What the?

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

  1. BigDub

    BigDub Fortissimo User

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    "...................but that may be codswallop too" (sethflagos)
    NOW WE'RE GETTING SOMEWHERE!
     
  2. kingtrumpet

    kingtrumpet Utimate User

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    as my Dad would say about watching tv ((where ole KT here, tries to figure out the ending before the ending is there)) --- my Dad always replies on my suggested way of how it should end ------ "son, I just watch the show, I don't go about analyzing it"

    so just play and be happy--- after all what do I know? -- I can't play much above the staff anyhow. ROFL ROFL ROFL
     
  3. Sethoflagos

    Sethoflagos Utimate User

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    Enough of this, trumpet nonsense. Instead I'll tell you about a little technical problem I once faced at work and how I ended up solving it.

    On the face of it the system was common and straight forward enough: pump liquid from one tank up to enough pressure to get it through a particular bit of kit, and through a level control valve that controlled the flow into, and hence the liquid level in a downstream tank. So far so good. But to explain the problems we had, I first need to tell you a little bit about the bit of kit.

    It's called a Jordan Refiner and looks like this:

    [​IMG]

    The main body of the equipment is a shaft driven spinning cone inside a stationary conical housing, the opposing faces of each are lined with metal bar "teeth". The disassembled parts looking something like this:

    [​IMG]

    Now the liquid flows in at the little end of the cone, through the narrow annulus between the refiner cone and housing, and out at the large diameter end. Of particular relevance is that the separation between the opposing faces of the equipment is very small and governed by a balance of forces between compression of the driving shaft and the pressure of the process liquid. These were relatively small 300 hp units, but they still made a racket when they were operating, and this rose to an ear-splitting wail as the operators turned the handwheel that mashed together the cone and the housing.

    If it was all setup and running steadily then everything was fine. But let the pressure of the liquid drop too low and the abrasion plates would come into contact with a "great wailing and gnashing of teeth".

    The thing is, whenever the downstream tank level was low, and the control valve opened up to let more flow through, it also dropped the the pressure in the refiner, which led to various great wailings from time to time, and a lot of maintenance and lost production.

    So I was asked to provide some means of not only controlling the flow through the refiner, but also to keep the pressure steady.

    There's no way of controlling both pressure and flow independently with a single valve, so we needed a second control device, and I opted for putting a variable speed drive on to the feed pump. This would now give us the ability to raise pump speed when we needed increased fluid pressure and vice versa. The only real fly in the ointment was that when we raised the pressure with the pump, just like the control valve, we also affected the flow. But with the pump, instead of raising pressure being associated with reduced flow as was the case with the valve, with the pump increasing pressure gave more flow. So the two loops would fight against each other, and particularly at low flows, they became dangerously unstable. So I had a little think.

    And then the fight started.

    It started because I decided to turn conventional wisdom on its head, and switch the duties around. Instead of the pump controlling pressure, and the valve controlling flow, I set the pump speed according to the flow required for the downstream tank and controlled the pressure with the control valve.

    Well, the new chief engineer went ballistic! Never in his working life had he come across such a stupid idea! And it was pointless really trying to explain all the technical analysis I'd done, the sheets and sheets of Laplace transforms, Bode plots, etc etc. The chief engineer was old school, he was a time-served mechanical engineer. He was a $%&!.

    But fortunately, I'd been there a while longer than he had, and built up some degree of trust with the other engineering department managers, and within a week or so, I'd got the system all tuned up and working near perfect. Which shut him up.

    Actually, the reasoning behind my idea was quite simple. Both approaches could work in principle. And in another case, the conventional approach would be more appropriate. But here, maintaining stable pressure through the apert... I mean annulus of the equipment was vital for preventing mechanical damage. So I wanted a fast loop response and I could turn the stem of a quarter-turn 4" valve much, much faster than I could get a quarter ton pump and motor up to 1800 rpm. As far as the flow was concerned, I really only need to ensure that the downstream tank neither ran dry nor overflowed so a slow loop was more than enough for that.

