Sound waves(The behavior of soundboards)

[pianolover 88]

YAWNNNNNNNNNN! :O)

tERRY

>From: Robin Hufford <hufford1@airmail.net>
>Reply-To: pianotech@ptg.org
>To: pianotech@ptg.org
>Subject: Re: Sound waves(The behavior of soundboards)
>Date: Sun, 16 Dec 2001 17:44:49 -0800
>
>Ron and all,
>      Have you some sort of reasoned refutation of the points I offered in 
>the post
>you so vigourously dismissed out of hand.   You say the energy transfer 
>model I
>referred to is in essence meaningless then immediately say, however, it is 
>not so -
>should the impact be that of an airplane instead of a mosquito.  It 
>requires no
>great powers of observation to conclude that the impacting plane will 
>greatly
>affect the ship - much  more so than a  mosquito.  This entire description 
>was
>preperatory to pertinent observations about  the string/bridge/soundboard
>interaction, as I pointed out.  .
>      I find myself in this debate reluctantly taking issue with you and 
>others
>whose lucid, informed opinions I generally agree with and always find 
>interesting
>but I do so for factual, intellectual reasons in the interest of presenting
>another,  and what I think is, a substantially better and more accurate 
>point of
>view.  Is it?  Beats me! but I think so.  In the dialogue generated thereby 
>we
>should all arrive at a better understanding and be the better for it.  This 
>is the
>utility of this list.  As far as I can see the only way this can be 
>achieved is by
>point and counterpoint, argument and counterargument.  Categorical 
>rejections of
>reasoned but opposing arguments are evidently useless.   We should proceed
>accordingly.
>      If the implications of the use of the fork analogy and its behavior 
>in driving
>the board are not convincing then try a little experiment which I have 
>already done
>myself.  Tape and weight a piece of copper wire to the sound board, cut it 
>off a
>few feet away and then bring it in contact with a tuning fork.  Even when
>completely slack the sound of the fork, albeit it rather weak, will be 
>heard coming
>from the soundboard.   This is because  periodic strain energy is 
>transmitted to
>the board through the wire and the board then develops flexing areas as 
>described
>in the earlier post.   In anticipation of the objection that I am applying 
>this
>test directly to the soundboard I would say that this the same whether the 
>point of
>application is the bridge or soundboard.  I used the board because the 
>forks I have
>are weak sounding. A stronger source would work as well when the point of
>application is at the bridge.    Surely no one would argue that the wire in 
>its
>slackened condition is physically shaking the board in the manner you 
>suggest is
>done to the bridge by the string, and this, when the point of attachment is
>substantially less stiff had the point of attachment been at the bridge.
>Admittedly, if the wire is put under tension it will transmit the strain 
>energy
>from the fork to the board more effectively but in neither case is there 
>any
>shaking of the board.
>      If one were to consider molecular motion to be the same as visible, 
>organized
>motion of a material,  which is a major, major stretch, then one could say 
>that
>some shaking is taking place.  This, however, will be invisible,  
>imperceptible,
>and is, in fact, what I come back to - stress disturbance.
>      A similar effect can be achieved, I am told, when using a violin, and 
>at a
>greater distance.
>      In the example given earlier of the fork placed in contact with the 
>plate
>surely you are not going to argue that the plate is now experiencing 
>ripples
>passing across its surface as in a pond as a result of this shaking?  Yet 
>it
>radiates sound in essentially the same fashion as the soundboard or any 
>structure.
>Where it differs from a soundboard in this regard is that  the standing 
>waves or
>modes, generated in it have less amplitude, of course, than those in a 
>soundboard
>due, at least partially, to the difference in materials. Similarly, would 
>one
>suppose that the stiff, hard rim of a good piano is actually shaking when 
>the fork
>is brought into contact with it and a perceptible increase in sound is 
>heard?
>Regards, Robin Hufford
>Ron Nossaman wrote:
>
> > >  The point that I am trying to make is that it is the
> > >ratio of the mass of the objects and the duration of contact that 
>determines
> > >whether the energy transferred will in fact cause translation, rotation 
>or a
> > >stress disturbance in the oject tself.
> > >      For example, a mosquito hitting head on an aircraft carrier  
>travelling
> > >in a direction opposite to it when both are travelling at  thirty miles 
>an
> > hour
> > >will not in any way affect  the velocity of the carrier even though 
>their
> > >closing speed is 60 miles an hour, notwithstanding vector addition,   
>because
> > >the energy of the mosquito on a molecular and atomic level  is not 
>sufficient
> > >to propagate a stress disturbance through the carrier that is adequate 
>to
> > >reorganize the individual vectors of the particules which comprise the
> > >carrier.  However, the particle velocity of some of the particles on 
>the
> > >carrier will be changed, they in turn transmit a change to others and
> > thereby a
> > >stress disturbance of limited duration passes through a part of the 
>ship which
> > >has gained a little bit of energy, essentially in the form of heat.  
>The
> > >mosquito however, will suffer  profound change both in structure, that 
>is as
> > >deformation, and velocity as the vectors of the individual particles, 
>so to
> > >speak, overcome by those of the ship and acceleration occurs.
> >
> > The velocity of the aircraft carrier will be influenced because the
> > mosquito has mass. That's pretty inescapable. The disturbance of the
> > structure of the carrier will be localized as it is pretty quickly lost 
>in
> > molecular "background noise" and dispersed as heat, but the disturbance
> > does take place. It's a matter of scale, as you said. The rough 
>equivalent
> > of the same event would be something considerably smaller than a grain 
>of
> > salt being dropped on a soundboard. In either case, the event has so 
>little
> > resemblance to a string driven soundboard as to be meaningless. I 
>propose a
> > more accurate analogy of your Mosquito being a British aircraft, which
> > would much more closely approximate the initial energy transfer between 
>a
> > string and soundboard assembly. In this case, I suspect the collision of
> > the Mosquito with the aircraft carrier will not only be clearly heard, 
>but
> > felt by the malingerers hiding out in the head. I suspect a transverse 
>wave
> > could be fairly easily detected in the hull as well.
> >
> > Ron N
>


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