[CAUT] Semantics

[Jeff Farris]

I'm waiting for someone to say something about imagining the "ideal banjo".

Respectfully,
Jeff


Jeff Farris
Piano Technician
School of Music
UT Austin
jfarris at mail.utexas.edu
512-471-0158




On 5/14/09 1:39 AM, "Ed  Sutton" <ed440 at mindspring.com> wrote:

> 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)
>