Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum "Oilcanning" Soundboard Skeptic

Gene,
I just asked a simple question. So I get it, you're taking educated guesses.

It doesn't matter to me what oil canning is or isn't because I replace old damaged boards with new ones.

And it looks like you're back to name calling again.

What a pleasure.
-chris

Your question was not simple. It had very selfish motive.
If you dont care about oil canning, why particiapte in this thread?

I think your mind reading skills are off Gene..

I've been collecting data for 4 years on soundboard structures with an emphasis on measuring soundboard stiffness. I created an algorithm and came up with a working Constant (K) that produces a pretty reliable curve. Especially useful when comparing one board to another and to circumvent any future mishaps.. Even a well known piano rebuilder near Modesto was impressed. I asked because there were formidable challenges in the process. I was wondering how others surmounted the challenges.

That's why i asked the question.
-chris

Well your way ahead of me
What I told you is how I quantify stiffness, as I said, I don’t have a formula, just knowledge of what components provide stiffness and where to put them and how to dimension them.

Maybe if i meet you person to person one day I won’t need to read minds and may think differently about you.

But again, this thread was about oil canned boards
It went sideways because you did don’t like my explanation.

Maybe publish your K constant in the Journal when it’s ready.

Here are some quotes from Del Fandrich that were taken from several of his posts in Pianoworld. I could have included many more, but I think these suffice--

"The peak compressive forces that can build up in a soundboard panel that is crowned this way is between 1% and 2% depending on the specific wood samples and the atmosphere the soundboard assembly is exposed to.

"It is generally accepted within the woodworking industry that to avoid rapid compression stress failure wood should not be under any more than 1% compression (perpendicular-to-grain) for even relatively short periods of time. Significant long-term compression set will occur at much lower levels of compression than this."



"Yes, compression can and does damage wood. The most extreme and visually dramatic occurrence of this damage in the piano soundboard are the compression ridges that often show up in soundboard panels crowned in this way. As the name implies internal compression is literally forcing the latewood layers up or down as the earlywood fibers fail in shear as the force from internal compression becomes greater than they can withstand.

"Even without exhibiting this kind of dramatic failure a wood member held in cross-grain compression over a period of time will physically change shape. In other words a panel that is held in compression across grain will gradually lose some of its overall width. If you were at all inclined toward experimentation I would suggest the following:

"Cut a 250 mm long (i.e., with the grain) by 1025 mm wide (across-grain) panel of nice new spruce. Dry this panel to 4% moisture content. (You’ll have to determine this by weighing samples, wood moisture content meters do not read accurately below 6%.) With the panel at 4% quickly cut it to exactly 1,000 mm and put it into a prepared frame that will hold it flat but which will not put any pressure on it at 1,000 mm but which will not allow it to expand beyond that initial 1,000 mm. Now set the whole thing aside in a normal atmosphere for a year.

"When you take your panel out of the frame and dry it back down to 4% moisture content you will find it is no longer 1,000 mm wide but somewhat less that that. Just how much less will depend on the specific characteristics of the wood you used and the extent of the humidity swings to which it has been exposed. If you leave it in your frame long enough you will eventually see it actually coming away from the ends during moderately dry periods. This is the effect of compression-set.

"This is the piano version of the illustration Hoadley gives on page 114 of his book, Understanding Wood. This illustration shows how constrained wood samples are damaged through the mechanism of compression-set after being exposed to varying amounts of humidity. The experiment I've described above is roughly equilivent to the middle sample. What has happened to the sample on the left is exactly the same as what happens to a compression-crowned soundboard panel over time. The soundboard panel is physically constrained by being solidly glued to all those perpendicular-to-grain ribs on one side of the panel. Those ribs don’t allow the panel to freely expand and the resulting stress-interface between the compressed (trying to expand) soundboard panel and the ribs forms the crown. Without that compression there is no crown.

