Isolated Air Movement, was: Rib Thinning

[Overs Pianos]

>Ron O. wrote:
>
>"...the primary purpose of the panel is to prevent air leaking past the
>ribs."
>
>We all know the acoustic effects of placing a hi-fi speaker on a large panel
>or on the panel of a sealed box compared to holding the speaker out in mid
>air - especially mid-range and bass speakers. What about holes for nose
>bolts through the soundboard and the limited distance from the top of the
>soundboard on a grand, around the outside of the outer rim, to the underside
>of the soundboard. Surely the two soundboard surfaces are not totally
>isolated from one another. Perhaps the distance around the rim is large
>enough that soundwaves do not interfere with one another. Perhaps the holes
>in the panels are not large enough for a significant amount of air to pass
>and cancel out soundwaves. But perhaps there is sound degradation from one
>or both of these sources. Any insight into this?
>
>Terry Farrell

Sorry Terry, no proven insights to be had from here. But I've asked 
myself the same questions.

We make the clearance holes for the set bolts as small a possible to 
minimise 'leakage'. I've also wondered about the idea of fixing a 
laminated sealed panel to the base of a grand to hear to the piano 
without the sound, which is 180 degrees out of phase, coming from 
under the board. It may also allow for a cleaner tone.

Furthermore, a laminated 'acoustic blanket' under a grand would 
likely be useful for preventing spill where performance grand pianos 
are being amplified. This is idea has been in my to do box for a 
while. We're planning to keep one of our next 225 pianos (No.s 6 & 7) 
as a promotional instrument, and we're planning to install a trial 
acoustic blanket for amplified ensemble use.

When Holly Cole performed here in Sydney using our rebuilt Steinway D 
few years ago, her sound people placed a series of foam blocks all 
around the perimeter of the piano to prevent spill. The resultant 
tonal clarity was impressive for a live gig.

Best,
Ron O.


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