[pianotech] Building Low and High Impedance boards was RE: Bridge agraffes FYI

[David Love]

Ron O:

I've changed the subject line here since we are going in a different
direction.

Having also built *a* board that was too stiff I would argue that it doesn't
take much doing at all for that to happen.  Nor do I think it is a problem
that only manifests itself in the killer octave.  Of course the killer
octave (or high treble) area can start to jangle if the energy can't get out
through the board itself and escapes through the capo.  Mass loading can
remedy that but I don't think a mass loaded board that is too stiff sounds
the same as one in which the impedance was right and is lighter in weight.
It will be diminished in power.  

Further, a board which is too stiff can have very negative consequences in
the midrange and bass as well.  While a controlled and focused tone can
result, the board can lack a certain liveliness and drive at the upper
dynamic level when needed.  

As to the stability of lower impedance boards I think it depends on how you
build them and what kind of hammer you put on them.  Rib crowned boards with
slightly less compression than, say, full compression boards starting with
flat ribs, will be much more stable over time.  Further, a smart choice of
hammers with lower density and strike weights which will offer plenty of
energy input for lower impedance boards will help balance the equation
(lower impedance boards should have lower tension scales as well).

My main point (at least for the sake of other soundboard builders out there)
is that thinking that you are building in a smart safety margin protecting
against impedance which is too low can easily get you building something
which is too high and the result may not be what you hoped for.  

Naturally, there are other considerations as well, rib scalloping, panel
thickness and thinning, etc...  These all factor into the equation as well.
I'm referring to the rib scale mostly.  Here I think the target is smaller
than we might think.

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Overs Pianos
Sent: Friday, October 26, 2012 4:14 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Bridge agraffes FYI

David and all,

I'd agree that building a board which is too stiff is less common. I have
built one which was too stiff in the killer area, but it takes some doing.
Your comment that most makers might err towards lower impedance - I'd tend
to agree with this. A lower impedance board tends to sound better when its
first built, unless it is taken to an extreme, as one of the high class
German makers still does. But it doesn't seem to take long for lower
impedance boards to start honking.

Ron O.

>Or its companion of overcompensation and building assemblies that are 
>too stiff.
>
>David Love
>www.davidlovepianos.com
>
>
>Hi all,
>
>Indeed, and the lower bridge root height would tend to allow the board 
>more flexibility over its speaking area, which would lower impedance 
>and would allow for something of a more distorted tone, ie.
>honking tone. Lack of board stiffness would seem to be one of the most 
>commonly overlooked factors, when it comes to tone building.
>
>Ron O.


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