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post #61 of 146 Old 04-25-2012, 05:39 AM
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Originally Posted by localhost127 View Post


Quote:
Originally Posted by arnyk View Post

No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies.

this is entirely incorrect.

That's because you are reading what you want to read, and not what I said.

And by the way, prove by means of actual math or experiments that higher density fiberglass won't help this specific project.

What you've done so far is run the phrase "gas-flow-resistivity" into the ground with a series of non-answer posts.

I never said anything about "gas flow resistivity". I was talking specifically about two different absorbent materials.

Quote:


first of all, gas-flow-resistivity is the key value regarding the porous insulation, NOT density as perpetually propagated so often.

No contest. I've never said otherwise. Your continual harping on this topic and false criticisms serves nobody but perhaps yourself.

I commented on some specific construction details, and in this post a lame attempt is being made to turn construction details into a global statement about how sound absorbers work.

Of course gas-flow-resistivity is of the essence, and no matter how you spin it, I've never said otherwise.

If you'd like to claim that loose fiberglass thermal insulation has more gas-flow-resistivity in the lower audio range than the same material in the form known as Dow Corning 705 please be my guest.

But, when you do that don't just make false claims about my comments, wave your hands, and throw some technical terms around. Actually contribute something. Do you actually know anything but a few catch-phrases and how to make false statements about other people's posts?

Please actually show what the materials being discussed do to system bass response in the application we are discussing.

If you haven't noticed, you've completely lost the OP.
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post #62 of 146 Old 04-25-2012, 06:07 AM
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Quote:
Originally Posted by arnyk View Post

That's because you are reading what you want to read, and not what I said.

so let's go back and re-read your original statement of which i replied,

"No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies."

you claim "fact" with zero measurements, models, etc of your own. so you expect the onus to be on ME to provide data for YOUR global claims?

and i provided modeling via AFMG SoundFlow that shows how pink fluffy (5000rays/m) loosely filled fiberglass will outperform higher GFR OC703 (and OC705 is even higher GFR) across the LF range.

you've probably been recommending OC705 for years and simply had your world turned upside down upon this "realization" and thus, need to make an attempt to save-face.

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Originally Posted by arnyk View Post

And by the way, prove by means of actual math or experiments that higher density fiberglass won't help this specific project.

actual math? you mean the transfer function forumulas from Acoustic Absorbers and Diffusers (D'Antonio/Cox)?

i didn't say the higher density fiberglass "won't help" - instead, i gave a more effective solution based on a different material. there is no getting around that porous insulation is a velocity-based absorber and LF content has long frequencies of which means the porous LF absorbers need to be 1) physically large with respect to wavelength, and 2) placed (or spaced away from rigid boundary) into areas of high particle velocity.

are you in contention with either of these two statements?

and from the "actual math", we know that as the traps get thicker and thicker (required for the longer wavelengths), a material with LOWER GFR is more effective across the bandwidth!

you've basically provided a more expensive and less effective solution for broadband LF absorption with respect to OC705 vs pink fluffy porous insulation.


Quote:
Originally Posted by arnyk View Post

What you've done so far is run the phrase "gas-flow-resistivity" into the ground with a series of non-answer posts.

I never said anything about "gas flow resistivity". I was talking specifically about two different absorbent materials.

uhh, and just what is the key value here that dictates the difference between the two material's performance?



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Originally Posted by arnyk View Post

No contest. I've never said otherwise. Your continual harping on this topic and false criticisms serves nobody but perhaps yourself.

I commented on some specific construction details, and in this post a lame attempt is being made to turn construction details into a global statement about how sound absorbers work.

Of course gas-flow-resistivity is of the essence, and no matter how you spin it, I've never said otherwise.

you've never said otherwise?
have you ever mentioned gas-flow-resistivity in your commentary? i don't see any reference to such correct terminology in your search history.

the only posts where you reference GFR is in response to my or dragonfyr's commentary.

hmm,
http://www.avsforum.com/avs-vb/showp...98&postcount=4

arny - "It's not clear at all what the above all means,"

and please detail to me the "global statements" im making based on "how sound absorbers work". why don't you provide detailed commentary of how sound absorbers work?



