[pianotech] David Love--Centering the bridge--was S&S something er other

[Delwin D Fandrich]

When I was designing the piano it seemed like a good idea. So my
"experiment" involved actually designing and building a piano with the
bridge located quite close to the center of the ribs. I was quite pleased
with the results. Since I was/am already quite familiar with the results
obtained with off-center bridges and here I had the results of one that was
nicely centered that-to my ear, at least-performed some better I'm not sure
how much more I would learn by taking the strings off one of these pianos
and poking around with a tuning fork. 

 

Of course the proximity of the bridges relative to the rim (or soundboard
liners) makes a difference in how it responds to the vibrating energy of the
strings. All other factors being equal the impedance seen by the bridge will
be higher the closer it is placed to the rim, but is this what you really
want? The closer the bridge is placed toward the rim the more it's mobility
is restricted as is seen at the high treble in hundreds of thousands of
pianos of all sizes and at the low bass of small pianos. Is the performance
of all those pianos with this design feature all that admirable? Not to my
ear, it isn't. Nor, apparently, is it to many other ears; if it were we
wouldn't see all the discussions about tone problems through the "killer
octave" and about struggling to get good performance out of the high treble
without lacquering the beejeebers out of the hammers. This is, after all,
one of the design features of traditional grand piano design; the bridges
are significantly off-center through roughly the upper third of the scale.
In my case, by placing the bridge closer to the center of the ribs I was
able to avoid these problems and achieve what seemed to me, at least,
superior performance. One can, of course, argue that there were/are many
other factors at work here and they would be right. Still, after having the
experience of building my own piano with this bridge placement were I able
to repeat the experience I'd put the bridge right back toward the center of
the ribs. Nothing I've seen, heard or read has provided anything like a
convincing argument to consider doing otherwise. 

 

If your only reason for considering off-center placement of the bridges is
to control impedances I would suggest that manipulating the cross-section of
the ribs would be a better approach. By using whatever combination of width
and height you want the soundboard assembly can be made as flexible or as
stiff as you want it to be while still keeping the bridge relatively
centered and giving it the mobility it needs while still controlling
spurious resonances. 

 

ddf

 

Delwin D Fandrich

Piano Design & Fabrication

6939 Foothill Court SW, Olympia, Washington 98512 USA

Phone  360.515.0119 - Cell  360.388.6525

 <mailto:del at fandrichpiano.com> del at fandrichpiano.com -
<mailto:ddfandrich at gmail.com> ddfandrich at gmail.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Thursday, May 24, 2012 7:22 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] David Love--Centering the bridge--was S&S something
er other

 

First, I do know better than to argue "better or worse" and that's not where
I was headed.  And you may be right about the issue of proximity to the rim
versus centerline location.  However, since this question I asked was
prompted by a discussion of how to get the high end of the treble bridge
more "centered" as if that was desirable, the question is relevant.  Do a
simple experiment, take a tuning fork and strike it and place it in the
center of a soundboard (unstrung piano will be easier) and time how long
until the sound dissipates.  Then do the same thing and place the fork
nearer to the rim.  I think you'll find that it takes longer but do it for
yourself.  The impedance characteristics (the rate of energy transfer) is
impacted by the location of the energy input with respect to the rim.
Since a centered bridge is as far from the rim as  possible whatever the
width of the piano at that section one has to assume that the energy will
flow through the system and dissipate more quickly the more centered the
bridge is.  With respect to the high treble where sustain is something that
is sought after (by some) seeking to center the bridge may not be desirable
and may, in fact, be undesirable.  With respect to the lower end of the
piano you certainly want it farther away from the rim for reasons mentioned.
For those who have built transition bridges and located those bridges more
toward the center of the piano (as in the old three bridge systems), you
know that you can encounter impedance problems unless you add support and
structure to the transition bridge and even then there can be problems.  So
proximity to the rim certainly can make a difference not just in how
sections might blend but in the overall quality of the sound as it is
impacted by the differences in impedance.  

 

Since the impedance characteristics impact the relationship between the
attack and sustain phases, an important consideration in targeting piano
tone, I think it's worth asking whether or not the location of the bridge on
a soundboard makes a difference.  I don't know how to answer it exactly but
then if I did I wouldn't be posing the question.  There are, will be, other
differences to be sure.  A wider soundboard will likely have a different rib
scale, for example.  A larger area soundboard will also tend to produce a
lower frequency when you pound on it.  Does that lower frequency have an
impact on the character of the initial percussive attack?  To my ear it
seems to but I can't be sure that's that actual source of the difference.  

 

A general philosophy of "make no assumptions" has a benefit in that it
challenges us to question the way things were done in the past.  But if one
is being faithful to that philosophy, it should also bring into question the
practices we find ourselves engaging in by virtue of having challenged those
old assumptions in the first place.  

 

David Love

www.davidlovepianos.com

 

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