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Posted By: partistic Why does a piano go out of tune? - 07/02/11 10:30 AM
In the short term, fluctuations in temperature can make the iron frame expand or contract, as well as the strings and the wood, slightly changing tensions and speaking lenghts. As the humidity along with temperature fluctuates, the wood expands and contracts also and this may slightly change the crown or the exact positioning of the bridges and termination points, but they are relatively minor and over the long term these fluctuations should average out.

The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?

What other factors are at play that cause pianos to go a semitone flat in a decade? The only other thing I can think of is that the strings stretch.

Is the stretching of the strings the only dominant factor that causes pianos to go out of tune in the long term?
Wow, a semitone in only a decade?
I've seen some pianos (for example 1950s Baldwin Hamiltons) that hadn't been tuned in several years (I don't know if it was a decade or not) that were within a few cents or so of A-440.
Posted By: partistic Re: Why does a piano go out of tune? - 07/02/11 11:33 AM
Yes maybe that is too fast, maybe it should be more like 2 decades, or one and a half. But I still have the same question.
Posted By: Phil D Re: Why does a piano go out of tune? - 07/02/11 04:12 PM
Originally Posted by partistic
The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?


I would say this assumption is wrong. For a piano to go a semitone flat, the pins must move. If strings stretched that much under tension, then the strings wouldn't be suitable for use in pianos!

The healthier the pinblock, the less pins will move over time so the closer the piano will stay at pitch.

If conditions are absolutely stable, then I would assume that the pins would be very unlikely to move in a healthy pinblock. It is when conditions change, and the pinblock swells or shrinks in relation to the pins, then the pins might make small, jerky movements as the interference fit is reduced.

Living in a room with a piano, one can occasionally hear this movement. A quiet 'ping' as a pin suddenly moves.
Posted By: BDB Re: Why does a piano go out of tune? - 07/02/11 04:18 PM
Gremlins! They give stronger formulas of Grem-B-Gonâ„¢ to better tuners.
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/02/11 05:06 PM

Pianos can easily drop as much as a sem-tone, especially when they are not looked after from new. Many manufacturers don't put the work into stretching the strings and bedding everything down now, before they release them for sale. New pianos need tuning much more regularly if they are to remain at concert pitch. On average I would guess that normally it's not until a piano is 2 - 3 years old that the pitch (as far as the strings stretching go that is) stabilises.

After that, I would say that the biggest change of pitch is firmly down to variation in humidity. If the soundboard absorbs moisture the crown increases and the tuning often goes wildly sharp .... the middle being the worst affected where the crown is greatest. On the other hand, dry the soundboard out and you get a wild drop in pitch. If you want a piano that is stable at concert pitch, then have it tuned evry 3 or 4 months for the first few years and keep the humidity constant so that the soundboard isn't constantly changing it's crown.
Posted By: Loren D Re: Why does a piano go out of tune? - 07/02/11 05:24 PM
Originally Posted by Phil D
Originally Posted by partistic
The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?


I would say this assumption is wrong. For a piano to go a semitone flat, the pins must move. If strings stretched that much under tension, then the strings wouldn't be suitable for use in pianos!

The healthier the pinblock, the less pins will move over time so the closer the piano will stay at pitch.

If conditions are absolutely stable, then I would assume that the pins would be very unlikely to move in a healthy pinblock. It is when conditions change, and the pinblock swells or shrinks in relation to the pins, then the pins might make small, jerky movements as the interference fit is reduced.

Living in a room with a piano, one can occasionally hear this movement. A quiet 'ping' as a pin suddenly moves.


I disagree. A brand new piano left untuned will go 1/2 tone flat in a few years without any tuning pins moving. Moving pins will certainly lead to multi-note unisions, a tell-tale sign. Old pianos that haven't been tuned for decades will also go 1/2 tone flat or more without tuning pins slipping. Pin slipping is only happening in pianos with pinblock problems, etc.

In general, pianos go out of tune because of expansion/contraction of the plate, soundboard, and wire, not because of pin movement.
Posted By: partistic Re: Why does a piano go out of tune? - 07/02/11 08:51 PM
If the speaking length of the string is roughly the same as the speaking length of a guitar string (around 60 cm?), then to change it's pitch by a semitone, the speaking length should change by roughly as much as the distance to the first fret. This is something like 3,5 cm. I cannot imagine the plate and the termination points warping so much, or do they?

Are we left with the explanation of the strings stretching or are there other possibilities?
Posted By: kpembrook Re: Why does a piano go out of tune? - 07/02/11 09:50 PM
The short answer to the topic is . . .

Why not??

But here's a longer answer. . . wink

"Should average out" is the main unsupported leap of assumption in this post. You have up to 40000 pounds of tension pulling in one (OK, two) directions and exerting pressure in a perpendicular plane, as well. And random fluctuations are supposed to average with no change given a huge force in one direction?

Think of it this way. . .

You are on a very steep slope composed of sand and gravel-- just short of the steepness required for a landslide to happen. Now, let's suppose you occasionally step down but also step up but your main direction of travel is sideways across the face of the slope. Will the "average" result in a path straight across the face of the slope?

No way. Gravity is working on everything and it exerts a constant downward force on you, the gravel, your shoes, and the pack on your back. If you assume a directly sideways direction across the face of this slope, your path in the sand will show that you are, in fact, trending downward. Every step you take results in a downward component -- even the ones where you step upwards.

Or, think of a huge tanker ship that is headed from Seattle to Japan. But, there's a 25 horse outboard motor on the bow which is aimed sideways to the right (starboard, if you're nautical). That ship will not arrive in Japan, but more likely Shanghai or Singapore.

When you have forces in random directions added together with a force in a consistent direction, the average must always be in the direction of the consistent force. So, what would be surprising is a piano (or any other string instrument) that didn't trend downward in pitch over time.

But wait, there's more. smile

You have at least 210 strings on 88 notes. Never mind what I just pointed out above. With all of this random movement, how could you think that all 210 of these strings are going to ever return at any point to exactly the same relationship with each other that they started out with? That's like putting 210 unsecured boxes in the back of a truck in a nice regular pattern and driving over a bumpy road. After a while you notice that these boxes are no longer in the same position as when you started. Do you really think that further driving over a randomly bumpy road will normally return those boxes to their original position?

Oh, and by the way, it's an open flat bed truck. How are the boxes that get bounced off going to come back? In a piano, you also may have random tuning pin tightness (and/or other factors, some of which are not well identified). So some amount of fluctuation may just put it beyond that pin/string's ability to hold.

It's kind of like asking why people die when the real question is how are we able to stay alive. Our normal bodily functions are an amazing miracle that shouldn't really happen. In the same way, a piano is inherently instable. It's amazing that the thing stays in tune at all -- and sometimes for months (and, in rare cases, years) at a time.
So has anyone ever done any testing to try to figure this out?

