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Dart-shaped viola case?


thirteenthsteph
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12 hours ago, thirteenthsteph said:

Hello Mr Musafia, 

since this is my thread I'd like to say that what you are describing was more or less understood and I have no objection whatsoever, but the question was more along the lines of how much is this going to be a real-life problem for a careful user who takes care to not subject the instrument to any extremities of weather, in a hot car for hours, for example, rather say a small walk on a hot day?

Because even though it sounds like a huge risk, the vast majority of the users of these cases, that I'm aware of, seem to be perfectly happy and their instruments just fine. Of course, I can understand the benefits when the heat is extreme, there is no shade in which to leave the case, the humidity is 100%, etc., and it's definitely good to be prepared rather than cry if it actually ruins your instrument... But then again, a car could hit it, since we're talking of extreme scenarios.

 

 

Any abrupt change of relative humidity will stress the instrument, as it is made of hygroscopic material (wood). I don't have access to any statistics in the sense of probability of damage during a given time/range of change (you may wish to ask some of the qualified restorers who post here) but usually when seams open they do so under changing atmospheric conditions. This is exacerbated in antique instruments which are usually structurally more delicate.

Think of a case able to reduce the abruptness and the scope of the fluxuation temperature and relative humidity as a form of insurance. You might not need it, but you'll be happy if you do. 

Cheers!

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1 hour ago, Dimitri Musafia said:

Any abrupt change of relative humidity will stress the instrument, as it is made of hygroscopic material (wood). I don't have access to any statistics in the sense of probability of damage during a given time/range of change (you may wish to ask some of the qualified restorers who post here) but usually when seams open they do so under changing atmospheric conditions. This is exacerbated in antique instruments which are usually structurally more delicate.

Think of a case able to reduce the abruptness and the scope of the fluxuation temperature and relative humidity as a form of insurance. You might not need it, but you'll be happy if you do. 

Cheers!

Thank you for the answer. I hope some of the restorers you speak of notice this and post here so I don't have to go knocking on doors, so to speak.

What would you answer to another member's post a few pages back which says, and I quote 'What happens when you take the violin out of its case in another place?  The temperature and relative humidity change.  Rapidly.  It happens all the time, and there's nothing you can do about it, unless you can keep the instrument in air-conditioned, humidity-controlled spaces all the time..' ?

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42 minutes ago, thirteenthsteph said:

Thank you for the answer. I hope some of the restorers you speak of notice this and post here so I don't have to go knocking on doors, so to speak.

What would you answer to another member's post a few pages back which says, and I quote 'What happens when you take the violin out of its case in another place?  The temperature and relative humidity change.  Rapidly.  It happens all the time, and there's nothing you can do about it, unless you can keep the instrument in air-conditioned, humidity-controlled spaces all the time..' ?

My job is limited to make sure that those changes are slowed and reduced within the confines of the case only :-)

But if it's 106°F outside like in San Francisco last Friday, you will likely open up your case in a more hospitable environment than outdoors. Indoor controlled atmospheric conditions are the norm for museums which host important instruments, but I know of many people who keep their music room climate-controlled for this reason. My dad was a pianist, and he kept his two Steinways, a B and a D, in a climate-controlled studio, detached from the house, with radiant heating always set to the same level, not so much to keep the soundboards from cracking but to keep the pianos in tune!  

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4 hours ago, Dimitri Musafia said:

My job is limited to make sure that those changes are slowed and reduced within the confines of the case only :-)

But if it's 106°F outside like in San Francisco last Friday, you will likely open up your case in a more hospitable environment than outdoors. Indoor controlled atmospheric conditions are the norm for museums which host important instruments, but I know of many people who keep their music room climate-controlled for this reason. My dad was a pianist, and he kept his two Steinways, a B and a D, in a climate-controlled studio, detached from the house, with radiant heating always set to the same level, not so much to keep the soundboards from cracking but to keep the pianos in tune!  

I see. Thank you for your answers. I hope that perhaps others will chime in with questions now that we have you here. 

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I too am a hopeless D. Musafia fan.  I have two violin cases and a viola case.  The repairs the first case saved me more than paid for all the rest!  It is seldom that one encounters a maker of anything who has as much passion for his product as Maestro Musafia.  I need to get off my rear and order another viola case.  I'm afraid school started and my brain didn't :-)

 

DLB

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On 9/2/2017 at 11:00 AM, Dimitri Musafia said:

...I'd like to address the Pressure Cooker Effect.

If you take a case and place it in the summer sun (waiting for a taxi, a tour bus, your limo etc.) it's going to heat up. Right? No question.

Now, some case manufacturers claim to make "air-tight" cases. I might not be a scientist (although I am a published researcher, currently in collaboration with the Milan Polytechnic University for an ongoing violin case safety study) but any high-schooler can tell you that if you heat up a given air mass it will try to expand.

