What the?

Discussion in 'Trumpet Discussion' started by Smrtn, Dec 2, 2014.

  1. Peter McNeill

    Peter McNeill Utimate User

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    Hi Stuart,
    How can I help? Ready to be enlisted - or take the plunge for you

    [​IMG]
     
  2. stumac

    stumac Fortissimo User

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    Thanks Peter, not quite ready have some ideas to refine method. See you tomorrow night?

    Regards, Stuart.
     
  3. rowuk

    rowuk Moderator Staff Member

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    Here is additional research on the lip motion for trumpets and trombones. You can judge how "scalable" formulas could be.........:

    Lip vibrations - Institute of Music Acoustics (Wiener Klangstil)

    We have to be extremely careful about over simplifying what is going on - from a description of the physics side. We have a DC component that is necessary so that we don't suffocate and causes the lips to initially "ignite". Then there is the AC component - the resonance of the standing wave in the trumpet that "controls" the lips. The amount of control is tempered by the pressure of the mouthpiece against the lips. After "ignition" the DC component is necessary to keep the lips "floating on air" and thus manipulatable by the AC component. It is not the "speed", it is the "air pressure" that has to counter the muscle tension/lip compression and keep the switch working. The balance is delicate. Too much force anywhere disturbs the monostable resonance.

    That being said, from the making music side, all of this physics gets in the way. We simply need to get the majority of arm pressure OFF of the lips so that the resonance of the instrument can manipulate the lips at higher frequencies. Simply increasing the DC component (our blow) is useless to build reliable upper register. It was never the real problem - or enemy.

    If you guys want to analyse this better, I'll give you a tip: figure out what you have for lip mass and resiliency and how to get that mass moving at high frequencies. Then look at the videos and figure out what happens when you want to play louder or higher. At what point can the muscle tension of the face, blow intensity or armstrong inhibit playing higher notes (remember the lips are not muscles and the lip mass can only be influenced by compression - with the face muscles or our blow vs the backpressure of the horn). Once you have reliable data for this, you will be much closer...........
     
  4. Sethoflagos

    Sethoflagos Utimate User

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    Hi Stuart,

    My post started life as a PM to Smrtn, but then it got too long......

    As I said above, there's nothing definitive in what I posted: most of the numbers are just plucked from the air, and all the overtone complexities, gas compressibility effects, frequency shifting phenomena etc etc are ignored in the interest of keeping the model illustrative of the main principles, but mathematically simple.

    However, since I am quite confident of my understanding of the underlying gas dynamics, I am prepared to defend it against all-comers providing they have read and understand the implications of the above paragraph.

    So onward.....

    So would I, Stuart. I've watched those videos too, and agree that the lip movements are highly irregular and complex. However, on general principles, I would say that as the lips open, the displaced flesh is going somewhere, and I don't think its either into the mouth or beyond the mouthpiece rim. That doesn't leave too many options. And if there is high oral pressure behind the lips and low cup pressure in front, they most definitely are going to flex forward to some extent. Basic mechanics of elastic materials.

    There aren't many jokes in chemical engineering, but one that I vaguely recall involved an invitation to bid on a livestock building design and a rejected proposal from a team of chemical engineers that had as a first line "Assume spherical chicken".

    Maybe some sort of vibrating drumskin would be closer to reality. But the piston assumption gets across the same basic idea whilst keeping the mathematics simple.

    The 2.5 mm figure is just plucked out of the air. The videos show more than 250 microns in motion but nowhere near 25 mm.

    When we say 'standing wave' we don't mean a static one. We mean one that has nodes and antinodes in fixed positions. At antinodes on the pressure wave the pressure swings at the appropriate frequency between some high value and some low value and back again, and those pressure variations are caused by air columns on either side of the antinode either converging to cause compression raising the pressure, or rebounding away elastically causing a decompression. In the ideal (100% acoustic efficiency) case, there is no net flow between the oscillating air columns (the total number of which varies with the harmonic you're playing), but there most definitely is significant air velocity within each column as the pressure gradient along them switches from positive to negative and back. This high frequency interchange between internal energy (~pressure) and kinetic energy (~velocity) is the only means the trumpet has for shunting energy from one end to the other and keeps the system firmly obeying the 1st law of thermodynamics.

