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Re: Two reed cutting questions

Author: mschmidt
Date: 2008-09-01 18:26

Well, I think about reeds a little differently...but I don't think anyone understands reeds well enough to be certain about these sorts of hypotheses.

You say that you don't want any "bad vibrations" that are caused by parts of the reed vibrating at different frequencies. But the fact of the matter is that the reed has to be able to vibrate at a whole range of frequencies if you are going to be able to play more than one note! I always thought the goal was to make a reed that could vibrate at many frequencies.

I also never thought of back as freeing the heart to vibrate. I always thought of the heart more as a relatively stationary fulcrum that allows for independent vibration of both the back and the tip. I see the function of the back as a sympathetic resonator that filters out the higher frequencies from the tip and supports only the lower frequencies. But, as I said, I don't think anybody has a rock-solid understanding of just how reeds work....

I also don't really get the "longitudinal" vs. "lateral" vibrations argument. What you have at the top of the staple is an oscillation of air pressure as a function of time. This is caused primarily by the opening and closing of the reed, with the pressure increasing as the reed opens to allow air from the mouth (at a higher pressure than the atmosphere) to enter the tube. Secondarily the volume of the reed cavity expands and contracts in response to the pressure changes caused by the opening and closing of the reed. I think this is where the back of the reed has the greatest effect; the sharp pressure changes caused by the sudden opening and closing of the reed essentially translate into high-frequency energy (if you know physics, think about the Fourier transform of a delta function...), and the flexibility of the back of the reed essentially acts as a damper, expanding ballon-like to reduce the suddenness of this change. The balloon-like expansion of the sides of the back would in fact have a "lateral component" of vibration relative to the comparatively immobile spine, but this doesn't matter--the derivative of the air pressure as a function of time at the tip of the staple is lowered, and this should damp out higher frequency overtones.

I think what frequently makes a good reed are precisely those things that "complicate" the above analysis. Blending the tip with the heart means that it is harder to define where the tip ends--and thus harder to define the fundamental frequency of the tip/airgate. The result is an "airgate" that can function at any fundamental frequency you choose by the fingering of the oboe. Blending the tip in with the sides, around the heart, allows the back to "couple" with the tip, perhaps helping the back to amplify the fundamental frequencies and filter out the overtones.

But all this is speculation; I am afraid we are stuck in a poorly-controlled experimental environment, and theory isn't going to help us much.

Mike

Still an Amateur, but not really middle-aged anymore

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