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Author Topic: Mass/Isolation/Frequency transfer data  (Read 4476 times)

Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #15 on: April 02, 2009, 01:56:47 pm »

index.php/fa/11852/0/
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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #16 on: April 05, 2009, 05:41:40 pm »

The current questions are these:
-Given the calculated Impedance of a boundary, how does this translate to (theoretical) reduction of SPL?
-Is this impedance the same as "acoustic impedance" I keep reading about in literature?
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Thomas Jouanjean

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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #18 on: April 06, 2009, 08:55:09 pm »

Ok, so I guess the answer is "Yes and no. Impedance of a boundary is only one form of acoustic impedance".

What about impedance vs. reduction in dB SPL? Do the results from my graph seem credible?
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Thomas Jouanjean

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Re: Mass/Isolation/Frequency transfer data
« Reply #19 on: April 07, 2009, 03:22:23 am »

Sigert wrote on Mon, 06 April 2009 19:55

What about impedance vs. reduction in dB SPL? Do the results from my graph seem credible?


On impedance VS reduction (in simplified terms): for sound to be "blocked" it implies a change of impedance. This happens when the energy meets a different surface (see isotropic vs anisotropic environments btw) with an impedance different of the air's impedance (or of the original transmitting medium). In this case when the energy goes in contact with the new surface, we are first talking of the "surface impedance" of the new medium. Part is (not always!) reflected (or diffracted) and part is transfered to the new medium which will tranfer it to adjacent materials, re-emit and there will be some loss in heat too. All depending on surface impedance and core impedance.

In this new "x" medium the energy will for ex "slow down" like in rockwool (resistance to flow), or "accelerate" like in concrete or metal (or water). Among other things, the denser (so the higher the impedance) the "faster" and vice versa.

http://en.wikipedia.org/wiki/Speed_of_sound

But what you ask is pretty straight forward and is more linked to mass: higher mass implies higher reduction. But what does higher mass imply in terms of impedance?

See where I'm going? Smile

Your graph is a lil weird...


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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #20 on: April 07, 2009, 04:57:25 pm »

Maybe if I redo one of my calculations here you could correct me.

A plane wave of single frequency 200Hz travelling through air at 344m/s is obstructed by a single leaf gypsum board wall, 25mm thick, with infinite X and Y dimensions.

Frequency f = 200Hz
Thickness h = 0.025 m
Young’s modulus E = 2,3*10^9 N/m
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Thomas Jouanjean

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Re: Mass/Isolation/Frequency transfer data
« Reply #21 on: April 08, 2009, 03:54:19 am »

Did it fast but I think you made a mistake in your Rigidity equation D. Looks like you forgot to square the poisson coeff.

FWIW, with my highly scientific "breakfast table napkin" calculation I get R=31,30 dB (rounded up) with your hypothesis (200Hz, and your found modulus etc).

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Thomas Jouanjean
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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #22 on: April 08, 2009, 05:47:11 am »

Bingo. Squaring Poisson's ratio does help. Very Happy

I'll be redirecting the rest of this thread to the physicsforums.com website. For those who wish to keep track of this thread, I'll post a link to its new home once I get a thread up and running.

Cheers,
Sigert
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franman

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Re: Mass/Isolation/Frequency transfer data
« Reply #23 on: April 08, 2009, 10:36:05 pm »

Sigert wrote on Wed, 08 April 2009 05:47

Bingo. Squaring Poisson's ratio does help. Very Happy

I'll be redirecting the rest of this thread to the physicsforums.com website. For those who wish to keep track of this thread, I'll post a link to its new home once I get a thread up and running.

Cheers,
Sigert



WHEW... Thanks Sigert... (FM   Cool )
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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #24 on: April 10, 2009, 07:39:53 pm »

I'll take that as a yes  Smile

The thread continuing this subject can be found here:
 http://www.physicsforums.com/showthread.php?p=2156032#post21 56032
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Sigert

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Re: Mass/Isolation/Frequency transfer data
« Reply #25 on: April 21, 2009, 07:01:21 am »

For people following this thread, physics forums isn't really helping out much. Anyone have any suggestions on another forum on which I could pose these questions?

By the way, I'm going through the Yale video's on physics. Brilliant source for those amongst us trying to get into the newtonian mechanics of things.
http://oyc.yale.edu/physics/fundamentals-of-physics
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