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StringJunky

Energy transfer to a guitar from different types of case when dropped

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Consider identical guitars, with one in a heavy case and the other in a light case. Both cases are indestructible, the guitars are snug-fitted in a similar padded interior for this scenario. If I drop both cases from some height, which guitar will fair better in terms of experiencing the least shock?

Another question: Would a loose fit or a tight fit be better in this scenario, given the cases are otherwise the same?

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I’m struggling with the heavy versus light distinction. Seemingly more important is rigid versus elastic, or firm versus cushioned. 

Based on mass alone, I’d imagine lighter is better since heavier means higher momentum upon impact (greater force being cascaded through the intricate bits of the instrument). 

Edited by iNow

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7 minutes ago, iNow said:

I’m struggling with the heavy versus light distinction. Seemingly more important is rigid versus elastic, or firm versus cushioned. 

Based on mass alone, I’d imagine lighter is better since heavier means higher momentum upon impact (greater force being cascaded through the intricate bits of the instrument). 

That's what I was thinking but many in a guitar forum I use think being built like a tank is better. The cases I use are lighter and looser fitting; the designer thinks this is better for guitars in most adverse situations.  

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I’ll defer now to those more expert in physics than me. Good luck

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Pardon the pun, but it is somewhat "case" dependant.

If you dropped one onto a fairly solid piece of glass, supported by a foot or so of fibreglass insulation, a heavier case might break the glass, allowing a lot more time and distance to decelerate the guitar than a lighter one that would not break through.

Now compare that to dropping them onto the same insulation supported by a concrete floor.

Wasn't there a thread previously on this?

Edited by J.C.MacSwell

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12 minutes ago, J.C.MacSwell said:

Pardon the pun, but it is somewhat "case" dependant.

If you dropped one onto a fairly solid piece of glass, supported by a foot or so of fibreglass insulation, a heavier case might break the glass, allowing a lot more time and distance to decelerate the guitar than a lighter one that would not break through.

Now compare that to dropping them onto the same insulation supported by a concrete floor.

Wasn't there a thread previously on this?

Assume the floor is unyielding. I looked and, yes, I have asked before, in July. :) 

Edited by StringJunky

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1 hour ago, StringJunky said:

Consider identical guitars, with one in a heavy case and the other in a light case. Both cases are indestructible, the guitars are snug-fitted in a similar padded interior for this scenario. If I drop both cases from some height, which guitar will fair better in terms of experiencing the least shock?

Another question: Would a loose fit or a tight fit be better in this scenario, given the cases are otherwise the same?

I think it boils down to why a case is heavier rather than just the weight. More importantly is how the content is suspended within the case to minimize impact damage. When dealing with delicate equipment, for example, it is often packed in foam coupled to a suspension system (i.e. shock isolation system). So in that case, a rigid container can be used as the kinetic energy is transferred and (hopefully) absorbed by the suspension system rather than by the outer case itself. That being said, many high-quality cases can be made with lightweight materials, provided it is properly shaped to have a high strength-to-weight ratio. Often, that is the difference between cheap cases and expensive ones, even if both use the same polymer.

I realized that I did not remain in the confines of OP. In that above scenario the first answer is unknown as it depends on the material as well as its structure how much impact is delivered to the inside. However, for a number of reasons polymers rather than, e.g. a rigid metal is preferred as they can be designed to transfer less impact but still be reasonably strong. 

For the second question the real answer is that it depends on the and how cushioning it is installed. What you typically want is the cushioning to sway, not your instrument.

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11 hours ago, J.C.MacSwell said:

Wasn't there a thread previously on this?

11 hours ago, StringJunky said:

I looked and, yes, I have asked before, in July

I thought so  -  that explains the de ja vu!   I couldn't find the thread though from the search engine... but found it by searching again without the typos.:

 

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13 hours ago, StringJunky said:

That's what I was thinking but many in a guitar forum I use think being built like a tank is better. The cases I use are lighter and looser fitting; the designer thinks this is better for guitars in most adverse situations.  

A greater mass means that for a given impact (force) means it will undergo a smaller acceleration.  i.e. it's a consideration for reasons other than the scenario in question.

