1 string, 2 strings, 3 strings or more

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: September 18, 2001 7:22 AM
Subject: Re: 1 string, 2 strings, 3 strings or more


> At 22:12 17/09/01 -0500, Ron Nossaman wrote:
>
>
> >...Blending the monochords into the bichords is usually more a matter of
> >keeping unison tensions similar across the transition and not making
> >enormous changes in core diameters. That's scaling.
>
> By 'unison tensions' do you mean the sum of the tensions of the strings of
> the unison?  If so, then you are saying that a bichord unison with strings
> at a tension of 180 lbs. each should be adjacent to a monochord at 360
> lbs.  That would indeed require a huge jump in core diameters and would
> take the tension of the monochord way above reasonable levels.

Well, not really. While the unison tensions don't have to exactly match
across the transitions, they should be fairly close. A 200 cm Bechstein
scale that I just looked up for someone else has the transition from
mono-chord to bi-chord between notes #13 and #14 (as modified--this was not
the original transition point). Note #13 uses a core of 0.051" and has a
tension of 345 lbs (156 kgf). This is approximately 53% of its breaking
strength. Not unreasonable, in my opinion. Note #14 uses a core of 0.046"
and each string has a tension of 180 lbs (82 kgf) giving a unison tension of
360 lbs (163 kgf). These graph with barely a blip in either the tension
progression or the inharmonicity line. In practice the transition point was
audibly undetectable. As was the bass/tenor cross-over with its several
bi-chord unisons placed on a separate bridge in the tenor section.


>
> >   Blending tone across the bass / tenor break is an exercise in both
> > soundboard/scale impedance balancing, and good scaling practice.
>
> Certainly many more factors come into play here, but in this case the
total
> mass of the top bichord on the bass bridge and that of the lowest trichord
> on the long bridge might conceivably be similar, especially since on all
> but the longer grands there is a fall-off in tension towards the bass at
> the break, often to about 120 lbs.  A large increase in tension is
required
> as the transition is made to the top bichords in order to compensate for
> the increased flexibility (decreased stiffness) of the covered strings.

While I acknowledge that many pianos do have the drop-off you mention, it is
certainly not desirable. Most of these (obsolete) scales do much better with
several bi-chord wrapped unisons in the tenor section ideally placed on a
separate bridge.

This doesn't do anything for the highest strings in the bass section which
are almost always too short, but it does allow blending the bass to tenor
crossover to the point of near inaudibility.

It may also be necessary to extend the ends of the various bridges to blend
the stiffness/mass characteristics of the bridge/soundboard system as well.
But that's another issue.


>
> As to "blending the tone", by which I understand matching as far as
> possible the harmonic balance of the adjacent break notes and not merely
> avoiding the most shocking of breaks, here the actual design and details
of
> manufacture of the strings also plays an important part.  I heard someone
> say not long ago in front of an audience that a piano needs to be 9'6"
long
> in order to achieve a satisfactory break between steel and covered
strings!

Not so. I would be very upset if the bass/tenor transition were
unsatisfactory even on a 150 cm (4' 11") scale. Especially if I get to start
from scratch.


>
> The transition from plain trichords to covered trichords on the long
bridge
> can be quite problematic and piano-dependent.

So far I have found no rationale for the use of tri-chord wrapped strings on
either bridge on any scale of any length.

Del
Delwin D Fandrich
Piano Designer & Builder
Hoquiam, Washington  USA
E.mail:  pianobuilders@olynet.com
Web Site:  www.pianobuilders.com