Here's the problem: if you heat up an air mass inside an air-tight ambient, and the expanded air cannot escape, it goes under pressure: the Pressure Cooker Effect. The same heated, compressed air mass has a lower dew point than that of the starting point, and thus the relative humidity increases: often dramatically, in a short time.  

It's not witchcraft or hype, just... science. Got it?

No, it really doesn't work that way.

If you heat air, the relative humidity drops.  That's why a cello cracks if you leave it in a case by a radiator.

Also, is it your contention that anyone really makes an air-tight case?  It's not relevant (keep reading), but nevertheless, I'm sceptical.

If they did, you would have trouble opening the case after descending from a tall building.  If you descend from a 300 m building, the air pressure increases by about 3.5 kPa and your ears will pop.  If you assume a tiny violin case with an opening of 25 cm x 50 cm, the additional air pressure would exert a pressure of 444 N, which corresponds to 45 kg.  If you did manage to open it, you would hear a pop or whoosh as air rushed in.  You can experience the same effect by opening a pickle jar.  It's not easy to make an air-tight container.  You can seal a case enough to retard exchange of water vapor, however.

I suppose that by selectively heating a source of water, you could briefly increase the relative humidity inside a case.  In this scenario the water source (humidifier) would have to be heated faster than the air in the case.  That would happen even if you put a small hole in the case, so air pressure has nothing to do with it, so "pressure cooker" is not the right term.

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1 hour ago, La Folia said:

No, it really doesn't work that way.

If you heat air, the relative humidity drops.  That's why a cello cracks if you leave it in a case by a radiator.

Also, is it your contention that anyone really makes an air-tight case?  It's not relevant (keep reading), but nevertheless, I'm sceptical.

If they did, you would have trouble opening the case after descending from a tall building.  If you descend from a 300 m building, the air pressure increases by about 3.5 kPa and your ears will pop.  If you assume a tiny violin case with an opening of 25 cm x 50 cm, the additional air pressure would exert a pressure of 444 N, which corresponds to 45 kg.  If you did manage to open it, you would hear a pop or whoosh as air rushed in.  You can experience the same effect by opening a pickle jar.  It's not easy to make an air-tight container.  You can seal a case enough to retard exchange of water vapor, however.

I suppose that by selectively heating a source of water, you could briefly increase the relative humidity inside a case.  In this scenario the water source (humidifier) would have to be heated faster than the air in the case.  That would happen even if you put a small hole in the case, so air pressure has nothing to do with it, so "pressure cooker" is not the right term.

Isn't there a difference in how humidity behaves between convective and radiant heat?

So, the sunshine Mr. Musafia mentions has a different effect from the radiator you mention?  Sorry, it's been too long since high school physics.

Also, BAM claims their case is airtight and waterproof.

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2 hours ago, Stephen Fine said:

Also, BAM claims their case is airtight and waterproof.

That's an advertising claim that I would not believe without evidence, but in any case I don't think it matters.

For your other questions, I suggest that you take it up with the engineers, scientists, and luthiers in The Pegbox if you're really interested.  But you could probably also heat a cello and cause it to crack by putting it next to a heat register.

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10 hours ago, La Folia said:

That's an advertising claim that I would not believe without evidence, but in any case I don't think it matters.

For your other questions, I suggest that you take it up with the engineers, scientists, and luthiers in The Pegbox if you're really interested.  But you could probably also heat a cello and cause it to crack by putting it next to a heat register.

I figured that considering the authority with which you were addressing an expert in the field (Mr. Musafia) that you must be some sort of "engineer, scientist, and luthier" yourself.

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31 minutes ago, La Folia said:

I am, in fact, but your question was open-ended and vague enough that I don't care to answer.  I also sense that you would not be very receptive to an answer from a single unknown person on the Internet.  If you really want to know, get a bunch of minds tossing it back and forth.

I'm perfectly happy to take your word over the internet assuming you say something I can verify.

But you made (only) two points against Mr. Musafia, and even I without much of a scientific background find issues with your points.

 

1.  The radiant/convective heat issue...  You said radiator, Dimitri said sunshine.  The radiator seems like a  straw man attack on his argument.  But, like I said, I don't remember the physical properties of radiant vs. convective heat.  Maybe it's exactly the same thing.  I asked because I was curious.

2.  The airtightness issue.  My pressure cooker isn't airtight but it still works as a pressure cooker, and I've opened BAM cases that seemed about as airtight as a pressure cooker.

 

So... that's all...

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4 hours ago, Stephen Fine said:

1.  The radiant/convective heat issue...  You said radiator, Dimitri said sunshine.  The radiator seems like a  straw man attack on his argument.  But, like I said, I don't remember the physical properties of radiant vs. convective heat.  Maybe it's exactly the same thing.  I asked because I was curious.

2.  The airtightness issue.  My pressure cooker isn't airtight but it still works as a pressure cooker, and I've opened BAM cases that seemed about as airtight as a pressure cooker.

