[pianotech] Tuning the duplex sections

[PAULREVENKOJONES at aol.com]

Del:
 
I just wanted to thank you for your articulate and concise  statement. My 
understanding has always been that the open front  counterbearing increased 
the sustain in the speaking length because of the  transfer of energy back 
and forth across the capo. Am I reading you  correctly?
 
Paul 
 
 
In a message dated 3/15/2011 11:50:34 P.M. Central Daylight Time,  
del at fandrichpiano.com writes:

1)   With an inefficient termination--i.e., a V-bar with shallow string 
termination  angles and "tuned" front duplex string segments on the other 
side--energy can  be transferred back and forth across the V-bar. Because the 
duplex string  segments are tuned (in theory, at least) to some calculated 
partials of the  speaking lengths, vibrating energy at or around the resonant 
frequencies of  the duplex string segments will pass back and forth across the 
V-bar with  relative ease. Among other things, this has the effect of 
increasing the rate  of decay in the desired speaking lengths because some of the 
energy that is  transferred across the V-bar to the duplex string segments 
is absorbed into  the plate at the front bearing bar. This loss is in 
addition to whatever  amount of energy is absorbed into the plate at the V-bar.

Since the  so-called "tuned" duplexes are rarely, if ever, accurately 
tuned, these  vibrating portions of string can, and often do, produce sounds at 
undesirable  pitches that are close to, but not quite on, some harmonic of 
the normally  speaking strings. As well, because the string deflection angles 
are shallow  and vibrating energy is being transferred back and forth across 
the V-bar, any  slight imperfections in the shape or surface texture of the 
V-bar can, and  often do, create undesirable vibrations or "string noises." 
In an effort to  control both dissonant vibrations and the string noises it 
is a common  practice to mute the front duplexes. This damping absorbs some 
of the  vibrating energy in the duplex string segments but it does not stop 
the  transfer of vibrating energy coming from the desired speaking lengths 
of the  strings to the duplex string segment. That transfer continues but 
it's now a  one-way street; energy is being dampened on the duplex side of the 
V-bar and  is now unavailable for any transfer back into the speaking side 
of the V-bar  so the decay rate in the speaking string increases even more 
and the sustain  time further decreases.

2)  When the string angles are greater  than about 15˚ to 18˚ and the 
duplex string segments are kept reasonably short  energy is not freely 
transferred back and forth across the V-bar between the  speaking string segments and 
the duplex string segments. The termination of  the speaking strings at the 
V-bar is more efficient and most of the energy  arriving at the V-bar is 
blocked and reflected back into the speaking string  segments. Some energy, to 
be sure, is still absorbed into the V-bar and/or  capo tastro bar but very 
little makes past the V-bar it into the duplex string  segments. In this 
case damping the duplex string segments makes little  difference because there 
is little energy there to be damped. 

As an  added benefit, because the strings are not "rocking"  back and forth 
at  the V-bar, its shape is less critical and string noises are virtually 
unheard  of. 

3)  The back scale is a whole other issue. Energy is not  being transferred 
from the speaking strings across the bridge terminations and  to the 
backscale portion of the strings. The backscale is set in motion by the  motion of 
the bridge(s). Whether or not the backscale string segments are  tuned does 
not materially affect the vibrating energy in the speaking portion  of the 
strings or their decay rates and, hence, will have little, if any,  effect 
on how they vibrate or how long they vibrate. 

Whether tuning  the backscale string segments has any positive effect on 
overall piano  performance is, for me, at least, an open question. I have yet 
to see it  conclusively demonstrated by even the most ardent supporters of 
the scheme.  Keeping an adequate backscale length is clearly important but 
deliberately  tuning the backscale to some partial lengths of the speaking 
strings has long  seemed an exercise in futility. Besides, given the broad 
spectrum of  fundamental waveforms and partials driving the bridge(s) at any 
given moment  (while the piano is being played) it would be well-nigh 
impossible to avoid  finding backscale lengths that are not "tuned" to some 
fundamental or some  partial of some note or other. 

ddf

Delwin D Fandrich
Piano  Design & Fabrication
6939 Foothill Court SW, Olympia, Washington 98512  USA
Phone  360.736.7563 — Cell   360.388.6525
del at fandrichpiano.com —  ddfandrich at gmail.com


-----Original Message-----
From:  pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On 
Behalf Of  David Love
Sent: Tuesday, March 15, 2011 4:10 PM
To:  pianotech at ptg.org
Subject: Re: [pianotech] Tuning the duplex  sections

Yes, that's right of course, went too far with that  idea.  

So then why exactly does muting the front duplex kill the  tone?  Even a 
light muting in which the rocking motion is presumably  unimpeded.  What does 
the front duplex contribute in that case (when it's  unmated) and how does 
it contribute.  Similarly, why does muting the  front duplex in a piano with 
a very short duplex not kill the tone nor does  the tone suffer, seemingly, f
rom having a very short front duplex.   

David  Love
www.davidlovepianos.com

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