Vibrator as Diagnostic

[Bill Kidd]

Bill Ballard 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). So I fastened
> anything inside I thought could be making noise: damper upstop rail, damper
> assy mounts, action brackets to key frame, the rails on the key frame. At
> first it seemed to go away when I pried downward on the action brackets
> from the pinblock. The key frame bedding was quite solid. I could not
> follow the sound over the strings, or under the keybed.
> 
> But for all this screw-tightening, I never had direct access to the sound,
> because it required the action being in place to play F4 (348 Hz).
> 
> What I needed was a signal generator, tunable to any pitch in the hearing
> range which could drive a speaker magnet to inject 348 Hz  onto various
> spots inside the action cavity. It would sure excite the sympathetic
> vibration.
> 
> Has anybody ever done this? Would a Dremel tool on a rheostat do this? (My
> first thought was a vibrator, but I would have no idea whether they are
> tunable or not).
> 
> Bill Ballard, RPT
> New Hampshire Chapter, PTG
> 
> "If we see you SMOKING we will assume that you are on fire and will take
> appropriate measures".......Sign in a Music Dept. HallwayBill:
The Accutuner has an audio output. Connect this output to the input of a 
good amp and the output of the amp to a good quality 8"speaker. You will 
have every pitch you need for your experiment.  Try placing the speaker 
on the soundboard, both top side and bottom side.  I somehow doubt that 
you will get the desired results, but its worth a try.

I had a Zimmerman with a similiar rattle on A4.  I thought it was inside 
the piano, but it turned out to be the fallboard lock (on the stretcher)
Good Luck,
Bill Kidd