"A free piece of wood like a soundboard panel (or the sample on the right in Hoadley’s illustration) will not develop any internal compression or tension due to changes in humidity. It will simply expand or contract depending on whether it is absorbing or desorbing moisture. It is only when the wood is constrained and not allowed to move that it will develop either internal compression or tension.

"Standard woodworking practice calls for wood to be at a minimum of 7% moisture content at glue up. To go below this can lead to starved glue joints as the wood will very readily draw the glue solvent (usually water) out of the glue. This is well above the 4% moisture content called for in the process of gluing up a compression-crowned soundboard assembly.

"Gluing up a soundboard panel at the 4% moisture content required to end up with a compression-crowned soundboard assembly is abnormal to the woodworking industry. Several of the wood technologists I have consulted on the subject expressed mild shock and something bordering on disbelief when the process was explained to them.

"Like it or not the soundboard panel in a compression-crowned soundboard assembly is under long-term compression and it remains under compression until compression-set has relieved that compression by physically altering the shape of the wood fibers. It is a gradual but certain process."


"The peak compressive forces that can build up in a soundboard panel that is crowned this way is between 1% and 2% depending on the specific wood samples and the atmosphere the soundboard assembly is exposed to.

"It is generally accepted within the woodworking industry that to avoid rapid compression stress failure wood should not be under any more than 1% compression (perpendicular-to-grain) for even relatively short periods of time. Significant long-term compression set will occur at much lower levels of compression than this."



"A compression ridge is ”by definition” damage to the wood fibers in the affected area.

"In the short term compression damage develops when wood fibers are subjected to compression stress greater than their fiber stress proportional limit, or FSPL. For Sitka spruce (in the perpendicular-to-grain axis) this is about 550 to 600 lbs per square inch. If a piece of Sitka spruce is loaded to, or much beyond, this point some fiber failure will be immediate. It is unlikely that anything approaching this amount of compression will be placed on a soundboard panel either during construction or in use.

"In the long term, however, fiber damage can develop when a piece of wood is forced into compression, again in the perpendicular-to-grain axis, by more than about 1%; an amount commonly found in certain types of soundboard construction. How much actual stress will be developed with this amount of compression is unpredictable but it will be well below the wood’s FSPL. But wood is also affected by a time dependent deformation known as creep. Some of the stress in a piece of wood subjected to long-term perpendicular-to-grain compression will dissipate over time. How long is “long term” depends on many variables but can be anywhere from a couple of weeks to some years.

"The presence of compression ridges in a piano soundboard usually indicates that its crown was developed by gluing a very dry wood panel to flat ribs. (It is rare to find compression ridges in soundboard systems that derive their crown from a pre-shaped rib.) As the soundboard panel absorbs moisture in a normal atmosphere it is physically restrained by the perpendicular-to-grain ribs. As a stress interface builds between the soundboard panel and the ribs a curve, or “crown,” is developed. These soundboard systems depend on some amount of continuous internal compression to maintain that stress interface and, hence, their crown. Over time some of that initial compression dissipates due to long-term creep and the amount of crown built into the soundboard decreases.

"Whether or not the presence of one or more compression ridges is affecting the tone of the piano depends on many variables, none of which is predictable with any accuracy. What is certain is that the stress interface between the strings and the soundboard that was initially built into the piano has changed. And it will go on changing—though at an ever-decreasing rate—over the life of the piano. Many pianos with clearly visible compression ridges sound just fine and they can go on sounding just fine for very long periods of time. Others begin showing signs of tonal degradation within months of their manufacture.

"If I am evaluating a used piano having a soundboard panel that has developed compression ridges I will pay particular attention to the decay rate through the upper third of the scale. This is where soundboard deterioration will be most noticeable. If the tone here is abnormally percussive and falls off rapidly the acoustical condition of the soundboard will certainly be suspect; it will be worth some time tracking down the cause of that decay rate. Especially if the piano is relatively new. If, however, the piano is, say, ten years old and the decay rate is normal through this area I’ll probably give the soundboard system a clean bill of health in spite of the presence of a few compression ridges.

