Aprons and holey bridges

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: March 04, 2002 1:54 PM
Subject: Re: Aprons and holey bridges


> >1)  The idea of placing strings having the longest possible speaking
length
> >on a piano of given size is itself flawed. It ignores the necessity of a
> >reasonable backscale length.
>
> Well I need to be convinced of this necessity too.  I've heard you
> and Ron several times emphasize the importance of the backscale
> length but I've not seen any evidence for your point of view.

If you can't hear the difference there won't be much else that will be
convincing.

Or, if you don't appreciate the difference you do hear. So much about piano
tone is subjective. I happen to like a nice clean bass sound with a
reasonable amount of fundamental lasting well into the sustain envelope and
without a lot of upper harmonic garbage in it. I want a lot of clarity in
the individual notes all the way down to A-1. The only way I can get that is
to give the bass bridge -- and the soundboard through the bass region -- a
lot of mobility while still retaining a fair amount of stiffness.

Obviously, the designer of the Bluthner Model 1 would disagree.


>
> >2)  Bass bridge cantilevers reduce the efficiency of energy transfer
between
> >the strings and the soundboard assembly.
>
> That would mean that notes on a suspended bridge sustain better but
> are not so powerful.

That means more energy is absorbed in the bridge system (as heat) and never
makes it to the soundboard. Both sustain and power suffer.


> >
> >3)  They absorb--and dissipate as heat--low frequency energy from the
strings.
>
> By what process?

They rock, or rotate, in response to the motion of the strings.


>
> >5)  There are better ways of accomplishing the same thing if it is
required.
> >One method is to simply undercut the tail end of the bass bridge.
>
> Ditto the end of the long bridge sometimes, but still you are left
> with a piano 3" longer than you would have wished or strings
> significantly shorter than if you'd acquiesced in an apron.

Not so. The Walter 190 grand is just one example. The piano is exactly as
long as it is supposed to be (190 cm) and so are the bass strings (the
speaking length A-1is 1490 mm [57.5"]). I would have preferred a longer
backscale--if I recall correctly it's just 90 mm, and that's with a vertical
hitchpin -- but the length of the piano and the speaking length of A-1 were
fixed design parameters. Without undercutting the bass bridge a cantilever
would have been required. Undercutting the bridge accomplished the same
fundamental function of a cantilever -- getting the first attachment point
somewhat back away from the rim -- while avoiding at least some of its
problems.

Were I doing the project again I would probably lobby harder for a shorter
speaking length and a longer backscale--which is not to say the manufacturer
would have gone along with my lobbying. Overall, though, I still think the
design is a reasonable compromise among the many disparate performance and
aesthetic requirements that make up a unified whole.


>
> Incidentally, the Kirkman has even tension (about 155 lbf.)
> throughout the plain wire scale with no jumps at the frame bars
> (canted bridge) and the long bridge is beech over spruce throughout
> its length, so there's another for Joe to put in his pipe :-)

Well, it's not like good tenor (i.e., plain wire) scaling practices were
unknown at the time; it's just that they were rarely adhered to. One of the
nicest tenor scales I've seen on a older piano was on a 4' 7" Howard (built
by Baldwin) grand of the 1930s. Miserable little piano in most other
ways--at least in its original configuration--but the tenor scaling was
wonderful.

Del