Soundboard Panel Grain Angle

[A440A@aol.com]

Terry writes: 
>Conventional wisdom suggests quarter-sawn spruce for soundboard panels.
 <snip>
>And perhaps more importantly, WHY? What difference does it make? Why might
>it make a difference? Is it because the panel will lay better? Because
>it looks better? Is it just so one manufacturer can claim "ours is better
>than theirs"? Because sound can "reflect" through some angles better than
>others - maybe a 45 degree grain angle refracts all the sound into outer
>space? 

Greetings, 
   There are acoustic reasons for quarter sawn wood being used.  Sound 
transmission is much better with the grain than across it, (something on the 
order of 3 times faster,too?)  I believe this is because there is a loss of 
acoustical energy every time there is a change from one medium to the next, 
and going across the grain requires the energy to go from one density of wood 
to another with every "ring line", effectively losing energy at every step.  
Harder material transmits the sound faster, too, so the harder grain 
transmits the sound better and faster than the softer "summer" wood.  
    The more truly quarter sawn it is, the more contact there will be between 
the harder grain and the bridge.  There is a reason that the best sounding 
boards have the bridges directly connected to the ribs, since the ribs 
transmit the energy to the entire board with greater efficiency than if all 
the energy had to spread across the grain from the bridge. (Del, Ron??? if I 
am sinking into a quagmire here, be gentle as you yank the rescue ropes!) 
   Stability may also be a question, as the quarter sawn wood is more stable, 
and doesn't "shelve".  That is one of the  only two questions I missed on the 
written exam, when it asked "why" was quarter-sawn wood traditionally used 
for soundboards? The correct answer was supposed to be because it was more 
stable, but I still think the answer should be the acoustic sound, not the 
stability, since the piano was developed in an era in which summer and winter 
didn't offer that much change in humidity as today.  Quarter sawn wood is 
used in the tops of fine guitars, violins, and hurdy-gurdys for acoustical 
reasons, (as well as the front and back of organ pipes). 
   (the other question was to do with papering flanges, I was thinking 
Steinway,which can be papered differently than flat flanges). 
Regards, 
Ed Foote RPT