[pianotech] Pitch Change (was: Grey market pianos, seasoned pianos, etc.)

[Ron Nossaman]

Tom Driscoll wrote:
> Question : Tuning a piano where pitch is 2-3 cents flat and a string 
> breaks @ let's say note C-64. Humidity hasn't changed unless profane 
> comments muttered under ones breath is a factor but now three or four 
> notes on either side of the break are  a few cents  sharp.
> I thought with less force bearing down on the bridge at that specific 
> point that the bridge rises and increases tension on the adjacent 
> strings.  Is this a convenient but  incorrect explaination of what is 
> going on here and does this fit somehow into our current  discussion?

Good question. What's the downbearing load difference when the 
string breaks? Let's say, arbitrarily, that the string would 
be at 160lbs at pitch. Let's be generous and give it 1° of 
downbearing on the bridge. Assume it's plain wire, around the 
hitch so the one string makes two speaking lengths. The total 
downbearing for that string is about 5.6lbs. That should be a 
fairly easy thumb press, so does pressing down on the bridge 
where the string was bring those surrounding notes back down? 
While the downbearing difference on the bridge is just 5.6lbs, 
the tension on the plate has changed by 320lbs, and the up 
bearing on the capo has changed by around 80lbs. A piano going 
out of tune with seasonal humidity changes hasn't incurred the 
same localized stress changes in the plate as occur when a 
string breaks, so direct comparison probably isn't very 
enlightening. If my laptop will work, I'll try the press on 
the bridge thing next week to see what it does. I don't know 
that it'll be of any use since it adds a big damping factor 
that wasn't there with the string, but it might prove to be a 
good source of further confusion. <G>
Ron N