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Klarinet Archive - Posting 000455.txt from 2004/10

From: Adam Michlin <amichlin@-----.com>
Subj: Re: [kl] Re: Air flow
Date: Fri, 15 Oct 2004 18:46:56 -0400

Just so you all know, I have refunded Tim's price of admission for
correcting my amateur physics.

Now I just have to figure out how to explain the Bernoulli principle
without thoroughly confusing everyone involved (including myself). Ah well.
I'll get back to you all in a year or so with my revised document!

-Adam

At 03:15 PM 10/15/2004 -0700, Tim Roberts wrote:
>On Fri, 15 Oct 2004 15:58:44 -0400, Adam Michlin wrote:
>
>>It is a mistake to think that the vibration of the reed is the only thing
>>required to create a clarinet sound. One can blow into a clarinet quite
>>easily and achieve only an "air" sound. The reed is, in fact, vibrating,
>>yet there is no clarinet sound?
>
>No, the reed is not vibrating at that point. The air is passing through
>the opening, thereby causing the hiss, but there is not enough air
>pressure differential to overcome the inherent strength of the reed, and
>it remains stationary. That's why we hear white noise instead of a
>single frequency.
>
>It's the Bernoulli principle at work: moving air causes a reduction in air
>pressure. When the air pressure behind the reed drops sufficiently, it
>overcomes the strength of the reed and it begins to move, which affects
>the column of air inside the clarinet, causing a feedback loop that
>eventually increases the air pressure enough to the point where the reed's
>inherent strength allows it to bounce back.
>
>>The answer, of course, is the reed must "strike" something, the
>>mouthpiece. To have a reed vibrating without a surface to strike is
>>roughly equivalent to the sound of one hand clapping.
>
>This is wrong. The reed only strikes the mouthpiece at dynamic levels
>of approximately mezzoforte and louder. When you play softer than that,
>the reed vibrates as lower pressure from fast moving air brings it
>closer to the opening, and feedback from the air column in the clarinet
>allows it to open. The opening never closes completely.
>
>There are several good web sites on reed response to air pressure. I
>believe one of them was mentioned just this week.

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