Duplex

[Delwin D Fandrich]

----- Original Message -----
From: "Overs Pianos" <sec@overspianos.com.au>
To: <pianotech@ptg.org>
Sent: November 05, 2001 12:43 AM
Subject: Re: Duplex


>
> 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.

And you have determined this how?

How did Stuart manage to stabilize the bridge to such an extent that he was
able to eliminate its 'rocking' motion? If you are evaluating this strictly
on the basis of sound, there were so many other things limiting the
acoustical performance of the Stuart piano I examined I'd hesitate to blame
much of anything on the bridge termination device.

The device he is using is nearly exactly like one I experimented with for a
time in the late 1980s at Baldwin. (Nearly, but not quite. Mine was machined
out of bronze. I think his is cast something or other, probably steel.) The
side-by-side performance of the device compared with bridge pins was
measurably identical. That is, when measuring adjacent unisons in the same
piano, one with standard bridge pins and the next with the bridge
termination device.

What measurements have you taken?

Del