Quote:
Originally Posted by arnyk View Post

If you'd like to claim that loose fiberglass thermal insulation has more gas-flow-resistivity in the lower audio range than the same material in the form known as Dow Corning 705 please be my guest.

i don't think you understand what the term means based on this statement.

Quote:
Originally Posted by arnyk View Post

But, when you do that don't just make false claims about my comments, wave your hands, and throw some technical terms around. Actually contribute something. Do you actually know anything but a few catch-phrases and how to make false statements about other people's posts?

yes, attack me for using "technical terms" while we discuss physics and actual acoustical behavior in the real world. is this some sort of default fall-back psychological behavior on this forum? when you are unfamiliar with a topic (or proven wrong on an acoustic misconception), you simply attempt to invalidate the other user by their use of "technical terms"?

face it - you were just called out.
and this is your response? why don't you provide some data, measurements, modeling of your own instead of commentary like this previous post of which has ZERO substance related to the topic.

"actually contribute something" -- yeah, let's see - i detailed to the OP how porous absorption works, where it must be placed in order to be most effective, a cheaper and more effective material to use as a solution, AND i also went into detail about more ideal LF absorbers (pressure-based) and even linked to many different commercial products for sale!! you don't call that "contributing"?

AFMG SoundFlow is free for 30day trial if you wish to experiment; and while you're at it, you may want to investigate REFLEX as well (wonderful tools).
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post #63 of 146 Old 04-25-2012, 06:20 AM
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Originally Posted by localhost127 View Post

so let's go back and re-read your original statement of which i replied,

"No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies."

you claim "fact" with zero measurements, models, etc of your own. so you expect the onus to be on ME to provide data for YOUR global claims?

I didn't make a global claim. I said that " higher density fiberglass can be more effective at lower frequencies"

All I need is one instance where higher density fiberglass is more effective at lower frequencies to have a correct statement.

For your claim that my statement "is entirely incorrect" to be true, you have to prove a global statement.

As far as your alleged Soundflow results go, I just searched for them, and I can't find any comparisons involving 705. Perhaps you have a URL and post number?
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post #64 of 146 Old 04-25-2012, 06:22 AM
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and speaking of arny's "global" statements - check out his history here on how he makes assumptions about users he doesn't even know -

arny's comments:
http://www.avsforum.com/avs-vb/showp...5&postcount=15

the response:
http://www.avsforum.com/avs-vb/showp...1&postcount=18
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post #65 of 146 Old 04-25-2012, 06:27 AM
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Originally Posted by arnyk View Post

As far as your alleged Soundflow results go, I just searched for them, and I can't find any comparisons involving 705. Perhaps you have a URL and post number?

why don't you simply tell us why you recommend 705 vs any other material - what data are you using to make your recommendations?

you've never used a porous absorber calculator? impedance tube (normal incidence) measurements? AFMG SoundFlow is available for free 30-day trial; why don't you explore and experiment for yourself!

and if you're so familiar with gas-flow-resistivity, then you should already know the approx. GFR values for the relevant materials we are discussing.

i gave a more effective solution based on a different material. there is no getting around that porous insulation is a velocity-based absorber and LF content has long wavelengths of which means the porous LF absorbers need to be 1) physically large with respect to wavelength, and 2) placed (or spaced away from rigid boundary) into areas of high particle velocity.

are you in contention with either of these two statements?
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post #66 of 146 Old 04-25-2012, 06:38 AM
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Originally Posted by localhost127 View Post

why don't you simply tell us why you recommend 705 vs any other material - what data are you using to make your recommendations?

I asked a simple question, namely where your alleged results disproving my simple comment were posted.

Since you don't want to respond to that simple request, but instead appear to to be ready to pick yet another fight, I conclude that the results you claimed don't actually exist.

