[CAUT] Lack of low-frequency response

[Richard Brekne]

Hi Jim

So... then it is quite feasible to assume that cross grain stiffness 
deviation from  along the grain stiffness in the tenor / bass bridge 
area of the soundboard could result in the soundboard breaking up into 
several smaller units as it vibrates and thereby inhibiting low 
frequency sound production ?

I agree that "stiffness"  needs to be more specific.  For example... in 
CC boards cross grain stiffness is created that is comparable to RC&S 
boards despite the much shallower ribs. It seems to me that perhaps this 
cross grain stiffness in CC boards must be at least in some significant 
part because of the panels cross grain compression.  I cant see how the 
ribs themselves can account for it... the formula for bending stiffness 
of ribs remains constant and shallower ribs means less stiffness. So the 
extra cross grain stiffness in CC boards must be from the panels 
compression itself... yes ?

In any case it seems to me that I am reading that the ribs have to 
supply some mechanism for equalizing the natural anisotropism of the 
panel... and that too little equalizing is bound to lead to acoustical 
problems.

Cheers
RicB


    Ric,

    What I'm saying does not disagree with either Conklin of Wogram. 
    Without
    the ribs, the board would be floppy.  We need to define what we mean by
    "stiffness".  We try to make the board stiffer in the middle and more
    flexible around the edges so it will vibrate as a unit at low
    frequencies
    instead of breaking up into standing waves.  At the higher
    frequencies, it
    always will break up into standing waves.  It's a matter of when and
    where.
     And yes, the rim does play an important part too.

    Jim Ellis