    So we have two 'standing' waves of interest, a pressure wave that maintains constant (near atmospheric) pressure at the nodes (one of which is close to the bell) and a velocity wave offset 90 degrees from the pressure wave, that maintains zero velocity (if 100% efficient) at the pressure antinodes (one of which is at the embouchure).

    Difficult concept I know. But it's just what gases do.

    Actually, this is where I'm 100% into VBs magic bubbles theory. It sounds like more metaphysical tosh, but it is exactly what we do: 'blow' (push may be better) little bubbles of air at the next pressure antinode, and the pressure antinode blows that little bubble straight back at us.

    Chemical engineers don't recognise 'impedance' since the word appears in no textbook on thermodynamics. However, a chappie called James Lighthill (James Lighthill - Wikipedia, the free encyclopedia) took our beloved Navier-Stokes equations and recast them in a form that was familiar to acoustics engineers who for historical reasons tend to have a background in AC electrical theory. Hence the field of aeroacoustics (Aeroacoustics - Wikipedia, the free encyclopedia) was born.

    You can approach this subject from either angle, thermodynamics/fluid mechanics or aeroacoustics - at a fundamental level they both describe the same natural phenomena, but in different languages. And each has its own strengths and weaknesses. Aeroacoustics deals with acoustic coupling of air with metal with spaces with walls etc far more comfortably, whereas having lost some of the fine detail of gas behaviour of Navier-Stokes, they struggle with stuff like GAP and grooved mouthpiece bores which fluid mechanics has a much firmer (though not necessarily simple) grip on.

    You can gain information from either approach but you can't mix them up.

    This is in 100% agreement with what I posted.

    Now this is interesting! (not saying your earlier comments weren't btw :-))

    If you google 'maximum lung pressure' or such, the references tend to focus on trumpet players as a focus group suggesting that we do the compression thing more than anyone else.

    I've seen record figures of around 4 psig mentioned which show your figures to be quite reasonable. Anything higher than that and you're getting too high above blood pressure to be consistent with continued consciousness. Good stuff!
     
  5. rowuk

    rowuk Moderator Staff Member

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    Stuart,

    you actually need to measure the pressure in the cup of the mouthpiece too (drill a hole from the side and then seal the sensor?). An impedance curve for your trumpet (glue a headphone driver to a mouthpiece and let it play a frequency sweep) would also be useful as well as the acoustic output for each note while measuring pressure. The output is difficult to measure as the wavefront is big and the trumpet is VERY directional at higher frequencies... I used 1 meter to the microphone outdoors on a windless day.


    When you are done, we can compare results.
     
  6. rowuk

    rowuk Moderator Staff Member

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    Tomaso,

    one last time: if you want to use special words, you need to know their significance. RAT is a group of advisors. GEHEIM means secret. This has significance in the medical world, in politics, in business as well as during the second world war........

    I only accuse you of NOT READING or NOT UNDERSTANDING. If you had, you would have responded to the information presented.

    Your books would interest me very much.


     
  7. BigDub

    BigDub Fortissimo User

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    Yes, I think much can be gained by #1, having an open mind. #2 Not taking everything so personally #3 Having a humble heart that can learn from everyone else #4 just play your own horn the way you feel comfortable (occasionally). #5 Don't think so much....and finally, #6 don't be a hater. I think I can say I have a lot less baggage to carry around than some people, and it is very freeing. I feel loved, so I share it with others.
     
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  8. rowuk

    rowuk Moderator Staff Member

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    I just found this and believe that it REALLY applies in the inverse to trumpet playing!

    Aerodynamics are for people who can't build engines. Enzo Ferrari
     
  9. mchs3d

    mchs3d Mezzo Forte User

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    Yep. You should NOT be allowed to express your opinion if it differs with mine.
     
  10. BigDub

    BigDub Fortissimo User

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    I guess you are not going to read this, but can I say there is opinion, and there are facts. Opinion pertains to taste, preference, feelings, those sort of things. I believe scientific and physiological facts are not opinions, but I only defer to those who have more knowledge in these fields. When I broke my femur this summer, I did not ask for a second opinion when I saw the MRI. This was not an opinion, this was a fact.
     

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