Vibrator as Diagnostic

[Jon Page]

Bill,
Is there a coil spring on the damper lifter tray?

My first guess,

Jon Page


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). 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. Hallway
>  

Jon Page,  Harwich Port,  Cape Cod,  Mass.  mailto:jpage@capecod.net
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