 The Oboe BBoard
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Author: vboboe
Date: 2008-08-29 17:29
OK, 2 simple questions, complex answers anticipated ... your insights please, and thanks in advance :-)
American scrape design
1. What playing characteristics or effects are there in the finished reed when the apex is designed steeper or flatter depending on where one starts the side measurements?
2. Do you deliberately cut your apex a bit more or a bit less to get specific characteristics out of your reeds? What?
For sake of discusssion, let's assume the following are consistent measurements
tie-on length 73/74 (let's average that at 73.5)
fold clipped length 72mm
measurement for finished reed length 70mm
(however, this is just the 'standard measurement', not necessarily the tuned reed's final length, which could be anywhere from 69-71.5)
side measurement for sides of apex is taken up to 70mm each time when making the crossbuck with pencil marks or diagonal knife blade cutting position
OK, terms in quotes are 'relative comparison'
if one starts the sides of the apex at 64 & measures diagonally to 70, this gives a 'steep' apex with 'long' sloping sides and a 'sharp peak'
and, if the sides are started at 66 to 70, this gives a 'low' apex with 'short' sloping sides and 'flat' peak
in the middle between these, measuring 65 to 70, moderate apex
At the moment i'm favoring the 65mm measurement, because after doing the blend there's just a bit more distance of thinned wood between top of apex and feathered tip edge, measuring this along the mid-line -- this makes the tip flexible enough for me
the 64 measurement took the peak too close to the tip edge, giving a midline distance from apex to tip edge that's too woody/resistant as a result, have to blow harder to get the tip to respond, can't do pp with it
Q. does the shape of the apex (as described above) significantly alter
-- mix of upper/lower partials?
-- tonal focus or spread?
-- relative stability in upper register?
-- resonance / richness of tones in upper / lower registers?
-- ease of response at ppp to pp, yet reed's still able to hold sturdy ff?
-- and / or ... ?
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Author: Dutchy
Date: 2008-08-31 12:47
It's Labor Day Weekend, I think everybody's out of town until Tuesday.
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Author: vboboe
Date: 2008-08-31 16:56
... yes Dutchy, the questions are out there and i'm not actually expecting responses until later because it's a matter of having a last fling long holiday weekend and thinking it over first before new season gets going (even though i'd impatiently like everything answered weeks ago!) ... so it's lovely to get your early response, thanks :-)
Where are you at with your reed choices these days?
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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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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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Author: vboboe
Date: 2008-09-01 20:48
jhoyla, thanks for your thoughtful answers, and clarifying the function of the midline bundle of continuous long fibres
Your Q & A follows
Q <<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>>
OK (2) answers to this
A1. If one draws diagrams on paper with ruler & sharp pencil (perhaps raising the measurement scale ratio 3:1 for easier-to-see results) and if one measures cross-bucks 64-70, 65-70 and 66-70 (or indeed, the same using 72 as the consistent measurement) it's clearly demonstrated that the peak of the apex *rises higher* when the sides are measured shorter (64) and vice versa = the higher the peak, the less distance there is between 70 clipped tip edge and the woodier midline blend in the tip
A2. On the other hand, if one is unconsciously competant and automatically positions the knife at the same diagonal angle either direction irrespective of the short, medium or long measurement on the sides, then the apex will be the same type of triangle each time -- try drawing that on paper using a protractor to mark the same angle for the diagonal line from 64, 65 & 66 -- and yes, the length of the tip gets longer for each mm further down the sides in this case
However, digest these concepts with clipping the tip back -- longer thinned tips end up quite raucous, whereas all we need for responsive playing is rowdy -- however, since we usually clip off the fold at 72, and since we always hope that we won't need to clip the tip any shorter than 70, it makes sense to proportion the length of the tip so it's raucous at 72 and when clipped to finished playing length is tamed nicely to rowdy
-- personally i hope that's 71.5 mm with a nice long flexible area 3-4mm between tip edge and mid-line wood, but that standard of excellence has not yet arrived in my knife hand's tip-thinning skills (which is why i'm favoring a file at the moment)
Q. <<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?>>
A. this is a very interesting question, and i'm going to analyse it as an isolated feature (!) some more so i can mentally visualise the topographical contours of reed-geography in microcosm before being able to answer it with any intuitive comprehension
Q. <<How deep and broad are your windows?>>
A. This is a bit confusing, since i end up with 3 pairs of windows, but assuming we're only discussing the most important heart windows
Depth -- only down the cane layers as deep into the mid-bark as necessary to stabilize the C tone in the heart
Broad -- my heart windows are W shaped, although often the W ends up knifed so the W looking more like 2 U's rather than 2 V's, so this means my heart windows are not much narrower at the bridge above the catch than they are wide at the blend
Q. <<How thick is the spine?>>
A. Again assuming we're only discussing the portion of spine in the heart, i usually aim to debark it as a result of shaving the heart windows, and i usually shave off the shiny bark on the rails in the heart section the same amount, to approximate the same height of heart midridge and rail ridges -- leaving bark on in the heart anywhere is too stiff for me
In the back, the spine isn't debarked at all, so it's as thick as the original GSF cane piece gouge made it. I usually try to keep the shiny bark spine about 2mm wide down centre of the back (ha! says my knife hand)
Yours thoughts re << a reed's job...>> and your 7 points, agreed in general principle with the following Q's raised ...