 

And I think acceleration is the key here. How the guitar responds to being accelerated is important, because that what causes the internal components to have stresses and strains and torsions, etc. I would think you don't want a loose fit, since that means motion within the case until the guitar hits an obstruction, and that's where damage occurs. You want snug, but in a material that has "give" to it. (padding materials generally have voids in them, so they can compress)

That's why there is internal padding — it increases the time it takes to come to rest, decreasing the acceleration. A heavier case would potentially make a greater indentation into whatever it hits, which increases the time of impact, reducing the acceleration. 

 

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14 minutes ago, swansont said:

A greater mass means that for a given impact (force) means it will undergo a smaller acceleration.  i.e. it's a consideration for reasons other than the scenario in question.

 

And I think acceleration is the key here. How the guitar responds to being accelerated is important, because that what causes the internal components to have stresses and strains and torsions, etc. I would think you don't want a loose fit, since that means motion within the case until the guitar hits an obstruction, and that's where damage occurs. You want snug, but in a material that has "give" to it. (padding materials generally have voids in them, so they can compress)

That's why there is internal padding — it increases the time it takes to come to rest, decreasing the acceleration. A heavier case would potentially make a greater indentation into whatever it hits, which increases the time of impact, reducing the acceleration. 

 

Yes I agree acceleration/deceleration is the key here.

Some additional points.

Dropping the case and protecting against a projectile with tank armour are different scenarios.
In the first it is the case and contents which are decelerated. In the second it is the projectile.
So tank armour would not help here.

A heavy case falling, will hit at the same speed as a light case (Galileo) but will transfer great momentum due to its mass.
Therfore producing a greater impact force unless the impact time can be lengthened.

So the issue might best be thought of in terms of a soft v hard case.

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2 hours ago, swansont said:

A greater mass means that for a given impact (force) means it will undergo a smaller acceleration.  i.e. it's a consideration for reasons other than the scenario in question.

 

And I think acceleration is the key here. How the guitar responds to being accelerated is important, because that what causes the internal components to have stresses and strains and torsions, etc. I would think you don't want a loose fit, since that means motion within the case until the guitar hits an obstruction, and that's where damage occurs. You want snug, but in a material that has "give" to it. (padding materials generally have voids in them, so they can compress)

That's why there is internal padding — it increases the time it takes to come to rest, decreasing the acceleration. A heavier case would potentially make a greater indentation into whatever it hits, which increases the time of impact, reducing the acceleration. 

 

Cheers. That makes sense.

1 hour ago, studiot said:

Yes I agree acceleration/deceleration is the key here.

Some additional points.

Dropping the case and protecting against a projectile with tank armour are different scenarios.
In the first it is the case and contents which are decelerated. In the second it is the projectile.
So tank armour would not help here.

A heavy case falling, will hit at the same speed as a light case (Galileo) but will transfer great momentum due to its mass.
Therfore producing a greater impact force unless the impact time can be lengthened.

So the issue might best be thought of in terms of a soft v hard case.

 

1 hour ago, studiot said:

Yes I agree acceleration/deceleration is the key here.

Some additional points.

Dropping the case and protecting against a projectile with tank armour are different scenarios.
In the first it is the case and contents which are decelerated. In the second it is the projectile.
So tank armour would not help here.

A heavy case falling, will hit at the same speed as a light case (Galileo) but will transfer great momentum due to its mass.
Therfore producing a greater impact force unless the impact time can be lengthened.

So the issue might best be thought of in terms of a soft v hard case.

Cheers. A compressible interior in a hard exterior would be equivalent to a soft case from the pov of the guitar, wouldn't it?

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2 hours ago, studiot said:

Yes I agree acceleration/deceleration is the key here.

Some additional points.

Dropping the case and protecting against a projectile with tank armour are different scenarios.
In the first it is the case and contents which are decelerated. In the second it is the projectile.
So tank armour would not help here.

A heavy case falling, will hit at the same speed as a light case (Galileo) but will transfer great momentum due to its mass.
Therfore producing a greater impact force unless the impact time can be lengthened.

