Just a thought: Whenever a string vibrates, it exchanges energy with other parts of the piano. During this "mutual" exchanges, the phase may very, and that's what the phase display is showing. The variation may be upward, meaning that impedance is getting higher, or viceversa downward. Maybe we should consider not only the coupling between the strings of the same unison, but also the coupling with all the other notes, even if with the damper down. They are all "damped tuned oscillators", ready to eat (and maybe rebounce) some energy from our playing note. To get a more "corporeal" idea of what I mean, just put your hand on the bass dampers while you play a note in the middle or treble, possibly on a good piano.... and you will feel that it's a MUCH MORE COMPLICATED question than just rising a little bit one string. This is something which is not under our control, besides the small correction we can do on unison. The only way we can change somehing, in his sense, is by stretch. I mean, if octaves, or maybe 12th, are more consonant, it will be easier for energy to go from our played note to the the other strings. If they are somehow further, the transfer will be slower, so the decay. Sorry I'm not very clear, but I'm not a phisician, nor I speak English. Greetings. Luigi Lamacchia Bari - Italy -----Messaggio originale----- Da: owner-pianotech@ptg.org [mailto:owner-pianotech@ptg.org]Per conto di Richard Brekne Inviato: mercoledì 14 agosto 2002 8.19 A: pianotech@ptg.org Oggetto: Re: Unison Flatter than each Individual string? Hi baoli liu I kind of get the feeling that both the soundboards vibrational modes as you point out, and also the condition of the bridge gets into the picture. How springy or massy the impedance characteristics are at the bridge, even before the soundboard modes get into the picture may come into play. For that matter the condition of the bridge pin (whether its tight or loose in the bridge) might play some role. In any case, I cant say that I have been able to observe that string coupling results exclusively in pitch drop. Actually I am not sure that this pitch drop happens significantly more often then other things. On the side, it seems more and more to me that both pitch decay and and whether the pitch rises or falls in coupling also have something to do with coincident partials to the note being played. I find what looks very much like increased sustain especially in the high treble when I use the perfect 12ths tuning. And it also seems to be that when this "extra" sustain is most apparent, the unison displays a slight rise in pitch as as it decays. Weird. But like I say, I believe the whole subject matter is not completely understood, and that like our understanding of just how the soundboard vibrates and other such subject matter, lots more hard research and experimentation is needed. RicB
This PTG archive page provided courtesy of Moy Piano Service, LLC