[pianotech] Tuning the duplex sections

[PAULREVENKOJONES at aol.com]

Actually, I'm unclear on this terminology. Can you distinguish "sustain  
rate" and "sustain time"? Thanks.
 
Paul
 
 
In a message dated 3/16/2011 1:11:13 A.M. Central Daylight Time,  
del at fandrichpiano.com writes:

 
My tests  demonstrated that when the tuned front duplex system is working 
as advertised  sustain rate increases and sustain time decreases. Think of it 
in terms of  conservation of energy. 
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 _ (mailto:del at fandrichpiano.com%20) —  
_ddfandrich at gmail.com_ (mailto:ddfandrich at gmail.com) 
 
 
From:  pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On 
Behalf Of  PAULREVENKOJONES at aol.com
Sent: Tuesday, March 15, 2011 10:46  PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Tuning  the duplex sections

 
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_ (mailto: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_ (mailto:del at fandrichpiano.com)  — 
_ddfandrich at gmail.com_ (mailto: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, 
from having a very short front  duplex.  

David Love
_www.davidlovepianos.com_ (http://www.davidlovepianos.com/) 



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