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The parts and functions of a piano

The Soundboard:

The soundboard is one of the most important and least understood parts of the piano.  Its purpose is to convert the vibrations of the strings into what we know as piano tone.   Without it there would be no amplification and in fact, there would be very little sound of any kind.   If the soundboard is not made of the proper kind of wood (if the size, thickness, curvature, grain direction, texture and other factors are not in balance), the end result can be unacceptable to the trained ear.

Sitka spruce is the species from which nearly all top quality soundboards are made.  Sitka spruce logs run up to eight feet in diameter but only 15% to 20% of the log is suitable for use in making fine soundboards.


The ribs (on the back of the soundboard) are also made of Sitka spruce and vary in length, thickness and width depending on the size of the piano and their position on the soundboard.

Strung back:

What is referred to in piano terms is basically the soundboard and back frame plus the plate, bridges and strings.   Altogether it is an assemblage of hundreds upon hundreds of parts and may kinds of materials:  spruce, elm, hard maple, iron, steel, copper, brass, nickel, wool felt, various types of lacquer and other finishing materials.

Plate/Steel Frame:

The piano plate or string frame is made of fine grey case iron to individual manufacturer’s specifications and design.  It is anchored to the back frame by heavy wood screws and bolts as well as bolts through the plate and into the back posts.  The soundboard, ribs, bridges and pin plank are in place before the plate is fastened to the back frame.


One of the most critical steps in making a fine piano is the shaping of the treble and bass bridges.  The bridges, made of hard maple, must be planed to exact thickness from end to end so as to provide the proper down-bearing of the strings upon the bridges.   It is this correct down-bearing which is so vital to the transfer of the string vibrations to the soundboard resulting in pleasant piano tones.

The bridges must be accurately notched at both the top and bottom in the case of treble bridges for each individual note.   This provides for the “stopping” of the string at a precise point in much the same way as a violinist “stops” his strings by fingering.  Bass bridges are planed on both edges for the same reason.  After notching of the bridges, copper-plated steel bridge pins are installed.   There are approximately 340 bridge pins on the treble bridge and 110 on the bass bridge of an upright piano.

Holes which have been pre-drilled in the iron plate where the tuning pins will be located, are then filled with tightly fitting hard maple bushings.   They are driven down to make firm contact with the pin plant.   Then the holes for the tuning pins are drilled through these bushings and into the pin plank.

Pin Block:

The purpose of the pin block is to firmly hold the tuning pins to which the strings are attached.  Adjustment of the pins is for changing the pitch or tuning each individual string.   To hold these tuning pins securely, the pin block should be of the finest hard maple which is properly and carefully seasoned and dried to exact tolerances and in modern pianos is laminated in a number of different directions so as to offer end-grain to the tuning pin for good retention of tuning.

Tuning Pins:

The tuning pins to which the strings are attached are made of a special alloy steel.   There is a hole drilled through the pin and the string passes through this hole and is wound around the pin to prevent slippage.  The wood fibres of the pin plank grip the fine threads which are cut into the pin.   The top of the pin must be square so as to fit the tuning hammer.   That part of the pin which can be seen is heavily plated with nickel to retard rust.


The stringer begins at the treble end of the scale drawing the piano wire from reels which carry all the sizes of wire.  These sizes usually range from #13 to #20 by half sizes e.g. #13, #13 ½, #14, 14 ½ etc. and from .031” to .045” in diameter.  The bass strings are also made of the same fine music wire but are wound or covered with one or two layers of pure copper wire.   The purpose of the copper is to add weight to the string, thereby reducing the frequency or number of vibrations when struck by the piano hammer.   The frequency determines the pitch of each individual note.   The lowest note of the piano is produced by a double wound string vibrating 27.5 times per second while the frequency of the high C is 4186.4 vibrations per second.  Were it not for copper wound strings in the lower range of the piano it would require a steel string over 20 feet long to produce the low A note of the instrument.