 

So... that's all...

1. If you heat air in a closed system, the relative humidity goes down.  It doesn't matter whether you heat it with radiant heat, conductive heat, or dragon's breath.  And by the way, a radiator and sunshine both heat by radiation (that's why they call it a radiator), and both cause convection.

2. Your pressure cooker works because it has a pressure regulator that maintains the total pressure to approximately 2 bars.  Air is excluded, so the gas is almost entirely steam at 120 deg. C.  If you manage to open it when it's hot, it will explode in your face, and the burns may kill you.  There's no comparison between that and a violin case.

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4 hours ago, WorksAsIntended said:

(p×V)/T = n R

Start from there and you will see in an air tight system (I have no idea if those cases actually are) the relativ humidity can increase with the temperatur rising. Of course this is not true for open systems. 

 

The ideal gas law that you cited is not particularly relevant.  Here's how it works.  Relative humidity is the partial pressure of water divided by the equilibrium vapor pressure at that temperature.  If you heat air in a closed system, the partial pressure of water doesn't change, but the equilibrium vapor pressure increases.  Total pressure has nothing to do with it except at extremely high pressures.

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And if you heat from 20°C to 80°C, what kind of pressure do you get? Of course it gets relevant (even if simplified), as you need to surpase the atmospheric pressure (or in this case the significant higher one) for vaporation.

Of course you are right about the cooker and the radiation. The point is, that the standard assumptions done for the relativ humidity fail here. 

 

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47 minutes ago, WorksAsIntended said:

...you need to surpase the atmospheric pressure (or in this case the significant higher one) for vaporation.

 

No, water can vaporize at any pressure.  You may be thinking of boiling--boiling occurs when vapor pressure equals or exceeds atmospheric pressure, but (1) you're not going to boil water in a case; and (2) increased atmospheric pressure makes it harder to boil water, not easier (you need higher temperature).

I'm sorry, I don't want to insult you, but you really don't seem to understand this stuff at all.  That's not a bad thing.  It's just that you don't seem to have the requisite background.  Science may seem easy until you have to solve the homework problems.  I really don't want to discuss it any more.

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8 hours ago, WorksAsIntended said:

And if you heat from 20°C to 80°C, what kind of pressure do you get?

OK, WorksAsIntended, one more. just for you.  :)  Just for fun.  You can use the ideal gas law for this.  You have to get all parts of this question right, or it doesn't count.

1. If you heat air in a closed case (completely sealed, air-tight) from 20°C to 80°C, what is the force on the lid if the opening is 25 cm x 50 cm?

2. What do you observe when you try to open the case?  What do you conclude?

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10 hours ago, WorksAsIntended said:

And if you heat from 20°C to 80°C, what kind of pressure do you get? Of course it gets relevant (even if simplified), as you need to surpase the atmospheric pressure (or in this case the significant higher one) for vaporation.

Of course you are right about the cooker and the radiation. The point is, that the standard assumptions done for the relativ humidity fail here. 

 

 

10 hours ago, La Folia said:

No, water can vaporize at any pressure.  You may be thinking of boiling--boiling occurs when vapor pressure equals or exceeds atmospheric pressure, but (1) you're not going to boil water in a case; and (2) increased atmospheric pressure makes it harder to boil water, not easier (you need higher temperature).

I'm sorry, I don't want to insult you, but you really don't seem to understand this stuff at all.  That's not a bad thing.  It's just that you don't seem to have the requisite background.  Science may seem easy until you have to solve the homework problems.  I really don't want to discuss it any more.

I suggest you mind your step - WAI has ( by his own account ) a Doctorate in "Quantum dynamics". :lol:

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8 hours ago, La Folia said:

OK, WorksAsIntended, one more. just for you.  :)  Just for fun.  You can use the ideal gas law for this.  You have to get all parts of this question right, or it doesn't count.

1. If you heat air in a closed case (completely sealed, air-tight) from 20°C to 80°C, what is the force on the lid if the opening is 25 cm x 50 cm?

2. What do you observe when you try to open the case?  What do you conclude?

You need to get all the parts of the question right, or it doesn't count. 

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Wow, i take the boat out a few days and look what happens...tch tch tch !!

I'm not going to argue this, because if La Folia disagrees that's perfectly fine with me.  Anyone interested can send me their email and their real name and I'll email back a graph, resulting from  actual experiments, depicting the abrupt increase of relative humidity inside a (relatively) air-tight case heated by direct sunlight, and the simultaneous decrease of RH inside an identical case exposed to the same conditions at the same time but left slightly open to allow the heated air to escape. We can debate about how it happened and what to call it, but fact is fact.

This discovery came by accident - I was simply testing the thermal insulation properties of different cases in the summer sun when, in addition to the temperature, I also checked the RH and was surprised at the amplitude and the abruptness of the spike. In one case, RH doubled in 20 minutes.

Cheers!

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