[pianotech] Diaphragmizing

[Ron Nossaman]

> Many people do it and the practice has been Steinways for some time.  I'm
> curious about when Steinway actually started the practice and since I
> haven't taken out many Steinway soundboards that are newer I'm curious what
> their current practice is and whether other makers historically have
> employed this practice.  I always thin the boards I do in the bass section
> graduating down to about 5 mm by the time one gets to the edge.  But farther
> up on the bent side and in the treble I don't, neither at the belly rail.
> While I understand the idea of creating greater flexibility in the bass
> section for those low frequencies I'm wondering what the reasoning would be
> for thinning higher up in the scale.  Also, if one is installing a cut-off
> bar, as I do, then were you to thin the perimeter it presents some questions
> about how to treat the cutoff area in the case where, as I tend to do, not
> cut the panel there but leave it whole.  Early Steinway pianos that I have
> taken apart don't seem to be thinned in that area and the thinning in the
> bass section is less pronounced.  
> 
> David Love

The Diaphragmatic patents are 1935 #2,051,633, and 1937 
#2,070,391. Nearly as I can tell from the patent texts, it's 
magic, as the descriptions don't seem to say much that's 
coherent other than it increases flexibility at the edges.

In compression crowned boards, like Steinway's, it may improve 
sound initially, but will also increase compression stress 
levels in the, now thinner, panel and further shorten the life 
of the assembly. I see no rational reason to thin a panel in 
the treble.

For the most part, I've found it to be unnecessary if I get to 
put in one of my boards. I don't use a thick high grain 
density panel, and can more easily float the bass than thin 
it. Rebuilding with an existing board, thinning the bass (or 
channeling like Overs and Seiler) can be very worthwhile.

Ron N