3. Materials & Components
The keyboard is the defining feature of the whole instrument the interface between the musician and the mechanism and usually consists of eighty-eight wooden keys, each of which controls an individual hammer and damper mechanism. This sits upon the keyframe, a wooden draw that slides out to allow technical access to the action, and which in turn rests upon the keybed, a wooden platform attached to the rim of the piano.
Piano keys are typically made of basswood, or spruce in the case of higher quality instruments. These woods are favoured for their lightness. Traditionally the black keys were of ebony and the white keys covered with ivory; in recent years the international ivory ban has resulted in the substitution of plastic.
Each key triggers its own individual action mechanism, which propels a felt-covered hammer upwards to strike the strings. The hammer immediately returns to its rest position, leaving the strings free to vibrate.
The mechanism that allows the hammer to withdraw from the strings, even when the key remains depressed, is called the escapement. Without the escapement, the hammer would remain in contact with the strings until the key is released, dampening the sound.
The hammers, which become progressively larger towards the bass end of the keyboard, are made of wood covered in densely packed felt. Over time this felt can become compacted, resulting in a harsh tone. A tuner can correct this by loosening the felt with special needles.
Once struck, a piano string can continue vibrating for some time; from the player's perspective, it is important to be able to control how long a note continues. The function of the dampers is to allow such control: when a key is pressed, the corresponding damper lifts, allowing the relevant string(s) to vibrate. When the key is released, the damper returns and cuts off the vibration, ending the note.
Each note on a piano is produced by a particular string, or 'choir' of strings. These are made of high-strength steel, tough enough to withstand up to 200 pounds of pressure and a constant barrage from the hammers. As the strings descend in pitch, they not only become longer, but also progressively thicker. This reduces the string length necessary to produce the lower notes, which would be over thirty feet if all the strings were of the same gauge. In order to equalise the volume of the notes across the keyboard, the treble notes are each produced by a choir of three strings tuned in unison, while each tenor note is produced by a choir of two, and each bass note by a single copper-wound string.
The strings themselves do not produce enough volume they need to be amplified by the soundboard. This is a large, thin piece of wood underlying the frame (see below) and linked to the strings by the bridge. Vibration from the strings transmitted through the bridge and into the soundboard, which is able to set in motion a greater amount of air than the strings alone.
The most common material for the soundboard is spruce, chosen for its strength, lightness, and most importantly its long, straight grain which transmits vibrations quickly. Many planks, each cut with the grain running along its length, are glued together to form a large sheet from which the soundboard is cut. Ribs are then attached to the bottom of the soundboard, running perpendicular to the planks, to increase its strength.
Two bridges, the long bridge and the short bridge, are glued directly to the upper side of the soundboard. The strings rest on the bridges as they pass over them, forming a tight connection that allows vibrations to be transmitted efficiently from the strings to the soundboard. The bass strings connect with the short bridge, while the rest connect with the long bridge. The bridges are typically made of maple or beech, as the strings would cut grooves into softer woods.
Pedals modify the sound of the piano in two main ways: sustaining the notes and softening the tone. In early pianos, hand stops were used, but these were inconvenient, forcing the pianist to play with only one hand while operating the stop. Developed in Germany in the 1760s, the knee lever would come to replace the hand stop. Foot pedals first appeared around the 1770s, and would not fully replace the knee lever until the early nineteenth century.
The pedals have performed various functions at various times during the evolution of the modern piano: Janissary pedals operated snares, cymbals, bass drums and other percussion instruments; lute pedals created a pizzicato sound; the swell pedal controlled volume by raising or lowering the lid of the piano.
Modern pianos feature three pedals: the una corda, sostenuto and the damper pedal.
The leftmost pedal, the una corda or 'soft' pedal, was conceived by Cristofori, in 1722. The una corda shifts the action to the right so that the hammers do not strike a full choir of strings, resulting in a softer tone.
The rightmost pedal, the damper pedal, lifts the dampers away from the strings, allowing each string to continue vibrating after its key has been released, and allowing the other strings to vibrate in sympathy, creating a richer sound.
The middle pedal or sostenuto holds up the dampers of the keys that are already pressed, sustaining those notes but not any that are played subsequently. This pedal is not usually present on upright pianos.
The frame, also called the plate or harp, is an enormous steel or cast iron structure that supports the strings. Early pianos employed a wooden frame, which would often warp under the colossal pressure exerted by the strings. The introduction of the cast iron frame allowed strings to be kept at higher tension, with the result that modern pianos have a much stronger sound than early models. It is important that the frame should not sap energy from the strings and soundboard.
In order to meet this requirement it must be extremely large (160-180kg in a grand piano).
Although cast in one piece, the frame can be thought of as divided into several distinct areas. The circular holes lining the top right curve of the frame are called the 'web', and serve to reduce the extent to which the frame traps the sound emanating from the soundboard. The stress bars provide support to the whole structure. At the front of the frame is the pin area, which is perforated with holes to hold the tuning pins. The strings are attached to tuning pins at the keyboard end, and the hitch pins at the far end of the frame, running along the inner edge of the right-hand curve. Behind the holes for the tuning pins is a line of holes for the agraffes brass screws which guide the strings. In the treble register, this role is played by a metal bar called the capo d'astro.
The frame is bolted into the back frame a structure of wooden braces supporting the frame and the soundboard.
The outer casing houses all of the piano's internal mechanisms and structures, and is generally made of a hardwood such as maple or beech.