    Hidden inside the design, was an interesting feature that I didn't mention to my colleagues. The real key to getting the two loops working in stable harmony was not to try and keep the pressure exactly at 60 psig (or whatever it was), but to add a small compensation to the setpoint calculated from how close the pump was keeping flow to set point. So instead of the valve positioning itself at the 'correct position' for the pressure at that instant, the system estimated roughly where the correct valve position would be when the pump caught up, and moved towards that instead. Sometimes this would be (a little) in the opposite direction to what you'd expect. But it worked, and that's what counts.

    Now if any of you have read this far and think I'm trying to draw parallels between supply tank (lungs), pump (abdominals), refiner (embouchure), control valve (aperture), equipment 'wail' (pitch) and flow (volume), then perish the thought! The mechanisms are totally different and so the analogy is completely bogus!

    But I can't help wondering if there's a significant difference in required response speed for pitch as opposed to volume. And which is inherently faster acting, lips or lungs. Just a thought :-)
     
  4. BigDub

    BigDub Fortissimo User

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    You can't fool me, Seth- that's a mechanical trumpet playing machine there! If it isn't, it definitely is wasting its time doing something less significant.
     
  5. tobylou8

    tobylou8 Utimate User

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    The throat on that "mpc" is huge!!! :roll:
     
  6. Vulgano Brother

    Vulgano Brother Moderator Staff Member

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    What I know about acoustics came from Arthur Benade. An example here: Trumpet Acoustics
     
  7. kingtrumpet

    kingtrumpet Utimate User

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    it's just fortunate for you that you did not create a harmonic resonance that would have destroyed the system all together ---- (either a mechanical or acoustical resonant frequency would have destroyed the system all together)) --------
     
  8. Sethoflagos

    Sethoflagos Utimate User

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    Are you pretending you understand that stuff, KT?















    ...cos I do ;-)
     
  9. rowuk

    rowuk Moderator Staff Member

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    I really wish that those that have obviously NOT looked at the evidence such as from the Institut Wiener Klangstyl links that I posted would do so.

    There really is no argument on how a trumpet works, there is conjecture and science. Neither have anything to do with playing better as much of the bodily functions required such as abs or diaphragm work are not changeable on the fly during playing. We can only talk about aperature when we are playing with low enough tension to not clamp it down. We can't have infinitely variable musical expression when we limit the necessary functions with force.

    The layman cannot separate speed or pressure. They work with simplistic visualisations that can make them play better - even if what they do is not what they describe. Seth has presented some VERY interesting science that has quite a degree of validity in the discussion. That (and the input of a few others) has kept me reading!

    My personal problem with these two threads is that I was in the speed camp 40 years ago. A physicist showed me what was flawed in that concept. We were in the same room, he was the professor and I was asking a thousand questions - not telling him how things work. On the internet, we have those that have NO IDEA WHY THEY CAN PLAY THE WAY THAT THEY DO, professing things that are absolutely ridiculous. We obviously cannot educate them, on the internet everyone is equal.

    I am very disappointed in the lack of curiosity in these threads. I am disappointed in the "speed agenda" as those professing it have not even commented on the scientific proof provided. The same mistake keeps getting made over and over again, the latest by KT with the flute analogy.

    I will ask a simple question, if only a few are even interested in expanding their knowledge, why should any of us even bother trying to show why things are the way that they are. No one needs this knowledge to play better.

    It isn't a question of agreeing or not. It is a question of expanding our knowledge base.

    Everything has been said. We know who is on what side of the camp. I am out. If any of the naysayers had even the smallest tidbit of evidence to back up their claim, it would have been presented. Instead, this thread continues to showcase "ignorance". My definition of ignorance is choosing to ignore solid evidence.

    Kingtrumpet, I simply challenge you to read the links presented and then without the clown act, simply and intelligently comment on what you have read as to how what was presented applies to your style of playing.
     
  10. Sethoflagos

    Sethoflagos Utimate User

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    Since you mention it, Robin, there is one particular point I'm curious about. One area 'Fast air', definitely does occur is in the mouthpiece throat where I suspect some appreciable fraction of sonic velocity occurs even with a normal piece, and even more so with a wide cup, narrow throat design like some of the Jet-tones.

    Do they live up to their name? I mean can you get choked, Mach 1 velocity peaks in the cycle with the corresponding backbore supersonic expansion and shock wave front you get in the De Laval type nozzle their profile resembles? (Nozzle Design for example of the sort of idea).
     

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