piano tuning info

Some background physical information regarding pianos and piano tuning:

It is a fact that the inspiration for the piano comes from the lute. The lute, a form of guitar, was first emulated by a keyboard instrument called the clavichord. The clavichord served as an inspiration for the harpsichord, and the harpsichord in turn served as the inspiration for the piano. The name "piano" is an abbreviation of the name of the "first" piano; "hammered harpsichord with soft and loud" or in Italian, "gravi cembalo con piano e forte". The gravi cembalo con piano e forte was the invention of Bartolomeo Cristofori of Padua, Italy, and dates from 1709. Bartolomeo Cristofori was a harpsichord maker until he produced his "advanced" harpsichord, and then he became the first piano maker. As the name implies, a major feature of the new invention was the ability to play both "soft" or piano and "loud" or forte. The harpsichord lacked this attribute and could only produce sound at one volume level for a given note. The piano was a great breakthrough in musical expressiveness back in 1709. An excellent book on piano history and historical construction details is "Pianos and Their Makers" by Alfred Dolge; a very interesting book and still readily available.

So, at its core, a piano is very similar to a guitar in certain ways. The guitar is a musical instrument that creates sound via vibrating wire, or "string". On the guitar, the musician plucks or strums the steel wires, or nylon strings with their fingers or with a guitar pick and this sets the strings in motion. The vibrating wires cause the guitar's soundboard to vibrate and one hears sound.

Very much like the guitar, the piano uses steel music wires to produce sound. The piano uses piano keys and a piano action mechanism to cause piano hammers to strike piano strings and produce sound; when you press a piano key, a felt mallet called a "piano hammer" strikes steel music wires that vibrate and in turn cause a wooden soundboard underneath them to vibrate. The soundboard moves enough air to move your eardrum, and you hear a musical tone.

If there were no soundboard present, the music wire would be vibrating, but you would barely be able to hear any sound because the surface area of the music wire is so small that it really can't move very much air. To understand this idea, think of a sailboat with the sail lowered to the bottom of its mast. The mast can't catch enough air to move the sailboat; the sail must be raised in order to catch enough air to move the sailboat. The soundboard is analogous to the sail with its large surface area. The soundboard's function is to move a large volume of air due to its large surface area and constitutes a mechanical amplifier, amplifying the vibrating music wire. To summarize, a vibrating music wire with no soundboard would produce sound, but it would be too faint to hear because the music wire can't catch and move enough air to cause one's eardrum to move in response.

You may have seen and heard a musical instrument where the lack of a soundboard is incorporated into the design; the electric guitar. You need a speaker and amplifier to hear the electric guitar because there is not a spruce soundboard under the strings. If you strum an electric guitar with no amplifier and you hear almost nothing because the strings just can't move enough air for you to hear much; your eardrum is not moving too much because the air around you is not moving too much either.

The point to understand here is that a piano produces sound because piano hammers strike steel music wires, and those steel music wires utilize a spruce soundboard to amplify their vibrations so we can hear sound.

Simplified "cross-cut" view of the piano music wire, bridge, and soundboard

The illustration above provides a very simplified model of the piano soundboard, bridge, and music wire. On the far left is the pinblock which holds the tuning pin. Moving towards the right, the next element is the capo bar. Continuing to the right, the next element is the soundboard and bridge, where the bridge is the rectangular element attached to the top surface of soundboard. Finally, on the far right is the hitch pin rail and hitch pin. The music wire is represented by the black line running from the tuning pin, under the capo bar, up to and over the soundboard's bridge, and then down from the bridge to the hitch pin on the hitch pin rail.

Piano strings have two ends and are divided into several partial string length segments. One end is attached to the tuning pin and the tuning pin is moved with a special wrench to increase or decrease tension on the string. There is a lip on the right edge of the pinblock that creates a angle running down to the capo bar. The capo bar is one end of the part of the string called the "speaking length". It is called the speaking length because it is the portion of the string that "speaks"; it is the part of the string that vibrates and creates the vibrations that are transmitted to the soundboard via the bridge. The other end of the speaking length is located at the left edge of the soundboard's bridge. After passing over the bridge, the string runs down to the hitch pin rail where it is affixed to a pin called a hitch pin.

Although this is an overly simplified two-dimensional illustration of what is actually present in a real piano, it is provided here to point out several physical realities that are part of the piano and what piano tuning is all about.

