Author: jhoyla
Date: 2008-09-01 12:14
I admit to a lot of confusion regarding your terms; I am not sure why, when you take the side measurement down to 64, that this somehow takes the "peak too close to the tip edge" - logically speaking, if the sides of my inverted chevron are at 64, the "peak" of the chevron will be commensurately lower, and my overall tip length so much greater.
Also, I am not happy isolating just one feature and analyzing it, without paying attention to the whole reed; it is not the way I think about reedmaking. For example in your description you do not mention the steepness of the slope from the heart down to the inner tip; I think this has even more of an effect on the overall performance of the reed than the chevron-angle subtended at the peak. And is this slope shallower at the peak, steeper at the sides? Or the opposite?
How deep and broad are your windows?
How thick is the spine?
And, as we all know, even if you make two reeds that look exactly the same externally, they can sound extremely different because of differences in strength of cane ... :-(
That said, here are the things I try and keep in mind when I make a reed. Are they the same thoughts that you have?
A reed's job is to set up longitudinal vibrations in the airstream, the exact frequency of which is governed by the length of tube (i.e., what finger are down) and octave keys etc. (which "leak" the fundamental component thus leaving the 1st or 2nd harmonic to sound). Any extraneous vibration - as an example, if one quadrant of the reed vibrates differently from the other three - will cause unwanted overtones that can sound "reedy", "buzzy" and "squeaky".
When we create a reed, we aim to encourage those longitudinal vibrations and minimize the "bad" vibrations. The only generalizations that I have found, are these:
1. The blades must seal perfectly, to within 1mm of the tip (escaping air, no matter how small, wreaks havoc with the standing-wave formation inside the reed).
2. The extreme tip must be thin enough to respond easily at low wind speed (a stiff tip is very hard to get vibrating, and will naturally tend to vibrate faster than needed). My corners are usually 3/100ths of a millimeter or less.
3. The center of the extreme tip must be marginally thicker than the corners. This relationship must continue smoothly all the way through the reed back from the tip, through the inner tip, shoulder, heart and back, providing a structural center-line and support. (this encourages the vibrations to move front-to-back and not laterally). Think of it as a "focus line", leading vibrations down into the instrument.
4. Balance. All four quadrants should ideally be exactly the same (otherwise cross-vibrations [== unwanted overtones] develop).
5. The inner tip (from shoulder to extreme outer tip) must grade uniformly with no hills or valleys, otherwise a section of the tip may vibrate independently of the heart (== unwanted overtones).
6. The tip "leads" the vibrations into the heart. The heart must be heavy enough to stay true to the fundamental note with few overtones, but light enough to vibrate easily at mp wind (this is usually accomplished by taking cane from the sides of the heart, not from the center).
7. Thinning the back allows the heart to vibrate independently, and reduces the heavy springing effect from the back (this has the effect of reducing high-frequency overtones). Over-thinning the back affects the structural integrity of the reed (a weak reed collapses very quickly). Free up the heart without affecting the structure.
That's about as far as I have got, and I welcome corrections or different ideas. I hope this helps someone!
J.
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