Piano Rims ./soundboard stiffness

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Erwinspiano@AOL.COM=20
  To: pianotech@ptg.org=20
  Sent: December 30, 2001 7:34 PM
  Subject: Re: Piano Rims ./soundboard stiffness


  .=20


     Del writes=20
    >=20
    > >Typically the loss of sustain time due to a low-mass,=20
    > >low-stiffness rim is countered by making the soundboard thicker =
and the=20
    ribs=20
    > >a bit stiffer. (Though ribs don't really have much effect on tone =

    > >performance through the last couple of octaves in the treble.)=20


  Phil Ford=20

    > Why do you say that?  Should the ribs be removed in=20
    > this area?  What then?  Make the board a little=20
    > thicker?=20

    With the bridge so close to the belly rail the stiffness of the =
soundboard=20
    panel has much more effect on the soundboard system impedance than =
do the=20
    ribs.=20
          Del=20
       =20
         Hi   Del=20
    That being the case  why is  the more modern/recent technique of =
using a spruce rib preferred in the capo treble areas as opposed to the =
lighter weight sugar pine version  which was original equipment?  Also =
if it is true that the ribs don't effect impedance as much as the board =
stiffness does then why so much weakness in the killer regions or is =
that the point where the rib stiffness/impedance really comes into play? =
My thinking is that right around note c- 6 must be crucial cross over =
point.
        It's clear from the diagram you posted that in radial version =
boards the soundboard grain and ribs don't cross at right angles in the =
upper trebles creating greater stiffness and the shorter grain angles in =
front of the bridge at the belly do as well (due to the non traditional =
panel grain orientation off the belly rail ). I think I'm starting to =
get it=20
        If the ribs have little to do with stiffness/impedance and tone =
production up high it would seem that all this stiffening shouldn't be =
needed. However the feedback is that the sustain is so much better in =
this radial board indicating that a lot of extra stiffness is needed =
from the board and the rib to get the improved sustain characteristics. =
Am I missing something?=20
        My experience is that too much stiffness can make the board a =
little stingy in the trebles including the killer region. I find that I =
personally like the sound from retaining the sugar pine configuration in =
the capo areas but crowning them from roughly a 50 ft radius graduated =
up to about a 25 ft. On the last rib. This obviously adds some stiffness =
the flat ribs lacked and it seems to have a good tonal balance between =
attack/power and sustain/power balance but doesn't make it to tight =
sounding. I hate subjective terms=20
        The on going question is how stiff is stiff enough?=20
        My qustions/comments are in relation to reproducing original =
designs and not really to redesigns all though I'm sure the principles =
are similar and applicable.=20
         I love this stuff.=20
      Best--------------------------------  Dale Erwin

Personally, I'm not convinced there is much difference in performance in =
the top octave or two that can be attributed to the use of spruce ribs =
vs. sugar pine ribs. I even tried maple ribs up there once--not much =
difference I could attribute to those either. There are so many =
variables involved in the process and the structure it's impossible for =
me to tell what to attribute to what. I've not ever heard of any =
controlled tests done to confirm just what changes in performance there =
might be.

The traditional piano (with its compression-crowned soundboard) depends =
at least as much on the internal compression of the wood in the =
soundboard panel (and the stress interaction this creates with the ribs) =
for its overall stiffness than it does on the ribs per se. With =
conventional soundboard design the region around C6 is a particularly =
difficult area for this.

Yes, I think got it. I should probably have said something like, "With =
the bridge so close to the belly rail the stiffness of the soundboard =
panel has much more effect on the soundboard system impedance than do =
the ribs in a soundboard assembly of conventional design." You might =
also note in my drawing that the ribs are a bit closer together than is =
common.

Del



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