Duplex, A Grotrian

[Richard Brekne]

Ron Nossaman wrote:

> >Ok... i remember last time I looked that the angle up from the capo was around
> >12 degrees. Bridge pins were angled at 10. Didnt check downbearing but I
> can if
> >needed. The angle up from the aggraffes in the bass was a bit less then the
> >capo area, but I havent measured that.
> >
> >Richard Brekne
>
> I didn't see a tenor back scale length, but if it isn't braided, I'd start
> there since it's not going to add anything desirable left open and can
> provide plenty of undesirable noises if not muted.

Braiding both the bass and the tenor lengths seems reasonable enough... I will get
the lowest and topmost backscale lengths for you in the next couple days as well as
the deflection angles off the counterbearing forward to the second halfrounds since
this seems of interest. But as if I am not mistaken the strings go over the first
halfround and at about the same angle as they come off the capo...perhaps just a
bit less if anything, and there is just enough bearing on the second half round to
form a termination of sorts so that the length of string between the two halfrounds
have a very clearly difined pitch and ring when plucked, as does the length from
the second to the tuning pins for that matter. Running your the back of your
fingernail over any of these sections is sorta like strumming a zither...grin.

You end saying that this is familiar tuned front duplex territory. Am I
misunderstanding something here ? How can the front duplex length being a uniform
30 mm througout the entire top two sections be a "tuned" duplex ?


> I'd likely braid the
> bass too. Then I'd listen to the result and decide on the next step. If a
> next step was necessary, I wouldn't expect any unusual noises from the back
> scale in the top two sections unless there is some bearing or plate
> clearance problem. I don't know what bearing angles there are across the
> first and second counter bearing bars, but you said both sections  are
> making noise. I assume they are fairly low. The best benefit from the least
> effort, with the lowest penalty should come from braiding or otherwise
> muting that 50mm second section. Remaining noises from the first front
> duplex should be comparatively minimal then, even with the low angle capo
> deflection. If not, you're now in familiar tuned front duplex territory.
>
> If I was rebuilding it, I'd want to increase the bearing angle, decreasing
> the front duplex length if possible depending on where that leaves the
> string height and angle to the pins.
>
> I can't say if this qualifies as an answer, but this is how I'd approach it
> as a work around.
>
> Ron N




--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no