 The Clarinet BBoard
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Author: Philip Caron
Date: 2014-10-11 06:20
In "How Music Works" by John Powell, the author states that the reed on a clarinet moves to rapidly close and open the gap between the reed and the mouthpiece, so that air flow through the opening is alternately blocked and unblocked, and that action is the exciter of the vibrations of the sounds made. This is what I have heard and read elsewhere, so I am happy to believe it.
However, reading this tonight suddenly gave rise to the realization that I would also be happy not to believe it, and to believe instead that the reed tip just vibrates back and forth in air, and that whilst playing, the air flow through the tip opening is continual, albeit changing with the vibration. When I sound a tone, I really don't think the end of the reed touches the mouthpiece; it would take additional pressure from me to make that happen.
Or maybe I'm doing it all wrong.
My little doubt aside, Powell's book is not only ingenious at simple explanations for things, it's very witty. I'm enjoying it.
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Author: Ken Shaw ★2017
Date: 2014-10-11 07:07
Slow-motion camera shots show that the reed seals completely against the mouthpiece. The only exception is a lightly blown sub-tone.
Several years ago, someone suggested that the "English" sound (e.g., Brymer) was an inflated sub-tone, but I know of no proof of that.
Ken Shaw
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Author: Chris P
Date: 2014-10-11 16:10
Subtone is the note but not the tone, almost a sine wave or pure tone like humming - you get this in sax writing by making them sound the notes, but not putting any tone into it as a special effect.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
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Author: Tony Pay ★2017
Date: 2014-10-11 18:20
The (German) instruction 'echoton' that you encounter sometimes in Mahler – for example, the pp passage for 3 clarinets 3 bars before figure 8 in the first movement of the Second Symphony – is achieved by addressing the instrument in such a way that the reed never closes at any point in its cycle. It's always a 'quiet' effect, as you might imagine from its name; Berg also uses it in his Vier Stücke.
I remember that Alan Hacker, a British user of German style mouthpiece and reeds, used to speak scornfully of what he called the 'hooty' sound of some British clarinettists, calling it 'just an amplified echotone'. And indeed, there is some rationale behind the accusation, particularly in the low register of a badly played non-German setup.
Tony
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Author: tims
Date: 2014-10-13 03:13
If you have a reference to the "slow motion" study, I would like to know what it is so I can understand how they did it. I know that the reed is capable of at least two modes of vibration:
1: The entire tip of the reed opens and close against the tip of the mouthpiece and remains flat throughout.
2: The reed flexes about the long axis of the reed where the left and right edges of the reed tip flex away from the mouthpiece and the middle of the reed flexes toward the mouthpiece until it touches. Then the middle moves away from the tip and the edges move toward the mouthpiece until they touch, and so on.
Looking down with the tip of the mouthpiece is on the left and the read is on the right...
---> |( || |) || |( || |) || |(
I've seen both modes demonstrated, but not inside someone's mouth. At the time (mid 1970's), there was no way to see inside someones mouth while they where playing the instrument, so this was done by creating a chamber to hold the mouthpiece that allowed the reed to be viewed while air was pumped into the chamber. Though most of the time the reed vibrated in mode #1, sometimes it would start in mode #2. Either way it started, it would stay in that mode until the air pressure was removed, meaning that both where stable modes of vibration. I could not hear a significant difference in the sound produced by either mode. No one at the time could say whether one or both modes actually occurred while playing.
The interesting thing about mode 2 is that the air is never completely blocked.
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Author: Tony Pay ★2017
Date: 2014-10-14 02:03
>> I've seen both modes demonstrated, but not inside someone's mouth. At the time (mid 1970's), there was no way to see inside someones mouth while they where playing the instrument, so this was done by creating a chamber to hold the mouthpiece that allowed the reed to be viewed while air was pumped into the chamber. Though most of the time the reed vibrated in mode #1, sometimes it would start in mode #2. Either way it started, it would stay in that mode until the air pressure was removed, meaning that both where stable modes of vibration. I could not hear a significant difference in the sound produced by either mode. No one at the time could say whether one or both modes actually occurred while playing.>>
Was this work ever published?
Was any attempt made in it to simulate an embouchure – eg, with a rubber pad pressed against the reed inside the chamber?
I wrote something about a similar device here:
http://test.woodwind.org/Databases/lookup.php/Klarinet/1998/12/000764.txt
...and that had an 'embouchure'. It was needed because without it, the sound was pretty terrible.
And naively, my intuition would be that the presence of an embouchure would tend to suppress your mode #2 – but what do I know?
My next step would be to write an email to the acoustics guys at UNSW.
