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We are looking for an artifact.
Does anyone remember that device made up of a tuning fork and a section of soundboard?
The idea was to bend the board and show how the response to the fork increased.
It was a dealer demo.
We want one for the museum.
Any information would be helpful, as well.

Thanks,
Craig


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Hi Craig:

Didn't Chris Robinson make one of these for demo purposes in his classes? (If memory serves me).


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Its applicability is another question. The demo uses tension along the grain the way Harpsichord soundboards function. When it was demonstrated at one of the many conventions I attended, in dinner conversations most felt it was gimmicky.
Many museums, when they can't obtain an "original" would manufacture a replica. I'm sure it wouldn't be hard to make.

-chris


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They were an advertising device for the Mason & Hamlin tension resonator.


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We were curious if anyone saw these things,Chris Robinson did a demo on soundboard construction in our shop about 1987. The one we had was different than Chris's but the result was the same.
He fastened a strip of wood about 1 meter long and about an inch wide and slid a tuning fork back and forth along the top and it revealed the wave motion in such an object in that there were definitely loud and quiet spots on this wood. And with another object attached to this same strip of wood dramatically affects the lively spots by adjusting it's position on this strip.
The demo did not include how crown height plays into it.
It stuck in my memory, I remember it well, too bad more piano guys didn't pay more attention to this phenomenon, I'm finding out nobody did. It is a strong clue Re: nodal /anti nodal behavior in piano SBs

Applicability?? it is a simple audio demonstration. If one has never experienced such an object then It is wasted time talking about it.

Ohhhh--it is not gimmickry, "magicians have gimmickry" they fool a lot of folks with it. all fake.
It is a reality that when a board is forced into a curve something happens to it, "projection"
Why would the same tuning fork get loud as heck when the board it is fastened to is forced onto a curve, and it is quiet and weak sounding when relaxed to flat position. It is amazing to my little brain, how can this be?

Yes we are going to make one or two, for the same purpose to demonstrate.

It is the reason why piano SB's have a crown, it's simple.

R.Blais.

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Thanks for the reminder Richard. That's about what I remember from Chris's demo.

BDB, if you ever met Chris Robinson, you would not call him a gimmick maker. A man with a strong and inquisitive mind, yes. I learned a lot from him, as have many others.


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I have no idea who Chris Robinson is, and I have no idea whether he had any relationship to the device I remember from Mason & Hamlin dealerships from 40 years ago.


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He retired about 10 years ago. A lecturer and national and regional PTG conferences for several decades, and widely regarded as one of the best rebuilders in the country during his time. Wicked sense of humor too.

I don't think he ever claimed to have invented it.


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BDB? Hi! did I ask if you knew Mr. Robinson?. I don't think anyone cares if you do.
He was very active in the Ct. P.T.G. And nationally known for many years. He was early in SB replacement activities.
And it could have been M&H. but I'm pretty sure the one we had here "the toy" was the Cable Nelson Co. you know the ones with the cable and turn buckle supposed to hold the crown?? maybe! it is long-long ago.

It would be instrumental in revealing SB behavior as part of a presentation Re:SB function.

We were a little hopeful someone had one and maybe strike up a conversation about it's applicability. Hah!

Just to say....it is what gives a guitar projection, no bending the top, no projection. "give that some thought"

Best to you all!
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The tuning fork demo is a tension along the grain example. Modern pianos use compression across the grain. The demo should represent that. Simple yes?

I don't think anyone is questioning whether nodes or anti-nodes exist. The concept has been around a couple centuries. But the pattern of which would be vastly different on a strip of wood than it would on an installed soundboard. So on both those counts a demo is not applicable. If the idea is to get more resonance out of a soundboard via tuning and arranging the nodal pattern, i don't think much will be gained as the soundboard has a large surface area, thus any perceived gain of function will be on a micro level. Whereas, on a guitar panel or violin top it has more significance.

-chris


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What about flattop guitars? Some are genuinely flat aren't they?
Certainly though, my experience with 1930s Maccaferri guitars implies that the arch massively influences projection.
My memory of the physics is that sound travels faster through wood under stress but I've no idea why that would increase projection.
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Chris.

Tension along the grain---yes--Well what about the ribbing?,
When all the ribs are forced into a curve by the moisture expanded panel and all working together. = mysterious forces are installed.
And this forced bending it is of the ribs, isn't it??? And they are pretty substantial in some.

It is more than a micro level. It is a force to be reckoned with Energy, --via--math,--placement of bridges the re-curve at the rib ends and distance from bridges to rim, for optimum results, not simple. but there are rules.

Piano guys do radical repositioning of internal components without the tiniest mention as to why something is incorrectly constructed?, I see things that do not make sense and until I began to ask about these things no one ever considered it. even if it is only to poo-poo and ignore this thoroughly.
It is probably the most important consideration in piano construction, like hammer strike point, the hammer doesn't strike in the middle of the string. Wave motion doesn't stop at the bridge

Show me where wavelength behavior is mentioned or spoken about in any P.T.G.journal or anywhere? maybe wave motion doesn't exist. And I'm the moron.
Even the Dell doesn't talk about these things????
This behavior exists in everything rigid, a telephone pole would exhibit the same wave motion as a broom handle.

