Drifting Unisons

[Jon Page]

Could it be that the wire on the treble & bass sides of the unison
react to the movement of the sounding board. I always thought it
was one of those mysteries of nature.

Still do,

Jon Page

At 03:15 PM 11/07/1999 +0000, you wrote:
>Ron,
>       I agree we would have to account for the total "waste length" of
every 
>string (whether toward tuning pin or hitch pin), and their relative 
>tensions, and the amount of friction involved, and bridge rise and roll, 
>to come to a complete analysis. I have certainly considered all these 
>factors in my musings while pitch raising/lowering for the ?thousandth 
>time. 
>       The puzzle for me is that uprights and grands both show the same 
>tendency for the right string to move most, whether to a large or small 
>degree. Hitch pin waste lengths vary, but typically not by much on any 
>given piano. Tuning pin waste lengths vary pretty consistently, so that 
>on all grands the right tuning pin's waste length is longest for the 
>unison, while on an upright the right is shortest. So why isn't the 
>pattern reversed for uprights? 
>
>Fred
>
>Ron Nossaman wrote:
>> 
>> Hi Fred, I doubt that this will answer anything well enough to clear this
>> up, but here are a few observations.
>
>> * Let's consider what we are looking at. There is more involved than just
>> the strings from the bridge to the tuning pins. You need to consider the
>> entire string length from the hitch to the tuning pin. When the bridge
>> rises and lowers with the soundboard, the strings render over the rear
>> aliquot, the V bar, the front counter bearing bar(s), and, unless the total
>> length of string segments behind the bridge equals those in front of the
>> bridge, the strings will render through the bridge pins to some degree. The
>> bridge is the high friction point, so it takes bigger tension changes to
>> move a string across it. In general, the longer the total string length is,
>> the less the tension change with bridge rise or fall (not roll). The left
>> string of the unison has the shortest length from the bridge to the tuning
>> pin, but not necessarily from the tuning pin to the hitch. This will change
>> from unison to unison depending on the distance from the bridge pins to the
>> hitch for any string. If the total back scale is significantly shorter than
>> the total front scale, here's what should happen when the soundboard and
>> bridge rises with humidity increase: The tensions in the back scale will
>> increase as a faster rate, and peak at higher values than the tensions in
>> the front scale segments. If the difference in tension is enough to
>> overcome the friction at the bridge, the string will render across the
>> bridge toward the hitch pin, further raising the tension in the front scale
>> as the back scale tension decreases. The pitch rise of the speaking segment
>> in this instance will end up being sharper than that of a string segment of
>> a neighboring unison who's tuning pin is closer to the capo than this one
is.
>> 
>> Just like everything else in a piano, you have to take fourteen different
>> things into account to make any sense of what you're looking at. After you
>> factor in the string segment lengths, proportions of front segments
>> relative to rear segments, vertical bridge movements, and friction, it
>> begins to make some sense. The biggest problem as I see it is that we can't
>> really know what the tension is in any given section at any given time (or
>> can we?). If we could measure segment tensions we could see exactly what's
>> happening.
>> 
>> Ron N
>  
Jon Page,  Harwich Port,  Cape Cod,  Mass.  mailto:jpage@capecod.net
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