trichord string splaying

[Stephen Birkett]

Thanks to Ron and others who responded to my musing:
>There are two design considerations which justify splaying trichord 
>string groups. One is the provision of adequate support wood in the 
>bridge cap, as Conrad mentioned,

In my application there are agraffes on the soundboard end. These 
eliminate the need to splay trichords to improve bridge pinning, but 
complicate the anti-jangling splaying layout into the tenor. On the 
latter point....

>and the other is providing sufficient clearance between the unison 
>strings to prevent them jangling under heavy playing.

This is what I was thinking to be the rationale behind the practice, 
but I'm not entirely convinced in the causality......

>In the tenor, there is definitely a risk of the unison strings 
>jangling under heavy playing if the string-to-string clearance is 
>insufficient. I know of two examples of grands around six foot which 
>have low-tenor string spacing at the bridge of 10 mm (centre to 
>centre of the outside unisons). Both of these pianos have 
>hockey-stick-tenor scales which make the risk of jangling even more 
>likely as the tension falls towards the break. Playing a note around 
>B27 heavily will cause the unisons to jangle. A local example of one 
>of these pianos which is quite new, is undergoing torture at the 
>hands of an up-and-coming young lady who looks destined to have a 
>performance career in front of her.

My Steinway S splays no more than 10mm in the bass and doesn't 
jangle. And over-strung modern pianos do seem to vary quite a bit in 
the amount of splaying. Of course into the tenor there is all that 
real estate sitting there to splay in, which isn't available on a 
straight-strung. I've seen biggie ca.1900 straight-strung grands with 
no splaying at all. With 13mm trichord centre-to-centre spacing the 
maximum splaying possible at the bridge gives 9mm across the outside 
strings in a trichord (if all wires are evenly spaced at the bridge). 
I've not come across one of these straight-strung beasties that 
jangles, so I wonder if splay-less string spacing is really the 
culprit if jangling is going on. The largest excursion of the string 
occurs during impact, which is before the onset of the note, and 
subsequently excursion is quite a bit smaller. It's possible that 
jangling may be caused by impedance problems at the string-bridge 
end, causing wierd phase changes and clashing elliptical paths of the 
individual trichord strings. If a suitable jangling splay-challenged 
patient were available in Rochester this could be examined with 
high-speed imaging. Before re-pinning the piano you mentioned, Ron, 
you could experiment with some pitchlocs and see if the jangling 
disappears....these change the phase behaviour of individual strings. 
If the jangling is eliminated it might be that increasing splaying 
may be a bandaid solution that happens to fix the problem. Can't help 
thinking about those biggie straight-strungs that have no splaying at 
all. My design being straight-strung it raises the issue.

>Unison splaying is also common in the bass bichord-string section 
>for the same clearance reasons as in the tenor (remind of this at 
>Rochester Stephen, and I'll point out a couple of observable trends 
>in the bridge pin line as a result).

Looking forward to meeting you in Rochester Ron.

Stephen