Guitar question?
Guitars, are flat-flat when unstrung, but after 180 -pounds pulling on the bridge there is a curvature that forms, without that forced curve it would be dead. Only a few got it right. Martin seems to have.
NW.... grab a thin board and do the experiment! you'll see.

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I agree, the PTG doesn't really get into the nuts and bolts working acoustics of the structure, and other societies turn it into academic exercises of calculus.
I disagree somewhat with your hypothesis that the ribs have an acoustic function of significance. In my mind, the panel moves the air and the ribs are a supportive part of the structure. I believe i have solved the riddle of getting the maximum output from a board which is weight. Getting a board to be light in weight without compromising the structure is key. I also control the deflection of each rib to create a graduated evenness across the panel. I remove roughly 3-5lbs off almost every board. This was the point i made to you at the beginning of our discussions regarding the problems of copying a boards dimensions or recrowning the original like you guys do. Obviously, by the experiments you are doing in acoustics, you are also not completely satisfied with re-using the original material and re-crowning if you're seeking improvements.

I enjoy your videos, thanks for sharing them.

-chris


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Just when you think you've heard it all!.
Now let me get this straight!!!you don't believe piano SB ribbing has any acoustic function of significance.

We restore all parts as best we can to original specs. Yes all the construction errors too, most often.
You see,,,,we don't need to worry about them things. Our clients want this and we are not lacking for something to do.
The acoustic ventures are being applied to guitar making, not only with the old wood from the piano's but the soundboard engineering. We learned much from this old piano thing we do and enjoy it.
Once again, get it straight-- we restore old pianos to original as possible.
And maybe you'll get to hear one of these re-crowned things and maybe we will hear one of your things someday.
If you ignore the the rib contribution to piano tone you need help.
You know what I think about uselessly arguing with someone this way!, round and round. Or maybe you don't remember, I should repeat it but I would be kicked off again --A BIG hah!

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I have been talking about piano soundboard mode shape, placement, and density for decades. Guess nobody pays attention or maybe I don't yell loud enough.


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Can you refer to any of your writings on the subject Ed?
-chris


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Originally Posted by N W
What about flattop guitars? Some are genuinely flat aren't they?
Certainly though, my experience with 1930s Maccaferri guitars implies that the arch massively influences projection.
My memory of the physics is that sound travels faster through wood under stress but I've no idea why that would increase projection.
Nick
Velocity of sound in materials is dependent on the density so if wood is in tension or compression the density will be altered slightly and so also the velocity of sound. With respect to sound projection I wonder if by placing ribs on a piano soundboard or by placing a soundpost inside a violin the soundboard is put into a stressed state (tension on one surface and compressed on the other) so that it behaves as a damped harmonic oscillator with a larger amplitude of vibration than if it was undamped.

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Oh-well.
Hi Keff. Fiddles and early arch top guitars are carved out from thick boards, fiddle sound posts were added when steel wires were applied and had to do something to stop the SB from collapsing.
Just to note,,,bridges on fiddles and arch top guitars are not in the center of the SB the center location would be well---dead! (a node) Same thing in piano SB's. Fiddle tops are fastened at 90deg. all around. that places the lively spot off to the side of center. if a piano rim is 90deg, or beveled--it's to make adjustments to crown shape.

Yes, forcing wood into a curve does alter it's physical properties, wood is stronger compression-yes,,,
so?? does one side, the stretching side, have more movement than the squeezing side.? give it some thought.
If there were equal movement than there would be no resistance and no spring back, like a fresh little branch from a willow. It's the stretching on one side that causes the spring back.

I discovered something when I did two very crude videos Re: wave motion in piano SB's . You tube.
When the rib subject was forced into a curve, the lively spots were not easily located, and I have to use the word homogeneous, the hot spots evened out! Hmmmm--when the curve was lessened the nodal properties were easily located. Too much curve seems to be not ideal, and that is a small amount.

Cool-man! I also discovered to my surprie hat the re-curve at the rib ends, determines the spot where the wave motion begins in the rib, but only if it is mounted 90deg. at the rim,

Hello Ed--I am frustrated too!! your not alone. Maybe we could have conversation about this.
I haven't had time to continue the wave motion investigation. It's coming.
I acquired a mechanical scale that can go to 400lbs. To measure how much force is exerted to the rim via the ribbing, we'll see! For it is the ribbing that delivers the impulses! between rim and bridges. It is the spring kicking back to the bridges in time. And the lower the crown-the stronger the impulses. That is why those good old Steinways sound pretty darn good even when most of the crown is down.

Best to most of you all.
R.Blais.

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It is all in my long suspended second book titled Grand DeLight. I have lectured about some of the points many times at PTG classes. I believe I have described some of it to you over the phone years ago.


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Hello R. Blais, I find your points very helpful and would imagine that in a crowned soundboard the tensile stress on the one side would not be equal and opposite to the compressive stress on the other and that the small difference would drive the amplitude response such that you would get an underdamped oscillator.

Last edited by keff; 06/23/21 10:37 AM.
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