For example, maybe take a 20- to 50-year-old Baldwin piano (old enough so the new piano instability is gone, it's not sourced from overseas (and was built before Baldwin's domestic quality had started to go down, from what I understand) and the soundboard has settled down from its wild fluctuations when new, but not so old that the pinblock is beginning to be compromised or the bridges are starting to crack) somewhere in a stable (climate) part of the southwestern USA that has lived there all its life. Have a good technician (preferably one who passed, with a perfect score, the exam to become a CTE) tune the piano carefully and make sure it's as solid & stable as s/he can get it. Also if desired, a DC system could be installed in the piano.
Then, periodically measure things like temperature, humidity, pitch of individual strings, moisture content of soundboard & bridges, etc, until the piano has naturally sunk to a full step flat (A sounding like G).

I wonder what that would tell us about piano pitch behavior over time, and why it goes flat?
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/03/11 11:23 AM
Originally Posted by Phil D
[quote=partistic]The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?




The healthier the pinblock, the less pins will move over time so the closer the piano will stay at pitch.
/quote]
I agree Phil D too.
Posted By: Loren D Re: Why does a piano go out of tune? - 07/03/11 11:51 AM
Originally Posted by Maximillyan
Originally Posted by Phil D
[quote=partistic]The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?




The healthier the pinblock, the less pins will move over time so the closer the piano will stay at pitch.
/quote]
I agree Phil D too.


If pianos went out of tune because the pins move, you'd be correct. Unfortunately.....
Posted By: partistic Re: Why does a piano go out of tune? - 07/03/11 06:00 PM
My family has a piano that wasn't tuned for 40 years. It was over a whole tone flat, even more in the treble. The plate would have to be very seriously warped and distorted to account for a significant proportion of that flatness, but it looks nice and straight to me. The plate is made of relatively brittle iron in my understanding and I don't think it can bend that much without cracking, or without any visible evidence.

If the bridge would move several cm due to the forces applied on it over decades, there would have to some serious cracks somewhere to make the movement possible.

The other possibilities I see are the tuning pins letting go and the strings stretching. It's probably hard to tell how significant each is, as it would require a long study on a deserted piano. It would be interesting if such a study would be made, where they exactly measure the strings for stretching, the tuning pins' positions and the exact speaking lengths to see how big of a role each has.

If the tuning pin needs 5 Nm of force to overcome friction, it isn't just going to come out of someplace someday and make the pin move. But then again, as the strings can creep and stretch, so should the wood grains around the pin?
Posted By: Withindale Re: Why does a piano go out of tune? - 07/03/11 06:46 PM
Originally Posted by partistic
My family has a piano that wasn't tuned for 40 years.


Question. When a piano hasn't been tuned for many years can the pins become more difficult to move and is there a greater risk of damaging the block?

Ian
Posted By: Phil D Re: Why does a piano go out of tune? - 07/03/11 08:42 PM
Originally Posted by Loren D
Originally Posted by Phil D
Originally Posted by partistic
The tuning pins shouldn't move at all just by themselves. I assume they would stay in the same position for decades in a piano with a healthy pinblock if they aren't touched?


I would say this assumption is wrong. For a piano to go a semitone flat, the pins must move. If strings stretched that much under tension, then the strings wouldn't be suitable for use in pianos!

The healthier the pinblock, the less pins will move over time so the closer the piano will stay at pitch.

If conditions are absolutely stable, then I would assume that the pins would be very unlikely to move in a healthy pinblock. It is when conditions change, and the pinblock swells or shrinks in relation to the pins, then the pins might make small, jerky movements as the interference fit is reduced.

Living in a room with a piano, one can occasionally hear this movement. A quiet 'ping' as a pin suddenly moves.


I disagree. A brand new piano left untuned will go 1/2 tone flat in a few years without any tuning pins moving. Moving pins will certainly lead to multi-note unisions, a tell-tale sign. Old pianos that haven't been tuned for decades will also go 1/2 tone flat or more without tuning pins slipping. Pin slipping is only happening in pianos with pinblock problems, etc.

In general, pianos go out of tune because of expansion/contraction of the plate, soundboard, and wire, not because of pin movement.


You seem very sure. To my mind, if a piano goes out of tune purely by expansion and contraction, then surely it would average out over time, and so not result in a general drop in pitch.
How can you account for the reduced tension needed for the pitch to drop continually over time?

The strings stretching is the only other possibility, and yes, I'd imagine this could simply be the answer. But do strings continue to stretch under a constant tension? My physics isn't up to answering, nor can my experience give me an answer.

I would disagree that the pins moving would lead to multi-note unisons. This is the case when the pins are actually too loose to hold a tuning. But the movements I am imagining are tiny, micro-movements, of the same size as the smallest possible pin movement we can make as tuners.

I imagine the friction between the pin and its hole to be a lot greater than the rotating force on the pin produced by the tension on the string. This is necessary for a piano to stay in tune. But with changes in humidity, there will be sudden movements around this hole as the wood swells or shrinks, and has to take up a new position around the more solid pin. As there is a constant rotating force on the pin, I would say that as the hole moves, the pin will creep around in the direction of the force, lowering the pitch.

As I say, this is what I imagine could happen, and I have no evidence for this. But I am not so sure that pitch dropping can be explained just by string stretching alone in pianos which have reached their 'stable' period.

Does anyone have evidence to support or refute this assertion? I'd be really interested to know if anybody has researched this!
I mentioned above and will try to paraphrase here....

Has anyone ever thought about trying to find out what makes a piano go flat over time? For example, take a Baldwin piano (either a Hamilton or a mid-size grand like an L or SF10) in a place like CO, NM, UT, AZ, or parts of CA or NV that's lived there all its life and is old enough to have settled and the board to have lost some crown, but not so old the pinblock is starting to go. (Optionally install a DC system, then) Have a few CTEs agree on the best tuning for that piano. Then, neglect tuning it until it's a full step ("A" sounds like G) or two ("A"=F) flat, periodically measuring the various things that are suspected to cause a piano to go out of tune.

So who's up for that project? laugh
Posted By: Chuck Littau Re: Why does a piano go out of tune? - 07/04/11 04:59 PM
There are three main enemies of piano health:

1) Humidity Swings
2) Lack of Professional Service
3) Poor quality parts

If the home environment, equaled that of an environmentally controlled laboratory ~ the customer’s piano would rarely need tuning.

Without a doubt pianos with loose tuning pins will not hold tuning as well as pianos with tight tuning pins, but what caused the pins to loosen. I contend it was the humidity swinging back and forth that almost always causes pins to loosen.

