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Re: Reed cuts

Author: Phil Freihofner
Date: 2007-02-02 03:49

d-oboe wrote:

> I think there are a few things to keep in mind as well...
>
> Mouth placement on the reed controls the air usage
>
> - higher notes require less air, therefore less reed should be
> vibrating. This is acheived by covering more reed to decrease
> unnecessary vibration.
> -lower notes require more air, therefore more reed should be
> vibrating.
>

I'm not sure what you mean by air usage. The higher notes actually require considerably more air pressure. Low notes can be played with a very light breath. There is a great diagram in "The Physics of Musical Instruments" Fig. 15.9, pg. 483 (in the 2nd ed., 1998, by Fletcher and Rossing) which also shows air pressures over the range of the bassoon, clarinet and alto saxophone. A low C on oboe can sound with less than 4kPa blowing pressure while a 3rd octave note can be above 12kPa. (Around 15kPa, an upper limit is set by systolic blood pressure in the arteries of the neck. Blowing harder than this can cut off blood flow and lead to dizziness. pg. 456)

I suspect more air actually makes it through the reed with a high note, at a high volume, than a low note at high volume, even though we may have to add bite to make the opening smaller (less needed at higher volumes). But I may be wrong. Consider that for the low note, one can't blow as hard without cracking the note, and this lower air pressure limits the amount of air that will pass through the horn.

As for the relationship of mouth placement to air, isn't the issue how much you bite rather than where you bite? One can bite at the tip, letting almost no air through. Conversly, one can relax while further down on the back, letting a lot of air through. Tip or back placement of the lips doesn't "control" the air unless you always go to a particular embouchure tension at a given location. Then it might seem so, but I still think it's the embouchure tension and air pressure that determine how much air passes into the horn, not the lip location.

Maybe the air pressure or the amount of air passing through the horn are not what you mean by "air usage"?

I'm not sure if more or less reed vibrates for high or low notes. I would agree that one may help a high note by damping the back (letting the tip vibrate freely) and one may help a low note by damping the tip (letting the back vibrate freely). One may seem like "more" than the other because the tip is smaller than the back? Or because the tension required to dampen tip vibrations is considerably lighter than the tension required to dampen back vibrations?

> The reed is a system of balances -
>
> The tip doesn't *actually* control higher frequencies, and the
> back doesn't *acutally* control the lower ones. Rather, it is
> how the whole reed acts together.
> Case in point: scrape the heart right out. It doesn't matter
> how much you scrape the tip, those high partials won't come
> back.
>
> So, it's the relationship between the various areas that
> affects reed functioning.

Well if you scrape out the heart, you don't really have much of a reed anymore. What comes out is probably buzzy (high partials) and flat, and very unstable. Possibly the reed won't even have the resilience to play notes in the highest registers.

The quantity of low vs. high partials has to come from somewhere. I can think of only two possibilities: the point on the reed surface that is vibrating (where the closer one gets to the tip, the higher the harmonics) or in the nature of the wave cycle as the air enters and is cut off by the closing of the reed (the more abrupt the transition from open to closed to open, the higher the partials). Maybe it is a combination of both.

http://adonax.com

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