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. > > Peace, > Sarah > > > ----- Original Message ----- > From: "Robin Hufford" <hufford1@airmail.net> > To: "Sarah Fox" <sarah@gendernet.org>; "Pianotech" <pianotech@ptg.org> > Sent: Monday, November 18, 2002 3:35 AM > Subject: Re: S&S D Duplex > > > > Hello Sarah, > > Distinctions should be drawn on the subject of > string/bridge/soundboard > > behaviors which take into account not only the difference between > transverse > > waves on the string and the possiblity of longitudinal waves there also, > but, > > additionally, the mechanical function of the soundboard/bridge and string > > interaction and the nature of relevant forcing functions themselves. > > The standing waves on the string itself do not move across the wire, > nor, > > in my opinion, do they "rock" the bridge up and down significantly. > Rocking is > > not necessary to transfer energy into the bridge or past it to the duplex > > segments, bridge, soundboard, agraffes, plate or whatever. Another > mechanism, > > which I called "stress transduction" in a very intense, controversial > discussion > > of this same subject earlier this year will easily account for this and, > > although it seems to be well understood by only a few, is available on > the > > archives under the subject lines "The behavior of soundboards" "Rocking > > bridges" and others which escape me at the moment. > > Briefly, at the terminations of the string the wire itself is > subjected to > > a periodic stress induced in it by the cycling standing waves occuring on > the > > speaking length segment and their interaction with the bridge/soundboard. > > These are separate from the traveling waves developed on the wire by the > hammer > > which superimpose to create the cyclic standing waves on the string. . > The > > resultant of the excursions made by the standing waves is along the > equilibrium > > point of the wire and, at the terminations, a periodic stress is > experienced by > > the, essentially, immobile wire segments there, held down there as they > are by > > the vastly greater forces of the other strings, the downbearing, etc. > This is > > not a free vibration of the wire but, rather, a periodic, mechanical > stress wave > > which passes easily across the terminations whether bridge pin or > agraffe. > > Touching a tuning fork to the bridge results in essentially the same kind > of > > stress transduction. > > In the context of the duplex segments, which, in my experience are > not > > necessary for a great sounding instrument, witness some Chickerings, but > which > > may well exist on one, it is important to understand that the energy > passing the > > terminations is a forced vibration; that is a periodic state of stress is > > imposed which has the frequencies contained in the string, and not a free > > longitudinal vibration. I think Steinway grasped this distinction only > poorly > > but refers, albeit clumsily, to it with the term longitudinal vibration. > As > > you point out, the frequency of a true longitudinal vibration in the > duplex is > > dependant on the lengths and wave speed of the medium, and this produces > > frequencies far too high to be much relevant to normal piano sound. > > The distinction between a kind of pseudo-longitudinal forcing > function > > which describes a state of stress and the ordinary, longitudinal wave is > > critical, I think, to understanding the intended value of the duplex. > Speaking > > as a pianist, I never know whether a piano has a duplex or not unless > there is > > sufficient whistling and jangling to draw attention. If a piano is like > this, > > usually, there are so many other things wrong with it that these > imperfections > > are merely a few of many and the connection with the instrument is > lessened. > > However, many times while tuning I have looked down at the front duplex > segment, > > silenced it with the touch of a finger, and immediately noted a kind of > drier, > > dull, sound. > > The stress wave, or pseudo-longitudinal state of forcing, passes the > > terminations or bridge into the duplex segments where a similar reflexion > and > > recurrency of effect as occured in the superpositions of the traveling > wave in > > the speaking length occurs, resulting again in a transverse set of > standing > > waves which, of course, are greatly attenuated. This can be tuned by > moving the > > duplex. > > Additionally, the transfer of energy into the bridge is easily > accomplished > > both by refraction and mode conversion of the wave type. > > Although it is heresy to some to claim such, in actuality, > approximately > > the same amount of energy leaves both ends of the wire at the speaking > length > > terminations - the difference in acoustic effect of the stress wave or > > condition passing into the plate on the one hand, and into the bridge/ > > soundboard on the other, being, fundamentally, the flexural rigidity or > bending > > modulus which is the product of the modulus of elasticity and the section > > modulus of the material, in conjunction with the degree of reflectivity > and > > size and shape of the medium. > > I believe the utility of the duplex in essence, is, exactly, what > the > > patentee claimed, and that is the tuning of the segments to harmonics of > the > > fundamental of the speaking length and the effect of this on the > sensibility of > > the notes, particularly, those of the treble which need some means of > becoming > > more perceptible than the more instrusive tenor and bass. That the > companies no > > longer take the trouble to tune them is no surprise to me, given the long > > decline of piano building. Numerous other examples exist of features > abandoned > > or in use in name only. This is characteristic of the industry itself. > > However, I do think, judging from what he says, that Ron Overs may be on > to > > something with regard to his method of altering the tuning of the front > duplex, > > that may, indeed be new, in this regard, although I have no personal > experience > > of this. > > Regards, Robin Hufford > > > > Sarah Fox wrote: > > > > > Hi Phil, > > > > > > > 3. If longitudinal vibrations can pass the bridge, it seems to me > that > > > they > > > > can just as easily pass the aliquot. So the aliquot position is > > > irrelevant. > > > > The plate pin becomes the relevant thing. In order to actually tune > this > > > > portion of the string for longitudinal vibrations you would need to > have a > > > > movable plate pin. This feature has not been incorporated into any > piano > > > that > > > > I have seen. > > > > > > Actually every contact point would be a sound reflection point, > resulting > > > from an abrupt impedance differential. If we're talking about > compression > > > waves in the string, which it appears is the implication, the free > resonant > > > frequency between any two contact points would be half of the speed of > sound > > > through spring steel (not through air), divided by distance. It would > be > > > *incredibly* high (bat frequencies and beyond, not dog frequencies), and > it > > > would only be tunable by moving contact points (assuming the spring > constant > > > is indeed constant -- or approximately so). You suggest the sound would > > > stop at the hitch pin. It would not. That is only another contact > point. > > > It would travel into the plate and beyond. It would also have a > difficult > > > time coupling into the bridge, except by rocking it. > > > > > > Personally, the importance of longitudinal vibrations doesn't seem very > > > probable to me. It is easy enough to see how transverse vibrations are > > > coupled into duplex strings from vibrations in the bridge, irrespective > of > > > what Mr. Steinway might have claimed to the contrary. Why invoke > mysterious > > > ultrasonic longitudinal vibrations? Just because Mr. Steinway got a > patent > > > doesn't mean he understood the acoustics of his invention. > > > > > > In the end, could it be that the biggest benefit of a tuned duplex scale > is > > > the "freeing up" of the vibrations of the strings and bridge by > eliminating > > > the need to mute the strings on the far side of the bridge? After all, > > > mutes of any kind work through frictional dissipation of vibrational > energy. > > > Isn't it reasonable to expect that muting adversely affects a note's > > > sustain? If the purpose of muting is to kill objectionable ringing in > > > nonspeaking string segments at inappropriate frequencies, isn't an > alternate > > > solution to tune those frequencies to where they are appropriate and > > > therefore not objectionable? > > > > > > I am reminded of a closed field speaker system I once designed for my > > > research. (Think of a tiny speaker in a very long, sealed tube.) The > > > objective was to make it flat (+/- 1 dB) from 100 Hz to 15 kHz and make > it > > > efficient enough to deliver 120 dB SPL to the end of the tube with > minimal > > > distortion products (-60 dB or better). I first attempted this by > muffling > > > the ends of the tube in order to avoid resonance peaks about every 120 > Hz. > > > (Think in terms of "muting" inappropriate frequencies.) I kept muffling > and > > > muffling until I had to deliver so much power to the speaker driver as > to > > > toast the voice coil. (We're talking about an EV1202 ferofluid driver!) > > > Eventually I learned to work *with* the resonances instead of against > them. > > > I removed almost all the muffling and filled the tube with smaller > > > open-ended tubes that were tuned to a variety of other frequencies. The > > > idea was to "resonate at all (or many) frequencies." I achieved enough > > > efficiency to deliver 120 dB SPL at 1000 Hz using only a half watt of > input > > > power! I was up to several watts at 15 kHz, but not nearly enough to > blow > > > the voice coil. In the end, my system achieved the flatness I desired, > > > along with far more efficiency than I had ever hoped for. It was sort > of a > > > "Bose" solution. Hopefully the parallels to the duplex scale are > obvious > > > here. Where possible, it seems best to correct the tuning, rather than > to > > > kill the sound. > > > > > > Peace, > > > Sarah > > > > > > _______________________________________________ > > > pianotech list info: https://www.moypiano.com/resources/#archives > > > > >
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