Interesting techniques on pitch raising that I have never heard. I will have to experiment with some of these methods.

Regarding original post:
I just wanted to thank everyone for helping me with the Whitney Spinet pitch drop episode. I don't know when I'll see this piano again, but I will let you know what I find out. One thing I did notice is that after the forced air heat stopped blowing, the pitch of the strings came up from 6 cents flat to about 3 cents flat, but I didn't stick around to see what happened after that. I plan on returning on a warmer day.

Referring back to the original post, even tho it's a Whitney spinet, it shouldn't have dropped like that. I concur that it's probably structural. No one has yet mentioned pinblock separation from the back. Also a plate crack may be developing at the treble strut.

I have seen even high quality pianos (Steinway B's & D's, Yamaha C7's) move several cents in as little as a minute or two when there is airflow around the piano such as forced hot air or AC. In one case the piano was a good 12' from the FHA floor duct and had a full DC with bottom cover. This was in a recording studio where the HVAC was just maintaining a normal temperature, not changing it. It's easy enough to check for this effect - just monitor A4 using your EDT while the HVAC is cycling on and off.

- Mark

Good Idea Mark. This is what I was considering... monitor the A440 and other notes as the temperature cycles in the room and while I'm there inspect for structural issues.