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Piano Tone and Hammer Voicing



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Don Kulak
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Piano Hammer Voicing
For A Clearer, Louder, Richer Tone

- an excerpt from the book Vital Sound by Don Kulak

This series is written in order to get a closer, more in-depth look at the sonic nature of the acoustic piano.This sound, familiar to us all, is a sound rich and clear, and yet very complex in terms of sound wave structure. So complex, in fact, that it defies any and all attempts at electronic reproduction in this age of digital technology, and synthesized sound - a tone that cannot be so easily reduced to a calculated system of 0's and 1's.

We will follow the actual production of the piano tone - from it's origin, or impact of the hammer and string, to the vibration of the soundboard and ultimately our eardrums. This entire process takes place of course in only a split second, but the tone quality is being formed and developed every step of the way. Like a stop action film, each part of the piano will be looked at during this process as it affects and alters the soundwave and the ultimate tone quality.

This is particularly important to piano owners, performers, recording engineers... who wish to alter the tone in some preconceived way, enabling then to pinpoint the cause of a certain type of sound, and later determine the action needed to produce the desired effect, all of course within the physical limitations of the piano.

This author has seen enough structurally sound pianos left for dead, or sold for pennies on the dollar, to fill up MadisonSquareGarden. In most cases all they really needed was proper hammer and string voicing - a relatively inexpensive procedure. Since this lack of information is normally the culprit in denying a piano of it's beautiful, rich, singing tone, we will begin with voicing the piano hammer.

Voicing, as the name implies, is the process by which one can physically manipulate the piano hammer in order to make it "speak" better, i.e. to brighten or soften the sound; to bring out the singing, and sustaining qualities; to make it come alive. The degree to which one can implement change on an existing piano hammer is dependent upon certain physical proportions within the hammer itself, those being tension and compression.

The hammer is comprised of many layers of felt. The high tension outer layers are wrapped around tightly packed inner layers, creating an inner compression with explosive rebounding capabilities. It is the manipulation of these 2 forces which can alter the tone quality substantially. This is done primarily with needles, and one might compare it to acupuncture on the human body. In both cases the needles are used to relieve tension in certain areas, enabling them to move and react more freely. When the inner felt is deep needled, tension is released, and the felt expands. This in turn puts more pressure on the outer layers, stretching them even further, and therefore increasing the tension there. The increased outer tension, combined with the expanded inner felt, creates at once a harder and more resilient hammer. This is the basic process which increases the rebounding action of the hammer off the string. This is important because a hammer which remains too long on the string after the initial blow, absorbs the energy of the vibrating string, producing a dull, weak sound.






This is because the higher harmonics are the first ones to be dampened by too long of a contact time between the hammer and string. These higher harmonics are the first ones to go not only because they are weaker than the lower harmonics, but also because the wavelengths are much shorter, relative to the fundamental and the lower harmonics. As the wavelengths of the higher harmonics become shorter and shorter relative to the amount of hammer surface which is touching the string, they are more easily eliminated completely.

One might compare the hammer-string rebounding action to a man on a trampoline. When the person jumps onto it, there is initial displacement of the webbing, but as it is resilient in nature, the webbing quickly reverts back to it's original form, while throwing the person off in the process. The man would represent the hammer hitting the string, first displacing it, then being catapulted off when original form, or equilibrium is restored.

It is probably appropriate at this point to define these tonal characteristics which are subject to alteration, and the tone we are ultimately striving for.

Attack - the time it takes for the tone to reach maximum amplitude. Qualitatively, attack may be described as the amount of percussiveness present. A short attack would sound more forceful, and abrupt, while a long attack would build-up a bit more gradually, or swell, into peak amplitude.

Dwell, or articulation - the time just before peak amplitude, including the sudden drop in volume just after peak amplitude, right up until the long, and gradual decay begins. A good dwell time adds to a well defined, precise sounding tone. On the contrary, a dwell time which is too long tends to create an ambiguous tonal center, lacking clarity, and definition. Each note would tend, as it were, to be lost in the crowd. The tonal centers would not be distinct, and would seem to run all together.

Sustain - the time between the initial large drop-off in volume until nothing is heard. The ability to sustain a note is as important to the acoustic piano as a good set of lungs are to a singer. There is no such thing as a piano sustaining too long. It is a percussion instrument where the player has very little control over the note after the hammer has left the string. If the note dies out too quickly there is nothing that can be done until the score calls for the next note.

Volume - overall loudness
All of these tonal characteristics can be altered individually (by a qualified technician) by needling the hammer in specific areas, but these methods are the subject of a whole different article.

More on piano acoustics