Duplex

[Overs Pianos]

Carl and Ron,

I won't go to the trouble of quoting your posts just to simplify 
replying to both of you.

As usual, nothing is black and white, and you both raised sensible 
doubts about tuned rear duplexes, of which I also am aware. I admit 
that it is a lot of trouble to go to, for what may appear to some to 
be questionable performance gains. I also realise that it is likely 
that pianos with tuned rear duplexes may be tuned by technicians with 
little or no understanding of how to deal with them. Nevertheless, I 
have taken the view that I have no intention of building pianos to 
accommodate inadequate work skills (and neither does Fazioli with 
regard to rear duplexes - he expects all dealers to come to the 
factory once per year to be educated on the finer points of Fazioli 
pianos - including tuning the rear duplexes). In any event, should 
such a piano be tuned inexpertly, it won't sound any worse than a 
piano with a non-tuned rear duplex which is poorly tuned. So the loss 
won't be huge. Eventually, when we have a dealer network for our 
pianos, I will expect them or their nominated technician to be able 
to tune accurately and to be fully capable of tuning the rear duplex 
system.

I also appreciate that for many pianos and for that matter many 
budgets, building-in tuned duplexes may well be a case of over 
engineering. Nevertheless Ron N, I have to tell you that when we 
compare two pianos, one with and one without tuned rear duplexes, the 
difference is immediately obvious. I really appreciate the lack of 
low-chorus effect on the tuned back scale piano. Of course it would 
also be a simple matter to list out the back scale to prevent the 
chorus effect - we do this for many of our recording studio pianos. 
This will slightly shorten sustain, but if the belly is well made and 
designed it will hardly be an issue - as you Ron N have also 
mentioned. But at least listing it out gets rid of the 'ringing 
rubbish'.

Regardless of all the pros and cons, we will continue to build tuned 
duplexes into our pianos, because I like the result. If folks feel 
strongly about not having it, there are plenty of alternative makers 
from which to choose. At least we will be providing an alternative, 
and hasn't the lack of choice been a favorite topic of many on this 
list.

Ron N and Del

Yesterday I noticed that you were both pretty sceptical about me 
supporting the claim Dan Franklin made about energy getting over the 
bridge to the rear duplex from the speaking length. I assure you both 
that I have found this does occur with conventionally bridged pianos 
which have tuned rear duplexes.

I realise that most of the excitation of the rear duplex will be in 
the form of vertical excitation in response to the movement of the 
bridge relative to the hitch plate, BUT, I have found that there is a 
small amount of longitudinal excitation which gets past the bridge 
pins from the speaking length to the rear duplex. If a bridge agraffe 
is used, as in for example the Australian Stuart piano, there will be 
virtually zero longitudinal excitation of the duplex.

You see, for longitudinal excitation of the rear duplex to occur, 
there must be some compliance on the part of the bridge pins, in 
response to the string side draft forces. But this does happen. I 
discovered this phenomena quite by accident with the pianos we have 
been assembling with tuned rear duplex (Since 1995). As I mentioned 
in an earlier post, it takes a while to get these tuned back-scale 
pianos properly tuned front and rear. But during the process I 
discovered that a small change in duplex tension occurs when the 
speaking length tension is raised or lowered. Now before you both 
reply, 'of course but the bridge is rocking over with the tension 
change', yes it is. But something extra is happening, the bridge pins 
are also yielding a little in response to the tension changes, and 
this will allow just a small amount of longitudinal energy from the 
speaking length to leak over onto the reap duplex segment.

Phew! I hope that made sense. This to me has been an interesting 
discovery. I am suspicious that this strange phenomenon just might 
increase the energy transmission across to the duplex when the duplex 
and speaking length share the same wire. Now I hope you guys don't 
think I'm due to be committed to some minding-institution on the 
strength of this stuff. I know it seems crazy, but after working with 
tuned duplexes for years I am sure that it is happening.

I don't know why some high end pianos with rear duplexes (which are 
pretty close to in-tune) are arranged such that the note below has 
its duplex length set to match the harmonic of the next note up, but 
is a fact of life - just pluck a few duplexes on some of the higher 
quality Japanese pianos and you will see what I am referring to. They 
may by suspicious of longitudinal excitation also being a factor 
which contributes to the duplexes being more dominant - I am not 
sure. Fazioli tunes his rear duplexes such that the tuned length 
shares the same wire, as we do also.

Anyhow Del, Ron N and others (Carl, and Dan if you're still with me), 
there it is for what its worth. I am quite sure that this phenomena 
is real, but it is pretty obscure to be sure.

Before I finish on this topic, I would like to add that we have 
plenty of debate in our workshop about the benefits of building in a 
tuned rear duplex -  we are far from unanimous here also.

It's been interesting reading all of your posts (sparks flew out of 
me on only a couple of  occasions).

Best to all.

Ron O.
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Website:  http://www.overspianos.com.au
Email:        mailto:ron@overspianos.com.au
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