So the issue might best be thought of in terms of a soft v hard case.

There is no difference between acceleration and deceleration other than choice of reference frame.

A heavier case will impact more heavily with the ground, generally speaking, a greater impact force as you say, but that is not the force on the guitar. The padding allows it to displace with respect to the case, as well as spreading the force over greater area.

Assuming the same outer dimensions of the case, any disadvantages of a hard case can usually be mitigated by the design of the padding inside, unless the thickness of the case significantly reduces room for it. Hard outer shells generally spread the load over a greater area of padding, which spreads it over a greater area of the guitar,

Sports helmets are a little more complicated in design, but generally all have a hard outer shell. 

Edited by J.C.MacSwell

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23 minutes ago, J.C.MacSwell said:

There is no difference between acceleration and deceleration other than choice of reference frame.

A heavier case will impact more heavily with the ground, generally speaking, a greater impact force as you say, but that is not the force on the guitar. The padding allows it to displace with respect to the case, as well as spreading the force over greater area.

Assuming the same outer dimensions of the case, any disadvantages of a hard case can usually be mitigated by the design of the padding inside, unless the thickness of the case significantly reduces room for it. Hard outer shells generally spread the load over a greater area of padding, which spreads it over a greater area of the guitar,

Sports helmets are a little more complicated in design, but generally all have a hard outer shell. 

No.

We are dealing with impulsive forces or impulse when talking about 'shock'

The shorter the time, the greater the impulse. This can be twice the static weight of the impactor.

Further there is a difference between acceleration and deceleration in this (and this is without breaking N3)

Consider dropping the same case or an egg onto

a) Soft sand or mud.

b) Granite or concrete.

 

In which case will the hard shell of the egg survive from the greatest height of drop?
 

Then consider the similar bullets hitting

c) Paper armour

d) 6 inch thick steel plate

Which will survive and what damage will happen to the bullet in each case?

 

The outer shell of a sports helmet is not to protect the wearer but to keep the soft inner together and clean.

 

1 hour ago, StringJunky said:

Cheers. A compressible interior in a hard exterior would be equivalent to a soft case from the pov of the guitar, wouldn't it?

No, I think a thick soft exterior would be better.

But sadly less maintainable.

 

 

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5 minutes ago, studiot said:

 

No, I think a thick soft exterior would be better.

But sadly less maintainable.

Depends on the problem you're trying to solve. There's more than one behavior you're trying to optimize, and there's no guarantee you can optimize all of them. A case is probably trying to protect against shock, but also sharper objects piercing it. The latter requires a hard cover.

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3 minutes ago, studiot said:

No.

We are dealing with impulsive forces or impulse when talking about 'shock'

The shorter the time, the greater the impulse. This can be twice the static weight of the impactor.

Further there is a difference between acceleration and deceleration in this (and this is without breaking N3)

Consider dropping the same case or an egg onto

a) Soft sand or mud.

b) Granite or concrete.

 

In which case will the hard shell of the egg survive from the greatest height of drop?
 

Then consider the similar bullets hitting

c) Paper armour

d) 6 inch thick steel plate

Which will survive and what damage will happen to the bullet in each case?

 

The outer shell of a sports helmet is not to protect the wearer but to keep the soft inner together and clean.

 

No, I think a thick soft exterior would be better.

But sadly less maintainable.

 

 

No, to what exactly?

Why twice?  Most guitars would be fine at well over that, even over a small area. The problem is that impacts can involve forces much greater.

A heavy hard shell case can afford a longer impact time for the guitar than a lighter softer one, it all depends on the design and conditions of impact.

It matters not a wit whether something is decelerating or accelerating.

Consider stationary bullets collided with

c) Paper armour at 1000 feet/s

d) 6 inch thick steel plate at 1000 feet/s

Which will survive and what damage will happen to the bullet in each case? (hint: assuming you had your bullet at 1000 feet/s...these are identical to your two scenarios...exact same events looked at from different reference frames)

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4 hours ago, swansont said:

Depends on the problem you're trying to solve. There's more than one behavior you're trying to optimize, and there's no guarantee you can optimize all of them. A case is probably trying to protect against shock, but also sharper objects piercing it. The latter requires a hard cover.