On my website I have written four short articles dealing with "Humidity & Pianos" I think every piano owner would benefit from reading them.
Posted By: meadpiano Re: Why does a piano go out of tune? - 07/04/11 07:28 PM
I think it is at least partly due to gentle string stretching. The reason I say this is because I tuned a small Kawaii grand that I had tuned a year prior. The interesting thing was that every time the string gauge changed the amount the string was off by a different amount. So if in the treble were the gauge stays the same for a time each note of a certain gauge was off on average the same amount. This was really just something I realized by ear since I do not use a device. The gauges were marked on the bridge instead of the plate which made it easier for me to correlate this. I think I will take a laptop and watch tunelab and get some numbers to see if I am right next time. I really don't know exactly what would cause this and I don't know if it is a common occurrence either. But I think it could be the difference in the gauges allows different stretch rates?
Posted By: Loren D Re: Why does a piano go out of tune? - 07/04/11 08:16 PM
Any string under any amount of tension is in an unrelaxed state, which I would think would want to return to a relaxed state (would want to return to 0 tension). How much physics are required to think that 230 or so strings pulled to pounds and pounds of tension would, over time, stretch?

Did you ever tune a piano and come back a year later to find a bunch of unsions nearly clean, but 10 cents or so flat? Is it likely that all three strings of those unisons turned the precise amount necessary to have each string land so that the unison is nearly clean?

I guess if you want to conduct a 20-year experiment to be sure, that's fine, but isn't it pretty obvious that the strings are stretching?
Posted By: BDB Re: Why does a piano go out of tune? - 07/04/11 11:31 PM
Stretching is asymptotic. It happens a lot when the strings are new and very little thereafter. If the piano is not tuned enough at first, it will go way out of tune from stretching, but not otherwise. After 4 or 5 years, it is not a factor.

Keith's description of what is basically entropy is more likely to be the reason a well-tuned piano goes flat with time.

Around here, the weather is fairly constant all year long, and pianos can stay not just close to pitch, but close to tune for a long time, bad tuners and gremlins notwithstanding.
Posted By: Phil D Re: Why does a piano go out of tune? - 07/04/11 11:45 PM
Originally Posted by BDB
Stretching is asymptotic. It happens a lot when the strings are new and very little thereafter. If the piano is not tuned enough at first, it will go way out of tune from stretching, but not otherwise. After 4 or 5 years, it is not a factor.


I agree with this. If the strings continued to stretch, then they would very quickly approach their breaking tension if repeatedly tuned, as the metal thins out as it stretches. This does not seem to happen.

Quote
Keith's description of what is basically entropy is more likely to be the reason a well-tuned piano goes flat with time.


Entropy is the general description for what happens. I would still assert that if the strings are not stretching, then it is necessary for either the pins to turn, or for the entire piano to gradually deform over time. As the latter does not happen in any particular consistent direction (the piano does not gradually fold up over time), then it must be the pins moving.
Posted By: BDB Re: Why does a piano go out of tune? - 07/05/11 12:03 AM
You might expect each string to be struck by a cosmic ray every so often, causing a force on the tuning pin to turn a nanosecond or so, and this would happen pretty much on a regular basis causing the piano go flat fairly evenly across its range over a few eons. Or it may happen faster than that, due to random changes in how tightly the pin block grips. In any case, I aim for some sort of logic in string tensions when stringing to minimize the effect.
Posted By: Gadzar Re: Why does a piano go out of tune? - 07/05/11 01:22 AM
For making a string stretch, we have to put it under a tension greater than its ellastic limit.

But, the piano is designed to never surpass this limit.

So, strings do not stretch, they only flex at the bearing points, and this flexion is what changes the tension of the string. That's why new strings and new pianos detune more often that old strings.

If the tension of the string is not even across all the bearing points then a small movement from the soundboard, due to a change in the humidity, can detune a string, and when the humidity returns to what it was before, the string remains detuned.

That's why a Dampp Chaser stabilizes tuning.

The deformation of the cast iron plate, due to changes in temperature, are so small that they can not detune strings. The strings themselves have a greater dilatation coeficient than the plate and a change in temperature is able to detune the string, not because it changes its length by two centimeters or so but because a little change in length becomes a considerable change in tension.

What detunes the piano, assuming it has a good pinblock able to hold the tuning pins and the tuner did a good job setting the pins and rendering the strings, is:

1. Changes in humidity that deform the soundboard.
2. Playing the piano, which make the string's tension to become even across the bearing points.
3. Deformations of the strings at the bearing points (in new strings).



Posted By: Loren D Re: Why does a piano go out of tune? - 07/05/11 11:26 AM
All stringed instruments begin going out of tune the minute you tune them. I can't for the life of me figure out why they'd be waaaay out of tune 10-20 years after a tuning.
Posted By: Emmery Re: Why does a piano go out of tune? - 07/05/11 02:03 PM
Originally Posted by Gadzar
For making a string stretch, we have to put it under a tension greater than its ellastic limit.

But, the piano is designed to never surpass this limit.

So, strings do not stretch, they only flex at the bearing points, and this flexion is what changes the tension of the string. That's why new strings and new pianos detune more often that old strings.

If the tension of the string is not even across all the bearing points then a small movement from the soundboard, due to a change in the humidity, can detune a string, and when the humidity returns to what it was before, the string remains detuned.

That's why a Dampp Chaser stabilizes tuning.

The deformation of the cast iron plate, due to changes in temperature, are so small that they can not detune strings. The strings themselves have a greater dilatation coeficient than the plate and a change in temperature is able to detune the string, not because it changes its length by two centimeters or so but because a little change in length becomes a considerable change in tension.

What detunes the piano, assuming it has a good pinblock able to hold the tuning pins and the tuner did a good job setting the pins and rendering the strings, is:

1. Changes in humidity that deform the soundboard.
2. Playing the piano, which make the string's tension to become even across the bearing points.
3. Deformations of the strings at the bearing points (in new strings).



Rafael, the condition that causes new strings to deform under tension is called "creep". The rate at which this deformation occurs is dependant of the material properties, exposure temperature, exposure time and the applied structural load. It has nothing to do with the bending or flexing at the bearing points.

http://en.wikipedia.org/wiki/Creep_%28deformation%29

Some techs will "massage" new strings with rollers or rubbing vigourously back and forth with pressure using leather thinking that they are pre-stretching the string to reduce the occurance of creep. The fact is that this process merely helps seat the string better and does not stretch the string or accelerate the creep process. The pressure applied is nowhere near the elastic limit of the string, nor does the temperature from rubbing get anywhere near the melting point.

Techs still go through the process thinking they are somehow circumventing scientific fact, which they are not. I re-strung a piano a few years back and purposely massaged and rollered every second octave and left the others alone. On all my subsequent visits there was no difference between the amounts that the piano dropped in pitch between the octaves. (I do lightly tap down all the strings with a brass punch to make sure they are firmly seated into the bridge and its pins).
Posted By: Phil D Re: Why does a piano go out of tune? - 07/05/11 07:02 PM
Creep! Thank you Emmery, finally someone who knows enough about the physics to make an informed description of the process involved.

