Vibrator as Diagnostic

harvey harvey@greenwood.net
Tue, 13 Jul 1999 15:37:40 -0400


BB,

No opinions on the signal Ginny, except it seems a lot of effort for what
could be disappointing results. Here are a few elusive grunts I found, in
no particular order -- 'cept for the first one from last week:

- decorative concrete cat on carpet, adjacent to rear leg with brass
ferrule. Strangely, F4 was the frequency that caused the cat and the leg to
get together;

- keyframe bedded, but one keyframe glide was waffling side-to-side in the
keyframe due to hole being drilled oversized (frequency dependent);

- bulkhead mounted sostenuto rail mounting bracket loose (freq & velocity);

- "dancing" washer under loose plate lag (freq/velocity);

- loose leg mounting plate; the part on the piano, not the leg (Kawai-style
mount, although it wasn't a Kawai);

- microscopic gap between plate and nose bolt "shelf" (Paul Monroe found
this one, and it may have been more of a buzz or sizzle than a grunt)

I'm sure there are more, equally elusive, but at the moment, they're
eluding my memory too! FWIW, I now have an F4, velocity dependent grunt on
a Yamaha CFIII. The typical/easy/reachable stuff has been checked, but nine
feet is a lot of area to cover from the keyboard, even with my trombonist's
arms. I too need to somehow excite the piano while doing a walk-about.
Funny, there's never an extra hand when you need 'em. Good luck!

Jim Harvey, RPT

At 10:45 PM 7/11/99 -0400, you wrote:
>I'd been listening to a grunting sound, like a fallboard-to-front-stretcher
>or loose metal lyre brace, during the tuning of a Falcone 74, sympathetic
>to F4. In trying to chase it down, the best I could come up with was that
>it was coming from inside the action cavity (loud and clear).
[cut]



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