"There is much good information on the various strength characteristics of wood can be found in The Wood Handbook, a publication of the Forest Products Lab (it's a free download from their website). See especially Chapter 4 (Mechanical Properties of Wood). Another good reference is Understanding Wood by R. Bruce Hoadley. Again, see Chapter 4 (Strength of Wood).
"

The Del Fandrich quotes are worthwhile. But they are not fully descriptive of what actually happens with a ribbed-up soundboard panel. Specifically....

The soundboard is constrained on ONLY ONE SIDE. Of course everyone -- including certainly Del -- knows that. But -- like so many things in the piano world, people are taking principles and applying the principle without corresponding rigorous experimentation -- or even adaptation to piano applications.

What this means is that one side of the board IS NOT CONSTRAINED. In fact that is where the power for crown comes from. So, the side that is not constrained will not necessarily suffer the cellular destruction that the constrained side does. Cellular destruction will be transitional throughout the thickness of the board. Has anybody ever looked at the cellular structure of soundboard wood to see how cellular crushing is distributed through the thickness of the board? I think not. Or, at least, if they have they haven't told me. Rather, people throw around theories and general principles (which may possibly even be valid).

Which gets to the whole idea of crown and what it's really about...
Crown was never identified as an ideal principle that needed to happen and was sought after as some holy grail by the beginning piano industry. Rather it's an interesting but fundamentally irrelevant phenomenon that occurs when there is dynamic tension in a particular wooden structure. The same thing happens when an archery bow is strung up. Also, when a string is pulled to tension or a drumhead stretched across the drum shell. This is what is significant:
Dynamic tension promotes vibration.
This may be one element of the Steinway sound because the rim itself is in dynamic tension.

So, achieving the appearance of crown without the presence of dynamic tension is missing the point. Soundboards are not floors -- whose design concept is to "support" a certain amount of load. Of course, it's true that there is (or should be) pressure of the strings against the soundboard and that can be considered a "load". But that's not the point. It's not how "solid" the soundboard "floor" is but rather, how "bouncy" it is. There are engineering tables for load bearing qualities of beams. But I'm not aware of tables that have been calculated for "bounciness" of beams. In any event, the enthusiasm for an overly facile application of stock engineering data is largely misplaced in my opinion.

Thus, at this point, we don't know as much as we may sometimes think we do. I think this situation is similar to the whole discussion about "touchweight" (a completely wrongheaded concept). We are like the astronomers of the Middle Ages who could predict planetary movements sometimes but not always. At this point, we don't fully have the rigorous science that would be nice if the piano industry had the financial resources for experimentation that some other industries enjoy.

By way of personal disclosure, I learned soundboard construction from the Trefz family of Philadelphia. I do a combination of natural crown and "cut crown" . But, I understand that the "cut crown" functions as nothing more than a particular way of tapering rib thickness (which may or may not promote flexibility) rather than somehow achieving a shape that magically causes good tone.

Dels post has two critical errors,

The first is that the soundboard is not in a constrained immovable frame that restricts its movement. The soundboard can breathe, that's why your tuning is affected at seasonal changes.


The second is performance as was discussed earlier. He's only presenting a biased structural argument. An analogy would be a drag race. You can have hard rubber tires or you can have soft tires. Notice the choice is the soft tires that have to be replace after a single race. Del is in essence arguing about the flaws of the soft tires.Structurally, you can argue how much longer the hard tires will last, but the point is to get down the track fast.

The purpose of soundboards is to give the piano a full cultured operatic type voice.

-chris

Well, what Del is describing is similar to the soundboard being glued into the rim. Since the soundboard can't expand as it normally, does, it bellies upward. But my point was that it is constricted on only one side -- so it does have substantial freedom of movement which should reduce the impact of compression.

Crown functions to allow for the soundboard to react to humidity changes WITHOUT splitting easily. It is an expansion joint.