Please correct me if I am wrong about your inability to back up your own claims about your own results.
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post #67 of 146 Old 04-25-2012, 07:52 AM
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Thanks for the encouragement, I hope you're right. I just can't help but feel that no matter what I do, the room will not change in sound. Dumb thought I know, but until I make a change that I can honestly hear, I will continue to think that way

One major thing to consider, your main listening position is going to be at the quarter wavelength, bad things happen in this area. That is why if you eq to your MLP, other parts of the room are going to sound boomy, vis a vis, the closer you get to the boundaries in the room, the more pronounced the bass is going to be. Since placement of the subs is obviously out of the question perhaps do the crawl test with your RS meter and see how different parts of your room are reacting, not just the two listening positions.

Oh and also, dropping that peak at 58hz is going to make a MAJOR difference. That frequency is smack-dab in the middle of where people perceive the peak in response as being "boomy" try this before all else.

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post #68 of 146 Old 04-25-2012, 10:02 AM
 
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Quote:
Originally Posted by arnyk View Post
I asked a simple question, namely where your alleged results disproving my simple comment were posted.

Since you don't want to respond to that simple request, but instead appear to to be ready to pick yet another fight, I conclude that the results you claimed don't actually exist.

Please correct me if I am wrong about your inability to back up your own claims about your own results.
Local, why even try? You are stuck doing actual research into topics whereas others foundation is faith and belief. And inertia from repeating he same misnomers over and over until they become fact.

Its a shame that none of the oft made original "simple comment(s)" are seemingly never substantiated.

Nor are texts such as Acoustic Absorbers and Diffusers ever read or referenced as well that would render this running gag where density is imagined to be a valid determinant of absorptive quality moot.

But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:
Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.

When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."


Don't worry about the part numbers - the operative terms are the GFR values.

...Maybe we should alert them to the ease of referencing density figures rather than GFR values?

Funny how the 'audiophile' community lags so far behind what has known within common acoustics and noise control engineering circles.

But why should anyone expect such notions more often derived from marketing brochures to be substantiated when belief is more important than objective substance?

Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.

But whatever you do b'rer fox, Don't throw me into that briar patch where one might actually read Acoustic Absorbers and Diffusors and find out how this stuff actually works!!

 

OC703 vs OC PF3350 Ames Wind Tunnel.pdf 77.677734375k . file
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post #69 of 146 Old 04-25-2012, 02:40 PM
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Originally Posted by Digital_Chris View Post

I agree, it is odd, I'm not sure why my response drops off dramatically that early. I used the Behringer ECM8000 mic with the generic calibration file from the REW forum. Maybe I can do a sweep with the mic right in front of the speaker(s) to see if it's the speaker or room? Could it be the AVR that is causing the decent?

First thing to do is calibrate your sound card. REW does this for you. Next, if you can capture the output from the processor and make sure there is no roll off there. If all is calibrated, then maybe you have too much high frequency absorption. What is the nature of the panels on the walls? How thick are they and what are they made of? Are you able to temporarily remove them and remeasure?

Also was the mic on axis from your center speaker? If so, that rules out off-axis response of the speakers being the culprit. BTW, if you can, it would be good to tilt your L&R speakers toward the center seat. Right now you are hearing on-axis for center but off-axis for L+R.

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I do have a FBD inline between the AVR and the EP4000, the 1124 I believe, so I will be able to tame those peaks. Will that one adjustment of -10db at 58hz make that much of a difference in the overall sound? I got the idea that it will take multiple adjustments and dramatic room treatments to cure most of that boomy bass, hopefully I'm wrong?!

As I described in my article, dramatic room treatment is not necessary to get there. Use the EQ to pull down that 58 Hz and pull that down. You will hear the difference immediately and clearly. Right now, your bass level itself as a whole is much higher and then top of that you have that resonance. Pull one of them down and it should make a big difference in that area. Your bass will become "tight."

Try turning your subs on and off while some music with good bass is playing. All you should hear is the speaker appearing to have better low end extension. If all of a sudden you hear booming, exaggerated bass, then you are not dialed in right.

