.. after the 'waves of vibration' seem to have subsided ... On Saturday, August 26, 2006 8:06 PM David van Ooijen wrote:
>> Beliefs and convictions ...? Just down to earth physics. > ... In my simplified way of looking at the physics' > world I should think the sound board must vibrate as much as possibe. Up > and > down that is. So if we give up and down energy to the string, the string > will impart that to the sound board. In a very simplified way indeed! The only situation that I can think of when soundboards would really 'obey' us is when they are blown with a hammer. Otherwise, they've got the mind of their own. It may seem paradoxical to you but the very idea of the lute soundboard construction that it has had evolved to is to minimize such up and down movements, or at least bring them under control. And for a good reason! A typical lute soundboard has a fairly developed transverse barring structure in front of the bridge and a really clever one behind it, sort of combination of transverse (j-bar) and 'mixed' (two to four fan bars) variety. The first of the main transverse bars is set close to the front of bridge and thus, quite effectively, helps to suppress its side to side and up and down movements. Fan-bars on the treble end of the bridge act a step further to stiffening the soundboard in this area and blocking such movements even more - not for the detriment but the most optimum way of energy transmission from vibrating string to the soundboard. As somebody have already noted earlier, the purpose for the nut and the bridge is to provide a firm 'resting' or 'nodal' points for a string to vibrate: the disturbance caused by plucking of the string spreads along it, reflects from the 'nodal' points at the bridge and nut and forms a standing wave of vibration. The nut, by default, is a fairly steady 'nodal' point; the bridge is a point of compromise. It can't be as steady as the nut (there'll be no sound transmission to the soundboard) but if it's too limply the vibrating string would start to 'carry it along', in up and down movements. This may give a louder initial attack to the sound but it will start dying out rather quickly: the standing wave of vibrating string will simply dissipate from the lack of a firm 'nodal' point. This sort of phenomena can be observed on lutes with over-thinned soundboards or too lightly constructed barring or both. The sound, of the first string in particular, is rather 'rough', distorted, lacking clarity, not 'defined in pitch'; the basses are boomy but lacking sustain. There is a very clever phrase describing how soundboard parameters affect the sound (don't remember where I came across this expression and who said it but it sits in my memory ever since): "Both stiffness and mass impede the sound, but mass impedes treble more than bass and stiffness impedes bass more than treble". This is exactly what barring arrangement in the bridge area of the lute does: fan-bars stiffen the soundboard at the treble end of the bridge and suppress its up and down movement (by saving the energy of vibrating string and, at the same time, optimising its transmission to the soundboard); while the j-bar curving around the bass end of the bridge gives it more freedom to vibrate in all planes. Such soundboard / bridge structure as well as its behaviour is further exemplified by the very idea of resting the little finger either on the soundboard, in close vicinity of or on the bridge itself. If only the mechanism of sound production 'relied', to some notable degree, on up and down movements of the bridge, they would inevitably be blocked by even the lightest pressure (which would also act as a "mass" in the quotation above). As for the rocking movements of the bridge though, they largely remain unaffected even with the little finger rested firmly on it - for the bridge is a 'nodal' point after all. It may well be that this particular barring structure was developed as a result of trial and error approach at utilising the maximum amount of vibrating energy from thick gut basses but in the later period (late 17th - early 18th century), with a possible use of open-wound (demi-file) or even close-wound bass strings began to be replaced with fan-barring type of arrangement (I mean in the area below the bridge). Anyway, this is just a thought ... --- The baroque guitar soundboard (if constructed in the authentic way, with just two bars, one above and one below the sound hole) has a noticeably larger degree of flexibility in the transverse direction (i.e. across the grain). The nearest transverse bar is much farther than that in the lute; no j-bar and fan-bars either. So its bridge's side to side and up and down movements are certainly less constricted than in case with the lute soundboard. The only way to control the soundboard (and bridge) behaviour here is mainly through appropriate thicknessing of it. Sufficient amount of rigidity which would in this case be associated with the presence of a fair amount of soundboard wood seems to be as a good idea: original soundboards of baroque guitars which have survived untouched by later conversions (not many of those unfortunately) are c.3.0mm plus in some areas. And just the last bit: I'm currently restoring a rare mid-18th century guitar which is attributed to Francisco Sanguino (perhaps even one of the earliest surviving guitars of this maker, there are six - seven of them in all). The soundboard and the bridge of this instrument have truly remarkable 'record' of wear marks on them from which one can almost re-construct the way it was played: With the palm of the right hand perpendicular to the strings, little and very much possibly ring finger both resting on the bridge, alternating strokes with i and m fingers, perhaps with nails (two really deep elongated marks are just next to the edge of the bridge) Was this their ideal type of stroke for an optimum sound? With a possible original string length c.71cm and frighteningly close spacing in-between individual strings in courses ... quite possibly so! > That's where a bridge on which the > strings rests (guitar) comes into play: a string 'bouning' on a bridge > will > give more energy to the sound board than a string 'sliding' on that bridge > . I just want to repeat again that there is no principal difference between the classical / romantic guitar and the lute type of bridge here. And if strings, as you say, start either 'bouncing' or 'sliding' or both on the bridge (or rather saddle) then it would be better to take the instrument to a local maker to fix. > But what do I know about physics? Perhaps a plucked string will very > quickly > vibrate in all directions alike, so it doesn't matter in what direction we > pluck it initially? Or perhaps the sound board wants to flex in all > directions, not just up and down? So hence my question. I don't know very much either, hence so many words ... Alexander Batov To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