There's a discussion about it here http://www.physicsforums.com/archive/index.php/t-230039.html

What I'd be interested to see is how much creep is needed to produce a semitone drop in pitch. (You wouldn't believe it, but I have a mathematics degree. Statics was never my strong point... ;))
Posted By: partistic Re: Why does a piano go out of tune? - 07/05/11 09:30 PM
Originally Posted by Withindale

Question. When a piano hasn't been tuned for many years can the pins become more difficult to move and is there a greater risk of damaging the block?

Ian


They feel alright to me, they aren't loose or too tight. I don't think there is a greater risk of damaging the block.
Posted By: BDB Re: Why does a piano go out of tune? - 07/05/11 09:53 PM
The risk is in breaking strings. Oxidization at pressure points can make the string weaker and adhere at contact points, so there can be disproportional tension that can cause the strings to break. Old strings that have not been tuned in a long time tend to break at the coil, where the string has rusted to the pin, and the tension builds between the coil and the pressure bar or agraffe.
Posted By: meadpiano Re: Why does a piano go out of tune? - 07/05/11 10:32 PM
Originally Posted by Phil D
Creep! Thank you Emmery, finally someone who knows enough about the physics to make an informed description of the process involved.

There's a discussion about it here http://www.physicsforums.com/archive/index.php/t-230039.html

What I'd be interested to see is how much creep is needed to produce a semitone drop in pitch. (You wouldn't believe it, but I have a mathematics degree. Statics was never my strong point... ;))


Thanks for the link I think it helps a lot! I actually live close to Mapes string and I assume the person under that name is from there. I will have to talk to the owner and see what he says about 'creep' or 'relaxation' of piano wire. I do know he was telling me one day about how piano wire loses its elasticity to an extent somewhere around 50-100 years under normal use. Hence the change in tone even on pianos that the wire has not corroded. I do not disbelieve that wrest pins can move but surely they can't all move so evenly.

Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/06/11 03:07 AM
Originally Posted by partistic

Is the stretching of the strings the only dominant factor that causes pianos to go out of tune in the long term?

The Strings only theoretically sprawl. Reality such sprain strings not vastly and does not influence upon climbing down sound. I assume dominant factor it is a healthy pinblock and good pins.
Posted By: partistic Re: Why does a piano go out of tune? - 07/06/11 08:23 PM
Here is a quote from the link posted before:

Quote

This was the case around the middle of the 20th century, but creep is quite well understood today: it is the time-dependent deformation of materials under stress, as brewnog stated.

Inkling, your guess about creep deformation is exactly right. There are several ways creep can occur, and they all involve diffusion. Generally, the bonds between the iron atoms in your piano string occasionally break and re-form due to random thermal energy. Any atomic rearrangement that lets the string be longer is favored because you are pulling on it so hard. Eventually, the lengthening of the string is noticeable.

Creep strictly occurs in all loaded materials above 0K. It is usually negligible in steel at room temperature, but you've found an exception, because the stress is large and the sensitivity of your detector (the human ear) is very good for detecting out-of-tune strings.

One of my professors liked this trick question: which creep mechanism [there are several, including bulk diffusion, grain boundary diffusion, and dislocation climb] is active in material xx at yy°C? The answer is always all of them (they just might be negligible).


I guess the question is how much does steel creep compared to wood. They both are under tension and the wood should also creep due to the constant tension that is applied for a long time in a constant direction. Couldn't find any information on the internet about the creep rates at low temepratures and no one probably hasn't done a long term study on a neglected piano either.

Oh well.
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/07/11 01:44 AM
Originally Posted by partistic
Here is a quote from the link posted before:

Quote

This was the case around the middle of the 20th century, but creep is quite well understood today: it is the time-dependent deformation of materials under stress, as brewnog stated.

Inkling, your guess about creep deformation is exactly right. There are several ways creep can occur, and they all involve diffusion. Generally, the bonds between the iron atoms in your piano string occasionally break and re-form due to random thermal energy. Any atomic rearrangement that lets the string be longer is favored because you are pulling on it so hard. Eventually, the lengthening of the string is noticeable.

Creep strictly occurs in all loaded materials above 0K. It is usually negligible in steel at room temperature, but you've found an exception, because the stress is large and the sensitivity of your detector (the human ear) is very good for detecting out-of-tune strings.

One of my professors liked this trick question: which creep mechanism [there are several, including bulk diffusion, grain boundary diffusion, and dislocation climb] is active in material xx at yy°C? The answer is always all of them (they just might be negligible).


They both are under tension and the wood should also creep due to the constant tension that is applied for a long time in a constant direction.


The Interaction by steels and tree certainly there is. But it measly in contrast with to the constant tension in wooden pinblock.
Posted By: Gadzar Re: Why does a piano go out of tune? - 07/07/11 05:02 AM
Emmery,

According to the article referred by you, "creep" is not possible on piano strings under normal operating conditions, because of the normal range of a piano's temperature:

"The temperature range in which creep deformation may occur differs in various materials. For example, tungsten requires a temperature in the thousands of degrees before creep deformation can occur while ice will creep near 0 °C (32 °F).[1] As a rule of thumb, the effects of creep deformation generally become noticeable at approximately 30% of the melting point (as measured on a thermodynamic temperature scale such as kelvin or rankine) for metals and 40–50% of melting point for ceramics. Virtually any material will creep upon approaching its melting temperature. Since the minimum temperature is relative to melting point, creep can be seen at relatively low temperatures for some materials. Plastics and low-melting-temperature metals, including many solders, creep at room temperature as can be seen markedly in old lead hot-water pipes. Glacier flow is an example of creep processes in ice."

From this I may believe that creep in iron at ambient temperature has no noticeable effects. 30% of the melting point of iron is over 500 °C.

And of course, when you "massage" a new string, its pitch changes because you bend the string at the bearing points. That's what I do every time I replace a string, and the drop in pitch after "massaging" is, in all cases, dramatic and immediate.

New strings drop in pitch in a few minutes, it is not a long term deformation due to creep.


Posted By: Emmery Re: Why does a piano go out of tune? - 07/07/11 12:58 PM
Rafael, temperature is only ONE factor in the process and is not exclusive of all the others. It simply effects the rate of creep, not the fact that it occurs or not. If the strings are under tension (below the elastic limit of plastic deformation) and exposed to much higher temperatures, the rate of creep (in the entire string) increases in the time line, thats all. At room temperature, the time line increases to the 1-2 year period we commonly see in newly strung pianos.