Chip Tuning:

After all the strings are in place, they are individually lifted so that the turns around the tuning pins will form a neat, tight coil.  The piano is now ready for chipping.   The chipping-tuner actually tunes the new strings well above the normal pitch of A=440 thereby putting more strain on the strings and other parts of the piano back than they will ultimately be required to bear.  He does this by setting the pitch of one note to a special tuning fork and then proceeds to tune the entire scale by plucking the individual strings using his tuning hammer or wrench.   The piano is then allowed to rest for a number of days, allowing the stresses and strains caused by the pull of the strings to settle down and equalise themselves.


The pedal on the right lifts the dampers from the strings so that the tone is sustained after the keys are released.   The pedal on the left called una corda softens or limits the power of the tone by shortening the distance the hammers travel.   On a grand piano this is accomplished by shifting the action slightly so that the hammers strike fewer strings.  The third pedal in the middle may sustain the bass notes only or it may serve to muffle the tone for practise purposes.   Where it sustains individual notes, it is truly a sostenuto pedal and is desirable in some classical works.

Key bed & keys:

The key bed, the part on which the keys of the piano rest, is then installed – this must be perfectly flat otherwise it would be impossible to level the keys or keep the keys and action properly regulated.

Each key is mounted on a key frame and are located in exact position by the centre pins which are at the balance point of the key.   Keys can be weighted to assure proper balance.   Near the front of the key is the oval shaped in which keeps the key in proper alignment while at the same time providing a means of adjustment.   Each individual key is bused with fine wool felt bushing cloth to insure silence as well as to provide proper clearance for the pins.

The white keys on modern pianos are covered with a plastic and will never turn yellow, crack, split or chip like ivory.   The sharps are made of similar material.


The action of the piano (about 1500 parts) causes the hammers to strike the strings when the keys are struck.  All wood parts of a piano action are made of the finest hard maple.  Several kinds of pure wool felt, bushing cloth, leather, steel, brass, nickel, and glue go into the making of today’s piano action – plus many hours of work.

The hammer not only strikes the string almost instantaneously, it also strikes at an exact point on each string.  The action must also provide damping of strings as well as allow the tone to be sustained as long as the key is held down.  There can be no lost motion in the action which would spoil the touch and must perform quietly and efficiently with a minimum of maintenance and under adverse conditions for many years.


Piano hammers are made of fine wool felt which is formed around a hard maple hammer moulding.  Hammers are made of two layers of felt – outer layer is white and inner usually purple, green or magenta.  The layers of felt are applied separately and the forming and gluing of the felt to the hammer is done with tremendous pressure applied by hammer presses – many tons of pressure are applied from different angles, forming the shape of the hammers resulting in one long hammer which is then cut into individual hammer heads.  Holes are bored at the proper angles on the underside of each head into which the hammer shanks are later glued.   Each set of hammers is then individually and painstakingly fitted to the piano.  It is often said that while a good hammer can’t make a poor piano sound good, a bad hammer can spoil the best piano.

Final Assembly:

Now come the seemingly endless adjustments and the regulation of the keys and action.   The keys must be perfectly level – they must be fitted so that there will be a minimum of side play or motion and yet they must be free to work smoothly.   The touch must not be too shallow or too deep.

The dampers, when in resting position against the strings, prevent string vibration.   They must be regulated so as to let off the strings at the proper point of key and action motion. Hammers too must be set and adjusted so that they strike the strings squarely at the proper point and rebound to a predetermined distance from the strings so that they will not block the vibration of the strings.


Expert tuners and voicers now take over the critical and painstaking work of transforming the whole into a musical instrument.  The piano is tuned and re-tuned several times.   The voicers, or tone regulators, adjust the tone quality by working on the hammers.   Their critical ears, together with an infinite amount of patience and a lot of pride, are responsible for the end result.

Piano hammers, in spite of being made from the best wool felt obtainable and under exacting control, will vary slightly in density and hardness.   This variance is corrected by the use of fine steel needles which are inserted into the hammer at the proper place and the proper depth.  By “needling” a piano hammer the tone regulator can make the tone of an individual note sound hard or mellow, full or thin.   This fine adjustment is called voicing.