NEWS FLASH! "Conover clobbers Steinway !"

[Steve Fujan]

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Ric,

I doubt Wogram is referring to the speed of sound within the mass of the
soundboard when  talking about "vibrating area" and "radiation efficiency".
Isn't the sound we hear primarily a result of the diaphragmatic motion of
the soundboard disturbing the air?

Imagine a square soundboard with the grain running parallel to two of the
sides.  If the soundboard bends easier across the grain than parallel to th=
e
grain, then the shape of the fundamental diaphragmatic deflection will be
more rectangular than square.

Then if you add stiffeners perpendicular to the grain to equalize the
stiffness, the shape of the deflection will be more square, and the
"effective vibrating area" will be maximized.

Respectfully,
Steve Fujan


On 2/4/06, Ric Brekne <ricbrek@broadpark.no> wrote:
>
> Mike and Terry
>
> Mike stated...
>
> "Wogram states clearly in the excerpts you provided, that the ribs are
> there to equalize the stiffness of the board across and parallel to the
> grain, to optimise the diaphragmatic response."
>
>  Actually Wogram  did not mention anything about optimising the
> diaphragmatic response. He said
>
> "If this anisotropism is not compensated for by the addition of ribs
> running across the grain, the effective vibrating area is reduced and the
> radiation efficiency is decreased over a broad frequency band."
>
>  And why would that be ?  I think we can agree that if anisotropism is
> fully compensated for, then the speed of sound through both directions is
> going to be quite equalized. And that if there is a significant differenc=
e
> in the speed with which sound propagates through the two directions in th=
e
> panel then anisotropism is not compensated for.  This follows from the ba=
sic
> formula for the velocity of sound through a solid.  *v* =3D root (Youngs
> Moduli */* density).  Density being equal in both cases, if Y is the
> same... (ie bending stiffness is equal) then *v* is the same.  And if *v =
*is
> different then Y must also be different (since density remains the same i=
n
> both cases).
>
> Now you can choose to simply relegate the speed of sound through wood as =
a
> by-product of all this if you want I suppose.  But I submit that it is
> precisely this speed of sound which is the objective of equalizing bendin=
g
> stiffness to begin with.  And that by doing so you in effect exploit the
> vibrational area of the board in both directions in as equal a fashion as
> possible.  Which to me at any rate put Wograms actual quote into a very
> senseable light.
>
> I am more then willing to hear why this reasoning is flawed mind you :)
>
> Cheers
> RicB
>

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