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I ask this because if the strings tension is supported by the cast iron frame, what is exactly the purpose of the beams?

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https://www.stephenpaulello.com/en/pianos feature a "barless" frame and with parallel stringing, rather than overstrung.

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Originally Posted by pyropaul
https://www.stephenpaulello.com/en/pianos feature a "barless" frame and with parallel stringing, rather than overstrung.

I mean the wooden beams underneath, not the bars in the cast iron smile.

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Because that 30 tons of tension is being deflected by the soundboard via the bridge which causes roughly a 1000 lbs of downward force into the wooden structure. Without the wooden frame, the cabinet is flexing causing energy loss out of the soundboard. The frame stiffens the structure so energy can remain isolated in the soundboard.

-chris

Last edited by Chernobieff Piano; 07/29/21 03:01 PM.

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There have been pianos made with no beams in the wooden frame. They tend not to be the best quality. They do help hold the rigidity of the frame, which results in less sound loss to flexing.


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Originally Posted by Chernobieff Piano
Because that 30 tons of tension is being deflected by the soundboard via the bridge which causes roughly a 1000 lbs of downward force into the wooden structure. Without the wooden frame, the cabinet is flexing causing energy loss out of the soundboard. The frame stiffens the structure so energy can remain isolated in the soundboard.

-chris


I find it hard to believe the soundboard is under 1000lbs of pressure. The frame has 20-30 tons of longitudinal tension from the strings, but the downbearing is only a small fraction of that or, in the Stephen Paulello pianos, zero as he's using bridge agraffes.

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Originally Posted by Chernobieff Piano
Because that 30 tons of tension is being deflected by the soundboard via the bridge which causes roughly a 1000 lbs of downward force into the wooden structure. Without the wooden frame, the cabinet is flexing causing energy loss out of the soundboard. The frame stiffens the structure so energy can remain isolated in the soundboard.

-chris

Isn't the soundboard bolted to the cast iron? If so, the downward pressure maybe it's not a problem.

Last edited by pold; 07/29/21 07:26 PM.
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Years ago here, Del Fandrich claimed that if you press down on a crowned soundboard, the sides of it would move inward. There is some possibility that is true, although it would depend on the shape of the ribs. In that case, the beams would actually be under compression, and various parts of the soundboard would be under tension, and other parts would be under compression. It is more math and physics than I am ready to do, and I suspect it would be beyond most piano designers' capabilities.


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By the way, if I had the chance I would experiment a piano without beams and without rim.

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Rippen and Lindner grands have the soundboard bolted to the aluminum plate, without a wooden frame. They also have negative crown.


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Perhaps some simple math will make it easier to believe.
Wolfenden quoted the industry standard a 150 years ago "The downward pressure of the strings should be 1/40th the string tension".
So if you take 30 tons (60,000 lbs) and divide by 40 60,000/40 = 1500lbs. This is why most set downbearing to a 1.5 degree angle

Another way is Tension x sine of the angle = downbearing force. Thus 60,000 lbs x .0262(sine of 1.5 degree angle) = 1572lbs.

A 20 ton tensioned piano would be 40,000 x .0262 = 1,048 lbs.

Some use a smaller downbearing angle something like - half a degree in the bass up to 1.5 in the treble. Lets average that out to 1 degree. 60,000 x .0175 (sine of 1 degree angle) = 1,050lbs
40,000 x .0175 700 lbs

The sad part is i know this all by heart, time to go work in the garden to think of something else.

-chris


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BDB,
It was actually Ron Nossaman.
-chris


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Another interesting one is the Klavins Una corda, the frame is not cast iron but stainless steel, and instead of wooden beams on the back you can see just a metal bar, stainless steel as well. And the soundboard has no ribs.

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(Disclaimer: I'm not a piano tech, but a mechanical design engineer who plays piano and builds guitars. And sorry, I didn't realize this was in the Piano Technician forum.)

The soundboard isn't bolted to the cast iron, it sits inside the interior wooden rim. I believe it's glued to the rim, hence why cracked or broken soundboards are such a big deal.

The beams support the weight of the piano, transmit the weight toward the legs, make the piano rigid so parts don't move or flex relative to one another, and importantly maintains the shape around the soundboard. The metal frame is designed to support the string tension but not the weight of the piano. The metal frame (per Yamaha's website at least) is made of a special blend of metals to have certain acoustic properties, so it's best left resting inside the piano rim without additional loads placed on it. If the metal frame were unevenly supported it would affect the tone. It could also affect the integrity of the frame since it's under so much compression and likely needs to be kept straight so there are no bending stresses.

So yes, there could be ways to build a piano without them, but using them is a tried-and-true process and doesn't require much in terms of engineering or manufacturing technology.

Last edited by Joe Garfield; 07/29/21 08:05 PM.
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This is also why I love the Klavins, you can see how light and thin is, the stainless steel is also acting as a rim, the soundboard is all contained inside:

[Linked Image]

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As far as I know, Ron Nossaman never posted here.


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