Point 6 needs a bit of clarifying, is your <<fundamental note>> the holy grail of C octaves blown on the reed itself, or some other fundamental?
Point 7 is puzzling -- on my reeds the back windows are usually shaved only as deep as the top layer of the mid bark, and are usually started as strips 2mm across, and can be 3mm+ wide when reed is finished -- this gives me a tone in the back that is considerably higher pitched than C but not as high as an octave above C, so i can't figure out why you think the back <<reduces high-frequency overtones>> ?
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Author: vboboe
Date: 2008-09-01 22:21
mschmidt
<<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>>
i 'heartily' agree with you here that there's a great deal of incomprehension out there about reeds, and i think it's a very important task that we do, trying to bring as much as possible out of the twilight zone into conscious realisation through a combination of hypothesizing, cutting experiences in real life, other people's conscious understanding and the various ways they visualise things, and what actually works in real-life playable reeds
<<Blending the tip with the heart means that it is harder to define where the tip ends>>
The light test helps me define tip from blend by comparing light & shadow
and for this each person's ability to visualize (or learn how to visualize) 'grey scale' will determine what one sees (or can't see) -- this is an individual, and subjective, judgement call, one could use that handy blade measuring gadget to objectively measure relative thickness / thinness instead, but then, does the gadget measure cane density, and is the presumption of one-size-must-fit-all in the reed-maker's mind willing to make adjustments for differences in cane when measuring with the gadget (sorry, its proper name escapes me at the moment)
When a wet reed is held up to bright light, one could mentally decide there are four main types of light and shade visible
semi-transparent wood - example, extreme tip edges
translucent wood - example, the thinner blend nearer the tip
semi-opaque wood - example, the thicker blend nearer the heart
opaque wood - example, the spine and rails
Each of these 4 categories could be further sub-divided into bright, light, shaded and dark respectively in order to describe relative woodiness in critical areas of the reed
Eyeballing it on grey scale, if shaded semi-opaque wood is found in the lower corners of the tip near the sides, it's considered too woody and must be eased off until this part of the tip is moderately translucent -- so i'd say the tip is defined by thin wood that is mostly translucent rather than semi-opaque
And again, if any of the blend area is thin enough to be bright or light semi-transparent, that's far too much wood off already, it should appear as dark translucent to bright semi-opaque in the blend
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Author: jhoyla
Date: 2008-09-02 12:55
Hi Mike,
I'll probably respond to your points piecemeal, here's the first installment:
<<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. >>
Okay, I didn't explain myself very well, but I disagree with that last sentence! Based on the rest of your email, I'm not sure you meant it in quite the way it sounds :-)
The reed vibrates. The fundamental frequency at which it vibrates is governed almost entirely by the physical properties of the instrument, and not of the reed itself (it is a function of the dimensions of the air column up to the first open hole). It is not the reed that crows at "C". it is the reed-plus-staple that crows at this frequency. Lengthen the staple, you'll get a different note.
If sections of the reed vibrate independently of the fundamental note (which is governed by the standing-wave in the air-column), they generate higher-frequency partials that we identify as harsh overtones (buzzes, chirps and the like). If the structure of the reed encourages the fundamental and discourages these independent vibrations, you get a cleaner, purer note.
More thoughts later,
J.
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Author: jhoyla
Date: 2008-09-02 13:26
Hi Mike, next installment
<<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 like this! It sounds very plausible. Why, though, do we need to scrape the heart at all? Obviously, because it does play some vibratory part in the sound production and is not a "stationary fulcrum" - at least, not in an American scrape. I can see how the barky part of an European scrape can fulfill this function.
