Allegro Piano Pages

Design & Construction Of The Piano

Keith T. Comparetto,
Piano Tuner-Technician

      The quality piano of the 20th and 21st centuries is a technological masterpiece, a dynamic arrangment of over 200 strings and 9,000 parts overall (Steinway claims over 12,000 for its grand). Though its concept may be relatively simple, its position as the ruler of instruments is undisputed. Yet most people who play pianos have little idea what is between the ends of the keys they play with their fingers, and the sound they hear with their ears. Let's take a look at what lurks inside your piano's dark inner chambers.

     Remember that the key you play is merely the finished end of a piece of wood (about 10" to 15" long) which functions as a lever, much like a see-saw, in fact. It passes over a middle rail that is higher than its front and back rails; thus when you press down on the key, the other end pushes up on a series of levers and other moving parts called the action.  In a grand piano, the strings are horizontal, and the keys and the entire action except for the dampers is mounted under them.  The hammer swings upward and strikes the strings from below, while the dampers are situated above the strings and fall by gravity to dampen them when the key is released.  To see an animated graphic of the grand piano action, click here.


     In an upright piano, the strings are vertical, and the keys and action are mounted alongside them.  The hammer is in a generally upright position, and swings toward the string from the side, while the damper, mounted just below the hammer, is powered to dampen the string by means of a spring: 


Vertical pianos traditionally have been built in four sizes, listed from shortest to tallest:   (1) the spinet is the shortest vertical, generally about 36 inches tall;  (2) the console, about 42 inches tall;  (3)  the studio upright, about 48 inches tall; and (4) the full upright, 52 inches and taller.  Among verticals, the major difference in addition to soundboard size and string length is the placement of the action.  In spinets (below left), the action is placed partially below the level of the keys, and is attached to the keys by means of a lifter wire which pulls up on the whippen to activate the mechanism.  In all three of the larger sizes, with a few exceptions, the action is generally mounted completely above the keys (below right) and the whippen  is pushed upward by the key.


     Whether the piano is a grand (i.e., horizontal) or an upright (i.e., vertical), the function of this action or mechanism is 4-fold (see the named parts in the illustration below):

  1. To activate the hammer, a felt-covered piece of wood that produces sound by striking the string to set it vibrating. The hammer is set in motion primarily by means of a lever called the jack.
  2. To get both the damper and the hammer away from the string, thus allowing the string to vibrate freely. This is accomplished primarily be means of the regulating button (which moves the jack out of the hammer's way) and the backcatch (which catches the hammer as it falls back from the string).
  3. To dampen, or stop, the vibration of the string after the player lets up on the key. This is done primarily by the damper lever and damper head with its soft felt pad.
  4. To prepare itself in a split second to repeat the above steps. This is done by a series of springs, by a special part (in grands only) called the repetition lever, and by the overall force of gravity helping to pull all the parts back into their original position.


     Now assuming the mechanics work correctly (and now that you're thoroughly confused), the strings will take over. Each string is a piece of extremely high quality steel, and each key or note has three strings (only two or one for the lowest notes). Each one is tightened to a tension of about 200 pounds (imagine a 200 pound man hanging from each string!) Multiply this figure by 200, the approximate number of strings in the piano, and you get a total of approximately 20 tons--thus the need for the metal plate that makes up nearly half the weight of your piano.

pinsinblock.jpg         fullbridge.jpg

Plate.jpg soundboard.jpg

Clockwise from left to right:  (1) side view of pins in the laminated maple pinblock; (2) strings crossing over the bridge; (3) metal plate with strings and bridge; (4) soundboard and bridges with plate removed

     Now, let's assume your keys are moving freely; your action is in working order and is adjusted properly; and your hammer is "voiced" to its perfect hardness. At this point something must amplify the string so it can be heard. This is the job of the bridges and soundboard. Without them, the vibrating string would scarcely be louder than a rubber band stretched between the fingers, or an electric guitar without an amplifier.

The bridge is a piece of maple about one inch square and running the entire length of the piano. Its purpose, in addition to holding the strings in position, is to transfer the vibration of the string to the soundboard. The soundboard, in turn, is a large, thin piece of soft wood about 1/4" thick and covering the entire inside area of the piano. It works like a big diaphragm, much like your own eardrum, to vibrate at the same pitch (or frequency) as the string, thus amplifying its volume.

If this final component is free to vibrate properly, it is the final step in producing the magnificent sound only a piano can produce. Now it needs only one last ingredient: something to transform its sound into music. And this is something no technician alone can offer--here we must turn to you, the pianist.



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