Thank you for extrapolating and putting my thoughts in clearer engineering terms. Much appreciated. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Nick Gravagne Sent: Wednesday, December 31, 2008 1:56 PM To: pianotech at ptg.org Subject: Re: [pianotech] Sustain First of all kudos to David L for a fine post; one in which an awful lot was said in the fewest words. The larger picture of piano tone, especially of sustain, is a complicated one; and it remains a picture in which the colors, shapes and outlines are not always perceived the same by all onlookers. Still, there are some physics and natural phenomenon which cannot be "subjectified". For starters, given the same hammer mass and acceleration interfacing with a given piano belly, a harder/stiffer hammer will impart a larger force to the string/belly, while a softer, more compressive hammer will impart less of a force to the same string/belly. Most of us are familiar with the natural phenomenon called the "conservation of energy" which basically says that the energy delivered to any system (that moves something and does work on a system) is never lost but merely changes its form: all input must be accounted for at the output, or outputs. Objects in motion are said to have Momentum which, like energy, is considered to be a conserved quantity in physics. A moving piano hammer contains a quantity of momentum, and this quantity is delivered to the waiting string and belly. Upon impact, which is elastic in that the two parties separate quickly, the string starts vibrating and the hammer rebounds, but the total system momentum has not been lessened, only changed. The hard hammer delivers more force to the string, but little (relatively) of the total force package is either lost as heat or stored as spring energy in the non-compressive hammer felt. The opposite is true in the compliant hammer which delivers less force to the string, but in compressing like a spring some of the force package is given back to the hammer as stored spring energy. In both cases, though, given the same hammer and acceleration, no energy or momentum is lost as these find different outputs or effects. David L stated very well that the belly assembly once in place contains an impedance lock-setting that cannot be changed by manipulating the hammer. So how can the tonal-package, especially sustain, be changed so dramatically by voicing? First of all, sustain is like cholesterol, there is good sustain and bad sustain (GS and, well BS <G>). Both are functions of the force delivered to the string, and that force is inversely proportional to the compliance of the hammer: more compliance - less force, less compliance - more force to the string. Now according to studies undertaken by Donald E. Hall, professor of physics, a hard hammer delivers (within milliseconds) a series of staccato blows and not really a "single" blow. The wave envelope thus produced is likewise choppy and the tonal package contains a sharp attack and carrying a plethora of high, tingling partials. The string may vibrate a good while, but in chaotic fashion at first, and the accompanying last vestiges of sustain (BS) may only be measurable with sophisticated equipment. Also in this case the bulk of the wave shape forms an early and steep, upfront spike thereafter audibly decaying (dB) at a fast rate. Conversely, a compressive, compliant hammer, rather than shocking the string with a series of staccato blows, "pushes" the string out of its resting mode. The wave envelope is smooth and the tone package contains a far less sharp attack with fewer high partials. The string may vibrate as long as with the hard hammer, with the difference that upfront chaos is lessened and the accompanying sustain (GS) can be appreciated by human ears. Also, the wave shape itself is less steep to begin with (no spike) but is "present" for what seems like a longer time period. Thus the tradeoff of upfront loud attack and BS to less attack with GS. Recalcitrant and stubborn hammers aside, every time a needle enters a hammer, attack goes down and GS goes up, and this whether you can hear it at first or not. Taken too far, the fundamental tone becomes quite present, but lacks brilliance and character. RE hammer rebound, the hard hammer bounces off the string faster than a soft one. The oft stated dictum to the reverse is the result of many fine PTG instructors making a claim for it based on intuition, results and with the sense that a compliant hammer is "bouncy" and that this is a good thing. And indeed it is a good thing. Sincerely, Nick Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Wednesday, December 31, 2008 10:04 AM To: pianotech at ptg.org Subject: Re: [pianotech] Sustain The length and quality of the sustain phase is clearly complex but I think it breaks down into three areas: soundboard, string, hammer. The manner in which the soundboard first captures energy from the string and the rate at which it dissipates it is fixed by the nature of the assembly itself in terms of both stiffness and mass. In simple terms, the stiffer the assembly or the more mass it has the greater the amount of energy required to move it but the longer it takes to dissipate the energy. The amount of energy that can be stored and made available for transduction to the soundboard is a function of tension and mass of the string. The manner in which the string is set into motion influences the way that the string divides, the amount of energy lost by virtue of initial chaos in the attack phase and the point in the phase that all the divisions become consonant, achieve their maximum amplitude as well as the amplitude itself. All we can really influence in the voicing or toning process is the manner in which the string is set into motion, the initial loss of energy in the chaos phase, the point in development when the chaos is turned into divisional consonance and the distribution or strength of the harmonics. So hammer manipulation is certainly not without consequence but whether it actually influences the length of sustain I'm not convinced. The quality of the sound especially in the beginning development phase is what we hope to effect and that certainly can change our perception of the quality of the sustain phase. The absolute endpoint of the sustain I don't think really changes with any manipulation of the hammer since at that point of low energy input it is the soundboard itself combined with the string's ability to store energy that is responsible for when things come to rest. That's how I view it anyway. I'm sure there's a better and probably more accurate scientific explanation. >From a perceptual viewpoint there is also the issue of what I've heard Del Fandrich refer to as "usable sustain" meaning the sustain that we actually hear musically as opposed to what might be measurable. The usable sustain might well be considered in two ways: first, the ability for the system (string and soundboard assembly) to store energy and the rate of decay; and second, the shape of the decay curve itself. While the first factor is not influenced by the hammer the second is and the shape of the decay curve certainly can influence our perception of the usable sustain. The swell effect when you lift the damper comes, in my view, from the growing sympathetic excitement of the strings that have been freed from damper constraint. David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20081231/20d6b5a3/attachment.html>
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