Soundboards bellied at too high humidity will split quicker in dry conditions than ones bellied dryer. This is because of the weak cross grain of the wood.

Cut for crown ribs can actually make it easier for a board to crack in dry times since they resist allowing the board to flatten as much.

I have dozens of pianos bellied in the 4% EMC range, (by this I mean it has dropped below 5%), that I see year after year and none have any cracks in over 30 years. They all sound rich with excellent sustain. Some do sound better than others, but after all wood does vary and we only can test for so much in one lifetime. And all the Steinway's sound like Steinway's. I can't say that for all the other rebuilders who replace soundboards that I have sampled.

I wonder how the Paulello soundboards, that have essentially no crown, hold up to seasonal changes of humidity.

Paul.

Sorry to ignore you fine folks. Been at deer camp.

So... Can we put aside the possible causes of "oilcanning" and the the likelihood of some soundboard construction methods to have "oilcanning" for the time being and see if there is a consensus on the definition? To me, "oilcanning" is a mechanical phenomena where the spring rate of an object suddenly becomes less as pressure is increased, but is not permanent. That is, it is not beyond a material's elastic limit. I don't believe this can happen with a soundboard and I don't think any of the fine posts say so.

Those of you that want to provide a clear definition may want to explain what indicates "oilcanning" while still strung, and after unstringing. Everything else being discussed is very valuable and I look forward to it continuing, just not sure we all have the same picture of an "oilcanned" soundboard.

I'd like to correct a few things. First, soundboards are not constrained only on one side. That would be the case if the ribs had no stiffness against bending. That is not the case, and the ribs are far stiffer than the board. Even if the ribs had no stiffness, that leaves one side of the board under full compressions. To say that the soundboard can breathe ignores the constraint caused principally by the ribs, and secondarily by the rim.

While it's true that some compression-crowned boards can last a long time, other examples fail quickly. Of course, it's also true than some builders may not dry their panels so drastically, and these boards, although compression crowned, would be under lower compressive forces.

If you don't mind an anecdote, I once inspected a Petrof grand of perhaps 10 or so years of age. It looked pristine, but its board was full of compression ridges--it seemed like they were at almost every board-to-board joint. It's hard to imagine such a board did not have serious compression set. FWIW, the piano didn't sound particularly good, either.

Finally, those who take Del's writings so lightly fail to remember the years of practical experience he had. No doubt, his opinions were backed up by his real-world observations.

Del has even questioned whether crown (in and of itself) is in fact necessary for optimum performance, but rather stiffness alone possibly a more important factor.

Personally I believe (though impossible to prove) that forced crowning came about as a way of controlling what COULD happen to the soundboard (reverse crowning...loss of bearing, etc) once it started getting exposed to the variabilities of humidity and dryness. And, as a side benefit of doing this they found that there was an overall improvement in the vibrational characteristics of the more successful ones. As a result they devised methods to consistently create crowned boards to reasonably specific specs. IOW it was sort of an accident.

This is just a theory of course (and unprovable in any way at present), however no one presently, or in writing seems to know when, where, or who made the first crowned soundboard, or did so consistently. There is no info on this. Can anyone dispute this with some facts? I'm open to it. I have asked around and so far the answer has been "IDK".

The fact (as mentioned) that CF soundboards have no, and need no, crown is strong circumstantial evidence that it is STIFFNESS coupled with lightness...not crowning (in and of itself) that creates the qualities we want. It is likely that if they had such a material back then (stiff and light together) they would have used it. Instead they figured out the best way they could to make a light material stiffer without adding too much weight. Thus the ribbed...and ribbed and crowned soundboard.

Just a theory...fire away!

Pwg

I

I’ll follow with a question: comparing two unloaded but crowned soundboards, both Sitka and ribbed, one compression crowned the other radiused with ribs, which one has more stiffness??

