Isolated Air Movement, was: Rib Thinning

[Lesher, Trent J.]

Hi,

I didn't see this post before.  I was just wondering what kind of laminated sealed panel would be rigid or massy enough not to just function as a second soundboard separated by an air-couple?  Or would it just be very lossy, or the cavity filled with lossy material?

If it wasn't completely rigid, you could potentially tune it like a passive radiator on a loudspeaker, so that it would be in phase with the top radiation at certain frequencies.

Either way, it would affect the impedance of the soundboard.

The information about trying to absorb the back-radiation from the SB, if I understood you correctly, and the apparently pleasing effects it had at the Holly Cole concert are very interesting.

I've enjoyed many of your posts since I started following this list.  

Regards,

Trent Lesher



-----Original Message-----
From: Overs Pianos [mailto:sec@overspianos.com.au]
Sent: Thursday, January 29, 2004 3:37 PM
To: Pianotech
Subject: Re: Isolated Air Movement, was: Rib Thinning


>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.


-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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