<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> Mike and Terry Mike stated... <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." </blockquote> Actually Wogram  did not mention anything about optimising the diaphragmatic response. He said <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." </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.  This follows from the basic formula for the velocity of sound through a solid.  v = 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 in 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 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 Wograms actual quote into a very senseable light.   I am more then willing to hear why this reasoning is flawed mind you :) Cheers RicB </body> </html>