|
Welcome to the Piano World Piano Forums Over 3 million posts about pianos, digital pianos, and all types of keyboard instruments. Over 100,000 members from around the world.
Join the World's Largest Community of Piano Lovers
(it's free)
It's Fun to Play the Piano ... Please Pass It On!
|
|
67 members (Abdulrohmanoman, Charles Cohen, accordeur, BWV846, Animisha, benkeys, Anglagard44, 11 invisible),
2,230
guests, and
440
robots. |
Key:
Admin,
Global Mod,
Mod
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Knocking crud away from the termination point? Some microscopic crud, it seems, Jeff. The backstring going down to the hitch pin may be a whole different story I wonder, Emmery. Your test certainly ruled out transverse vibrations, so it's a good bet changes in longitudinal vibrations explain the improved tone of my piano. As one can work out from the spectrograms, the relative power of the partials, before and after, increased by an average factor of about 5 for the lower ones rising to 12.5 at the tenth. For this to have happened the longitudinal waves must have been well reflected at each end of the strings, at the tuning pins and the hitch pins.
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Apr 2008
Posts: 2,481
2000 Post Club Member
|
2000 Post Club Member
Joined: Apr 2008
Posts: 2,481 |
I think the waves are reflected at the termination point on a v bar or or aggraffe and the section between that and the tuning pin are pretty well null for sound. An additional pressure bare would even deaden it some more if there is something extremely faint going on there. In fact, only some pianos have a weave of cloth in there, and often I just think its for looks. With that string length being so short, even the faintest sounds would be on a high order of frequency magnitude, something nearer to the same speaking string lengths we see in the top treble notes.
The back string from the bridge to the hitch pin is a whole different thing. The bridge is not as rigid or solid as the steel termination points at the other end and will allow vibrations to leak through to the other side.
Last edited by Emmery; 02/14/12 12:36 AM.
Piano Technician George Brown College /85 Niagara Region
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
I think the waves are reflected at the termination point on a v bar or or aggraffe and the section between that and the tuning pin are pretty well null for sound. An additional pressure bar would even deaden it some more if there is something extremely faint going on there. What you say, Emmery, is what I would have said; that is until a question came up about the effect on tone of the non-speaking lengths. It turns out there is more to the full story - piano hammers produce longitudinal waves in the strings as well the tranverse waves you describe. If transverse waves were the only game in town, there is no way tweaking the strings at the pressure bar would have had anything other than your extremely faint effect on my piano. There had to be something else to explain the release of energy I heard. The obvious candidate was longitudinal waves, by which I mean waves within the strings themselves. These waves will not stop at the v-bar but will carry on behind the pressure bar until reaching the end of the line at the tuning pin and coil. As there is nowhere else for them to go they will turn round and go back along the string towards the hitch pin, and so on back and forth. From my experience it appears that a good proportion of the energy will leak into the pressure bar if the string is stuck to it with some amalgam of dust, must and rust. A search of this forum yields no mention of longitudinal waves at all, other than a crop of posts about the (sometimes objectionable) longitudinal mode in bass strings. As Giordano and Korty's paper, [i]Motion of a piano string: Longitudinal vibrations and the role of the bridge[/i], is not mentioned either, it may be helpful if I summarise some of its key points: - Longitudinal vibrations are generated by the hammer blow stretching the string.
- Transverse waves show no sign of longitudinal vibrations but the motion of the bridge and soundboard does.
- The relative power of the higher partials in the string spectrum [i.e. the transverse waves] is much less than their power in the sound spectrum [i.e. produced by the soundboard].
My answer to the $64 question, in my recent post showing the before and after frequencies, was that much of the energy stored in the longitudinal waves was being dissipated in the pressure bar. When this energy was released, as a result of flexing the strings, the motion of the bridge and soundboard increased in a way that boosted the power of the partials.
Last edited by Withindale; 02/15/12 08:15 PM. Reason: typos
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Nov 2008
Posts: 6,425
6000 Post Club Member
|
6000 Post Club Member
Joined: Nov 2008
Posts: 6,425 |
.....
The obvious candidate was longitudinal waves, by which I mean waves within the strings themselves. These waves will not stop at the v-bar but will carry on behind the pressure bar until reaching the end of the line at the tuning pin and coil.
..... Uh, why wouldn't the waves stop at the pressure bar? I think they would. My understanding of longitudinal waves is different. It is the same as tone bars. The frequency depends on the length and thickness. The tension (stretching) has nothing to do with it.
Jeff Deutschle Part-Time Tuner Who taught the first chicken how to peck?
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
.....
