Weights of Common Metals

[Ron Resnick]

It turns out that copper and bronze and stainless steel and gunmetal all have similar weights per cubic foot. So the differences in "sounds" among these materials must derive from their inherent nature, and not merely differences in mass per cubic foot.

Even lead is only moderately heavier per cubic foot than these other metals. (For some reason, I have no idea why, I assumed lead was like double the weight per unit of size than these other materials.)

 

[ddk]

It turns out that copper and bronze and stainless steel and gunmetal all have similar weights per cubic foot. So the differences in "sounds" among these materials must derive from their inherent nature, and not merely differences in mass per cubic foot.

Even lead is only moderately heavier per cubic foot than these other metals. (For some reason, I have no idea why, I assumed lead was like double the weight per unit of size than these other materials.)


View attachment 64424

Yes and there are subcategories of each metal made from different alloys and/or manufacturing processes. Depending on where the metal is used and why everything will make a difference in the sound. Of course dimension and mass are the other variable but purely a material level, not all copper, stainless, brass, etc. is the same.

david

 

[microstrip]

It turns out that copper and bronze and stainless steel and gunmetal all have similar weights per cubic foot. So the differences in "sounds" among these materials must derive from their inherent nature, and not merely differences in mass per cubic foot.

Even lead is only moderately heavier per cubic foot than these other metals. (For some reason, I have no idea why, I assumed lead was like double the weight per unit of size than these other materials.)


View attachment 64424

Admitting the same size and shape, the way a material sounds depends on its sound velocity, that depends on the bindings of its atoms. Even very small changes in composition or the way it is manufactured can change its sound properties.

 

[Ron Resnick]

All interesting, gentlemen! And confounding for our audio purposes!

 

[Stacore]

Apart from density, the second important parameter is the Young (or elasticity) modulus, describing the elasticity of the material. Both these parameters determine the sound velocity in a given material. For example for longitudinal waves the velocity = Square root (elasticity / density). But also other things, like materials matching, e.g. how much of a given wave will be reflected and how much transmitted through a boundary of two materials.

Cheers,

 

[microstrip]

Apart from density, the second important parameter is the Young (or elasticity) modulus, describing the elasticity of the material. Both these parameters determine the sound velocity in a given material. For example for longitudinal waves the velocity = Square root (elasticity / density). But also other things, like materials matching, e.g. how much of a given wave will be reflected and how much transmitted through a boundary of two materials.

Cheers,

Depending on shape we can make it even more confusing for Ron - we have to consider also the bulk modulus and the Poisson ratio!

 

[Stacore]

Yes, although the elementary principle of elastic deformations of solids is very simple - masses on springs, it then grows to some baroque variety of waves, modes etc. The main message was that density alone does not determine the behavior. Must be considered with some measure of elasticity following the basi principle of masses on springs. Density ~ mass, elasticity modulus ~ spring coeefficient. Usually Young modulus is enough as a rough guide.

A historical note: Freshly then developed theory of vibrating membranes made such a great impression on Schroedinger that he used it as a starting point for his famous equation and development of quantum mechanics.

Cheers,

 

[tima]

the Young modulus, is a mechanical property that measures the stiffness of a solid material. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear elasticity regime of a uniaxial deformation.

https://en.wikipedia.org/wiki/Young's_modulus

Admitting the same size and shape, the way a material sounds depends on its sound velocity, that depends on the bindings of its atoms

Apart from how a material sounds (and writing as a layman) I speculate that vibration moves through different materials at different speeds. Thinking of some constrained layer type object, say a footer or a platform, when vibration moves from one material to another I'm guessing its velocity changes. Is that correct? Does a change in velocity cause a change to the mechanical energy that is the vibration? Speed up and/or slow down - is mechanical energy 'lost' - converted into some other form? That is, causing (encouraging?) a vibration to move through different material with different 'sound velocity' can expend it to some degree?

I'm sure I'm being simplistic and maybe don't have the right vocabulary here, so be gentle.

 

[Stacore]

Apart from how a material sounds (and writing as a layman) I speculate that vibration moves through different materials at different speeds.

Indeed, sound velocity is one of the basic parameters of a given material. It depends on the wave type, the basic for a longitudinal wave is:

c=sqrt(Young modulus/density)

In more, detail the speed of sound is governed by the dispersion relation.

Thinking of some constrained layer type object, say a footer or a platform, when vibration moves from one material to another I'm guessing its velocity changes. Is that correct?