Tony
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Author: tims
Date: 2014-10-14 03:01
As far as I can remember it was just a box, but it has been a long time. My clarinet teacher at the time (Dr. Jerry Hierman) had studied the dynamics of reeds as part of his doctoral dissertation and he showed me still pictures of the setup and tape recordings of the sound (I don't even remember if this was his own or research by someone else), but he also showed that you could demonstrate these modes simply by sucking air in on the tenon of a mouthpiece with a reed attached and your thumb against the reed to give a little pressure like an embouchure. You could actually see the two modes clearly without special cameras or lighting. If any of this was published, it would have been in the late 1960's. I think Dr. Hierman attended Eastman, but I'm not sure if that is where he obtained is doctorate.
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Author: derek_b
Date: 2014-10-15 04:20
Yes, the reed dynamically blocks the air flow. This is well documented in many research papers. I included some links at the end, they may be worth looking at, specially for nice drawings - but be warned, they are not for a casual reader: heavy on math and theory.
What you describe is usually referred to as "reed beating". Here is probably the most readable description which also includes very nice animation: http://www.the-clarinets.net/english/clarinet-sound.html
From the above: "you blow into the mouthpiece of your clarinet. This lets the air (blue arrows) flow through the reed tip opening into the bore. Then the air presses the tip of the reed against the lay of the mouthpiece, which for a short time blocks the airflow. But the reed is elastic: it swings back and air flows in again, until the pressure lets the reed close the opening again and so on. As result we have a nearly steady flow of air (blue) that is rather slow and pressure waves (red) that travel through the instrument by the speed of sound. It is the pressure waves rather than the air flow that is important for the tone."
Here is another reasonably clear description, I edited it for clarity, full version is here: http://arxiv.org/pdf/0705.2803.pdf
"Beating reed... investigated the effect of reed curling and beating against the lay of the mouthpiece, and proposed a model of variable stiffness. We include in our model the modelling of contact between lay and reed by considering an additional elastic force when the tip gets in contact with the lay and completely closes the channel. Further investigations would carry the case where the contact point is not the tip: as the reed curls against the mouthpiece, stiffness increases as the part of the reed which can freely move decreases, and then grows abruptly when the tip hits the lay. Another consequence of reed beating is that the volume flow vanishes when the reed closes the channel..."
Finally, some relevant theoretical papers:
* https://hal.archives-ouvertes.fr/file/index/docid/474990/filename/2003_Dalmont_al_Jasa_NonlinearCharacteristicsOfSingleReedInstruments.pdf
* http://dafx04.na.infn.it/WebProc/Proc/P_095.pdf
* http://www.dei.unipd.it/~avanzini/downloads/paper/avanzini_acu04_scanned.pdf
* http://www.theory.physics.ubc.ca/341-current/clarinet-reed.pdf
* https://hal.archives-ouvertes.fr/hal-00810980/PDF/hal-00810980.pdf
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Author: Ed Palanker
Date: 2014-10-15 20:48
That's just one reason that an "opened" facing generally takes a soft reed. It has to travel a larger distance. The tongue is far more likely to block the air from entering the mouthpiece.
ESP eddiesclarinet.com
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Author: tims
Date: 2014-10-17 05:55
derek_b---
Thanks for all the links. I've download the documents and will read them (I'm an engineer and a physics teacher, so the math and theory doesn't bother me). The animation on the first link, I think, incorrect and misleading. First, what occurs inside the clarinet is not a traveling wave, but a standing wave. The best explanation and illustration of what is actually happening can be found here:
http://www.acs.psu.edu/drussell/Demos/StandingWaves/StandingWaves.html
Also it appears to be showing the clarinet producing a sound out the barrel as twice the frequency as the frequency of the reed. They should be vibrating at the same frequency.
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Author: jonok
Date: 2014-10-17 10:03
It's my understanding that it CAN block, but it's not required to make a tone, and in fact the best tone comes from it NOT blocking.
Experience shows that using a too soft reed, which will close up much sooner (in the ppp to fff range) than a firm reed does, has an undesirable harsh-ish tone, which can be explained by the reed fully closing, which is effectively clipping the wave form.
I have no definitive scientific evidence for this position, but it makes sense to me in relation to the change in tone quality from soft to loud, and was led to this understanding by a mouthpiece and clarinet maker of long standing and good reputation.
Jon
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Author: Tony Pay ★2017
Date: 2014-10-17 15:34
tims wrote:
>> The animation on the first link, I think, incorrect and misleading. First, what occurs inside the clarinet is not a traveling wave, but a standing wave...
Also it appears to be showing the clarinet producing a sound out the barrel as twice the frequency as the frequency of the reed. They should be vibrating at the same frequency.>>
The frequency mismatch is because the reflected wave should be a rarefaction rather than a compression as in this animation; but the fundamental idea is right.
