Rolled bridge: cause? diagnosis? treatment? Or maybe a floating pinblock?

Thomas Sheehan TSheehan@nyc.rr.com
Wed, 13 Jun 2001 00:30:55 -0400


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Dear colleagues -=20

The piano is a 1972 S&S Hamburg B. It was restrung about 5 years ago, =
and had the pinblock replaced (Falconwood, unfortunately), and also had =
new hammers (S&S - Hamburg), shanks & flanges installed. The company =
that did the work is an experienced rebuilding outfit.

The piano came back "dead". Very limited sustain - less than 5 seconds =
in octaves 6 and 7 (many notes). Extremely dead rear duplex - less than =
2 seconds in top two sections. Weak upper partial volume and sustain =
throughout. Bass is tubby. False beats throughout; weird out-of-tune =
partials in the bass. All these tonal phenomena occur whether the string =
is struck by a hammer, or is plucked.

After racking my brains about this piano (I service it about 2x per =
year), I finally had the idea to measure the height of the bridge cap =
above the soundboard, on both the speaking length side, and on the rear =
duplex side. The rear duplex side is anywhere from 2/32" to 6/32" inch =
_higher_ than the speaking length side.=20

The piano is extremely unstable. It is impossible to get absolutely =
beatless unisons for more than 2 - 5 mf to ff hammer strokes. The =
beating that does creep in is very slight, but noticeable to my nearly =
28 years of tuning experience ears (credited tuner by name on many =
Grammy Award-winning recordings, as well as concert piano factory =
trained by Yamaha, Steinway & Baldwin; occasional tuner at Carnegie Hall =
and Lincoln Center).=20

Although I really dislike Falconwood blocks, this one is measuring an =
average of 140 inch/lbs. Not too tight. 2/0 pins with about 3/8" =
clearance between the bottom of the coil and the plate. I have squeezed =
the wire gently around the hitch pins so that the strings are parallel =
to each other. I have also used CLP at the capo, agraffe, understring =
felt, and the apex of the rear duplex, and at the raised projection that =
terminates the upper duplex in the top two sections.=20

No or maybe a little improvement in stability.=20

All plate perimeter screws are tight, as are webbing screws.

Does this sound like a rolled bridge? How is a rolled bridge caused? Is =
there an accurate way to diagnose a rolled bridge? Can it be fixed in =
the field?=20

Thank you very much in advance for your comments and advice!

See you in Reno!?!?!?!?!?!!!!!

Sincerely,

Tom Sheehan, RPT
NYC Chapter

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