The obvious candidate was longitudinal waves, by which I mean waves within the strings themselves. These waves will not stop at the v-bar but will carry on behind the pressure bar until reaching the end of the line at the tuning pin and coil.
..... Uh, why wouldn't the waves stop at the pressure bar? I think they would. My understanding of longitudinal waves is different. It is the same as tone bars. The frequency depends on the length and thickness. The tension (stretching) has nothing to do with it. Longitudinal waves in strings are sequences of stretching and compression along their length. Click here for an animation; don't worry about the time axis. As the stretching and compression movements are within the string there is nothing to stop them at the pressure bar. Think about liquid flowing through a pipe curving round the pressure bar. There must be reflection at either end, at the coil and tuning pin and at the hitch pin; otherwise energy would disappear and the note would be deadened, as sometimes happens. By tone bar do you mean as in percussion instruments such as a xylophone, as described here, for example? The vibrations shown in the diagram on that page are transverse. Giordano and Korty have quite a bit to say about stretching and longitudinal waves but the fundamental point is that you can't have transverse waves in piano strings without inducing longitudinal waves as well.
Last edited by Withindale; 02/16/12 09:41 AM.
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Nov 2008
Posts: 6,425
6000 Post Club Member
|
6000 Post Club Member
Joined: Nov 2008
Posts: 6,425 |
Ian:
I would think that the bearing friction would stop the longitudinal waves.
But let's say it didn't. Would goofing around with the "non-speaking" part change anything if the high friction bearing points do not have an effect either?
Jeff Deutschle Part-Time Tuner Who taught the first chicken how to peck?
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Jeff: OK, let's follow up on your suppositions and look at two imaginary pianos. In the first, the longitudinal waves stop at the v-bar and the bridge. The non-speaking lengths are just guy-wires at constant tension. - FFF blows never knock any notes out of tune
- beckets never slip out
- tightening coils never has an effect on tone
- flexing strings at the pressure bar affects unisons but not tone
- re-seating hitch pin loops has little or no effect on tone.
In the second, longitudinal waves carry on past the v-bar and the bridge pins. They are reflected at the tuning pin and and the hitch pin. - FFF blows can affect the tuning by the end of a concert
- beckets sometimes slip out or break
- tightening coils improves the tone of some notes
- flexing strings at the pressure bar may liven up some notes
- moving strings back and forth at at the v-bar may improve a note
- re-seating hitch-pin loops sometimes improves the sound; badly made loops can break.
Which is more like a real piano?
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Nov 2008
Posts: 6,425
6000 Post Club Member
|
6000 Post Club Member
Joined: Nov 2008
Posts: 6,425 |
Ian:
I do not play poker with someone that stacks the deck.
You are completely ignoring sloppy stringing and poor pin setting.
Jeff Deutschle Part-Time Tuner Who taught the first chicken how to peck?
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Jeff:
The pianos were strung, tuned and serviced by the experts on this forum. What happens is what they describe.
You might say the first piano is one that is not played and the second one that is.
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Apr 2008
Posts: 2,481
2000 Post Club Member
|
2000 Post Club Member
Joined: Apr 2008
Posts: 2,481 |
Jeff:
The pianos were strung, tuned and serviced by the experts on this forum. What happens is what they describe.
You might say the first piano is one that is not played and the second one that is. Ian, many of those changes occur because of the speaking length being effected. Sometimes grooves form in v bars and pressure bars and moving a string off them effects the speaking length tone. Also, part of a piano going out of tune during heavy playing is simply uneven string tensions equalizing out as they slip over the bearing points, something that we try to avoid with a good pounding in but nobody gets it perfectly even I think.
Last edited by Emmery; 02/16/12 04:11 PM.
Piano Technician George Brown College /85 Niagara Region
|
|
|
|
Joined: Nov 2008
Posts: 6,425
6000 Post Club Member
|
6000 Post Club Member
Joined: Nov 2008
Posts: 6,425 |
Ian:
So the "imaginary" pianos are actually anecdotal pianos. And you picked and chose them for your own purposes. One is an ace for your hand and one is a duece for my hand.
I am finished with this Topic. Maybe things will go better with your next one.
Jeff Deutschle Part-Time Tuner Who taught the first chicken how to peck?
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Jeff:
All the things that happen in the second piano, and don't happen in the first, depend on the transfer of energy between the speaking and non-speaking lengths.
I have one torpedo left - marked TONE - and it's down to your invaluable persistence that it's almost ready to go. We'll see if it's an ace or a deuce.