Here's a correct animation and explanation:
http://newt.phys.unsw.edu.au/jw/flutes.v.clarinets.html
Tony
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Author: tims
Date: 2014-10-19 01:52
There are two sources of sound from the reed. One is simply the air being moved by the vibrating reed itself, like the sound produced by a vibrating string or a vibrating block of metal in a vibraphone. The magnitude of this sound is proportional to the amplitude of the vibration (how far it moves) and the surface area perpendicular to the motion. With a string instrument we can effectively increase the surface area by transferring some of the vibration to the larger wooden body of instrument. With a vibraphone, placing a tube under the vibrating bar that resonates at the same frequency reinforces the vibration of the bar and makes the sound appear louder. Since the clarinet body acts as a resonator tube, the sound produced by the vibrating reed alone would be much greater than if that reed were vibrating in free space (in the open).
It would be an interesting experiment to try this on an actual horn. All you would need to do is glue a thin piece of steel near the tip of the reed and force it to vibrate with an electromagnet (say from a small speaker or ear piece) attached to an electronic oscillator tuned the frequency of the note being fingered. I would be interested in how much sound that would actual produce.
The other source of sound is from the reed periodically disturbing the air stream. As the reed vibrates it varies the size of the opening into the horn through which the air you are blowing must pass. When it is wide open, you have maximum air flow, and as it closes, the airflow becomes more and more restricted. It is not necessary that the reed close completely to produce a sound. As long as the reed vibrates, the air flow will vary periodically producing a sound.
One might assume that as soon as the reed reaches the point where the reed completely closes, that you would reach the maximum volume because the reed will neither open any further or close any further. This is not the case. As you blow harder, the air pressure increases behind the reed so when the reed opens, more air flows past than will when you blow less hard. The only limit to how loud you can play is when the pressure becomes so high, that once the reed has closed against the mouthpiece, the elasticity (the springiness, or stiffness) of the reed is no longer enough to open it.
The reason the reed vibrates when we play is due to the Bernoulli principle. This principle states that the faster air moves, the lower its pressure. When you blow into a clarinet, the air travels quickly over the side of the reed facing the inside of the mouthpiece. This causes the air pressure to drop on this side of the reed. There is little or no air movement below the reed and thus it remains high relative to the top. It is this difference in air pressure that pushes the reed up. As the reed begins to close off the air, the air begins to travel slower and the pressure on the top rises so that eventually the difference in air pressure between top and bottom is no longer enough to overcome the elasticity of the reed and the reed begins to move back the other way. As the reed begins to open again, the air begins moving faster again and the pressure differences begins to increase starting the whole process over again.
It is never necessary that the reed ever close completely to start the reed vibrating. If you play with a hard reed and try to play very softly without tightening the embouchure (which reduces the distance the reed must travel to close completely) then you will hear a very "airy"/"hissy" sound. This is because you are having to blow fairly hard to get the reed to vibrate, but without pressing down on the reed, the reed stays open allowing large amounts of air to pass causing the hissing sound. This means that the air is not being used very efficiently. The air has to move a certain speed to produce sufficient pressure differential to get the reed to vibrate, but if this is not enough to cause the reed to close completely then air will be wasted. You can produce the same note at the same volume more efficiently by either pressing harder against the reed so as to shorten the distance the reed must travel to close, or use a softer reed which can bend further at a lower pressure difference.
I think we notice quickly when the reed is not closing completely. It becomes harder to maintain a constant volume and the tone becomes masked with a hiss. I think the comment regarding "clipping the waveform", and the harsh sound heard is due to other factors. Regardless of hard or soft reeds, almost all of us play with the reed closing completely at all the dynamic levels we play. The reed should only remain closed briefly and should open almost immediately regardless of how loud we play or the hardness or softness of the reed (within reasonable limits). It should, in effect, seem to bounce off the tip. The reed begins to open when the spring tension of the reed is greater than the difference in pressure between that inside of the mouthpiece and the inside the player's mouth. Since the pressure in the players mouth remains constant for a given volume of sound, the change in pressure is due entirely to the change in pressure inside the mouthpiece. This change in pressure is due primarily to a propagating wave moving away and a reflected wave moving toward the reed. These two waves combine to raise the pressure at the reed in a predictable way that is proportional to volume. Therefore blowing harder doesn't make the reed stay closed longer because the louder sound one produces the stronger the waves are and this compensates for the higher pressure inside the mouth. This is simply the effect of resonance. The motion of the reed is primarily dictated by the combined resonances of the instrument, the reed and the interior of the mouth, not how hard we blow or how hard we bite.
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Author: Tony Pay ★2017
Date: 2014-10-19 04:35
I'm afraid that Tim's analysis above fails to take into account how the reed/mouthpiece/clarinet system works. For a start, you cannot think of the clarinet body as amplifying what the reed does, as you can (roughly) think of the violin body as amplifying what the string does.
The reed and the tube beneath it interact in a system; so it's as partial a view to say that the tube is acted on by the reed as it is to say that the reed is acted on by the tube. Both are true, simultaneously.
You need to read up on it, Tim. I haven't looked at the papers that Hephaestus cites, but probably they are close to the truth of the matter. (I usually cite Benade: 'Fundamentals of Musical Acoustics'.)
Tony
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