[CAUT] Semantics

[Greg Soule]

I am usually just a lurker here on CAUT, but allow me to chime in.

Every standard definition of "transducer" that I looked up puts it in  
the context of an electrical system - microphone, loudspeaker, TV  
picture tube, etc.  Other people here with some background in that  
field have echoed this definition of changing one kind of energy into  
another (sound or light energy to electrical, etc.).  It seems we are  
borrowing this term from the field of electrical engineering, but I  
still don't see how it applies precisely to the string-to-soundboard  
relationship.

Whether it is the string that is vibrating, or the soundboard, or the  
air molecules, it is all vibrational energy.  What we call  
"sound" (because we have ears) is still vibrational energy of the air  
molecules.  To me, the string-bridge-soundboard chain could be likened  
to the bones of the middle ear, which function as a discrete unit to  
transmit the vibrations along the chain (with varying degrees of  
efficiency).  In the ear, the cochlea is the actual transducer,  
changing vibrational energy to electrical nerve impulses.

In the piano, are some people saying that, because the string and  
soundboard are such dissimilar materials, and because the perceived  
character, or nature, or volume, of the vibrational energy is so  
different between them, that they say the energy is not just  
transmitted, but transduced (and definitely not "amplified")?  But, it  
has not changed types of energy, is still vibrational energy.  That is  
where I am still confused.  David Love asked a good question, "Isn't  
there such a thing as a mechanical amplifier?"

If we want to talk about the transducer in a mechanical system like  
the piano, shouldn't we be talking about the action-to-string  
relationship, not the string-to-soundboard?

I think I see my next chapter technical taking shape . . . invite in a  
local physicist or acoustician (or whatever) to give us the beef on  
this whole topic!

Greg Soule
Marginal CAUT
CAUT list lurker
PTG Assoc.


On May 11, 2009, at 10:52 PM, Fred Sturm wrote:

> On May 10, 2009, at 2:48 PM, Escapement wrote:
>
>> My understanding of a transducer has always been that it is a  
>> device that
>> takes one form of information or energy and converts it into  
>> another form.
>> (Like the speaker example given where *electrical current* is  
>> converted to
>> physical vibrations through the electromagnetic voice coil).  The  
>> speaker
>> isn't a transducer because the voice coil vibrates the membrane - 
>> it's a
>> transducer because it takes the *electrical current* in the wire and
>> converts it to vibrations *(sound)*.  In the same way that a  
>> microphone is a
>> transducer because it takes *sound* and converts it to an *electrical
>> signal*.
>>
>> But with the soundboard I don't see this conversion.
>
> 	After thinking it over, I agree with you on this. A classic series  
> of transducers would be a coal fire (heat energy) heating water to  
> make steam that is directed at a turbine, causing it to spin  
> (mechanical energy), which, by means of magnetic field and copper  
> coils makes electric current (electrical energy), which, directed  
> through the filament of a light bulb makes light energy (and heat  
> energy). All are real conversions to obviously different forms of  
> energy.
> 	With a piano, though, we have the mechanical energy of a finger  
> moving a key, which causes a hammer to hit a string and sets it to  
> vibrate. Mechanical energy converted to mechanical energy in a  
> different form via the action of intermediary mechanical devices.  
> The string is coupled to a soundboard, and energy is transferred  
> causing the soundboard to vibrate, again a mechanical transfer to a  
> mechanical form of energy. The soundboard, having a large surface  
> area, and operating in atmosphere, transfers some of its vibrational  
> energy to air particles, which oscillate creating waves. This still  
> seems like mechanical energy to me. The air oscillations reach an  
> ear drum, setting it vibrating. IOW, a whole series of transfers of  
> mechanical movement from one device or medium to another. Not being  
> versed in physics, I don't know whether there is a difference I am  
> missing, but it seems much more like a continuum than any two steps  
> in the example above.
> 	I wonder also about referring to sound as energy. It takes energy  
> to make sound happen, so sound can be said to be a manifestation of  
> energy. But is sound a "form of energy?"
> 	Maybe this is too abstruse to worry about, but some of the  
> confusion in this discussion seems to come from assumptions like the  
> notion that sound is equivalent to energy, and similar analogies  
> that maybe aren't actually valid.
> Regards,
> Fred Sturm
> University of New Mexico
> fssturm at unm.edu
>
>