general movement of air through the length of the bassoon.  Of course, sound waves themselves travel both directions on this slowly moving river of air, both down the bore and back up to the reed.

High E [optional stop on our journey…] The 4 openings we have seen so far are all made with metal tubes. Our next stop is the first hole with exposed wood and a ‘seating’ cut on the outside surface to accommodate a pad cup, the tone hole for E5 [659hz].  High E is a 20th Century development, built in response to challenges like Ravel’s Piano Concerto.  This larger tone hole [4.5 mm] has the added advantage of allowing a really good trill over the break from open F3 to G. You will see that this hole is always opened in conjunction with an identically sized hole a couple of centimetres lower…

F# trill hole – trills from E3 to F#3 would be an absolute nightmare without this hole. It does double duty by assisting the previous hole in allowing a good high E!

F hole – this is the first of the 3 open holes on the ‘wing’ of this joint. All that odd-shaped extra wood is acoustically necessary to allow longer tone holes as well as comfortable ergonomics for our left hand and first three fingers.  Unlike the smaller vents, these tone holes are all cut at pronounced angles to the direction of the bore.  Without these angles, the F hole would have to be much higher…

E hole – …and this next big hole would have to be much lower unless you happen to have fingers like a lemur…See how it angles up to accommodate the spread of your first and second fingers.

D hole – …Without spaghetti fingers, this D hole would have to be another couple of centimetres lower.  In addition to their different angles, these three open holes also have different sizes, a way of balancing tuning and sonority to their different entry points in the bore.  [We’ll talk later about some of the principles involved in this process.]  Take careful notice that the three open holes are all lined – either with rubber or metal tubes. This is necessary to avoid the damage and size distortions that occur when bare wood is exposed to condensation and spit.

woodwind acoustic tone holes vents bassoon

I want to remind you of an important concept when talking about bassoons: the names given to these holes are associated with the pitches that sound when the holes are open. For example, F3 sounds when the finger is open; when the finger is closed, we bring E3 into play, and so on.  This nomenclature becomes important to understanding the larger tone holes in the boot and long joint.

Eb trill hole – several centimetres of travel and we arrive at another angled exit from the bore. When its pad is open, this hole produces Eb3 [155 hz].  What’s so odd here is that this hole is past the D hole! You might expect that to produce a half-step higher pitch this hole ought to be between the E and D open holes.  But while this hole is further down the bore, opening it creates a higher resonating frequency than the open D hole alone.  Typically, this hole is opened by a key in the left hand; when it’s controlled by the right hand on the boot it also gives us a couple of extra functioning trills, including the trill from C4 to D4 in the Mozart bassoon concerto.

C#/D# trill hole [also high B vent…] – the exit for this hole is just slightly further down the bore. It has two functions; when combined with an open C# hole it will give a decent whole step trill. But it is more frequently needed for playing high B.  The complex cross-fingerings are difficult to explain in the mathematics of bore acoustics.  Suffice it to say, high B needs to have a relief of acoustical pressure to work well, and this position near the bottom of the wing joint has proven to be the best spot.

C# hole – here we are with the last stop on the wing portion of our cruise. Obviously, this hole turns C3 [231hz] into C#3.  But it’s in a compromised position due to the larger structure of the bassoon; you need to make a connection to the boot somewhere.  You probably tend to think of the full length of the wing joint producing a C natural, right?  Actually no. We need a couple more centimetres to accommodate C3, so we ‘borrow’ this from the boot.  So, why isn’t the wing longer?  It’s not to fit into the case… The problem is the two sides of the boot really need to be the same length.  If we didn’t have to place the low F tone hole where it is, it’d be possible to make the wing joint longer!!  That horse left the barn in the early 19th century, leaving us accommodating the tenon connection and positioning the C# hole where we can.  To make the C# work with the tenon and socket we have, its hole needs to be at an acute angle and quite long.  That length requires some extra wood, which is why the wing joint has a sloped ‘nose’ where the C# tone hole exits.

In Part 2, we’ll move into the boot joint.

woodwinds acoustics bore bassoon

All sketches by Nadina.

Continue your Cruise in Part 2!