The shadow knows

From Ron N --
Tuning a "new" university sale Yamaha GC1 Disklavier
(naturally) this morning, sitting there in direct sunlight
(naturally) in a new house (naturally), I (oddly) noticed
something. Since I was stuck in the sun, I got to watching the
string shadows as I pulled the unisons in. I could see the
difference as they came in tune with one another. The first
two strings were just generally fuzzy and dim, then darkened
and sharpened as they phased together. Cool! The third string
was dim and fuzzy, without bothering the other two, then
sharpened and darkened as it came in tune. One string out of
tune to the other two also pulsed visibly with the beat. Way
cool! This worked best around octave four, but that may just
be because that's where I could see it best.

My reply --
Yesterday I was tuning a J. B. Tiffany Limited Edition (134/200) Steinway B, celebrating Steinways 200 year anniversary - 1797-1997. A beautiful piano in a very wealthy home. They bought it new. Nobody plays it. This is the second time I have been called to tune it in two years. Last time it was for a party for which they had hired a piano player. This time was for the same reason.

Due to direct sunlight through the window it was sitting in slowly moving across the piano as I tuned, it was going out of tune at about the same rate as I was attempting to put it into tune. Sadly, when I left it sounded about the same as when I arrived. Yes, I thought of closing the curtains, but I knew that tomorrow they would only be left open again as I'm sure is the usual. Had I only known to look for those shadows I would have at least found some interesting scientific entertainment to pull my thoughts away from being frustrated at the owners of this abused instrument. Now I'm looking forward to the next tuning in the sun when I can actually experience the visual additive and subtractive effects on adjacent strings going in and out of phase with each other. Very cool observation. Thank you for sharing.