Yes, indeed it does.

So if SJ carted his guitar up to the top of the Matterhorn and dropped it on the point bit then a hard case would guard best against piercing penetration.
Also fixing the guitar to something rigid within the case would guard against flexural shock breaking the vulnerable neck.

But no system is perfect, as you say.

 

4 hours ago, J.C.MacSwell said:

Which will survive and what damage will happen to the bullet in each case? (hint: assuming you had your bullet at 1000 feet/s...these are identical to your two scenarios...exact same events looked at from different reference frames)

You haven't answered my question.

 

In the past sensitive and delicate electrical/electronic meters with pointers had hard cases, but the better ones has a tough softer more resiliant exterior case as well.

More modern elctronic equipment has carried on this tradition when 'ruggedisation' is considered.

Here is a picture of such.

The dark blue inner case is hard and (fairly) rigid.
The light blue outer is soft and flexible.

meter3.thumb.jpg.e36de8afe00ab3a914297629497c99b8.jpg

 

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1 hour ago, studiot said:

You haven't answered my question.

 

In the past sensitive and delicate electrical/electronic meters with pointers had hard cases, but the better ones has a tough softer more resiliant exterior case as well.

More modern elctronic equipment has carried on this tradition when 'ruggedisation' is considered.

Here is a picture of such.

The dark blue inner case is hard and (fairly) rigid.
The light blue outer is soft and flexible.

meter3.thumb.jpg.e36de8afe00ab3a914297629497c99b8.jpg

 

I thought it was rhetorical. If it wasn't...

The light blue is a common type of additional protection...flexible enough to put on and reduce the forces further in case of a drop or whatever. It is not optimized for it's size to protect the device any more than another hard outer shell with an even lighter padding inside could be. It is just very simple and practical.

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16 minutes ago, J.C.MacSwell said:

I thought it was rhetorical. If it wasn't...

The light blue is a common type of additional protection...flexible enough to put on and reduce the forces further in case of a drop or whatever. It is not optimized for it's size to protect the device any more than another hard outer shell with an even lighter padding inside could be. It is just very simple and practical.

 

An eggshell is 'designed' to protect from considerable steady crushing pressure, which that outer  light light blue casing is not and will not do.

However that light blue outer casing is designed to protect from a British Standard drop height onto a hard (concrete) floor.
Such a drop  would certainly break the egg.

Are you suggesting that the time to complete the impact with and without the light blue casing would be the same?

Deformation of that light blue casing extends the impact time over a longer period, which is another way of saying it reduces the deceleration of the protected  item.

This is the same principle as crumple zones and energy absorbing bumpers in vehicles to protect occupants from excessive deceleration forces.

Edited by studiot

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10 minutes ago, studiot said:

 

An eggshell is 'designed' to protect from considerable steady crushing pressure, which that outer  light light blue casing is not and will not do.

However that light blue outer casing is designed to protect from a British Standard drop height onto a hard (concrete) floor.
Such a drop  would certainly break the egg.

Are you suggesting that the time to complete the impact with and without the light blue casing would be the same?

Deformation of that light blue casing extends the impact time over a longer period, which is another way of saying it reduces the deceleration of the protected  item.

This is the same principle as crumple zones and energy absorbing bumpers in vehicles to protect occupants from excessive deceleration forces.

No. 

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I have asked this to a luthier. He said that the unbreakable case would be better if it had a little flexibility. And he said that if I'm thinking of throwing the bundle from the terrace, it would be better an internal padding that does not copy the shape of the guitar and that was parallelepiped, so that the ends of the guitar in length and width support tangentially on the padded.

Now an aggregate of mine. The weight of the case is not interesting, because the acceleration in free fall is independent of the mass.

Uniting everything is the following. If everything is identical except the weight of the case, no guitar is less likely to be damaged. Regarding the padding, in case of not meeting the tangentiality suggested by the luthier, it would be better loosed, because the effect is a little closer to what the tangential support would do.

Edited by quiet

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