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Piano Sustaining Qualities

Since the piano is a percussion instrument with limited note durations, the length of decay, or sustain is critical to a musical performance. There are many factors that contrubute to a piano's tone duration.

The following is an excerpt from Don Kulak's book "Vital Sound'" which details the key components that affect piano sustaining qualities.

One need not mention the importance of the decay, or sustaining capabilities of the piano. A beautiful, rich, clear tone would be unnoticed without the ability to hold. Like a singer out of breath, a beautiful sound would fall short of its time, becoming inert and paralyzed.

The propensity to sustain is determined by many factors in design and construction, all of which will be covered in their appropriate sections, i.e. bridges, soundboard, strings etc. For now, decay, or sustaining characteristics and factors will be considered not in terms of structural influences, but rather regarding the nature of the vibrations themselves.

When the piano hammer strikes the string, the direction in which the string vibrates is not limited to that in which it was hit, i.e. perpendicular to the sound board. There are vibrations which run parallel to the soundboard as well. There have been tests conducted in which the decay rate of each mode of vibration was recorded using pick-ups which were responsive to only one direction of vibration. Figure 10 shows the decay rates for each of these modes of vibration on note A - 4.

This diagram shows the vibrations parallel to the soundboard to have a much lower amplitude (about 15 db on the average) but they also sustain longer. Thus, this parallel mode of vibration adds considerably to the sustaining capabilities of any given note. In addition, if there are any large fluctuations in either mode, there doesn't appear to be any noticeable effects upon the other. In other words, a defect in one mode of vibration wouldn’t necessarily adversely effect the other.

Another "sustaining" factor is the presence of three strings per note which are vibrating together. There is a marked difference between the decay rate of three strings played separately, as opposed to them being played simultaneously.

Figure 11 shows the decay time of each separate string in a unison, (the other two strings being muted), along with the composite effect of all three. The interference between the strings has a reinforcing effect, thus prolonging sustain time.

These decay characteristics are altered even further when the strings of the unison are slightly out of tune. Figure 12 shows the overall decay rate for slightly detuned unisons. The initial in phase condition, moving to a subsequent out of phase condition of these slightly detuned unisons, is the major reason for increased sustain. The initial steep descent is the result of the in phase condition, which levels off during the out of phase condition.

The effects of this detuning may seem irrelevant, because who would want to play an out of tune piano? This same effect, however, still does occur even on what appears to be a perfect tuning.

Let us assume there is a piano which is in perfect tune, and which has a rock solid stability that would remain unaltered throughout an entire performance. The upper harmonics of each note are still altered due to string inharmonicity.

Therefore, even if all of the other factors effecting the tone were in perfect working order(which is physically impossible, as the conditions within the piano are constantly changing, due to climatic conditions, normal wear and tear, raw material characteristics, manufacturing imperfections, etc.) there would remain that imminent condition of out of tuneness and the resulting beats.

To eliminate these slight alterations, is to take the life out of the tone. One may as well get the latest digital synthesizer and program a certain harmonic structure. The tone will sound nice, and clean, but void of the inner harmonic movement, and the constantly changing patterns and phase relationships. The basis of music is rhythm, the driving force which moves our body and soul. The tones comprising this music are no less important, as they create movement within themselves, contributing more than we realize to the overall effect of the music.

The fact that our ears do not hear in a straight line, linear fashion, also adds to the scenario. Our ears are more sensitive to the higher registers, and as a result are less tolerant of a dissonant or inharmonic sound there. The characteristics of the piano accommodate this sensitivity to a certain extent, as the very upper treble usually contains no more than two to three overtones thus eliminating the dissonant upper partials.

The middle register contains an average of approximately 5(c)10 per note, and the bass has a blend of harmonics sometimes up to 42, with very little fundamental. Not only are our ears more sensitive to the high pitches in relations to the middle and low, but also to the section E4(the second E above middle C) to G4, or 2640 HZ to 3168 HZ. Many people notice that certain pianos have a peculiar cutting sound in this range. It is not that there are any major differences in the sound production of that area, but rather that the human ear, by its own resonance, seems to favor these tones E4 to G4.

When we speak of piano tone we are dealing with the innate, living characteristics of raw materials - wood in particular. The grain of wood, with its beautiful contours and intricate patterns is to the eyes what its aural resonant qualities are to the ears - a beautiful complex pattern in a perpetual state of change.

The piano is a remarkable refinement of manufacture and design but controllable only up to a technical limit. From then on the raw materials take over in their own unpredictable ways, producing a sound for which countless musical compositions were written. A sound which justifies the enormous price tags of concert grand pianos, a sound fervently, but unsuccessfully sought after by the digital world, in order to define it and reproduce it.

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