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Knabe grand a few decades old - so built in Asia. Serial number starts with YG...

While I've observed unison smear in other pianos, (as humidity shifts individual strings of the unisons move by different amounts - sometimes even one going sharp and another flat...) this one is the most drastic example of that phenomenon.

The owner is going to try room humidity control first, but this one will most likely require a full Dampp-Chaser with bottom and top covers to help...

But here's my question: I'm having a hard time coming up with a hypothesis for what could cause it - any ideas? The best I've been able to imagine is if the pinblock is expanding and contracting; that way the pins farthest away would possibly push and pull more???

Today was 32%, a few weeks ago was 45% The amount of smear was 10 cents or more around the middle of the piano... Crazy!

Ron Koval

Ron,

Yes, I have noticed this in various pianos over time. Usually there is a specific pattern to it (I once thought I had it figured out, but then I figured that I didn't have it figured). Yes, the pinblock is highly suspect IMO (check for fit at flange perhaps, but if it has plate bushings that's not so important). However, I would also check for excessive downbearing which will exacerbate any problem, but especially tuning stability. When I suspect this I take a quick look at the crown (If any) and try to see if there is any tendency for "oil-canning" directly under the bridge. If so, I strongly suspect excess DB. If the crown looks smooth and consistent everywhere then I would cross that off my list.

I would second the advice for HCS but I would also encourage use of a room humidifier NEAR the piano. This really works, by giving the piano "first crack" at benefiting from the humidity output (not an effort to humidity the whole room).

This "smearing" (first time I have heard this term) has puzzled me for decades. Ultimately, perfect humidity control is the solution.

Peter Grey Piano Doctor

And I still don't know what it means.

"Normal" unisons that start going out will get a little busy, then over time get worse.

Pianos with "unison smear" have an excessive amount of pitch movement that seems to show a pattern in some sections - Like the left string will be 10 cents or more flat while the center string is right on and the right string might even be a bit sharp. But then the pattern reverses or goes away... The effect can happen over weeks during large indoor humidity shifts.

I literally tune only one piano that does this to such a drastic degree.

I had forgotten Ron Nossaman's theory about lateral soundboard movement during humidity shifts - combined with poorly designed backscale angles could possibly cause this...

Ron Koval

I don't think I've ever come across this in UK in 40 years.
It must be rare surely?
Nick

The UK climate is very stable compared to, saw, New England or South East Canada with weather that's "damp" year round. In NE and South East Canada it varies from excessively dry in winter to very humid in summer.

Paul (in Montreal)

Ron,

I've observed this on our church's RX2 (about 10 years old, I think). I was tuned by someone else; I just observed it as a player with a tuner's ear. It had been tuned in the more humid season (60 - 70% RH), and at the end of the dry season (perhaps 30%), the unisons weren't shimmering, but positively howling. In the whole middle section, almost without exception the right strings were significantly flat, the middle ones on pitch or slightly flat, and the left ones were on pitch or even slightly sharp. This really puzzles me, because I would expect the shortest non-speaking lengths to be the most sensitive, so if RH drops, I would expect the left strings to drop in pitch. Above the treble break, many unisons were still OK, and those that were out of tune, had no specific pattern to them. It was just the middle section that had the sharp-mid-flat pattern to each unison. I was actually wondering whether there is a problem with the pinblock.

It's been tuned by another tuner now, once again in the humid season, so I'll observe it once again.

I am convinced though that it is not a singular cause (i.e. pinblock, soundboard, bridge, etc) but rather a wholistic thing in that ALL of these factors play a part PLUS the case and plate all together in some way. I do not believe there is any mechanical solution to it, since simply good humidity control (and I mean really good) causes the problem to fade away (as a problem). It would still exhibit thge same pattern as it drifts, but to a far lesser degree (a tolerable one).

Peter Grey Piano Doctor

What an interesting phenomenon.
Mark R, might it be worth knowing the arrangement on the hitch pins? I've seen pianos where each unison has one pair and one tied. Just a thought.
Nick

Thanks, Nick, that is an interesting question indeed. I'll have a look-see next time I play.

I have noticed this on many pianos perhaps because it is typically years between tunings in this area. What I noticed is the biggest change in each unison is in the strings with the shortest NSL, the ones with the pins closer to the bearing point. I figure these have less of a "cushion", "buffer", "shock absorber" for when the string renders across the bearing point due to tension changes in the SL from the soundboard crowning or uncrowning with humidity changes. The same effect you many notice when "setting the pin". The ones with shorter NSLs are much touchier, have a much smaller window of where the pin can be placed and still be stable as evidenced when rendering/setting the pin. The higher you go the touchier they are. I keep wondering why they don't leave the NSLs as long as practical as you go up the scale. Probably just optics. <sigh>

Jeff,

Indeed, I was expecting the short NSLs to be most affected by the lower pitch of the dry season. What puzzled me, as I wrote above, was that the longest NSL had dropped the most.

I wonder whether this had nothing to do with humidity, but rather with technique, e.g. that the previous tuner may have left all the NSLs at insufficient tension. When the NSLs "bled" their slack into the SL over time, there was obviously more slack available in the longest NSLs. Not sure whether that's right, or even plausible, but other than a systematic pinblock error, it's the best explanation I could find.

Yeah Mark, I noticed you observed the opposite of what I observed. (if I DO remember right... Once I figured it out, I didn't bother paying attention anymore, just tune...) And yeah, if it is "easy" to set a pin (as with a longer NSL), there is a temptation to not be as particular. Hammer technique can certainly allow strange things to happen.