Firstly, notice that the soundboard is slightly dome shaped. The soundboard is dome shaped for several reasons. A dome is a very strong shape in relation to pressure applied to it from above so the pressure of the piano's strings bearing down on the bridge does not collapse the soundboard. If the strings, which are made of steel music wire, do not bear down on the bridge there will be poor transmission of vibrations from the strings to the soundboard and the tone of the piano will be hollow and have an annoying "knocking" aspect to it. Conversely, if the strings bear down on the bridge with too great pressure, the piano tone will be choked off since the pressure from the strings actually acts to stop the soundboard from vibrating. This aspect of piano construction is referred to "downbearing" as per the fact that it is the physical quality of the strings "bearing down" on the bridge.

The soundboard of the piano is made from a wood called spruce. There are many different kinds of spruce, but in general spruce is light in weight and in density and is hence referred to as a "soft wood". It is related to the trees we commonly refer to as pine trees.

When a piano is placed in a humid environment the domed shaped or "crowned" soundboard depicted in the illustration above will tend to physically expand. Given the crown shape of the soundboard the degree of crown will increase which will effectively increase the tension on the piano's strings. Increasing the tension on a string will cause the pitch of the string to increase. In musical terms, the pitch of the string will become sharper. Conversely, in a dry environment the degree of crown of the soundboard will decrease, in turn decreasing the pitch of the string; in musical terms, the pitch will become flatter.

Seasonally, as environmental humidity increases during the summer months in the Northeastern United States, your piano will become sharper in pitch. Conversely, when environmental humidity decreases during the winter months, the pitch of your piano will become flatter. You could even think of your piano as a form of hygrometer, a device which measures humidity. Your piano would by this analogy be an "aural" hygrometer since the difference in humidity would be measured by the pitch of the piano. In fact, your piano soundboard is a hygrometer, it just isn't very easy to read.

These physical properties of your piano's soundboard and strings are why a piano goes out of tune. No matter how well your piano technician tunes your piano, daily and seasonal variations in humidity will undo the work that she or he has done tuning your piano. This situation is made even worse when the piano's environment is altered even further by the introduction of aggressive heating in the winter. The relative humidity of a typical home in the Northeastern United States varies from about 75% in the summer to about 15% in the winter, given indoor heating. You should run a humidifier during the winter months in your home to preserve your piano as well as keep it in better tune. In fact, the use of a humidifier during the dry heating season is the single most important maintenance procedure a piano owner can and should perform.

A second factor which influences your piano's tuning is how out of tune you allow the piano to become. Referring to the illustration of the simple piano soundboard and string model shown above, realize that the crown of the soundboard is pushing up on the strings while the strings are pushing down on the soundboard. This is part of the downbearing phenomenon discussed earlier. Let's assume that your piano has become flat because the environment is dry. A piano technician arrives to tune the piano and informs you that the piano is about 1/2 of a semitone flat. A semitone musically is also referred to as a "half step". When the technician tunes the piano, she or he will increase the tension on the strings causing them to become sharp. But as this occurs, the amount of pressure from the strings bearing down on the bridge and soundboard physically push the soundboard down, effectively lowering the pitch as the technician attempts to raise it. In order for the technician to overcome this phenomenon, the technician must raise the pitch of the piano MORE than where it is expected to end up, because by the time the technician increases the tension on all of the music wires, the overall pitch will have decreased relative to where it was initially set. The same holds true if the technician is attempting to lower the pitch of the piano; as the tension on the strings is lowered to decrease the pitch, the soundboard will push up on the strings and effectively raise the pitch. In general a piano technician must raise or lower the pitch of a piano 25% more than the desired pitch if the piano.

The point to understand, is that once the piano is allowed to deviate from concert pitch of A440, getting the piano back to A440 is not as simple as just doing a one shot tuning; in fact I usually end up doing several quick rough tunings to get the piano soundboard and string opposing forces close enough to be able to do a fine tuning even when the piano is relatively close to A440. Once your piano is really out of tune it will take a fair amount of work, in the form of rough, compensating tunings, for the technician to get the instrument physically stable enough to be fine tuned at A440.

Playing the piano is another factor which drives the instrument out of tune. The more the piano is played, and particularly, the more intensely or aggressively the piano is played, the more it tends to go out of tune. To give you an idea of what I mean, in a concert hall setting, the piano is usually tuned before each performance. Recording studios and hotels, whose pianos get a lot of use, tend to tune them one or more times per week. It also isn't uncommon for recording studios to have the piano tuned before each recording session.

The information provided here is to help you to understand what physical factors cause the piano to go out of tune, and once the piano is out of tune, what the piano technician is dealing with physically when they tune your piano.

If you have questions regarding any of this information, feel free to call or email me, and I will try to answer your questions.

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