Last edited by Withindale; 02/17/12 02:29 PM. Reason: misfire
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Sep 2006
Posts: 3,983
3000 Post Club Member
|
3000 Post Club Member
Joined: Sep 2006
Posts: 3,983 |
Go for it Jeff. Tilting at windmills is a thankless task, but someone has to do it!
JG
|
|
|
|
Joined: Apr 2008
Posts: 2,481
2000 Post Club Member
|
2000 Post Club Member
Joined: Apr 2008
Posts: 2,481 |
Go for it Jeff. Tilting at windmills is a thankless task, but someone has to do it!
Piano Technician George Brown College /85 Niagara Region
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Did George Brown College invite the Star Trek crew to a piano recital?
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Returning to reality; Harold Conklin measured longitudinal vibrations at the hitch pin over 15 years ago. See [i]Generation of partials due to nonlinear mixing in a stringed instrument[/i] J. Acoust. Soc. Am., Vol. 105, No. 1, January 1999. Experimental set upthe sensor marked FS measured the tension end force. Longitudinal wave frequency spectrumLongitudinal wave spectrum - higher partials In summary of this thread, longitudinal waves are the reason it makes sense to seat strings really well at all bearing points, from the tuning coil to the hitch pin. Loss of energy at any of those points will likely have a disproportionate effect on the power of the higher partials and tone. Ironically, Harold Conklin was looking for "phantom" partials.
Last edited by Withindale; 02/18/12 04:33 PM. Reason: Higher partials spectrum
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Aug 2009
Posts: 315
Full Member
|
Full Member
Joined: Aug 2009
Posts: 315 |
Ian, I'm going to start by saying that I believe that you're probably right about the pressure bar having something to do with tone. Something interesting is going on there, for sure. However, I think you've misapplied the conclusions of the ASA paper you've cited. The ASA paper actually contradicts what you showed in your spectrograms in your earlier posting. From what I gather, you ran an informal experiment, and recorded two spectrograms before and after a treatment to the strings at the pressure bar. Your spectrograms show an increase in the relative amplitudes of the upper partials, yes. All of the partials that were enhanced appear to be (roughly) integer multiples of the fundamental. Look closely at the ASA paper again. The authors are showing that the longitudinal vibration components are creating what they call "phantom partials". Correct me if I'm wrong, but the phantom partials don't fall in line with the partial ladder normally seen created by the transverse vibrational energy. That's in direct contradictions to what you show in your spectrograms. Longitudinal vibrations along a string can be and often are different than the partial series set up by the transverse vibrations. Give a listen to any of the sound files at the following site, and you'll hear how this can be true. http://www.speech.kth.se/music/5_lectures/conklin/longitudinal.htmlSure, the longitudinal vibrational energy may have had something to do with the results of your experiment. Again, I agree that there's SOMETHING interesting going on in the nonspeaking portion of string under the pressure bar - to be investigated further. But I think some of the assertions you've made in this thread cannot be substantiated on the references you've cited. Correlation does not equal causation. Chris S. Acoustician by Day, Piano Tech by Night.
Chris Storch Acoustician / Piano Technician
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Hallo Chris, I agree with your point about spurious correlation. I was once asked to analyse the socio-economic factors stunting the growth of children from deprived backgrounds around Manchester in England. Some doctors had sponsored a study and the data, collected at some expense, showed two distinct groups. They had not noticed Group A were all boys and Group B were all girls. I hope I haven't fallen into the same trap with my interpretation of Harold Conklin's paper on the generation of partials due to non-linear mixing. Chris, I do not believe I have misapplied the results of the ASA paper or that my spectrograms are conflict with them. As I see it all the overtones we hear result from the non-linear response of the bridge to the vibrations in the string. You have to consider the longitudinal wave component at all frequencies, not only for longitudinal modes. To my mind you have a reasonably complete model of a piano string when you include both longitudinal and transverse waves. I am not so sure you need look much farther unless you want to understand the mechanisms which dissipate energy or, more importantly, generate sound. Please say if you think this wrong or if there are still some unwarranted assertions. In the hope of avoiding any further misunderstandings I think I'd better go back to square 1 and run through the whole argument. My "experiment" was to see if anything would happen if I reseated the strings of D7 at the pressure bar. To my (untrained) ear, the note had livened up considerably in comparison with its neighbours. This was after I had revived that note by reseating them at the v-bar. I then repeated the exercise on the other 58 notes under the pressure bar, with similar results. The question was why this occurred. As Del said, and as Emmery observed, the v-bar and the pressure bar are very effective at terminating the transverse vibrations of the string. It follows