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Discussion in 'Trumpet Discussion' started by Smrtn, Dec 2, 2014.
There we go again! You have mischaracterized my use of the word "Geheimrat". In your ignorance you instruct me that I don't know how to read and do not understand its meaning when in fact it is you who doesn't understand its several meanings.
Look it up in its medical context. You might also want to look up the use of quotation marks.
And by the way, considering I don't know how to read I have authored and published several books; 2 medical books and 2 novels, plus seven short stories. And I have another novel coming out this winter. So I don't need a lecture from you on my ability to read.
Enough already! I'm 'outta here!
Kind of a drastic response, but I have to say that you don't tell a guy who lives in Germany what a German word means....
You're joking. And here I was thinking this was all about back and forth with a possible natural resolution. Okay, so I was wrong about that. It isn't. But so what right? It's just a forum. In the end though, the quality of discourse will suffer because of your hasty and, quite frankly, anal attitude to 'what is correct'.
As I wrote in my OP in this thread, I did some research whilst the original discussion was going on in a sincere attempt to dialogue the situation. There is ample evidence to contradict the ingrained beliefs that go along with that particular area of trumpet technique. I would've thought that it's a good thing to expand on that knowledge. I'm not interested any longer though so that's it from me.
Personally, I find medical books make great door stops!
Let me put life in a different perspective... After returning from Saudi Arabia, I am sure glad it is Christmas time in Dayton Ohio.
I would agree. A lecture would not help. I would suggest you start with reflection using this line: Judging a person doesn't define who they are. It defines who you are.
Let me say at the outset that what follows below is pure conjecture, not backed up by any proper research, nor subject to any in-depth analysis, but simply the musings of a semi-retired engineer who has some experience of gas dynamics.
Please take it as a 'thought experiment' intended to help reconcile our differing viewpoints.
In the other thread I developed a line of thought where aperature air speed was more like 5 metres per second over a distance of 2.5 mm per half cycle. (Ballpark estimates but let's run with them).
Now consider what happens if rather than visualising the air travelling forwards relative to the aperture, we think of the air being carried forwards 2.5 mm in a pocket in the aperture as the lips are driven forwards by excess pressure in the oral cavity. Now we can forget the air for a moment and visualise instead the lips as a kind of piston moving forward 2.5 mm into the mouthpiece cup rather like the diaphragm on a loudspeaker. The id of my mouthpiece is 17 mm, giving a cross-sectional area of 227 mm2. So the volume of air displaced in our 1/2000th of a second is 2.5 x 227 = 567 mm3.
This forward movement also creates a pressure wave pulse that travels forward into the instrument, not at 5 m/s but at sonic velocity, ~330 m/s. Now this sort of wave velocity reaches deep into the instrument even in such a small time frame. 330 divided by 2000 = 165 mm. Now the air itself doesn't travel at that speed, but the pressure pulse provides the driving force for a local forwards air displacement of 567 mm3 at every point until well down the lead pipe.
Now consider what that means at the mouthpiece throat.
Again, my mouthpiece has a bore diameter of 3.7 mm so the cross-section is 10.75 mm2. A volume displacement here of 567 mm3 translates to a linear displacement of 52.7 mm. Now we are talking real air speed because 52.7 mm in 1/2000th of a second equates to not 5, but 105 metres per second!!
Now we have an air speed that means something!
Now we have rapid air flow through a precision venturi in rigid conduit!
Now we can start looking at mechanical energy balances and see what the implications are on both the velocity and pressure waveforms!
I was tempted to say 'Now we can use Bernouilli' but Bernoulli was really intended for steady state liquid flows rather than gases so we need something a little more sophisticated. If you were to pursue this in detail, its actually going to involve simultaneous solution of the continuity equation, Navier-Stokes equations in cylindrical coordinates and a reasonable equation of state for moist air. Head-banging stuff.
Notwithstanding that, we can follow through our line of thought at a back of an envelope level and see how far we get.
Okay we've moved our flesh piston forwards 2.5 mm and been able to infer a pressure pulse and airflow moving well into the lead pipe. Now consider an earlier pressure pulse that pumped an earlier parcel of 567 mm3 of air out of the bell. As that pressure pulse decayed there was no more pressurised air left in the bell to maintain the flow and it went into 'suck' mode creating a negative pressure wave that travelled back down the instrument (again at sonic velocity). This 'suck' was a part of the pressure profile that assisted oral pressure in pulling our lips forward at the start of the cycle. But now something very interesting happens: the room is beyond the bell is (very, very slightly) pressurised; there's a low pressure trough in the bell; so the room blows back!
If the trumpet (or coupled trumpet/room acoustic system) were 100% efficient, then 567 mm3 of air would be pushed back down the bell in 1/2000th of a second. Ultimately (a physically different) 567 mm3 gets accelerated through the reducing taper of the leadpipe and backbore to whistle through the bore at 105 m/s (-ish), pressurising the mouthpiece cup (shades of Bernoulli again!) to a pressure higher than that in the oral cavity so that the lips are pushed back 2.5 mm restoring them to their original position.
Actually, no trumpet is 100% efficient so you don't quite get 567 mm3 back. Say you only get 500 mm3. Now we can go back to that little pocket of air carried forward in the embouchure aperture. If the volume is 67 mm3 (corresponding plausibly to an aperture length of 2.5 mm and diameter 5.8 mm) then we are in business because we have a self-sustaining system.
Of course we need the various parts of the system locked in the appropriate phase relationship to get our resonance. An embouchure flow of 67 mm3 per cycle corresponds to 4 litres of air a minute which also sounds plausible (not too loud, not too free-blowing).
In short, if I were to start doing serious fundamental research on this (I'm not! Life now is too short!) I don't think it's a bad start for a working hypothesis.
What do you think?
What some people choose to get upset over....
an interesting concept, however several flaws I think I can see, 2.5mm of lip movement is excessive, the high speed photography of an embouchure operating shows the lips open and closing rather than moving in and out as a piston, I would like to see more work on this.
There are not pockets of air travelling too and fro down the length of the horn, rather a wave front travelling back down being reflected by the impedance mismatch between the bell and surrounds causing a standing wave to be set up, the air flow through the horn is small and only necessary to supply the energy to maintain the standing wave, see where a diaphragm has been fitted across a mouthpiece with a side arm to exhaust the air flow isolating it from the horm, the standing wave is still formed.
I have been doing some research of my own on pitch verses blowing pressure. Using my Penwalt precision gauge 0-125" Water with a 1/8" tube inserted through the corner of the mouth and my Selmer B700L and Bach 3C mouthpiece I am measuring the pressure at which a note played ceases to sound, I have done this many times and the results are pretty consistant
Low C (C4) 3"wg, second line G 6"wg, third space C 9"wg, top of stave G 20" wg, high C 30"wg. 30" water gauge = 1.08 pounds/ square inch.
My next step is to enlst my friends to repeat the experiment. All comments appreciated.