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Re: Does the reed block the air flow?

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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