Quote:


Thanks for the encouragement, I hope you're right. I just can't help but feel that no matter what I do, the room will not change in sound. Dumb thought I know, but until I make a change that I can honestly hear, I will continue to think that way

That's cool. If gives you motivation to try these ideas .

Quote:


What do you mean by making sure that my subs have clean proper output and how would I filter the unwanted dirtyness out?

Thanks a lot amirm

Just measure them by themselves and notice what the frequency response looks like when they get outside of their comfort zone/crossover frequency. Say you have that set to 80 Hz, measure up to 500 Hz and see what you have. Ideally it would just slope down to nothing. But if all of a sudden you see peaks going up in amplitude as frequencies go up, then put a filter there and pull them down. You never know if there are resonances that set in from your front wall, etc.

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post #70 of 146 Old 04-25-2012, 02:46 PM
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Quote:
Originally Posted by dragonfyr View Post

But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:
Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.

When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."

great reference - thanks,

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Originally Posted by dragonfyr View Post

Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.

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post #71 of 146 Old 04-26-2012, 06:16 AM
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Quote:
Originally Posted by localhost127 View Post

and speaking of arny's "global" statements - check out his history here on how he makes assumptions about users he doesn't even know -

arny's comments:
http://www.avsforum.com/avs-vb/showp...5&postcount=15

Since the comment began with "LOL", this is obviously a pathetic effort to make a mountain out of a molehill.


the response:
http://www.avsforum.com/avs-vb/showp...1&postcount=18

"And I have worked more hours with professional SR systems than you have listened to them. Hell, I will bet I have spent more hours actually designing large SR systems than you have spent listening to them."

Given that I'm not exactly a spring chicken, does he really know what he is claiming? Besides, he does not rebut my actual claim directly.

If you are going to fault people who make global assumptions about unknown people, then you need to first work over this dragonfyr guy. ;-)

Your intent with this post is to tell a joke, not make a fool out of yourself, right? ;-)
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post #72 of 146 Old 04-26-2012, 06:35 AM
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Originally Posted by dragonfyr View Post

Local, why even try? You are stuck doing actual research into topics whereas others foundation is faith and belief. And inertia from repeating he same misnomers over and over until they become fact.

Its a shame that none of the oft made original "simple comment(s)" are seemingly never substantiated.

Nor are texts such as Acoustic Absorbers and Diffusers ever read or referenced as well that would render this running gag where density is imagined to be a valid determinant of absorptive quality moot.

But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:
Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.

When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."


Don't worry about the part numbers - the operative terms are the GFR values.

...Maybe we should alert them to the ease of referencing density figures rather than GFR values?

Funny how the 'audiophile' community lags so far behind what has known within common acoustics and noise control engineering circles.

But why should anyone expect such notions more often derived from marketing brochures to be substantiated when belief is more important than objective substance?

Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.

But whatever you do b'rer fox, Don't throw me into that briar patch where one might actually read Acoustic Absorbers and Diffusors and find out how this stuff actually works!!

The comparison fails on several grounds.

(1) My comments related to this application and this application only:



Critical points:

(1) This application involves home thermal insulation which has a typical density of 0.4 to 0.6 pounds per cubic foot.

(2) This application applies to an absorber whose average depth appears to be about 5 inches.

(3) This application applies to an absorber that opens up into the space it serves through an apparently acoustically transparent grille cloth.

The Ames research paper exists in several forms, more complete versions of which reveal the following significant differences:

(1) As mentioned above the thickness of the Ames absorber was about twice the depth of the absorber I commented on.

(2) A little research suggests that the PF 3350 material Ames used has a density of about twice - more specifically about 1 pound per cubic foot.

(3) More complete versions of the referenced paper show more details about the Ames wind tunnel application. Please see: http://ntrs.nasa.gov/archive/nasa/ca...1988003624.pdf Figures 1 and 2.

I see no effective comparison between the two applications. The Ames wind tunnel application involved multiple layers with spacing between the layers and was covered by a perforated metal cover, not an acoustically transparent grille cloth.