The lowering of tension that we experience to varying degrees from massaging a newly applied string is dependent on how well the string was initially formed around the hitch pins and other fixed points that cause angular change in the string. We must form the string well beyond 180 degrees (and beyond its elastic limit)on a hitch pin in order to get it to sit in a relaxed state close to 180 degrees (its actually slightly less than 180). These points are the only areas where plastic deformation occurs because of compression on the inside radius and expansion on the outside radius of the string. The small fulcrum point multiplies the tensile load over the elastic limit in this tiny area much like a lever has a mechanical advantage.

Because only the outside radius deforms by elongation, the entire process cannot be defined as "stretching". The inside (smaller) radius correspondingly compresses and the entire process would best be called a "multi directional deformation". Also, since this deformation is limited to probably less than a few percent of the entire string length and certainly not the areas we massage, it is incorrect to think we are "stretching" the string.

The three mechanisms of creep are:
- Diffusional flow
- Dislocation slip and climb
- Grain boundry slide

One of the theories about how creep effects the entire string length under tenion is that some atoms randomly dislocate in the crystaline lattice and realign in a more relaxed location. This does defy the accepted law that states the material must exceed its minimal shear stress level to do so, but so far nobody knows exactly how it happens.

I must add that the more a string drops in tension in a short period of time after stringing it is a proporional indication of how poorly its angular change and shape deformation conforms to the fixed points it contacts. Bend a string around a hitch pin aprox 220 degrees prior to stringing and another string only 180. The latter one will exihibit a slight bow from the tangent point off the pin when brought to tension and will eventually drop in tension more than the other.



Posted By: Emmery Re: Why does a piano go out of tune? - 07/07/11 02:50 PM
I want to point out in regards to "creep" that one must be careful of what type of definition one uses. As a rule, creep is often defined specifically as the creep rupture strength, i.e. the stress that causes rupture after 10 000 or 100 000 hours (Rkm 10 000 and Rkm 100 000). Creep however does occur in lesser amounts for high carbon steel and can be measured from room temperature right up to about 550-600 deg C rupture point. Engineers must account for creep in steel cable structure designs such as suspension bridges ect..., both for the steel cables and the for the materials they anchor to in order for them to remain within parameters of specified tension over long periods of time. These cables are not exposed to the highly elevated temperatures to induce rupture, but they still exhibit enough long term creep for engineers to design an adjustment to the initial tension to compensate. Piano strings exhibit the same type of long term creep as these cables do.
Posted By: UnrightTooner Re: Why does a piano go out of tune? - 07/07/11 03:27 PM
Huh! Reminds me of when we would order new stays made of wire rope for the masts. It was best to subtract a foot or two in addition to what was needed for the turnbuckle. Some chain would be added to make up the difference. Then when the turnbuckle ran out of adjustment, some of the chain could be removed to give the turnbuckle more adjustment. If you didn't do this, you needed to get new stays the next year because they were too slack to support the mast. damhik
Posted By: Emmery Re: Why does a piano go out of tune? - 07/07/11 04:49 PM
Actually there are several different methods I've seen for properly seating and forming the small bends on the string. A tech I know who apprenticed in a European piano factory told me it was frowned upon where he worked to roller or rub the strings after installing. They overbend on the hitch pin exactly the right amount to form a near perfectly conforming radius, then they put enough tension on the string to remove slack, and with a brass hook they yank the string at bridge pins and other fixed transition points at a greater angle then they normally take. Additional strikes with the right force and direction using a notched brass punch takes care of the other transition areas. It does the same thing that the rollering does and takes much less time and labour to do so. They also took individual string loops and preformed the radius with tension on jig using a slightly undersized pin. When released it sprung back and the contact point radius was properly sized for a regular pin.

The more the piano drops in pitch immediatly from rollering indicates a poorer conformity to these fixed points of contact in the first place. Thats how they seen it, and I tend to agree. The other reason they prefer this to massaging the string afterwards is that repetitive flexing and bending to a greater magnitude then the string normally vibrates, work hardens the string and makes it more brittle in that area. It could dull or change the tone a bit and could shorten the strings' lifespan. I'm not sure if the lifespan issue is valid since you would have to sit around for 50-100 years to find out but theoretically it makes sense.
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/08/11 01:22 AM
Originally Posted by Gadzar
Emmery,



From this I may believe that creep in iron at ambient temperature has no noticeable effects. 30% of the melting point of iron is over 500 °C.

The String changes their own characteristic under plastic deformation only. However this does not occur at moment of (its) pull. Springy deformation not in count.
Posted By: Gadzar Re: Why does a piano go out of tune? - 07/08/11 08:04 AM
So, strings elongate the first and/or second years and then they stop creeping?

What about strings that are 100 years old?

I really think that creep is not an issue in piano strings.

Posted By: Emmery Re: Why does a piano go out of tune? - 07/08/11 03:29 PM
Originally Posted by Gadzar
So, strings elongate the first and/or second years and then they stop creeping?

What about strings that are 100 years old?

I really think that creep is not an issue in piano strings.



No, as long as they remain under tension they don't ever stop the cycle of random atoms breaking the link (slip mechanics)and reforming, its just that it is a non linear process in some materials. With piano strings one must factor in that the material does not remain the same in regards to hardness through its life. Billions of accumulated vibrations will work harden the string over time.

100 year old strings typically end up more brittle from work hardening. Take a very old used piano string and a new one (same diameter)and bend back and forth (90 degrees) between two pliers and you will find the old one snaps in half much sooner because it has become work hardened.

I only mentioned creep in regards to tuning stability because it is factually wrong to imply you are stretching or permanently elongating a string by rubbing or rollering it...it defies several laws of physics. The causes of pitch dropping in this case are because bowed angular deflections are straightened and the strings radii become more perfectly matched to the surfaces they contact. It is also possible that contact surfaces could become flattened a bit also.

As a side note, many things are designed and implimented taking creep into account. The power lines you see strung between poles are properly tensioned based on sag and compensated for by calculated long term creep formulas. This is done to avoid the likelyhood of Aeolian vibration.

Posted By: Gadzar Re: Why does a piano go out of tune? - 07/08/11 04:53 PM
I agree with that. The pitch drop is due to the angular deflections being straightened and not because the steel has stretched.

Posted By: Loren D Re: Why does a piano go out of tune? - 07/08/11 06:42 PM
Entropy.
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/11/11 04:23 AM
Originally Posted by Emmery
Originally Posted by Gadzar




The power lines you see strung between poles are properly tensioned based on sag and compensated for by calculated long term creep formulas.

I agree with Emmery.
Posted By: partistic Re: Why does a piano go out of tune? - 07/11/11 02:46 PM
Originally Posted by Gadzar
I agree with that. The pitch drop is due to the angular deflections being straightened and not because the steel has stretched.



The angular deflections can only straighten out over time because the string stretches or creeps. It doesn't straighten out immediately, but it creeps under the constant force.

