Tuesday, May 15, 2012

The Bassoon Reed as a Valve or a Lever

I threw out some challenging opinions about profilers and reed making in my most recent post.  Although it's really tough to discuss reed making in this medium, I think it's time for me to back up what I've said with some facts about bassoon reeds.

I've tried really hard to discover "laws" or "rules" that work for ALL German scrape reeds by reading articles on reed making, comparing notes with colleagues and gleaning information from prominent former students of major bassoon teachers.

While everyone must ultimately find his/her own way with reed making, I believe there are some very simple concepts that apply to all players of German style reeds.

The bassoon reed is a VALVE -- it is the gateway through which air enters the instrument.  The valve works in four phases:
  1. A static phase -- this phase can be observed by taking the reed off the bocal and look through the tip.
  2. An inflated phase -- this is the nearly doubling of the tip opening caused when air first enters the reed from the mouth
  3. The acceleration of air inside the reed tip causes suction, making the tip opening go back through the static phase into the 
  4. Closed phase -- here the reed tip is forced shut  
Then, due to the pulsation of the air column in the bassoon and a steady supply of air from the player, the reed's vibrating cycle becomes operated by the air column in the bassoon which is pulsating.  The reed tip opens again and the cycle starts over. The reed repeats this cycle many times per second.  This is called a steady state oscillation.

Thus, when making reeds, it's very important to build reeds that will reproduce this four-phase cycle exactly.  The reed tip must open and close many times, passing through the most open and closed positions and returning to the static phase when finished.

A material that has the ability to reproduce these four phases exactly many times is said to be elastic.

By this I don't mean that the material is especially flexible or stretchy. Rather, when a well-made reed tip is manipulated by the lips and air stream out of its static position, it is elastic if it has the ability to return EXACTLY to the static position thousands of times.

We've all had reeds whose tips collapse after playing on them a short while.  These reeds are not elastic and will not reproduce the static position for very long.  The response, pitch and tone quality of the reed change during this short time.

Over time, all reeds lose their elasticity.  Notice what happens with older reeds.  They tend to close down and feel weak in the mouth.  Bacteria in the mouth and other factors have weakened the cane and made it less elastic.

So how do we make reeds that are elastic?

Symmetry is extremely important.  The top blade must be as thick as the bottom blade at all points.  This is accomplished through accurate gouging and profiling and ultimately precise scraping.

Symmetry is also maintained through forming the tube, shaping and wire roundness.

This brings me to the next simple description of the bassoon reed.

It is a LEVER.

In order for the reed tip to stay open (and for it not to open too much when soaked), parts of the reed act as a lever.

These would be:
  • The wires -- they keep the two blades together, but also prop open the tip and provide contour to the tip opening.
  •  The bevel -- this activates the lever action of the back part of the tube.  The third wire and wrapping hold that end of the reed in place, providing "lift" to the other end -- the tip.  The fulcrum for this "see-saw" is the second wire.  You can see the lever action of the bevel in action by holding the folded, formed blank with wires off in your fingers. Press the tube ends together with the fingers of one hand while holding the blank together at the second wire placement with the fingers of your other hand and notice that the sides of the reed blade will gape open.  
 There's your lever!
  • The shape -- the back of the shape (the amount of back flair towards the butt end) contributes to the lever action.  More flair/less lever, less flair/more lever.
I want to credit bassoonist, reed maker, and author, Jim Kopp for these ideas.  I highly recommend his excellent articles on reed "theory":

"Physical Forces At Work in Bassoon Reeds"

"A Conversation About Resistance and Compliance in Bassoon Reeds"

These can be found by searching the IDRS website.

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