deep in the unison, (was Bluthner something)

[ed440@mindspring.com]

Jim Ellis published a series called "Unisons-the Effect of Tuning on Persistence and Timbre" in the Sept, Oct & Nov 1982 PTJournal.  My impression is that he shows a deeper understanding of unisons than Weinreich. (Weinreich is a physicist, not a tuner.)  Here's a quote from Jim Ellis' conclusion:

"Piano tones exhibit two separate decay rates.  There is a high amplitude prompt sound that decays rapidly, and a lower-amplitude aftersound that decays slowly..... Very precise tuning accentuates the prompt sound, eliminates subdued beats, reduces the total persistence of the tone, and provides maximum tuning stability.  Slightly staggered tuning decreases the duration of the prompt sound, increases the persistence of the total sound, generates subdued beats even though the lower partials may frequency lock, and provides minimum tuning stability.
Very slightly staggered tuning has its place for special occasions when both the artist and tuner know what they are after....."

I recommend this article as probably the best available on unison behavior.

Ed Sutton

-----Original Message-----
>From: A440A@aol.com
>Sent: Feb 3, 2006 7:50 PM
>To: pianotech@ptg.org
>Subject: deep in the unison, (was Bluthner something)
>
>Mark writes:
>
><<  With all  due respect, I think the analogy to a swing is not quite 
>perfectly 
>
>applicable, 
>
>         Agreed, it is not perfectly applicable.  At least, not perfect in 
>the sense of a mathematical model.  
>
>>>     If the swing's period is 5.0 seconds, and you always apply your push 
>.1 
>
>seconds after the swing has changed directions, so that you are adding 
>
>force in the same direction the swing is now travelling (this is what I 
>
>think you meant), then the period of your push is also 5.0 seconds, not 
>
>5.1 as you suggested. Your push is slightly, but consistently, late, or 
>
>out of phase, and therefore is simply adding amplitude, as to a pendulum.<< 
> 
>>>    If instead you actually did time your pushes to 5.1 seconds, with each 
>
>successive cycle you would get .1 seconds further behind the 5.0 second 
>
>phase of the swing, until you were actually colliding with the swing 
>
>coming at you from the opposite direction. Where at first you had been 
>
>adding amplitude, this would gradually change until you were acting 
>
>against and cancelling out the opposing force. 
>
>
>     There is a distinct difference in a pendulum that is free and one that 
>is driven. ( I am too far removed from the physics courses to exactly explain 
>the differences).  What I remember is that the pushed pendulum steadily 
>increases its speed AND amplitude, so the 'collision' would be farther down the line 
>than the simple timing of the two factors would indicate.  Even so,  the 
>collision would only happen once, and then the cycle would begin anew. As soon as 
>the swing crossed the line and met the push, it would be reset to its original 
>timing and the push would once again be in phase.  
>     Not sure what the hell that has to do with Bluthners, but coupled string 
>behaviour is not so well understood that we shouldn't continue to kick the 
>possibilities around.  Sooner or later, somebody with an engineering or physics 
>background will stroll out onto this playground and paint the lines for us.  
>    It may be my own imagination, (rogue scoundrel that it has shown itself 
>to be), but when I tune two strings of a unison as exact as possible, and then 
>tune the remaining string slightly sharp,  it seems that the sound has less 
>power and sustain than when the third string is slightly flat.  I am talking 
>about the least amount necessary to cause the SAT to indicate direction.  There 
>is no beating, but I swear I hear a different sound. 
>Could others please try this and let  us know if the effect is real or 
>imagined to them?  
> 
>>> I think we can agree that when one string is slightly out 
>
>of tune with another, the rate of the beat that results exactly equals 
>
>the difference in their frequencies, and this brings me to my main 
>
>point: I have never been able to detect any kind of locking, coupling, 
>
>or accomodation of one string to another, and believe me, I've tried, tuning.
>
>and I wish I could.  <<
>
>        I have found that all three strings can be so close together that the 
>unison sounds dead, and I don't hear that 'aftersound'.  Move one of them the 
>smallest amount possible and the unison seems to fill out and last longer.  
>Is this caused by there being a beat that is twice as long as the audible 
>sustain, so we only hear half of it before there is a collision between the push 
>and the swing?  I dunno.  I know that organ pipes draw frequencies together if 
>the pipes are close enough to be air coupled.  Sails on sailboats certainly 
>affect one another by the coupling of their laminar frequencies.  (angry people 
>can make those around them angry, etc).  
>I am not ready to say that one string's behaviour doesn't have any effect on 
>its neighbor.  
>
>
>>> And here's one point: it is in 
>
>manipulating the rise time of this beat that we are able to create the 
>
>illusion that the decay time of the note has been increased.<< 
>
><snip>  We can no more make the note last longer than the 
>
>input energy through the string-bridge-board-air makes possible, than we 
>
>can make water flow uphill.>>
>
>        I can't quite go that far.  I think that what we hear is a result of 
>the efficiency of the system, and the frequencies must certainly have 
>something to do with that.  I also don't know how to tell the difference between the 
>illusion of increased decay time and what is actually there.  Seems like if it 
>sounds like it is sustaining longer, it is.  
>    Anyone else wandered around in this thicket?? 
>Regards, 
> 
>Ed Foote 
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