that what I did could not have directly affected the transverse vibrations in the speaking length. Conventional wisdom is that what happens in the speaking length determines the sound. This is true of course for most practical purposes associated with tuning and voicing. Wave diagrams and formulae are about the speaking length. The non-speaking lengths do not feature in the Five Lectures on the Acoustics of the Piano you mention. Earlier in this thread rxd mentioned transference of power from the hammer to the string; it is that energy which is at issue. Once the hammer has left the string its energy can either be dissipated or turn into sound. When you enliven a note by seating its strings you increase its energy by reducing the amount of energy being dissipated at one or more of the bearing and end points. This is where conventional wisdom comes into the argument. This appears to be that all waves are in the speaking length and virtually none of their energy transfers across the termination points. Therefore making adjustments at the pressure bar, tuning coil and hitch pin can have no effect. The elephant in the room had better come out into the open now; all the vibrational energy in the string is in the longitudinal vibrations. These waves are periodic stretchings and compressions along the string itself. They result from the hammer hitting the string and the transverse movements of the string that follow. Rather than take my word for it, read this short article on Longitudinal Waves quoted from "Physical Audio Signal Processing" by Julius O. Smith III. By the way, longitudinal modes are only one aspect of longitudinal waves. The mathematics associated with waves in taut strings are moderately complex and have been the subject of some debate over the years. However a paper published in 2011 may have resolved the matter, "The potential energy density in transverse string waves depends critically on longitudinal motion", David R Rowland 2011 Eur. J. Phys. 32 1475, see the abstract here. I do not have a copy of this paper but the general conclusion makes sense. This is that [to derive] the correct formula for the potential energy density in transverse waves on a taut string ... the longitudinal motion of elements of the string needs to be taken into account, even though such motion can be neglected when deriving the linear transverse wave equation. In other words, when you are talking about the behaviour of the speaking length, i.e. the transverse wave equation, you do not need to worry about the longitudinal waves. On the other hand, you should when talking about the behaviour of the piano, especially the bridge and the soundboard, as Giordano and Korty's work showed. The next question is whether the longitudinal waves are mainly reflected at (a) the v-bar and bridge pin or (b) the tuning pin and the hitch pin. It seem obvious to me that much of their energy must reach the tuning pin ... It honestly depends. For a normal person, probably three months. For a professional pianist, maybe a month. For a concert at Carnegie Hall, probably until intermission. ... and the hitch pin but in this forum such it seems such a conjecture needs solid proof. Giordano and Korty measured the longitudinal motion at the bridge and then Conklin went one step further and measured the force of the longitudinal waves at the hitch pin. His experiment shows that a significant amount of longitudinal wave energy, if not all, is travelling along the whole length of the string. This is key point from Conklin's paper for this thread. Once one knows that there is wave energy in the non-speaking lengths one can see why adjusting strings at the tuning coil, hitch pin, pressure bar, and bridge pins might affect the tone. As might any other bearing points where energy can be lost. The point that extra longitudinal wave energy enlivens a note by increasing the power of the higher partials originally came from Giordano and Korty. This was a general observation they made without mentioning phantom partials. Conklin says he spotted the phantom partials in Giordano and Korty's spectrograms and, in that sense, his work extends theirs. You will see in the following diagrams that there is longitudinal wave energy in the partials as well as the phantom partials. In fact he goes on to discuss how the phantoms smear the partials, see Fig 18 in the paper. I am including the diagrams here because it will be easier to compare them one above the other than spread about in the pdf. Sound Transverse waves at the bridge Longitudinal waves at the bridge
Last edited by Withindale; 02/19/12 03:58 PM. Reason: Clarification
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
Joined: Jun 2011
Posts: 824
500 Post Club Member
|
500 Post Club Member
Joined: Jun 2011
Posts: 824 |
|
|
|
|
Joined: Feb 2011
Posts: 4,331
4000 Post Club Member
|
OP
4000 Post Club Member
Joined: Feb 2011
Posts: 4,331 |
Johnkie, taking a leaf from your book, there was no need for that ... or for most of this thread! As The Honourable Mr Justice Lindsay once said, after listening to the contrary opinions of experts and leading counsel about mental disorders caused by stress at work, it becomes necessary to spell things out.
Last edited by Withindale; 02/19/12 03:17 PM.
Ian Russell Schiedmayer & Soehne, 1925 Model 14, 140cm Ibach, 1905 F-IV, 235cm
|
|
|
|
|
|
Piano
by Gino2 - 04/17/24 02:34 PM
|
Piano
by Gino2 - 04/17/24 02:23 PM
|
|
Forums43
Topics223,405
Posts3,349,434
Members111,637
|
Most Online15,252 Mar 21st, 2010
|
|
|
|
|
|