Compression ridges was :Do you dry the ribs, along with the board, prior to gluing ?

[Dean May]

I'm pretty sure I got it right. As Del presented it in his workshop, the two
work against each other. Where you need more mass you also need less
stiffness. How do you make it heavier but more flexible? Where you need less
mass, you need more stiffness. How do you increase stiffness without
increasing the mass? 

Think of it this way, which requires more air movement, A0 or C8? Which
requires a greater excursion of the board? The frequency that requires a
larger movement of the board will also require minimal mass, as mass by
definition is the quality that impedes acceleration. (A0 is my pick)

And as has been discussed here before a quick fix to improve high frequency
sustain is to add mass. 

Also, which frequency produces a larger sound pressure wave? It is the one
that will require a more rigid panel, i.e., more surface area to produce the
larger pressure wave. (again, A0 is my pick) This stiff panel will need
flexibility at the edges so it can make its deflections, hence the concept
of "floating" the board at the bass end. 


Dean

Dean May             cell 812.239.3359 

PianoRebuilders.com   812.235.5272 

Terre Haute IN  47802

 


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Richard Brekne
Sent: Friday, February 01, 2008 2:36 PM
To: pianotech at ptg.org
Subject: Compression ridges was :Do you dry the ribs, along with the
board,prior to gluing ?

    "Stiffness is desired in the high treble but what about the bass
    where flexibility seems to rule? "

        According to Del (and I believe it) high mass and high
        flexibility isdesired for treble. High stiffness and low mass is
        desired for bass. Low bass frequencies require a very rigid
        moving panel. If the panel is not rigid it absorbs all the
        energy before pumping out the fundamental frequency.
        Dean


Er... I believe you have it backwards Dean.

Cheers
RicB