The Inner Workings of the Piano
As the title suggests the inside of the piano is hidden from view and its workings are mysterious for most people including piano players. Unfortunately there are no piano technology classes offered through music schools and conservatories thus contributing to confusion about the mechanical part of the instrument and what care and maintenance it requires. I hope this little piece contributes to your understanding of the instrument that we spend so much time with.
The frame is the wooden structure that is seen from the back of the upright and underneath the grand. It helps support the tension of the piano strings.
The soundboard is a large section of wood, usually made of spruce wood, that creates the sound by means of vibration from the strings. It is glued just at the edges in order to allow a large area to vibrate. It can be compared to the speaker of as stereo speaker.
The front portion (towards the player) of the soundboard has two bridges, a long treble bridge and a shorter bass bridge which allow the energy of the vibrating string to be transmitted to the soundboard. The bridges can be seen as the raised portions of wood.
The back portion is supported by ribs which run perpendicular to the grain on the soundboard. This helps maintain the shape(crown) of the soundboard
The pinblock is located above the soundboard in an upright piano, and near the front in a grand. The pinblock is a piece of wood, usually made up of several layers of hardwood, that contains the tuning pins. The tuning pins are manipulated by the tuner to change the pitch of the string. The pinblock is one of the most crucial areas in the piano. If the tuning pins are loose in the pinblock, the piano cannot hold a tuning for very long or at all.
The plate is a large piece of cast iron that covers the pinblock and a large section of the soundboard. Its purpose is to allow the piano to hold the tension of the strings. There is usually enough tension on the piano to pull up a two car garage! At the bottom of the plate there are protruding hitch pins which hold the bottom part of the piano wire.
The bass strings are wrapped with copper in order to make them heavier in order to slow down the vibration and produce a lower sound. The lowest A note on the piano would have to be over 20 feet long if it was not wound! Also to get as much length out of the strings as possible they are angled(overstrung) behind the treble strings.
If one looks at the strings of a piano, there are appears to be three strings per treble note, however one string shares two tuning pins as each string winds down to the hitch pin and then back up again.
The keybed is the section of the piano that contains the keys and the action mechnaism. The action is a system of levers and moveable parts. The most important feature is the idea of an escapement mechanism. At a certain distance from the string, the hammer goes into free fall, bounces off of the string, and is caught by the backcheck. If this mechanism wasn't in place the hammer would block against the string until released.
The grand action is a little more complex. The biggest difference is the use of a repetition lever. This allows the action mechanism to be reset quicker, thus affording the player quicker repetition and speed.
Renner USA's virtual upright piano action model.
A great demonstration of a grand action in motion.
Renner USA's moving grand action model.