[CAUT] Semantics

[Ed Sutton]

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)