EDIT: I should have said by stretching and creeping or compressing. Probably both happen over time as the string takes a shorter path around a turn.
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/12/11 03:48 PM
Originally Posted by partistic
[quote=Gadzar]I agree with that. The pitch drop is due to the angular deflections being straightened and not because the steel has stretched.

but it creeps under the constant force.

More exactly say that string has a very small changes. Iron structure is not changes because of constant power load
Posted By: Mario Bruneau Re: Why does a piano go out of tune? - 07/12/11 07:15 PM
Hi,

My take on this is that the piano goes out of tune mostly because of its wood components and not because of the metal either it be the plate or else.

So tuning shift is due (IMHO) to the added thickness of the maple bridge and spruce soundboard

[Linked Image]

When losing its humidity, wood retracts so the 5 centimeters total thickness of the bridge and the soundboard shrinks in volume thus releasing the string tension. The piano’s pitch goes down. On the opposite, the 90% to 100% humidity encountered during the summer will expand the thickness of the bridge and soundboard so the string tension is raised. The piano’s pitch goes up.

Because it lose more tension during the winter than it gain tension during the summer, the piano needs to be tuned each years. After two years without tuning, a piano will most likely need two tunings to bring it back to standard pitgh (A-440Hz). Contrary to popular belief, a piano that is as low as a semitone can be put back to pitch with only two tunings and the famous 24 hours delay between the two tunings is unnecessary. We must then consider the 20 tons of tension and understand that the firsts strings which tension was increased will become looser as we increase the tension of the other strings, since each string acts as a clamp.

To compensate this clamp effect, the first tuning will be higher than the target pitch of A=440. We will start with the basses at 442Hz and the middle region will get a 443Hz tuning and gradually progressing the highest strings that will be tuned to 445Hz and higher. After this first tuning, guest what? The piano will be at 440Hz throughout its entire length but wont be perfectly tuned yet. Only with the second tuning executed the regular way, that one can achieve perfection because the 20 tons of tension wont be altered that much anymore.

Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/13/11 04:06 AM
Originally Posted by Mario Bruneau

[Linked Image]

When losing its humidity, wood retracts so the 5 centimeters total thickness of the bridge and the soundboard shrinks in volume thus releasing the string tension.


The basic reason why piano loses the tone out?
The imperfection how made piano (the imperfection pin-string. Pressure, moisture, temperature must not essential image be reflected on tuning
Posted By: Gadzar Re: Why does a piano go out of tune? - 07/13/11 04:44 AM
I tune pianos year after year, and every time season changes from humide to dry and visceversa pianos go out of tune.

You only have to install a Dampp Chaser system to see how the tuning of a piano gets stable.

Changes in the humidity affect the tuning of a piano in less than one month and by 10 to 30 cents in pitch. That is much more than you can suspect from creep in the steel of strings.

Am I talking with professional piano tuners here?

From your experience in maintaining pianos you should know what I say. This is not high tech, this is all days routine work.



Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/13/11 08:17 AM
Couldn't agree with you more Gadzar ...... If you can stop changes in humidity then tuning becomes nothing more than tidying up the odd unison and octave. I often have to tune a Steinway D that is housed in a picture gallery that is constantly controlled for temperature and humidity ( because of the priceless paintings ) and it never needs more than a few tweeks here and there. Creep, and stretch accounts for very little instability after the first couple of years of a piano being strung.
Posted By: Maximillyan Re: Why does a piano go out of tune? - 07/13/11 09:59 AM
Originally Posted by Johnkie
Creep, and stretch accounts for very little instability after the first couple of years of a piano being strung.

Bravo, Johnkie! Much briefly, capacious and essentially
Posted By: Bill McKaig,RPT Re: Why does a piano go out of tune? - 07/13/11 04:00 PM
Humidity changes and creep are two different events. Creep is most evident in the first couple of years depending on use and then decreases considerably. The affects of humidity start on day one and continue for the life of the piano.
Posted By: Emmery Re: Why does a piano go out of tune? - 07/13/11 06:01 PM
Sometimes humidity can be totally driven away with extreme heat, such as this...

[Linked Image]
Posted By: DoelKees Re: Why does a piano go out of tune? - 07/13/11 07:17 PM
Originally Posted by Gadzar
Changes in the humidity affect the tuning of a piano in less than one month and by 10 to 30 cents in pitch. That is much more than you can suspect from creep in the steel of strings.

But why does the overall pitch of a piano drop if not tuned for several years? A related question: if the humidity and temperature is controlled does the overall pitch still go down slowly over the years?

Kees
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/13/11 07:37 PM
I've known many pianos that have not moved away from their pitch having not been tuned for 10 years or more. These are examples of instruments that been tuned both properly and regularly over the first few years, when the strings are most prone to stretch and the bridges and soundboard are undergoing settling compression, and where the humidity has been kept in check. Any serious drops in pitch are always associated with either improper tuning techniques or wild changes in humidity/temperature. Stretch or "creep" has very little to do with pitch change after the initial first couple of years. If pianos could be kept in a constant humidity and temperature ...... we'd all be pretty much out of work though frown
Posted By: partistic Re: Why does a piano go out of tune? - 07/13/11 07:45 PM
Originally Posted by Gadzar
I tune pianos year after year, and every time season changes from humide to dry and visceversa pianos go out of tune.

You only have to install a Dampp Chaser system to see how the tuning of a piano gets stable.

Changes in the humidity affect the tuning of a piano in less than one month and by 10 to 30 cents in pitch. That is much more than you can suspect from creep in the steel of strings.

Am I talking with professional piano tuners here?

From your experience in maintaining pianos you should know what I say. This is not high tech, this is all days routine work.





10 to 30 cent differences in pitch in a month after the season changes, I agree, happens. However they should not add up over several changes in seasons, as the piano structure would have to be collapsing for that to happen.

I agree the strings don't just start actively stretching one month. It must be the humidity and temperature having their impact on the wood, changing the crown, the exact positioning of the bridges maybe etc. But how long can it keep going like that? Over 30 cents?

In the short term I absolutely agree weather has an effect, but I am trying to figure out what happens in the long term.

I am not a professional piano tuner.
Posted By: Gadzar Re: Why does a piano go out of tune? - 07/14/11 03:42 AM
Originally Posted by Johnkie
I've known many pianos that have not moved away from their pitch having not been tuned for 10 years or more.


That is what I believe.

If the pinblock is in good condition, the strings are not new, and the tuner did a good job in setting the tuning pins and rendering the strings, then the piano will hold its pitch for years, even with seasonal changes in humidity and temperature.

Of course it will get out of tune and sharper in the humid season and flatter in the dry season, but the average pitch will be stable through the years.

