string calculations threads

[Frank Emerson]

Regarding unwrapped end segments of bass strings, I think the length and
location of the swedge of the core wire is equally important.  This was
alluded to earlier, but the point was not driven home that some string
makers over-kill by making the length of the swedge too great.  Their
intent is to reduce the risk of loose windings, but it is at the expense of
inharmonicity considerations.  While this may not be something to be
calculated in a scale analysis, it is something of which to be aware.

We must also be aware that where the windings begin and end will change as
the string is drawn to pitch.  For purposes of scale analysis, you want to
base your calculations on where you want the windings to end up after the
string is drawn to pitch.  Depending on how sophisticated you want to get
with a spreadsheet, you may want to use a "rule of thumb" elongation of
1-2mm that the winding will move away from the front bridge pin, and 6-8mm
that the other end of the winding will move toward the agraffe.  The latter
will vary considerable depending on the size of the piano.  Or, you could
calculate the string elongation from the hitch to the beginning of the
winding, and the elongation from hitch to the end of the winding for each
string, which, of course, would be more precise.  My string specifications
for the hitch to beginning of the winding may be 1-2mm short of where I
expect it to be after drawn to pitch, while the specification for distance
from the hitch to the far end of the winding may be 6-8mm short of where I
expect it to be after drawn to pitch.   An unknown factor is the tension to
which the string maker will draw the core while winding the string.  To
what extent is a portion of the elongation accounted for by the tension of
the core while being wound?  If you want to produce specifications to the
string maker from your spreadsheet, you will want to incorporate these
calculations into the spreadsheet.  However, if you order strings from
Arledge, he will do that part of the calculation for you.  

I am not aware of any studies that address the question of how much, if
any, a piano string will continue to elongate over decades of use, beyond
the elongation when it is first drawn to pitch.  My suspicion is that it
does, but only slightly.  With this in mind, I like to calculate for 10mm
from the front bridge pin to the winding, and 12mm from the agraffe to the
other winding end, after drawn to pitch.  On the other hand, what I specify
to the string maker, or what one would measure with the string under no
tension might appear to be 8-9mm from the front bridge pin, and 18-20mm
from the agraffe at the other end.  Regardless of how much you factor in
for this movement of the termination of the winding, you can count on the
fact that the winding end will always move away from the bridge, and toward
the agraffe.  

I have nothing to contribute regarding hexagonal core wire, since this is
nothing I have, or would consider in a new piano design.

Frank Emerson
pianoguru at earthlink.net


> [Original Message]
> From: Ric Brekne <ricbrek at broadpark.no>
> To: pianotech <pianotech at ptg.org>
> Date: 10/4/2006 11:12:25 AM
> Subject: string calculations threads
>
> Hi folks
>
> Ron O, thanks muchly for the long and insightful post. Lots of good info 
> coming through now.  Our little group hopes to put together and release 
> soon a basic spreadsheet with an interface that lends itself well to 
> learning about scaling work fairly soon.  It is my hope all interested 
> will be able to share various scales on this same platform for 
> discussion and collective enlightenment. 
>
> One thing I'd like to get really crystal clear on this theme.  The 
> calculation of end lengths for single and double wounds.  I am getting 
> the sense that while end lengths are extremely important to get 
> consistent during the actual string making process, they are not so 
> important to consider in a scale design program / spreadsheet.  I've 
> read a couple exceptions to that position... but much of what I read 
> seems to point in that direction.  Is this correct or have I
misunderstood ?
>
> One other point.... Hex string.  I would very much appreciate any 
> comments pertinent to how inharmonicity  works out when hex core is 
> used.  I seem to recall that inharmonicity is generally lessened when 
> hex core is used.  Any info would be greatly appreciated.
>
> Thanks
> RicB
>
>
>