1 string, 2 strings, 3 strings or more

[Ron Nossaman]

>By 'unison tensions' do you mean the sum of the tensions of the strings of 
>the unison? 

Yes.


> If so, then you are saying that a bichord unison with strings 
>at a tension of 180 lbs. each should be adjacent to a monochord at 360 
>lbs.  That would indeed require a huge jump in core diameters and would 
>take the tension of the monochord way above reasonable levels.

No, I'd expect the tensions to be climbing as you go up scale, from, say,
328lbs at #12 in an example I have at hand, to 175lbs each at #13. The
monochord is at 54% with 0.048"core, and the bichords are at 34% with 0.44"
cores. This hardly strikes me as unreasonable or unacceptable considering
the original figures were 343lbs @61% for #12, and 233lbs @41% for #13. My
choice in core diameters in this instance isn't all that huge a jump
either, being 0.004" rather than the acceptable 0.003". The original core
diameters remained the same across the transition, which did strike me as
unreasonable.



 >Certainly many more factors come into play here, but in this case the total 
>mass of the top bichord on the bass bridge and that of the lowest trichord 
>on the long bridge might conceivably be similar, especially since on all 
>but the longer grands there is a fall-off in tension towards the bass at 
>the break, often to about 120 lbs.  A large increase in tension is required 
>as the transition is made to the top bichords in order to compensate for 
>the increased flexibility (decreased stiffness) of the covered strings.

I added a third bridge to this piano and produced a quite acceptable
transition between breaks, both in tensions, and tone.


>As to "blending the tone", by which I understand matching as far as 
>possible the harmonic balance of the adjacent break notes and not merely 
>avoiding the most shocking of breaks, here the actual design and details of 
>manufacture of the strings also plays an important part.  I heard someone 
>say not long ago in front of an audience that a piano needs to be 9'6" long 
>in order to achieve a satisfactory break between steel and covered strings!

Whatever blending the tone means, I've produced pianos in which pianists
and technicians couldn't find the monochord/bichord, bichord/trichord, or
bass bridge/tenor bridge transitions without looking. All well under 9'6"
long, incidentally. It's doable, but you have to give up the old soundboard
and bridge configuration in favor of one that works.


>The transition from plain trichords to covered trichords on the long bridge 
>can be quite problematic and piano-dependent.
>
>JD

It certainly can.

Ron N