Posted By: Mark R. Re: Why does a piano go out of tune? - 07/14/11 08:08 AM
The fact that a soundboard which undergoes many humidity cycles eventually cracks, shows me that the cycle of shrinking and swelling (losing crown and re-gaining crown) is not completely reversible. The structure of the wood fibres/cells is eventually crushed. This would suggest to me that if a piano is tuned to 440 Hz in summer, e.g. 65% RH, and drops pitch in winter, e.g. 35% RH, it would'nt quite get back to 440 Hz the next summer, because the re-swelling under load has compressed the soundboard fibres ever so slightly. (Mario Bruneau already alluded to this).

2 cents from another person who is not a professional tuner.
Posted By: Chris Leslie Re: Why does a piano go out of tune? - 07/14/11 10:59 AM
Mark R

Can you explain why you suggest that soundboard swelling cycles, cracking and crown loss due to humidity cycles will cause the pitch to change.
Posted By: UnrightTooner Re: Why does a piano go out of tune? - 07/14/11 11:01 AM
Originally Posted by Mark R.
The fact that a soundboard which undergoes many humidity cycles eventually cracks, shows me that the cycle of shrinking and swelling (losing crown and re-gaining crown) is not completely reversible. The structure of the wood fibres/cells is eventually crushed. This would suggest to me that if a piano is tuned to 440 Hz in summer, e.g. 65% RH, and drops pitch in winter, e.g. 35% RH, it would'nt quite get back to 440 Hz the next summer, because the re-swelling under load has compressed the soundboard fibres ever so slightly. (Mario Bruneau already alluded to this).

2 cents from another person who is not a professional tuner.


That is what I have noticed, too. And I think a soundboard can get to the point where there is no "life" left to it: where changes in humidity make very little changes in the board's crown.
Posted By: Withindale Re: Why does a piano go out of tune? - 07/14/11 12:41 PM
Originally Posted by Mario Bruneau


So tuning shift is due (IMHO) to the added thickness of the maple bridge and spruce soundboard

[Linked Image]


Because it lose more tension during the winter than it gain tension during the summer, the piano needs to be tuned each year


Originally Posted by Mark R
...the cycle of shrinking and swelling (losing crown and re-gaining crown) is not completely reversible.


Mario, Mark, All

Does Mark's suggestion that the cycle of shrinking and swelling is not completely reversible explain Mario's point that there is more loss of tension in the winter than gain in the summer?

Does movement in the crown add to changes in the thickness of the maple bridge and spruce soundboard?

Are there any other ways humidity can affect the tension in the strings? For instance through the back frame and pin block in an upright?

Ian

PS Pianos need tuning after moving, presumably because the positions of the parts are slightly disturbed. Can temperature and humidity fluctuations over time have a similar effect, beyond their effects on the soundboard?
Posted By: Mark R. Re: Why does a piano go out of tune? - 07/14/11 03:09 PM
Originally Posted by Chris Leslie
Can you explain why you suggest that soundboard swelling cycles, cracking and crown loss due to humidity cycles will cause the pitch to change.


OK, I'll try. But this is my understanding as a non-pro, so anyone is welcome to correct me.

Firstly: to be clear, I'm speaking of compression-crowned soundboards. I'm not sure whether this logic would apply to rib-crowned soundboards as well. I would imagine that it applies to any soundboard which has its grain running perpendicular to the ribs.

So this is my logic:

At higher humidity, the soundboard absorbs some extra moisture. Wood swells almost exclusively perpendicularly to the grain. Hence, the soundboard expands in the longitudinal direction of the ribs. But the ribs remain roughly the same length, because wood hardly expands along the grain. This results in tension on the ribs, and compression on the soundboard, i.e. increased (compression) crowning, which in turn results in a higher pitch.

At lower humidity, the SB loses some moisture and shrinks slightly, resulting in a slight loss of crown, and correspondingly lower pitch.

If the SB panel could withstand this cycling without taking harm, then it wouldn't crack. But the fact that it does crack tells me that at times of high humidity, the wood fibres are actually compressed irreversibly. Then, when humidity falls, the SB panel is actually too small for the ribs. This puts the SB under tension (at least locally), and the ribs under compression, and hence a crack forms in the SB.

Each period of high humidity (high crown) does a bit of irreversible fibre damage, resulting in a slight loss of crown compared to the previous year. Therefore, the pitch this summer is also not quite where it was last summer.

Once the SB is so compression-damaged that no further damage is done by high humidity, I would imagine (this is conjecture!) that the pitch would finally become stable from year to year.

Again, all of this is just a layman's understanding. I'm not a pro, and gladly stand corrected.
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/14/11 07:29 PM
When a soundboard developes cracks, it's because it has shrunk enough for the crown to flatten completely, sending it concave instead of convex. Once this happens the grain of the wood is pulled apart (causing the split(s)). The ribs keep the soundboard from total collapse under the emmense pressure of the string tension, but the tuning stability is totally lost. Instead of the soundboard being a solid mass where the grain is compressed, it becomes like a springboard. The only way to cure this is to remove the strings, and insert fillets of spruce having first restored the "crown" by applying sufficient force from underneath the soundboard.
Posted By: BDB Re: Why does a piano go out of tune? - 07/14/11 08:09 PM
Quote
When a soundboard developes cracks, it's because it has shrunk enough for the crown to flatten completely, sending it concave instead of convex.


No, that is not the reason. A soundboard develops cracks because the cross-grain motion due to moisture cycling is constrained by the ribs. You could take a perfectly flat board and glue ribs across its grain, and with enough moisture cycling, it will crack. Whether there is a crown or not is immaterial.
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/14/11 09:38 PM
With the greatest respect BDB - The whole reason for a soundboard having a crown is so that the grain is subjected to a huge amount of compression - this compression makes it virtually impossible for cracks to appear and also adds to the sound transference properties. Of course a flat board will split .... it's not under compression, and likewise a soundboard that has lost it's crown will split because it's grain will be torn apart by the down force exerted by the tension of the strings. Your statement that "Whether there is a crown or not is immaterial" is utterly wrong I'm sorry to say.
Posted By: BDB Re: Why does a piano go out of tune? - 07/14/11 10:41 PM
You can read just about any woodworking book written in the past 30 years and you will find what I wrote.

You can also go argue with Del Fandrich about whether soundboards should be compressed or not.

It does not matter to me. I have a good formula for Grem-B-Gon!
Posted By: Chris Leslie Re: Why does a piano go out of tune? - 07/14/11 11:43 PM
Thanks Mark R for your detailed description. I am trying to imagine and conjecture a long term process in my mind with little experience or knowledge about the material behavior, but the interplay between ribs and soundboard under the conditions is a bit unclear to me.

