And it seems to me that the more rigid a body, the
more rapidly "shock wave" vibration would pass from
one end to the other, as long as it was of uniform
density to avoid internal damping. So if someone had a
very stout steel rod, say 2" in diameter and 6 feet
long, and tapped on one end, more vibration would pass
through to the other end than on a rod which flexed,
thereby dissipating the energy into the air, and
losing it as heat in the internal flexion. And this
longitudinal transmission would be virtually
unnafected by bearing points, clamping, etc. Is this
the sort of energy transmission we are speaking of
here?
Gordon Stelter
--- Robin Hufford <hufford1@airmail.net> wrote:
> A correction of one of the, unforntunately,
> frequent typos in postings of late. rh
>
> There is a reasonable analogy to drawn between the
> flexural, bodily,
> behavior of the tines of the fork and the
> transduction of this to a cyclic
> vibration or stress wave passing through the(STEM
> )(corrected version) and the
> flexural, standing waves on the string which are
> transduced similarly by the
> terminations at the
> bridge/board and agraffe/capo interface.
>
> Robin Hufford wrote:
>
> > Hello Sarah,
> > The "pseudo-longitudinal wave" is, in fact, a
> true longitudinal wave but it
> > is a forced vibration and contains the
> frequencies of the forcing function. It
> > is the normal mechanical wave or density
> fluctuation passing through a medium
> > as the particles of the medium oscillate around
> their equilibrium positions in
> > the waveguide which, in this case, is mostly the
> continuing portion of the
> > string threaded across the bridge, the bridge
> itself, the bridge pins, or the
> > part of the wire passing through the agraffe,
> along with the agraffe, Capo bar
> > and plate. This is not a variation in tension
> but, rather, again, a density
> > fluctuation passing through the medium with a wave
> velocity which is a function
> > of the inertial and elastic properties of the
> medium itself, imposed upon this
> > is the frequency and extent or lack of
> periodicity.
> > This can be viewed in another way and that is
> as a state of cyclic stress
> > passing through the medium.
> > Not to be too repetitive on the list as this
> has been thoroughly explored
> > in the threads referred to earlier, although
> vehemently disagreed with by others
> > here on the list: this can be easily comprehend
> by considering the behavior of
> > a tuning fork. The tines oscillate back in forth
> at a right angle with regard
> > to the stem. Their flexural, oscillating, bodily
> behavior is mechanically
> > transduced to a cyclic stress, strain, or density
> fluctuation, as you will,
> > which is a forced vibration passing along the
> bass and stem of the fork. When
> > placed in contact with the bridge, and it matters
> little where, this vibration
> > then passes into the bridge and board where
> reflexion, superposition and its
> > attendant interference, both positive and negative
> create distortional and
> > dilational waves in the board itself; momentum is
> then radiated away as acoustic
> > radiation. Precisely the same thing happens with
> the vibrating string itself:
> > the standing waves are enabled by the,
> essentially, rigid termination
> > mechanisms which transduce the strain energy
> associated with the standing wave
> > behavior in the wire into forced longitudinal
> vibrations at the terminations.
> > There is a reasonable analogy to drawn
> between the flexural, bodily,
> > behavior of the tines of the fork and the
> transduction of this to a cyclic
> > vibration or stress wave passing through the tines
> and the flexural, standing
> > waves on the string which are transduced similarly
> by the terminations at the
> > bridge/board and agraffe/capo interface.
> > The longitudinal wave energy, at the
> frequency of the forcing function,
> > passes into the bridge with out need of flexion,
> although I have never argued
> > that flexion is completely absent for several
> reasons, and, crosses the bridge
> > and continues along the duplex where again,
> reflexion and superposition create
> > audible, tunable vibration.
> > I don't know whether these segments increase
> sustain or not, although, I
> > have no doubt that, in some cases, the difference
> in total sound, as I said in
> > the previous post, increases the perceptibility of
> the note produced by the
> > speaking length, possibly in a kind of
> gestalt/figure interaction. This would
> > be very difficult to pin down, accurately.
> > This view, which is rather unpopular here,
> requires a subtle distinction to
> > be drawn between the flexural, bodily behavior of
> the vibrating portion of some
> > object or structure, and the nature of wave
> motion, or, again, localized
> > density fluctuations which pass through a medium
> and do not require actual
> > bodilty motion of the medium itself for their
> propagation. These are just the
> > normal, ordinary mechanical waves encountered
> everywhere. The function of the
> > soundboard and bridge stabilize the endpoints of
> the string and allow the
> > transduction through mode conversion of strain
> energy of the standing waves
> > which are of course, primary, but, in another
> sense secondary phenomena.
> > Regards, Robin Hufford
> >
> > Sarah Fox wrote:
> >
> > > My other attempted post, accidentally directed
> to Robin Hufford in
> > > private...
> > >
> > > ----- Original Message -----
> > > From: "Sarah Fox" <sarah@gendernet.org>
> > > To: "Robin Hufford" <hufford1@airmail.net>
> > > Sent: Monday, November 18, 2002 3:35 AM
> > > Subject: Re: S&S D Duplex
> > >
> > > > Hi Robin,
> > > >
> > > > OK, thanks for explaining the "longitudinal"
> wave to me (i.e. which isn't
> > > > really a longitudinal/compression wave at
> all). Steinway's "longitudinal"
> > > > wave, if I understand you, is little more than
> the variation in tension of
> > > > the wire as it vibrates, resulting in lateral
> forces (in direction from
> > > > tuning pin to hitch pin) across the bridge.
> Correct? I would think there
> > > > must also be some transverse (e.g. vertical)
> vibration in order for
> > > cyclical
> > > > tensional variations to result in any sort of
> string vibration. Really I
> > > > view the pseudolongitudinal wave (as you
> explain it) as yet another aspect
> > > > of a transverse wave. Of course I'd need to
> think about it... and my
> > > brain
> > > > doesn't work all to great at this time of
> night. <yawn>
> > > >
> > > > I suppose I would still echo Del's concern:
> Does a pseudo-longitudinal
> > > wave
> > > > travel to the duplex segment through the wire
> or through the bridge? I
> > > > would argue that unless the string slips
> freely on the bridge pins, which
> > > it
> > > > clearly doesn't, that the bridge would have to
> move in order for
> > > vibrations
> > > > to pass into the duplex segment. I don't
> think there's anything magical
> > > > about it. On either side of the bridge, we're
> still talking about
> > > > garden-variety transverse waves, which are
> tunable in every sense to which
> > > > we have grown accustomed.
> > > >
> > > > As I see it, the fundamental questions are
> still:
> > > >
> > > > (1a) Does an unmuted duplex segment increase
> sustain? (1b) Does the
> > > tuning
> > > > of an unmuted duplex segment affect sustain?
> > > >
> > > > (2a) Are the tonal effects of a duplex segment
> desirable? (2b) How does
> > > > this differ between tuned and untuned?
> > > >
> > > > The first question can be answered
> quantitatively. The second is a
> > > > subjective matter, not unlike the age-old
> argument as to whether a large,
> > > > echoing concert hall sounds better than an
> "anechoic" chamber -- or vice
> > > > versa -- or some compromise inbetween.
> Different strokes for different
> > > > folks.
> > > >
> > > > Anyway, thanks for explaining what is really
> meant by this "longitudinal
> > > > wave" thing. It makes much more sense now.
> > > >
>
=== message truncated ===
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