Thanks Bill,
I'm beginning to understand.
Regards,
Domenico
----- Original Message -----
From: "Bill Jurgenson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 17, 2010 7:23 AM
Subject: Re: Delin info
> On Mon, 15 Feb 2010 17:46:36 +0100, Domenico Statuto wrote:
>> But then, the string load must be resisted by the case walls alone,
>> that in your little maple italian are thin and simply mitered, I
>> assume? Maybe the liners add to the overall stability? Or the ribbing
>> of the soundboard?
>
> sorry for the delay.
>
> The main brace of the bentside IS the soundboard. It is a simple as
> that. As long as the SB remains flat there is nowhere for the bentside
> to go.
> Of course this pressure against the enge of the soundboard is one of
> the causes for deformation of the SB, just like side and downdraft at
> the bridge for instance. So the SB has to have reinforcing structures -
> ribs - to help it stay reasonably flat. Here again, ribs fall into two
> basic catagories:
> -stiffening - these run for the most part crosswise - more or less
> -increasing mass - these run mostly lengthwise
> (careful, very generalized)
> As far as I have been able to see pratical all early schools (pre 1600)
> had only cross ribbing to do just that, keep the SB flat and help it
> hold the walls apart. For instruments with a relatively high tessatura
> like all the very early ones, this sort of ribbing also has no tonal
> disadvantages; in the context of (in my opinion) very vocal, "single
> note" sound of these, it has decided advantages. And in the context of
> instruments build on the bottom, it is really the only way to do it.
> It must be by now obvious, that the diagonal RB is basically diagonal
> because of its job in reinforcing the BS. The adoption of the diagonal
> board, which can be considered to be almost universal outside of
> Antwerp in the 17th.c, shows that the builders knew what it was about,
> that they were not stumbling in the dark. The diagonal board has some
> other advantages: the bridge must be place further from the BS, moving
> toward greater fundamental response; becuae the board alone is very
> stiff in the case, it does not need stiffening ribs or fewer of them
> and weaker; Weight ribs have greater influence. It also has decided
> disadvantages: it is wider as a piece of wood so it repsonds more to
> climate making it generally less tuning stable and of course it is
> prone to cracking more for the simple reason that is is wide. However
> as a rule, it does not crack in the high treble where the poorly
> designed franco-flemish all show there cards.
>
> Ruckers (there is nothing prior to Hans Ruckers so we can omly assume
> that he was the first) made radical changes to the traditional style -
> or rather it looks like he started with a clean slate.
> - he designed a radically different, thick-walled case which he
> purposely weakened in vertical flex. That way the case could respond
> symetrically to the stringband as a whole while remaining locally much
> stronger as individual parts.
> - he divorced the cross ribs from the soundboard, moving them from
> their housings ONTOP of the liners to a similar position on the
> underside of the liners. This is no big step for a working builder,
> accustomed as he was to fitting the ribs to the case and liners before
> transferring those positions to the SB. Modern pracice of fitting the
> SB complete to the rim is just that,modern. it is very unworkmanlike.
> Typical piano shop where the SB-man doesn't even see the rim, let alone
> fit the board.
> -he increased the tension on the board to counteract the deformation
> and for tonal reasons of course, by installing the upper braces after
> the SB was glued in, forcing them back to "tighten the skin of the
> drum" as it were. But he did not glue them, allowing the liner to flex
> vertically.
>
> cut
>
> depending on how high liners are in a franco/flemish case, they always
> tip toward the inside, flex. that is why Hemsch put them between the
> liners and ther put small "knees" on the ends. This fles is mostly waht
> cuase the SB to cave in behind the bridge, that and insufficient
> tension to start with and of course being much too thin as well.
> (no names)
> Braces are helpless here as are italianate knees and buttresses unless
> they retain the liner; Many do not.
>
> getting into a lecture.
>
> running out of time
> b
>
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