BDB, If a soundboard has no crown then what will stop the string compression on the bridge from pushing the soundboard and ribs downwards and tearing the soundboard apart as Jonkie said, and shearing from the ribs?
Posted By: BDB Re: Why does a piano go out of tune? - 07/15/11 12:11 AM
You should ask that to manufacturers that use reverse-crown soundboards. Rippen is out of business, but I think there are others these days.
Posted By: UnrightTooner Re: Why does a piano go out of tune? - 07/15/11 11:05 AM
Originally Posted by Johnkie
With the greatest respect BDB - The whole reason for a soundboard having a crown is so that the grain is subjected to a huge amount of compression - this compression makes it virtually impossible for cracks to appear and also adds to the sound transference properties. Of course a flat board will split .... it's not under compression, and likewise a soundboard that has lost it's crown will split because it's grain will be torn apart by the down force exerted by the tension of the strings. Your statement that "Whether there is a crown or not is immaterial" is utterly wrong I'm sorry to say.


...this compression makes it virtually impossible for cracks to appear...

And yet they do appear. Your explanation is incomplete unless it includes the reasons for cracking. Like which comes first, loss of crown or appreance of cracks, and why?
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/15/11 11:05 AM
Perhaps the big names in piano manufacture should revise their designs of soundboard technology so that their instruments become as good as Rippen ! Oh hang on a minute though ..... weren't Rippon piano's so bad that everyone regretted buying one? I also wonder why the design of all string instruments have crowns on both the back and belly when it would be such a good idea to not have a crown and watch the instruments weaken and tear the grain apart. The idea of "reverse crown" is cloud cuckoo land.
Posted By: Bill McKaig,RPT Re: Why does a piano go out of tune? - 07/15/11 03:16 PM
Johnkie, I have to disagree with your concept of how cracks are formed. Using Steinway as an example, they dry their boards down to about 4% moisture content. That is just about the driest you can get a piece of wood. Then they glue on straight ribs and allow the board to return to normal moisture content. The board swells and creates the crown (being bound on one side). Even if the piano was in the desert, the sound board would not be dryer than the original 4%.

Cracks form when the board is subjected to high humidity. The board swells to the point to where the internal compression exceeds the elastic limit of the wood forming compression ridges. The wood in these ridges is crushed and when the humidity goes back down, a crack appears. The sound board may or may not still be functioning.
Posted By: Dan Casdorph Re: Why does a piano go out of tune? - 07/15/11 06:22 PM
I think its pretty rare to see an oil-canned soundboard in my area. Even cracked soundboard pianos are fairly close to pitch, usually, and I would expect an oil canned soundboard to result in a piano that is 3-400 cents flat.
Posted By: MU51C JP Re: Why does a piano go out of tune? - 07/16/11 11:09 AM
Thanks for that Bill - I totally agree with your point of view. I realise that minor cracks are due to crushing of grain fibers due to excessive humidity ...I was thinking more about the huge cracks (that you could post mail through) where the soundboard has completely lost any crown, leading to structural failure. In any case the fact remains that when a soundboard shrinks or swells, it will go wildly out of tune.
Posted By: partistic Re: Why does a piano go out of tune? - 07/18/11 06:12 PM
How much crown does a typical piano have? How much higher is the point where the strings pass over the bridge from the point in the same place when the strings would go in a straight line?

Then I could calculate how much losing all the crown would change the tension, length and diameter of the strings, and then also the pitch.
Posted By: UnrightTooner Re: Why does a piano go out of tune? - 07/18/11 06:30 PM
Crown and downbearing are two different things.
Posted By: partistic Re: Why does a piano go out of tune? - 07/18/11 06:44 PM
Could you elaborate? I guess what I mean is that how much the point where the strings attach to the bridge could lower.

Also, what would be an average speaking length and diameter to use for example for an A4 string? Speaking length is around 55 cm I think but I don't have anything to measure the diameter with.
Posted By: beethoven986 Re: Why does a piano go out of tune? - 07/19/11 03:15 AM
A PTG conspiracy so tuners can stay employed.
Posted By: antonZanesco Re: Why does a piano go out of tune? - 07/19/11 06:16 PM
if I may add to the portfolio , thank you.
the variations of building a board are numerous and the
results therefore are too.
the cracking has differnent reasons, depending on
climat, downbearing/tension, quality of wood/selection
etc.
england is a climat where boards swell easely and the
technicans have to deal with that in a very different
way then a technician in arizona.
I replaced a soundboard in a Knabe 120 years old
and was asked to see if I could copy the soft and velvety nature of this sound.
the ripps were crowned to 1cm !!! and the board was
was 7mm thin all around.
but the cracks were everywhere.
I replaced a board in a Ronish 125 years old and the crown was 4 mm and the board was 9 mm in the treble and
7 in the bass. in another grand the ripps were FLAT.
they have been glued with the prinicple of "one sided
gluing, which should have little downbearing.
the last one did not have cracks, but was 85 years old.
all boards had good material. even colored, grained etc.
seems like lots of tension will eventually take its
prisoner. i glued a board together with mateial from one log ! but had to replace on small section later
when I noticed a number of inperfections . the replacement board was 3 years less cured and cracked later.
just a few thoughts that could shed some light n the reasons of cracking soundboards. ( there are more ! )
Posted By: antonZanesco Re: Why does a piano go out of tune? - 07/19/11 06:41 PM
but their relation is essential !
Posted By: antonZanesco Re: Why does a piano go out of tune? - 07/19/11 06:46 PM
there are reasons and they vary from climat to climat.
a pdf file is available for serious tuners that have
their customers best interrest in mind.
Posted By: antonZanesco Re: Why does a piano go out of tune? - 07/19/11 06:50 PM
some big cracks occur close to the glue jonts which inticade too much pressure in the gluing process.
crushing the softer summer fibers.
Posted By: partistic Re: Why does a piano go out of tune? - 07/20/11 04:37 PM
If a string has a total length of 70 cm, 5 cm above the v-bar, 50 as the speaking length and 15 cm after the bridge, and the string goes over the bridge 1 cm higher (reasonable?) than it would if it would go in a straight line, then the overall length of the string would decrease by about 0,43 mm when it loses all downbearing. If the tuning pin's circumference is 2 cm, then losing the 1 cm downbearing should be equal to turning the tuning pin 0,43/20*360=7,74 degrees.

How much does turning the tuning pin 7,74 degrees change it's pitch?

Using Young's modulus and if the string's diameter is 0,85 mm and frequency is 440 hz, I get that the pitch would go 76 cents flat if the pin is turned roughly 7,74 degrees counterclockwise. Could that be believable or is that too much? How much turning of the pin would you guys say it takes to change the pitch of a note in the middle range by a semitone?
Posted By: UnrightTooner Re: Why does a piano go out of tune? - 07/20/11 04:58 PM
That may be about right as a ballpark figure. On bass strings, one third of a turn (120 deg) is about an octave. So around 10 deg per semitone if we are thinking linearly... So sure, 7.5 degrees might be something like 75 cents.
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