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  The primary structural components
            of the
harp are:

   •Soundboard

   •Pinblock

   •Plate

 

Soundboard

As the name implies, the soundboard produces the sound. When the hammer strikes the string, the vibration begins. The string has very little surface area. An average string will have a .035" dia and an average length of 36", resulting in approximately 4 in2  (.035 in X 36 in X PI). Not much air is displaced. (Sound level is comparable to playing an electric guitar minus the electricity.) However the string is in direct contact with a strip of wood known as the bridge. On the other side of the bridge is a large diaphragm of wood called the soundboard. As the string vibrates, so does the bridge, so does the soundboard. Including both sides, an average soundboard has about twenty square feet of surface area resulting in a huge displacement of air when it vibrates. Doing the math, that's 20 ft2  X 144 in2  / 4 in2 = an amplification of 720! No problem hearing that.

Soundboards are subjected to enormous stresses. Each string exerts about 5 lbs of downward force (Down Bearing) onto the bridge, which in turn transfers it to the soundboard. An average piano has 230 strings so that's a total force of around 1/2 a ton! As mentioned earlier, they also have a lot of surface area, which does a lot of stretching and shrinking with changes in humidity. Lastly, as the board vibrates it is constantly pushing and pulling against the rim or band of the piano.




 

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Imagine a 1000 lb gorilla bouncing up and down on your chest while a couple more yank on your arms and legs and you'd be living the life of the soundboard. Is it any wonder they sometimes crack?Fortunately, a cracked board can be repaired. Contrary to what the name implies, a soundboard is not a single board. It is several planked together much like a hardwood floor. Repair consists of cutting or routing out the crack, gluing in another plank (shim), and refinishing. A closely associated repair involves replacing a bridge, a bridge cap, or apron.
 

 
 



Pinblock

The pinblock is a multi-laminated plank that is about
55". long, 1 ½" thick, and 8" in wide on one end and  tapers down to 3" in at the other. Its mission in life
is to maintain the string tension. It accomplishes this task by gripping the tuning pins. No small task con-
sidering there are about 230 strings and each one is stretched from 250 lbs to 800 lbs of tension. Even-tually, the tuning pin holes ream out and the piano becomes untunable. By the time a piano hits 50 years, the block is on borrowed time. When it fails that usually signals the end of the piano's life. The finish is checked, the strings are stretched out, and the hammers are shot. Unless it has added value like a prestigious name, or sentimental attachment, they are relegated to serve as furniture for a few more years, bouncing from buyer to buyer until winding up as landfill.

The only sure remedy is to replace the block. This is the most costly essential repair. The only way to replace it is to first remove the plate and strings. Since the strings are probably at least 50 years old  they should be replaced as well. For uprights, the block is anchored to both sides, back, and posts. Replacing it isn't practical. In this circumstance replacing the tuning pins with oversized pins is an  effective repair.



 

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Plate

The plate is cast iron and responsible for a third of the piano's weight. It could be considered the "Spine" of the instrument. Since there are about 230 strings with tensions varying between 250 lbs to 800 lbs the result is 18 to 20 tons of compression. The plate's job is preventing the front of the piano from meeting the back. It also provides support for the frame. Generally speaking, the less amount of wood that went into building the frame, the thicker the plate casting.

Remembering the amount of compression force the plate is fighting, any sudden jolt, like dropping the piano, can cause it to snap. Another cause is careless alignment during rebuilding. The result of which pro-duces  shear stress before it is ever strung. Adding the strings only compounds the stressful situation.

If the plate breaks or cracks, the piano is permanently crippled. Repair by welding is not an option because it requires heating a localized area to a temp of 3000° F. As a result the plate warps. Bolting it down to conform to the frame will re-introduce the shear stress. If the weld was poor, it re-cracks. If the weld was excellent, it cracks else-where.

 
 

About the only repair made to the plate is refinishing. Occasionally, "A-graphs" (Brass inserts that strings thread through) are replaced . Refinishing is purely cosmetic and is usually not recommended unless the rest of piano is being refinished. The contrast between a "New and Shiny" interior  vs. a "Scuffed" exterior can look a little "Strange".


 

 


 

 


 

 

 

   

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Servicing the Kansas City, Gladstone, Overland Park
metropolitan area
with
moving • tuning • repairing • rebuilding • concert rentals

     
Jones Piano House

5742 N. Lenox Ave 
          Kansas City,  MO  64151

 816.587.1544

© 2012 - Stephan Cantu.  All rights reserved