Ric, <br><br>I doubt Wogram is referring to the speed of sound within the m=
ass of the soundboard when talking about "vibrating area" a=
nd "radiation efficiency". Isn't the sound we hear primaril=
y a result of the diaphragmatic motion of the soundboard disturbing the air=
?
<br><br>Imagine a square soundboard with the grain running parallel to two =
of the sides. If the soundboard bends easier across the grain than pa=
rallel to the grain, then the shape of the fundamental diaphragmatic deflec=
tion will be more rectangular than square.
<br><br>Then if you add stiffeners perpendicular to the grain to equalize t=
he stiffness, the shape of the deflection will be more square, and the &quo=
t;effective vibrating area" will be maximized.<br><br>Respectfully,
<br>Steve Fujan<br><br><br><div><span class="gmail_quote">On 2/4/06, <b c=
lass="gmail_sendername">Ric Brekne</b> <<a href="mailto:ricbrek@broa=
dpark.no">ricbrek@broadpark.no</a>> wrote:</span><blockquote class="gm=
ail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt =
0pt 0pt 0.8ex; padding-left: 1ex;">
Mike and Terry<br>
<br>
Mike stated...<br>
<blockquote>"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."<br>
<br>
</blockquote>
Actually Wogram did not mention anything about optimising the
diaphragmatic response. He said<br>
<blockquote>"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."<br>
<br>
</blockquote>
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
difference in the speed with which sound propagates through the two
directions in the panel then anisotropism is not compensated for. Thi=
s
follows from the basic formula for the velocity of sound through a
solid. <i>v</i> = root (Youngs Moduli <b>/</b> density). Dens=
ity
being equal in both cases, if Y is the same... (ie bending stiffness is
equal) then <i>v</i> is the same. And if <i>v </i>is different then
Y must also be different (since density remains the same in both cases).<br=
>
<br>
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 bending 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 Wogram=
s
actual quote into a very senseable light. <br>
<br>
I am more then willing to hear why this reasoning is flawed mind you :)<br>
<br>
Cheers<br>
RicB<br>
</blockquote></div><br>