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

[Dean May]

Thanks, Ron, for bearing with us. Your post is perhaps one of the most
succinct and easy to understand descriptions of what is going on that I've
seen. Please keep stoking.

>>The bass works well when the assembly is light 
>>and flexible down there. The purpose of floating the bass in 
>>small grands, and moving the bridge to increase back scale 
>>length, is to add flexibility and amplitude of movement.

If I consider a woofer speaker, it is designed to be very rigid/stiff to
produce a large area pressure pulse without deflecting/deforming the cone,
otherwise the pressure pulse would disintegrate. The cone is also very low
mass so that it can accelerate quickly back and forth with large amplitudes.
It is very flexible around the edges but not the cone. 

This is what I would like to see a little clarification on. You and others
speak of the need for increased flexibility in the bass section. When you
say you need increased flexibility in the bass for amplitude of movement,
aren't you really saying you need the flexibility around the edges, or even
a floated edge? The panel itself needs to remain rigid or stiff, but for it
to move it has to be able to give around the perimeter. 


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 Ron Nossaman
Sent: Saturday, February 02, 2008 11:05 AM
To: Pianotech List
Subject: Re: Compression ridges was :Do you dry the ribs, along with the
board,prior to gluing ?


You quit stoking the fire for a minute, and the darkness 
creeps back in.

A flexible treble goes "dink". The treble needs to be stiff, 
which is what the fish is for. The bass cutoff diminishes 
unwanted spurious resonances and makes the ribs shorter in the 
killer octave - to stiffen them.

Too stiff a treble shrieks, which adding mass cures. So an 
overly stiff treble that's mass loaded is highly functional 
while still being well above minimally adequate stiffness. 
That's a built in safety margin for future climatic aging and 
deterioration.

Too stiff a bass is thin and lacks fundamental. Too heavy a 
bass clangs. The bass works well when the assembly is light 
and flexible down there. The purpose of floating the bass in 
small grands, and moving the bridge to increase back scale 
length, is to add flexibility and amplitude of movement.

The use of mass loads on the low tenor or high bass bridge is 
an after the fact attempt to blend any existing tonality 
mismatch across the break if the builder didn't get exactly 
what he wanted with the design. Nobody's perfect, so there's 
make up.

Ron N