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Old 25th July 2008, 03:57 AM   #11
poptart is offline poptart  Canada
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Quote:
More dense mediums will support better sound transfer, due to the reduced distance between molecules. Molecules in everything move (even the densest substances), and when they do they bump into each other, transferring energy.
I'm sorry but this is just plain wrong. Everything else being equal, more dense mediums will have a slower speed of sound. It just so happens that more dense materials are often stiffer as well and the effect of the stiffness swamps the density increase. No matter how stiff water may appear to be at a macroscopic scale it's molecules move, you've just acknowledged as much in your quote above, and when they move over closer to their neighbors that's the compression we're all talking about. Molecules have moved closer together = compression. No it's not a giant compression of the whole volume of water (which seems to be what you're focussing on) but in it's tiny locale those molecules have temporarily been moved closer together. Some distance away some others have been spread apart so there is no overall compression of the medium.

If this isn't what you picture when you think of a wave something is wrong:

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Old 25th July 2008, 04:03 AM   #12
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Quote:
Originally posted by Sheldon



They are measuring directly changes in the density of water as ultrasonic (high frequency sound, but sound all the same) sound compresses the water. Simple motion does not change the refractive index of a liquid.

They are imaging pressure changes.
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Old 25th July 2008, 04:04 AM   #13
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Originally posted by poptart


I'm sorry but this is just plain wrong. Everything else being equal, more dense mediums will have a slower speed of sound. It just so happens that more dense materials are often stiffer as well and the effect of the stiffness swamps the density increase.

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Old 25th July 2008, 04:20 AM   #14
SY is offline SY  United States
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They are imaging pressure changes.
When the pressure changes, do the molecules stay the same average distance apart? If "no," how does the pressure change on a molecular level? If yes, then isn't that the definition of compressibility?
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Old 25th July 2008, 04:27 AM   #15
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Quote:
Originally posted by poptart


I'm sorry but this is just plain wrong. Everything else being equal, more dense mediums will have a slower speed of sound. It just so happens that more dense materials are often stiffer as well and the effect of the stiffness swamps the density increase.
I'll challenge this statement.

http://www.engineeringtoolbox.com/so...ids-d_713.html

note speed of sound in aluminium is 4.9km/s while in steel is 6.1 km/s. In diamond (stiffest!) is 12km/s !!!
Water lags at 1.4km/s ...
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Old 25th July 2008, 04:30 AM   #16
poptart is offline poptart  Canada
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I have no idea where this is getting hung up. Are you just unhappy with the use of the words "compression and rarefaction" instead of "areas of low and high pressure"? These are equivalent to me.

You've already agreed the molecules move over toward their neighbors to transmit the vibration = what everyody has been trying to say. Argument over as far as I'm concerned.
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Old 25th July 2008, 04:36 AM   #17
poptart is offline poptart  Canada
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Bratislav, maybe I wasn't clear or I'm not reading you right but I think we're agreeing.

It's my understanding that:

Stiffer = faster
denser = slower

and it's the balance of these two effects that determines the speed. The density of water would make the speed of sound slower than air if it weren't for the greatly increased stiffness that more than makes up for that.
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Old 25th July 2008, 04:38 AM   #18
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by tinitus
Allow me a stupid question, but I dont understand this HOM when no one seems to have done any measurements to show its behaviour
How can you know the OS is superiour regarding HOM, is it by mathematical proove
Still, the OS also needs a foamplug
To me it sounds more like a matter of precise design of throath and curved mouth, which should be of benefit to any waveguide, and as I recall you have said so yourself

Its not dissbelief in any way and I dont mean to sound harsh ... only curious
Look at piston baffle radiation pattern and energy distribution is all I'm going to say.

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I'm interested in anything that you have to say if you don't claim things that you are guessing at as facts.
And I wish to give you the honor of explaining things, even though I already have a feeling what you might say.
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Old 25th July 2008, 05:23 AM   #19
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by MJL21193
They are imaging pressure changes.
Indirectly, of course. In a given substance, refractive index is a function of density. So to the extent that a material is compressible, its density changes with pressure. If the density did not change (i.e., the material did not compress/expand) no change in refractive index would be observed.

You seem to be saying that your mind is made up, and you will accept neither long accepted physical principles, nor actual measurement of the phenomenon as evidence. If so, it's a matter of faith and is not subject to the scientific method, and there is no point in discussion based on that method. If that's not the case, what evidence do you require?

Sheldon
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Old 25th July 2008, 01:35 PM   #20
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MJL21193

“Compressibility has absolutely nothing to do with sound. Zero.”

“Density has everything to do with sound transmission.”

“Is there not one reader of this thread that understands this? I encourage him or her to jump in.”


Woa dude you have such a confident grip on this, Who would continue to try to explain to you?
Perhaps you can deduce the answer on your own.

Here is a thought experiment for you, pretend you are in space, zero G, at 1atm air pressure.

You take microscopic lead powder and evenly disperse it in the air so that say a fourth of the total volume is powdered lead.
Now, you have raised the density of the atmosphere / gas significantly above water with lead powder and you measure the properties of sound traveling through this medium.

Is the sound velocity higher like you say because of greater density, or lower becasue the mass driven by each spring is greater but the spring constant unchanged.?

Can you picture where the spring force comes into play?
Can you picture that any spring regardless of how “incompressible” it appears to you personally, is compressible, only the ratio of force to motion changes (like V and I or in impedance) and this is a continuum.
Can you picture the mechanism that transfers force from one air or water molecule's mass to another, IS a spring?
Can you picture this connection of springs driving masses forms the equivalent of an L&C electrical delay line and produces a finite speed of sound?
Can you imagine that all compressional sound waves travel by this mechanism, even in water or metal or Diamond?
Best,

Tom


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