Nice try guys, but no cigar!
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post #73 of 146 Old 04-26-2012, 12:04 PM
 
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Quote:
Originally Posted by arnyk View Post

The comparison fails on several grounds.

(1) My comments related to this application and this application only:



Critical points:

(1) This application involves home thermal insulation which has a typical density of 0.4 to 0.6 pounds per cubic foot.


LOL!!!! Let's see, is that mass comprised of one large strand? Or is that mass comprised of thousands of smaller strands? Mass simple tells you how much of something there is, it tells you NOTHING about how the mass is distributed.

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Originally Posted by arnyk View Post

(2) This application applies to an absorber whose average depth appears to be about 5 inches.

Let's see. A Superchunk style absorber, being 24 inches on each wall boundary and 34 inches on the face - which is typically covered with a minimum of 6 mill plastic in order to retain specular frequencies above 600 Hz in the room, but which can easily be covered by luann or MDF in order to render is more effectively as a bass only low frequency absorber.

The maximum normal depth of the Superchunk absorber using those dimensions is 17 inches. Ironically, that is less important than the effective width of the material.

The irony is that perforated metal covers can easily be used to extend the mid frequency effectiveness, as is so commonly done in industrial application where resiliency is required.

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Originally Posted by arnyk View Post

(3) This application applies to an absorber that opens up into the space it serves through an apparently acoustically transparent grille cloth.

First, the presence of a perforated membrane is moot as the configuration would be equal for both the compared PF3350 and the OC703 materials.

And furthermore, if one were knowledgeable about the use of perforated materials and their very mature use in noise abatement, one would know that they are effective as mid-high frequency absorbers. And technically, a cloth is a perforated membrane as well. Again, "acoustically transparent" is a misnomer, as it is only pertinent to the degree that it significantly affects the behavior of sound at frequencies of which we are concerned. It does NOT mean that it is truly acoustically transparent at ALL frequencies. Damned that fisiks stuff.

But as we shall see, the perforated covers were not used for the advantages they can offer in terms of increased mid and high frequency absorption. Instead they were used to address matters of resiliency! And the issue of their negligibly small contributory effects with regard to absorbancy are noted in the conclusion as well.

To quote from the oft ignored Acoustic Absorbers and Diffusers:

"Often porous absorbers are covered by a thin membrane; this might be achieved by wrapping the material in thin plastic or similar. This is done to prevent the absorber being damaged or to stop fibers from the absorber being lost. The effect of the membrane will be to reduce the high frequency absorption."

But in any case, their effects would be the same, regardless of the materials chosen, materials whose own effectiveness was rather radically different - which speaks to the very point of the thread and the critical causal nature of the effect of gas flow resistivity on the issue rather than density - ironically, a measure not mentioned once in the paper.

Quote:
Originally Posted by arnyk View Post

The Ames research paper exists in several forms, more complete versions of which reveal the following significant differences:

Hmmm... I am only aware of it in its complete form. Perhaps that is why some might be aware of the effects of gapping and the effects of the perforated panels that contribute only structural resiliency unlike others commenting on the paper who are obviously unaware of the facts. I might suggest referring only to the complete paper, as apparently much of the substance was missing in alternatively referenced copies whereas the complete paper more than adequately addresses the points raised here.

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Originally Posted by arnyk View Post

(1) As mentioned above the thickness of the Ames absorber was about twice the depth of the absorber I commented on.

Yes, it was 8 inches with a 2" gap, which, as they observed, performed equivalent to a 10 inch porous absorber. A fact clearly stated in the conclusion.

The maximum effective depth of the Superchunk is 17 inches, and as mentioned, the more critical dimension is the effective width, of which the maximum face is 34 inches.

A point superfluous to the absorptive capacity measure of the porous material itself, assuming it is sufficiently large to be effectively 'seen' by the wavelengths in question. And since 100 Hz is 11.25 feet long, and 1/4 of that equals 2.81 feet or 33.72 inches. And as a material must be at least 1/10 the wavelength to have any effect (p.131 of AA&D 1st ed.), that corresponds to 13.5 inches....

