Hi Kurt, Precisely!!! You've hit on the concepts of energy and power (your "shorter, louder span" thing), two terms often confused to mean the same thing. More later. NG On Thu, Feb 17, 2011 at 6:14 PM, Kurt Baxter <fortefile at gmail.com> wrote: > Hmmmm.... Agreeing that the total about of energy obviously does not > increase that must mean that all other things being equal, a freely open > vibrating string (no soundboard) would have much longer sustain, right? I > imagine the soundboard to be "condensing" the energy, releasing it in a > shorter, louder span; > > "That which burns twice as bright burns half as long" > > -k > > On Feb 17, 2011 4:41 PM, "Mark Schecter" <mark at schecterpiano.com> wrote: > > Hi, Nick. > > Thanks for presenting this definition, I appreciate it, and I think it is > generally helpful. But I would like to raise some questions about it, in the > interest of clarity. I am not an engineer or physicist, but I am a tech and > musician who's been thinking about these questions for a long time. I > present these thoughts hoping to clarify and improve the usefulness of your > definitions, and I welcome your corrections to any misstatements I might > make, or misconceptions I may be trying to apply. That said, ... > > You say: "... thus in a broad but accurate sense the piano string’s > uncoupled and feeble attempt to excite large zones of air demonstrates a > very low amplitude." > > If I may say, characterizing the string as attempting feebly to excite large > zones of air, puts the emphasis in the wrong place. The string is not > attempting anything, it's just vibrating. That its ability to excite much > vibration in air is small, is true. But coupling it to the soundboard does > not raise the energy level/amplitude of the signal. What such coupling does > do is propagate the vibration to many more air molecules than the string > can, due to the soundboard's much larger surface area. But the energy was > never feeble at all, in fact it was always entirely sufficient to the task. > It just needed to be transferred to a material whose form and structure was > better suited to moving air, in order to transmit that vibrational energy to > the listener's ear as sound. But the basic form of energy, mechanical > vibration, has not changed - only the material or medium through which it is > propagating has changed. (Or so I would assert - is any of this wrong?) > > Later you say: "Any device that converts one form of energy, say > vibrational, to another form of energy, say sound, is a transduction device > or transducer." > > I think this statement obscures the fact that sound already IS vibrational > energy, and therefore there is no transduction needed. The only difference > between vibrating string and vibrating air is in the material that is > vibrating, metal to wood to air to eardrum. What IS needed is efficient > propagation of that vibrational energy, from the source (string) through the > bridge and soundboard into the medium (air) which the soundboard provides. > Of course, the soundboard is temporarily the medium as well, but only as a > link in the mechanical chain from vibrating string to vibrating air to > vibrating eardrum. Thus there is no transduction or change in form of > energy, only a change in the physical characteristics of the vibrating > material or body. (Or am I conflating two actually different forms of > energy? If so, what is the difference?) > > Later yet you say: "We can say that the job of piano sound amplification is > to take the weak vibrational signal of the uncoupled string (low amplitude) > and “boost” it via coupling in order to generate a powerful signal (high > amplitude). It doesn’t matter that additional energy is not present for this > to happen." > > Again, I would say that this mis-characterization as "weak" actually > confuses the issue, as the vibrational signal is inherently as strong as it > needs to be to cause its ultimate intended result, sound. It is only "weak" > in its ability to move air, due to its small surface. When we connect it to > a large surface, voila', without adding energy, we create sound (vibrations > in air) of much larger (apparent) amplitude. I am saying that coupling does > NOT "boost" the signal - it merely broadcasts it much more effectively. > Thus, the soundboard is less like an amplifier, and more like a mechanical > broadcast antenna. > > You go on: "Still, an analog to electrical amplification exists in that a > ppp blow to a key can be barley audible; now add more energy with a fff blow > and we have increased amplitude, hence more amplification with the attendant > volume and power." > > Here, I feel that the analogy to electrical amplification is also confusing > as presented, because amplification takes the SAME signal and makes it > larger, whereas your example contrasts a smaller original signal with a > larger original. This is not analogous, as it happens at the source, not the > broadcast end of the chain. > > I do agree that it's perfectly acceptable to call the soundboard an > amplifier for purposes of explaining to lay customers what it does. > > So, what do you think of these thoughts? > > Thanks, and all the best, > > -Mark Schecter, RPT > > > On 2/17/11 10:05 AM, Nicholas Gravagne wrote: >> >> ENERGY TRANSDUCTION VS SIGNAL AMPLIFICATION >> ... -- Nick Gravagne, RPT AST Mechanical Engineering
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