Air Support/Faster Air

Discussion in 'Trumpet Discussion' started by eliserachel, Nov 30, 2014.

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  1. Smrtn

    Smrtn Pianissimo User

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    I have been polite through out this discussion, addressed the issues without resorting to ad hominems, and I believe I have a valid point. So far all I've received are references to how long such and such has been playing and that I should acquiesce to their experience. That would be fine, except for the fact that I am backing my pov with evidence and all I'm getting back are tired old memes.

    If you can refute my stance, then do so. It really is very simple.
     
  2. Shifty

    Shifty Pianissimo User

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    I think that what they are saying is that it's irrelevant if your diagram is correct, since it doesn't describe what goes on when you play a trumpet.
     
  3. Sethoflagos

    Sethoflagos Utimate User

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    Okay, some physics:

    Your diagramme indicates a simplified representation of steady-state, unidirectional flow of a fluid through rigid conduit incorporating a venturi throat. And you're suggesting that it tells us something about non-steady-state, oscillating flow through a compressed elastic conduit incorporating an aperture that's closed half the time.

    First question. What is the maximum speed of air through the aperture?

    As a first order approximation, I suggest it's about fast as you can spit. Say 5 metres per second.

    Second question. What note are we playing?

    Let's keep the numbers simple and take 1000 cycles per second, around a high C#. Now we know (from high-speed photography) that the aperture is closed for half of each cycle, so what air passes during each aperture opening must do so within 1/2000th of a second.

    So how far has our air travelled?

    Easy. 2.5 mm (about a tenth of an inch)! Not even enough time for the air to get across the 'venturi' before the direction of flow reverses. And this distance gets smaller as the pitch rises.

    So your attempt to do a mechanical energy balance across the flowstream from oral cavity to mouthpiece cup is doomed to failure. The air does not take the direct route. And the masses of kinetic energy (air speed if you like) that you want the Bernoulli equation to provide you with, is actually lost as work in forcing the aperture open, entrance losses, viscous drag, exit losses, turbulent dissipation. You know, all the boring stuff your 'simple and logical' approach simply ignores.
     
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  4. rowuk

    rowuk Moderator Staff Member

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    Repeating the "vastly incorrect" doesn't change it. Your mistake is very common for those that ignore the complete system. If we take the trumpet and mouthpiece away, your simplistic argument CAN be true. Add the rest of the circuit and you are completely wrong. This is one of the most problematic things in the trumpet world, half truths.

    I am not confusing anything. Here are some links that may open your eyes, if your mind is willing:
    Brass instrument (lip reed) acoustics: an introduction
    http://people.clarkson.edu/~wardjm/trumpet_physics.pdf
    http://mafija.fmf.uni-lj.si/seminar...physics_of_the_trumpet_(Bostjan_Berkopec).pdf

    I can explain the math if you get stuck.

    We are talking about a very complex relationship of connecting the face to a leaky Helmholz Resonator. The impedance of the horn is highest when we play in tune. The impedance maxima are where every pitch "slots"! Impedance is RESISTANCE TO FLOW. Blowing harder is extremely stupid because it accomplishes nothing except wasting your face. The resonator does not work in the simplistic linear fashion described by you. When we start playing intelligently, the horn does "most" of the work. Even having to spend time defending this is what I hate about the internet. Plain BS (when viewing the entire issue) wastes space and time. Why can't you guys do some legwork and get informed before posting - or get some lessons from the guys doing it correctly as shown in the above links!

     
  5. rowuk

    rowuk Moderator Staff Member

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    YES - when applied to the trumpet as you are leaving the Helmholz resonator off of the picture, if you had even bother to read what I posted you would also know why. Bernoulli does not apply as has also already been explained. It is plain stupid to leave the trumpet out of the equation and argue the rest as if it didn't even exist.

    I have closed this thread. It is not going anywhere except backwards. Dialog requires that both sides can read. We addressed every point and you ignored them all. If you just want to senselessly argue, there are better forums for that.


    Just for the record this is what smrtn has to say about himself at his website:


    My advice: don't try and explain things if you are not willing to look at the whole picture. The saxophone does behave considerably different than a trumpet, which is why the saxhorn died an ugly death.
     
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