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Distinguished Technician & SOTW Columnist. RIP, Yo
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Unless I am mistaken, in which case somebody will surely correct me, or I can delete this to avoid confusion. However, if I am corrected, it would be nice if the correction could be made in lay terms that the majority of people understand. :)

Woodwind instruments create sound by creating "standing waves".

A standing wave consists of a defined column of air (defined by the shape of the bore containing it) which has certain regions where the air pressure rapidly increases and decreases (in sync with the frequency of the note being played).

For this air pressure to change in a certain region (or regions) of the air column, air must very rapidly travel towards that region and away from it, many times per second. (This oscillating movement is superimposed upon the general slow flow of air down the instrument, which is relatively irrelevant, being merely a byproduct of the method used to initiate the sound - at the reed.)

This rapid, oscillating flow of air is over only short distances, but is very fast. It is turbulence associated with THIS flow that has the potential to affect the way a sax plays.

A location where there is always great flow of this kind is at a tone hole. The air whizzes in and out of a tone hole in an effort to maintain stable air pressure in that part of the bore. This air, whizzing in and out, has to negotiate a tortuous route around the tone hole wall, and between the pad and the tone hole edge. To make this easier, we have the pad lifting a decent amount above the tone hole. For saxes and flutes, we have large tone holes top assist the flow. For clarinets we undercut the tone hoes, so the tortuous bend from the bore into the tone hole is made less tortuous.

Now for another question... Could it be that some turbulence at CERTAIN locations is actually DESIRABLE? It could reduce the flow of air in the locations where pressure changes are NOT desired.
 

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Distinguished Technician & SOTW Columnist. RIP, Yo
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17,204 Posts
Hmm. I thought you would resort to acoustic jargon. Even reading "nodes" constitutes reading frustration for most readers. Even I have forgotten which are the noes and which are the antinodes terminology many times over the decades. I deliberately avoided the term.

".. at displacement antinodes the pressure remains constant but the air molecules are moving rapidly back and forth at that frequency. "

I think this is altogether too simplistic. It is an ideal model. In reality, air being a flexible medium, air is sloshing/swirling about all over the place in the vicinity, in order to attempt to maintain this pressure-neutral state. If this was not so, then why would the standing wave have to extend beyond the beginning of the first open tone hole. Even that first open tone hole does no manage to completely create a pressure node, which is surely why the venting of the next tone hoe has some influence.

I like your string analogy. But the tension also is changing to some degree along the whole length of the string, including the centre. Our tidy models gloss over the messy detail.

"... So you seem a bit confused in the last sentence: .... where there is pressure change there is no airflow... "

So take that second (or third or whatever, depending on the pitch) open tone hole. Somewhere around there is a theoretically and possibly idealised location of constant pressure, but in order to get that pressure constant, air is rushing in and out of the FIRST open tone hole, which is actually neither at a node, nor an antinode.

"... Where there is no airflow there is no possibility for turbulence...."

So in view of what I wrote above, at this first open tone hole, there most certainly is a lot of oscillating airflow.

"... The "torturous" bend is not really a problem for the air, since air is not solid."

By tortuous bend, I refer to air oscillating up and down the bore towards that first open tone hole, and then suddenly turning a right angle to exit/enter the tone hole (in order to equalise the pressure a little further down the bore.) I called it a tortuous bend; I believe you called it a sharp edge. Same thing. A lot of turbulence. Turbulence drastically reduces fluid flow, be it air or liquid.

"... Undercutting flute toneholes or sax toneholes, insofar as it is possible, should be just as efficacious as doing the same with a clarinet."

Sax/flute tone holes offer far greater venting than clarinet tone holes. This is how I, in a simplified way, picture sax tone holes:

Take a 20 mm radius tone hole. Imagine it is really only 17 mm radius. That extra 3 mm made of air, effectively constitutes some undercutting and overcutting, with some relatively stagnant air half way up the tone hole wall, acting as tone hole wall. A clarinet or oboe does not have the luxury of this region of air that stands in as under/overcutting, because it is so small in diameter, for the needed oscillating airflow.

So yes, I agree with you, but any large-tone hole (wrt the bore diameter) effectively has its own built in undercutting, as I described. In lay terms, we could simply say it has better venting. (So it does not need further undercutting to maximise the venting by reducing turbulence.)
 

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Distinguished Technician & SOTW Columnist. RIP, Yo
Joined
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17,204 Posts
brasscane said:
1. I don't understand "somehow". Is the implication that the mouthpiece is "rocking" on the cork and that causes the gurgle?

2. A repairman pointed out to me that a good neck cork is tapered and fat at the end so the end of the mouthpiece pushes against it. Is this because it prevents gurgling? (In that case neck corks out to be longer on alto necks.)
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If the cork at the open end of the tenon is slightly smaller diameter than the bore that it encounters in the mouthpiece, then this is most definitely a likely source of burbling, no matter how well the rest of the cork seals.

Both this and a leak between the neck and body can have quite dramatic acoustic effects, including buzzy noises at the upper end of the second octave.

On a soprano especially, and on some sax models more than others, burbling is also induced by the mouthpiece not being pressed on far enough. Try it.
 
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