I can relate experience working with 3 concert instruments two SSd’s and a B
All three have zero string bearing in the 5th 6th octave ares, the B a bit more extensive and all three lack sustain compared with the rest of the piano/s compass and all 3 have no measurable crown in the affected area.
Voicing gave a presence so they are noticeable as having power at the expense of getting hammers so hard they border on buzzing or that excessive bright sound when playing FF.
I’ve tried many things over the years to get some sustain so I can voice a bit different and it is the simplest thing that helped. Not tension resonator. Ribblett helped a little adding stiffness. But what gave the added sustain needed to blend these areas with the rest of the compass was a simple spring placed between rib and board.
So did the spring add stiffness or maybe a very small amount of crown (could not measure any)
But spring back against the force of string bearing happened and I got results.
One interesting bit of info was when I restrung one of the D’s earlier this year - slight crown appeared in the affected area after strings removed. So there was some stiffness and impedance even if lacking power and sustain

After studying many photographs of soundboards( and the ribbing) of Ruckers, Cristofori, and Silbermann. I found that Silbermann was starting to use compression as a means of adding mechanical strain. Silbermann made many copies of Cristofori type pianos inventing improvements along the way. I found one photo in which Silbermann changed the rib orientation from perpendicular to the bridge (which puts the ribs at a varying angle to the grain) to 90 degrees to the grain. When building instruments every day of the year, it wouldn't take long to figure out that the instruments made in the dry winter sound better in the humid summer.
Conjecture is just that, but looking and studying their work says a lot more.
-chris

I have heard several pianos that I was told Del had installed a new board in. I never cared for the sound in the least. Several were Steinway's and they did not sound like what I expect one to sound like.

When he lectures, he says many things I agree with. But his work and I disagree.

The impedance modeling he explains is not in the least bit useful to my work. I above all prize utility.

I have tried and heard the valve spring under the bridge trick and I never found it caused an improvement and in fact found in most cases removing them improved the sound.

I have found and proven the "killer" octave is much better addressed by reducing hammer mass, idealizing pivot termination, setting proper strike point, having tight bridge pins, having maple bridge caps that are properly made, inline string spacing, and reducing the ability of the bridge to rock to longitudinal mode energy can make a treble blossom.

I have seen several quite new European grands that have splits in the board. There was no sign of compression ridges in them like you often see traces of in Steinway style boards. I suspect they split because they were made at too high RH and this left them highly vulnerable when exposed to humidity in the low 30% range. Which we do experience indoors in the Pacific Northwest sometimes during winter cold snaps. I have to think a few Nebraska winters would destroy them unless the room/piano was humidified to not go below 40% RH..

Well, strike point, friction, tight bridge pins, optimum action geometry and regulation are a given for concert
Instrument and maybe the spring and riblett worked because I don’t reduce hammer mass. Never cared for the thin sound or feel of the action with light hammers.
Some of the best artists on the planet have complemented my pianos.

I thought I gave a reasonable idea of what I thought could oil can a board. Likely not the clear definition desired but it’s my opinion. Anyone else?

Wow
Don’t know how the duplicates happened
Sorry

I've done the automotive valve spring thing. Seemed to help.

But a compressed spring is a dynamically opposed force -- which is what I said promotes good tone -- rather than some mystical shape in and of itself.

So how does a 100 year old RCS board age?
I may have an example. A 1927 Vose and Sons Grand came into my shop and it was the earliest example of an RCS soundboard system that I have seen. Same rib scales as seen today with a cut off bar keeping ribs to no longer than 37"., and the typical cut crown carved on top of the rib and the bottom of the ribs were flat and or inverted. All the same ideas used by some "rebuilders" today. The soundboard had about 8 cracks in it. Since it would be "impossible" to have acquired compression set, then why so many cracks?

Here's a pic:
http://forum.pianoworld.com//ubbthreads.php/galleries/2919952.html#Post2919952

Here's how it sounded"

https://www.youtube.com/watch?v=YmES7rTRNGU