Rims and such...

[Delwin D Fandrich]

> -----Original Message-----
> From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
> Behalf Of gordon stelter
> Sent: April 09, 2004 4:34 PM
> To: Pianotech
> Subject: Rims and such...
>
>
> Sorry Del, all,
>      When I am fatigued I fail to express myself well
> so, for the record, THIS is my opinion on rims.
>
> 1) Rims should be deep enough so that, when coupled
> with the plate, they keep it from flexing.

How deep is deep? Steinway's rims, at approx. 250 mm (10"), seem to be quite
deep enough. I agree that rims should not be flexing, but the inner rim
alone is generally stiff enough to prevent this. Besides, flexing is better
handled by appropriate belly bracing.


>
> 2) They should be made from some really hard stuff
> which, as much as possible, transmits, rather than
> absorbs vibrations.
> ( And also adds to rigidity. )

True, you don't want the rim to absorb energy from the soundboard. But, what
do you mean by transmitting vibrations? Not in my rim, you don't.


>
> 3) They should not be SO big that they absorb
> vibrations unecessarily, due to excessive mass.
>     Make sense?

No. You can't have it both ways. If the rim needs to be stiff and massive to
prevent it from absorbing energy (your "vibrations") making it more massive
won't cause it to absorb energy. So, yes, it should be both stiff and
massive to prevent the excessive absorption of energy from the soundboard.


>
>     Yes, I know about Bosie rims. Spruce is naturally
> resonant ( even when not positioned as a diaphragm
> )but it is also a good transmitter of vibration, as
> the anular rings are quite stiff and dense.
>      That is my opinion.
>      Your comments are welcomed,
>      Thump

All woods are naturally resonant. What sets spruce apart from most other
woods, either hard or soft, is its particularly high stiffness-to-weight
ratio. The one thing you don't want in a rim (or a soundboard either, for
that) is resonance. In either place resonances are voicing problems. The rim
is generally braced well enough to either prevent, or at least dampen, most
spurious resonances. I don't happen to think spruce makes a particularly
good rim and rim don't make particularly efficient soundboards.
Bosendorfer's work moderately well because they are huge, they are well
braced and they have relatively stiff and massive soundboards. As well, they
are meticulously crafted and prepared. It would be interesting to see what
they would be like with a better rim.

Del