In the simplest scenario, some of the wave gets reflected, some passes through and it changes the velocity

Does a change in velocity cause a change to the mechanical energy that is the vibration? Speed up and/or slow down - is mechanical energy 'lost' - converted into some other form?

You can perfectly approximate some of the materials neglecting the losses: waves just travel, getting reflected and transmitted at material boundaries. Imagine perfect springs: the energy you use to compress it = the energy you get when it decompresses. But this is not how the constrained layer works. There you need to add losses. You need a material where the "spring" (intermolecular structure) is very losy and converts the energy of wave into heat. This adds one more parameter - damping coefficient. The wave then decays in the lossy medium (gets transformed into the heat). The trick is to have a low reflection at the boundary to the lossy medium so that most of the unwanted waves gets transmitted rather than reflected back.

Cheers,

 

[tima]

The trick is to have a low reflection at the boundary to the lossy medium so that most of the unwanted waves gets transmitted rather than reflected back.

Is that the case when the goal is isolation? Or does that want to reflect the wave back? Burn up the energy or turn it away, as it were. Two different approaches?

Thank you Jarek for your contributions and time.

 

[Stacore]

Is that the case when the goal is isolation? Or does that want to reflect the wave back? Burn up the energy or turn it away, as it were. Two different approaches?

Yes, the goal is then to isolate. Or more precisely to damp (in theory, to isolate - to turn the virbrations back, to damp - to burn them; but real life solutions are usually a mix of the two). In CLD approach, you want to divert as much of the vibrational energy to lossy medium as you can. If it bounces back, it stays in the object you are trying to damp (e.g. a TT plinth). The vibrational wave is then loosing energy working through the lossy medium plus deforming the hard substrate at the other side of the CLD sandwitch. I hope to find time and write more on how CLD works on our subforum, where I am explaining how our products work as we use CLD extensively.

Cheers,

 

[tima]

Yes, the goal is then to isolate. Or more precisely to damp (in theory, to isolate - to turn the virbrations back, to damp - to burn them; but real life solutions are usually a mix of the two). In CLD approach, you want to divert as much of the vibrational energy to lossy medium as you can. If it bounces back, it stays in the object you are trying to damp (e.g. a TT plinth). The vibrational wave is then loosing energy working through the lossy medium plus deforming the hard substrate at the other side of the CLD sandwitch. I hope to find time and write more on how CLD works on our subforum, where I am explaining how our products work as we use CLD extensively.

Cheers,

Thank you again.

Take the case of a turntable sitting on a vibration mitigating platform (VMP) and that platform sitting on a rack. I say VMP because that platform seems to do or want do two things: damping and isolation.

1. It wants to isolate the turntable from vibrations coming from the floor or through the rack, by turning them back or prevent them from entering itself.
2. It wants to damp by allowing vibrations coming from the turntable to enter into itself, to burn them up.

You note real life solutions are usually a mix of the two.

I speculate an effective VMP would or could contain different 'systems' for these two jobs and no single system optimally could do both. Or is that incorrect thinking?

 

[Stacore]

Thank you again.

Take the case of a turntable sitting on a vibration mitigating platform (VMP) and that platform sitting on a rack. I say VMP because that platform seems to do or want do two things: damping and isolation.

1. It wants to isolate the turntable from vibrations coming from the floor or through the rack, by turning them back or prevent them from entering itself.
2. It wants to damp by allowing vibrations coming from the turntable to enter into itself, to burn them up.

You note real life solutions are usually a mix of the two.

I speculate an effective VMP would or could contain different 'systems' for these two jobs and no single system optimally could do both. Or is that incorrect thinking?

Hi Tima,

My pleasure

Re 1. First and foremost It wants to prevent external vibrations from reaching TT. How it does it - isolates, damps, both, in what proportions, by which mechanism it's in a sense secondary.

Re 2. I have no idea where all this obsession with damping internally generated vibrations by external means come from. Internal damping of the device is the job of the device designer. Sometimes something can be improved here by e.g. tight coupling to a massive, well damped platform. Then if one can divert internally generated vibrations to the platform, it will get burned there (a caveat - whatever marketing magitians say there is no "vibrations diode", vibrations travel both ways by their nature so be careful).