<< 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. >>
I like this too - I like it a lot! I think your "balloon" analogy is a bit over the top, but I can see how a sympathetic resonator can absorb the higher partials. Also explains why a broader, deeper back makes the sound more mellow (absorbs more partials).
<< But, as I said, I don't think anybody has a rock-solid understanding of just how reeds work....>>
TOTALLY agree with you here.
<<I also don't really get the "longitudinal" vs. "lateral" vibrations argument. >>
I hope I explained it well enough in my last post? All vibrations in the cane itself will be reflected in the vibrating air column. If sections of the reed are vibrating laterally at a different frequency to the fundamental, you will hear this as a buzz or chirp.
<<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...),>>
well, a square wave, but yes your point is made ..
<< 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, >>
Not if the reed is well balanced, it won't. Any lateral movement will cancel out as they will be in mutual counter-phase.
<<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. >>
Agreed - I really like this analysis!
<<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. >>
Hmm .. Is there a "fundamental frequency of the tip/airgate"? I don't think so. The forcing function of the air-column dimensions is what governs the fundamental, much more than the physical properties of the reed. Otherwise, I agree that the "blend" is extremely important, in that it "drives" the heart, making the entire tip-plus-heart vibrate at the fundamental. The heavier the heart, the fewer high-frequency components it can generate but more energy is needed to set it in motion.
<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.>
Sounds good.
<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.>
sigh.
Thanks for giving such a great response!
J.
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Author: jhoyla
Date: 2008-09-02 13:41
vboboe, thanks for this thread!
Regarding the inverted "V", I am definitely in the "A2" camp so that explains our differences.
Thanks for the detailed answers to my questions. Interesting that you leave a 2mm-wide strip of bark down the back of your reed! I strip the shiny bark, but leave a narrow line (less than .5 mm) of inner bark down the spine. Sometimes I eat into that more than I should.
regarding my "point 6" - I am referring to any note that is played. According to fourier analysis, any continuous wave can be analyzed as a sum of sine-waves of varying frequencies (multiples of the fundamental frequency). The character of the note (the "quality of the sound" if you will) is determined by the amplitudes (size) of each of these sinusoidal components. The lowest component is referred to as the "fundamental", and the other components are usually called "partials" or "harmonics" (at least, that is the terminology I am used to).
To see Fourier analysis at work (and also to play with adding and subtracting different frequency components) there is a great little java applet here:
http://www.falstad.com/fourier/
J.
Post Edited (2008-09-02 16:08)
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Author: vboboe
Date: 2008-09-03 02:46
<<... Interesting that you leave a 2mm-wide strip of bark down the back of your reed! I strip the shiny bark, but leave a narrow line (less than .5 mm) of inner bark down the spine. Sometimes I eat into that more than I should>>
Uh-oh, Nynynyah, this is not what i said, and this is not how the back spine ends up on my finished reeds
My original statement was:
<<on my reeds the back windows are usually shaved only as deep as the top layer of the mid bark, *** and are usually started as strips 2mm across and can be 3mm+ wide when reed is finished ***
If the two long windows down the back are started at 2mm wide and are widened to 3mm+ what has to be cut so they get widened ? Some comes off the spine, some comes off the rails
During this widening process, the knife grazes off most of the shiny bark on the spine in the process, and by the time i'm finished, if i'm lucky, there's maybe a fine hairline of shiny bark left, most of the time the spine ends up completely debarked, like you said <<Sometimes I eat into that more than I should>>
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Author: vboboe
Date: 2008-09-03 03:03
... oops again (:-{
i ALSO said
<< I usually try to keep the shiny bark spine about 2mm wide down centre of the back (ha! says my knife hand) >>
"try" being the operative word !
What starts as 2mm wide & shiny ends up maybe as 1.75mm lightly debarked after widening the back windows
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Author: GoodWinds ★2017
Date: 2008-09-06 08:00
Well, I hate to interrupt a perfectly detailed dialog, but I agree with Mike's comment on 'poorly controlled experiment'.
I did not see in the discussion anyone's comments the thickness, density, dryness, or source of the cane itself (maybe I read too fast).
I find that my cutting depends quite a bit on these factors, and I don't measure mm that much.
I was taught (very old school) by a Tabuteau student that one cuts the reed so that it plays. I buy reeds from time to time from professionals, but find my teacher's advice very sage and dependable. I think (and I might be wrong, but I doubt it) that everyone cuts a wee bit differently, and you'll get results if you tinker and try.
It's good to get input as long as it doesn't confuse you. As for me, all the mm measurements make me dizzy!!
a numbers-dyslexic player
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