Thanks Martyn and Martin,
The physics is very interesting.
The issue of downbearing seems to play less of a role than
in other instruments. It is very important in pianos, which I
tune and repair. (There is side-bearing at play here also.)
It is also a factor in banjos, which I play.
On banjos with adjustable tailpieces more downbearing gives
a louder but shorter sustained tone while minimal downbearing
does the opposite. Is it plausable to assume that the same
effect might be found in other string instruments where the
strings are attached to a hitch-pin then float over the bridge?
(i.e. Violin family, Arch-top Guitar ... )
I have found that, on my steel-string guitars with bridge pins,
(i.e. Martin D18 etc.) a higher saddle (thus more downbearing?)
creates a similar result. (It also throws off intonation!)
Thanks again for these great explanations!
Tom
Date sent: Fri, 1 Aug 2014 12:02:34 +0100
To: Lute Dmth <[email protected]>
From: Martyn Hodgson <[email protected]>
Send reply to: Martyn Hodgson <[email protected]>
Subject: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning
From: Martyn Hodgson <[email protected]>
To: Martin Shepherd <[email protected]>
Sent: Friday, 1 August 2014, 10:40
Subject: Re: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning
Dear Martin, Thanks for this. I mentioned string slide in the
context of modern guitar bridges with a straight top to the saddle
(ie no notches). The notches on the nut of a lute (and modern
guitar) avoid the problem of such slide (provided they're not made
too wide of course). As you'll know, citterns (like some modern
guitars) do generally have a 'zero' fret just before the nut but
since the maximum amplitude of the pluck is at closer to the bridge
end the displacement (slide) at the nut is minimal. regards Martyn
_________________________________________________________________
_
From: Martin Shepherd <[email protected]>
To: Martyn Hodgson <[email protected]>
Sent: Friday, 1 August 2014, 8:11
Subject: Re: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning
Dear Martyn, Thanks for this clear explanation. It seems there
must be a tradeoff between bridge height and mass, in the sense
that a higher bridge would presumably increase the volume of sound
but the greater mass would decrease it. I've often wondered about
the issue of bridge flexibility, entertaining suspicions that a
bridge which is too stiff may have a damping effect, but this is
only intuitive. I'm interested that you raise the issue of string
slide - it occurs to me that this can't happen at the nut on a lute
because of the extreme angle of the pegbox, but could happen on
baroque guitar/vihuela nuts and theorbo lower nuts? Best wishes,
Martin On 01/08/2014 08:29, Martyn Hodgson wrote: > In fact both
lute and guitar bridges function in the same way. In > short, a
horizontal force (imposed by the string) is momentarily >
increased when the string is displaced (plucked); this in turn >
increases the turning moment of the bridge (ie force x height of
string > above belly at take-off point) which in turn causes the
belly to > vibrate with mostly a wave action (tho' some vertical
pumping action > too) and thus amplifying the sound by varying
the air pressure within > the soundbox. Whether the vibrating
string leads from a loop (lute) or > from over a saddle (later
guitars) is immaterial - it is the height of > the string at
take-off which is relevant. Vibration patterns have, in > fact,
been studied: eg the Galpin Society Journal (Hellwig I recall) >
which contains relevant papers. > Differences in timbre between
instruments may well be due to many other > factors rather than
the way the physics of the bridge works, including: > mass of
bridge (size and density), surface area of base of bridge, >
stiffness of bridge, barring, internal shape of soundbox and its >
volume, etc. > An illustrative example: many years ago I made
a 5 course guitar after > Sellas and fitted an ebony bridge
(thinking the original had one). The > sound was quiet and
muffled (tho' with considerable sustain). I had a > rethink and
after further investigation decided to remove it and fit a >
fruitwood (actually pear) black stained bridge to precisely the
same > design: the resulting sound was considerably freer and
increased the > output ie volume. In fact the much greater mass
of the ebony bridge was > acting as a considerable dampener
requiring more of the vibrational > energy of the string to set
it in motion than that of the fruitwood > bridge which had a
mass less than half that of the ebony. On the other > hand, the
ebony bridge's greater mass meant that it had more inertia > and
thus continued to oscillate for longer than the fruitwood bridge -
> thus giving the greater (if much quieter) sustain. > MH >
PS Incidentally, drilling the string holes low down on a modern
guitar > bridge does not increase the string tension/force and
hence the turning > moment of the string at the bridge (and it
could not be otherwise, > since for a given string the pitch is
simply a function of transverse > force/string tension) but does
increase the resultant vector > downbearing on the saddle which
avoids excessive frictional string > slide (and hence loss of
energy ie output) across the saddle. The > discrete loop
take-off point used on lutes and early guitars avoids > this
problem. >
__________________________________________________________________
> >
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Tom Draughon
Heartistry Music
http://www.heartistrymusic.com/artists_tom.html
714 9th Avenue West
Ashland, WI 54806
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