Yes, combining different systems is the way to go. For example in our 2-stage Advanced platform (if I may use it as an example being most familiar with), moving from ground up:

- pneumatic suspension to isolate at LF
- the suspension is additionally pneumatically damped to burn some of the vibrational energy in air pushing and expansion/contraction cycles
- high mass as damping at upper LF (most difficult region) - vibrations burn their energy moving a high mass; the higher the mass, the lesser the movement with the same vibrational energy
- CLD damping from lower MF up - burning vibrational energy in metal/viscoelastic lossy layer/slate composite; slate itself also provides some of CLD damping
- highly sensitive hardened steel bearings to addionaly isolate in the horizontal plane; the lower bearing racings damped at MF by embedding in the slate
- one more layer of CLD damping - the top bearing racings are embeded in a massive 32kg metal/viscolayer/slate plate

Cheers,

 

[Stacore]

Forgot to add that slate itself provides some form of CLD damping due to its layered structure. A well known and explored in audio fact. However, it is not a wonder material by its own and comes with its own set of problems if used just like it is. Mainly adds colorations on lower MF. Hence some additional measures, like ones I described above are necessary.

Cheers,

 

[tima]

I hope to find time and write more on how CLD works on our subforum, where I am explaining how our products work as we use CLD extensively.

I very much look forward to reading this.

 

[morricab]

Is that the case when the goal is isolation? Or does that want to reflect the wave back? Burn up the energy or turn it away, as it were. Two different approaches?

Thank you Jarek for your contributions and time.

Damping is basically conversion of kinetic energy to thermal energy. In viscoelastic materials, the kinetic energy is lost in the molecular vibrations of the polymer bonding. Stiff materials will have a high Q, which will store energy quite strongly but only in a narrow bandwidth. In laser optics, there is a mixture of isolation (ofter air suspension or viscoelastic in more cost conscious setups) and high mass/rigidity (steel tables with honeycomb inside structures). The combination seems to give the best results for that field. I would think a combination approach to audio gear vibration control would also work well.

 

[tima]

I would think a combination approach to audio gear vibration control would also work well.

Yes, combining different systems is the way to go. For example in our 2-stage Advanced platform (if I may use it as an example being most familiar with), moving from ground up:

While Jarek views the job of damping internally generated vibrations as the job of the component designer, we do get varying results from different designers, and reducing component generated vibration remains a desirable, particularly in mechanically active source components. That seems like a different job, requiring a different system from one whose goal is preventing external vibration from entering a component.

Externally entering a component typically means from the ground or from things in contact with a component's support that themselves are vibrating, eg a rack hosting a turntable platform. I see almost nothing devoted to mitigating vibrations or waves in the air from their direct impact. (Forces such as wind can cause structures to vibrate which turns into ground originated.) I remember seeing large noisey dot matrix printers inside sound absorbing boxes, so I'm thinking crudely of the reverse. I haven't heard of anyone paying attention to that external source. (And I can't imagine bling-desirous audiophiles hiding their little gems in boxes.)

This all seems like a thorny set of problems that are context and component specific. If there's any truth to that, maybe single solutions cannot meet the need. My naive speculation...

 

[Stacore]

While Jarek views the job of damping internally generated vibrations as the job of the component designer, we do get varying results from different designers, and reducing component generated vibration remains a desirable, particularly in mechanically active source components. That seems like a different job, requiring a different system from one whose goal is preventing external vibration from entering a component.

I like very much the idea of the member Stehno - a clamping mechanism that would clamp the equipment to the rack/platform/shelf. Combined with a properly designed shelf/platform, I can imagine this providing a working solution for internally generated/captured vibrations.

Externally entering a component typically means from the ground or from things in contact with a component's support that themselves are vibrating, eg a rack hosting a turntable platform. I see almost nothing devoted to mitigating vibrations or waves in the air from their direct impact. (Forces such as wind can cause structures to vibrate which turns into ground originated.) I remember seeing large noisey dot matrix printers inside sound absorbing boxes, so I'm thinking crudely of the reverse. I haven't heard of anyone paying attention to that external source. (And I can't imagine bling-desirous audiophiles hiding their little gems in boxes.)

We did this experiment at one of the Munich shows - we asked visitors to hold a vibration sensor in a hand. We then clapped and let people watch the vibration trace. Mind you, flesh is one of the best vibration dampers so no way the observed vibration would propagate through the body. We haven't commercially researched that direction yet, but as a first try I'd use acrylic "chimneys" (like some big tube amps have around the output tubes).

Cheers,