Just think of "transducer" in terms of its simple Latin roots: it "leads across" power from one system to another system. Now, imagine an "ideal banjo," i.e. a membrane with zero impedence, in a large open space. If you strike the string, all of the energy is immediately transduced into the air "Pow!" There is no reflection, no period motion. Eveything is displaced once, and returns to rest as the impulse radiates out into the atmosphere. There is no "vibration," but there is still transduction of the energy. In the piano and recital hall, there are many impedences which reflect the motions and form them into standing waves, which we call vibrations, sounds, overtones and such. It is still transduction. The sound always fades away as the energy is absorbed by the many resistances in the situation. Ed S. ----- Original Message ----- From: "Greg Soule" <afmamh7 at bellsouth.net> To: <caut at ptg.org> Sent: Thursday, May 14, 2009 1:05 AM Subject: Re: [CAUT] Semantics > Wow, this has been an interesting thread. (some of you probably > abandoned it long ago) > > When I wrote, "I think it is incorrect to consider sound and vibration as > two different types of energy. Sound IS vibration." I hoped it would > elicit responses (and I think it did) that would finally clarify to me > why it is claimed the soundboard is a transducer. The way the term > "sound" was repeatedly defined simply as "what we hear" I found a > distraction, because it said nothing to differentiate the types of energy > found in the string, board, air, etc., which is the key to understanding > the whole kaboodle. It sounded to me more like some fuzzy philosophical > tangent on human perception ("If a tree falls in the forest . . ."). > > So, bear with me while I lay this all out, and tell me if I'm on track > here . . . > > The energy of the string or soundboard has the characteristic of > vibrating from a fixed point, and the vibrating body is under tension; > these factors cause it to want to return to a point of repose. The > vibration has frequency and amplitude. (Finer points of distinction > could be made between the ways the string and the board vibrate, but not > by me.) > > Although the vibrational energy imparted to the surrounding air also has > frequency and amplitude, air is a very different kind of medium because > air molecules are not anchored to anything. Since the energy has no > fixed point of vibration, it disperses in all directions like ripples in > a pond. It is a vibration that leaves its point of origin and never goes > back unless acted upon by an outside force. This is the critical > distinction of acoustic energy. Sound IS acoustic energy. > > Del Fandrich's illustration brings it home . . . a panel of wood that > vibrates when struck CREATES acoustical energy in the surrounding air. > This is a different type of energy than that of the string or soundboard, > and this is why it is proper to refer to the soundboard as a transducer. > > Furthermore, even though the term "transducer" in its most common usage > is borrowed from electrical engineering, and electrical engineers might > scratch their heads in confusion when they hear piano technicians use it > about their pianos, it is indeed the best term to apply to how the energy > changes between the soundboard and the surrounding air. We use it > knowingly and confidently. > > For further reading class, please see: > http://www.pianobuilders.com/soundboards.html > http://en.wikipedia.org/wiki/Sound > http://en.wikipedia.org/wiki/Acoustics > http://www.sfu.ca/sonic-studio/handbook/Theme_sound_medium.html > > Forgive me for being both dense and persistent, thank you for your > patience and I respect you all very highly, > Greg Soule > (and with a final flourish of self-deprecating humor, he returned to join > all the other lurkers)
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