51539133   
   XPost: sci.physics.acoustics, sci.physics   
   From: dpierce@cartchunk.org   
      
   RichD wrote:   
   > On Dec 9, Dick Pierce  wrote:   
   >>What you're missing in the trumpet, the sax (and oboe,   
   >>clarinet, bassoon) is that there is a physical vibrating mechanism   
   >>that interrupts the flow of air. In the case of brass   
   >>instruments, such as the trumpet, it's the vibrating   
   >>lips of the performer. In the case of reed instruments,   
   >>it's the single or bouble reeds.   
   >>   
   >>The rest of the instrument is essentially an acoustical   
   >>filter and impedance matcher. The filter portion enhances   
   >>those components of the very "buzzy (wide-band, very complex   
   >>waveform) nature of the lip-reed or real-reed needed to   
   >>give the instrument it's characteristc sound, while at the   
   >>same time the length of the vibrating air column "pulls"   
   >>the reed closer to the desire note by resonance, and the   
   >>bell at the end provides a better acoustical mtch wth   
   >>the surrounding air and increases its efficiency.   
   >   
   >   
   > That's news to me.  Though watching Louis Armstrong,   
   > it's easy to see -   
   >   
   > So the 'vibrating lips' act as a wideband noise source?   
   > Then the valves filter it, as I thought.   
   >   
   > I wonder, is the performer able to control,   
   > consciously or not , this lip vibe, to get particular   
   > effects?  Or is it continuous?   
      
   Absolutely, the better the player, the more control the   
   player has over the musculature controlling the exact   
   position of the lips, the tension and hardness of the   
   lips, and thus the frequency at which the predominant   
   output occurs.   
      
   WIth valved trunpets, it might be easier to imagine how   
   notes are generated: due to the resonant frequency of   
   the air colum. BNut this is only partially true.   
      
   Take, for example, older trumpets, which had no valves   
   at all. In such an instrument, the player is depending   
   upon the fact that if you get to high-enough overtones,   
   they all line up reasonably well as a diatonic or, higher   
   still, chromatic scale. The skill in playing such an   
   instrument invlves very exact control over the "lip-reed"   
   such that it's already vibrating at close to the desired   
   note, and when it gets close to one of the resonant modes   
   of the trumpet air column, it actually mode-locks to   
   that frequency. But, in such an instrument, if you simply   
   put your lips together, blow hard and produce "pfffft!",   
   what you will get out is a louder "PFFFFT!   
      
   >>This will be on Friday's quiz.   
   > Will you accept a fresh picked apple?   
      
   Only if it comes with one of the really good wide-screen displays.   
      
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