This is a follow-on from another topic (m21).

BDB wrote in that topic, and others confirmed, that the partial structure [Edit: or even the pitch of some partials?] of bass notes can change after voicing the hammers.

I'd like to ask whether one can actually turn this around, i.e.:

Can one control the partial structure, e.g. improve mismatched bichords, by voicing the hammer, and if so, how?

Background information:
My Ibach has a mismatched bichord at F3. Granted, this is the highest note on the bass bridge, and might not be so amenable to "partials voicing", but I wanted to ask nevertheless... The irritating aspect is that of all the partials, it's the fifth that is beating when the unison is in tune. That puts me in a quandary as to which of the two strings to use for setting a temperament, especially when using CM3s.

If one string of a bichord does not match the other, something is wrong with one of the strings. You have to replace them both.

There is more than one thing that can be wrong, and you need the right solution for the problem.

That's really interesting. I hate it when that happens and it seems to me that it's when the copper windings are not exactly the same length. In the past on really bad cases I have had both strings re-made by my maker, which solved the problem 100% but cost the customer the price of a tuning.
I wait with interest to see if voicing the hammer can subdue this

BDB that's spooky, we thought that at exactly the same time!

Many of the bichords in this piano are slightly unequal in wound length - and yet, F3 is the only one that actually presents a clearly beating partial. There are a few others that are difficult to tune "clean", but none of them presents one clearly beating partial.

Anyway, I'm considering to try a pitch-lock-type spring for starters. And of course, replacement is the surest solution. I was just wondering... because it's in my nature to try and trace defects to rectify or compensate them, rather than simply "chuck out the old one and buy a new one".

(Hex core bass strings, by the way.)

I think the pitch lock idea is a good one for a low cost, non-invasive solution.

Voicing does not change inharmonicity or the pitch of any partials. It can only suppress or enhance them. Inharmonicity is determined by string length, tension and wire mass. Certainly, if you have two wound strings and one has more winding than the other, their inharmonicity will be different and cause a tuning problem.

Depending on how long the swedge is, you may be able to peel off enough of the winding on the longer one to make the two match.

If the two strings do not match, it is caused by something wrong with the quality of the winding of one of them, not the length of the winding. Most of us technicians have seen mismatched strings that sound fine, and matched strings that have problems.