One should note that the lower in frequency that one desires to treat with porous absorption, the larger the treatment must be in order to address the physics of longer wavelengths, right? Too small and the sample is not even effectively 'seen' by the wavelengths in question, and the energy simply diffracts around it as if it were not there. Thus, if the sample is too small it really doesn't matter what material is used. I am assuming that anyone worried about this issue is cognizant that this condition be met...

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Originally Posted by arnyk View Post

(2) A little research suggests that the PF 3350 material Ames used has a density of about twice - more specifically about 1 pound per cubic foot.

Only someone preoccupied with an inconsequential measure would go to so much trouble to try to extrapolate inconsequential units which are not even addressed in the paper!

They utilized a material whose gas flow resistivity was 4100 mks rayls, as compared to 27,000 mks rayls. Roughly 1/7 the GFR. And the amount of material was sufficient to be 'seen' by the wavelengths at issue.

If one wants to misuse the density figures, so be it. Assuming a linear relationship, if OC703 is ~3 pounds/unit measure, then the PF3350 was roughly .43 pounds/per unit volume. ...As if the density has necessarily anything to do with gas flow resistivity give the differences in mass distribution within the material structure! ...Its that fisiks stuff again...

Quote:
Originally Posted by arnyk View Post

(3) More complete versions of the referenced paper show more details about the Ames wind tunnel application. Please see: http://ntrs.nasa.gov/archive/nasa/ca...1988003624.pdf Figures 1 and 2.

I see no effective comparison between the two applications. The Ames wind tunnel application involved multiple layers with spacing between the layers and was covered by a perforated metal cover, not an acoustically transparent grille cloth.

Multiple layers?
It involved ONE layer of porous material and a 2 inch gap of air. The effects of the perforated membranes is discussed at length in the piece, and you can refer to their conclusion for a well stated synopsis of their relative lack of acoustic pertinence here, whereas it was actually employed for mechanical resiliency.

The fact that no comparison between basic material absorption characteristics and the fact that such a causal comparison is dependent upon gas flow resistivity is quite apparent.

We have already addressed that issue of the gapping (which should be well understood even here on this forum by now) and the effects of perforated material; but apparently some still lack an awareness of such issues as the effects of spacing porous absorptive material from a wall - given its near free lunch effective attributes where the advantage is stated rather clearly in the report.

But rather than explain them once again, here they are in a very neatly summarized form as quoted from the Ames document:



The conclusions can be summarized as follows:

Sound absorption in the low to mid-frequency range can be increased by the use of PF 3350 fiberglass (nominal flow resistivity 4100 mks rayls ) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches. When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap.

The presence of the fiberglass cloth improves the sound absorption of the lining, but there appears to be reasonable latitude in the choice of flow resistance of the choice of the flow resistance of the cloth.

Increasing the thickness of the perforated plate from 22 gauge to 12 gauge, increasing the plate open area from 33% to 40%, or introducing a perforated backing plate has only a small effect on the predicted sound absorption coefficient.

It is recommended that the perforated plate be thicker than 22 gauge for structural reasons.

The installation of a wire mesh screen between the perforated face plate plate and the fiberglass cloth is recommend for erosion protection. The mesh should be sufficiently open that it does not effect acoustic performance of the lining.

Representative characteristics of the wire mesh screen are given in Table 1.




In fact, I would suggest folks take a look at the figure on pages 36-41 and note that the performance of the perforated plate varies only slightly among the various sample changes in the mid-high frequencies. Again, a fact one would easily know if they were familiar with the mature design and use of perforated materials for noise abatement in industry.

AN ANALYSIS OF SOUND ABSORBING LININGS FOR THE INTERIOR OF THE NASA AMES 80x120-FOOT WIND TUNNEL

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Originally Posted by arnyk View Post

Nice try guys, but no cigar!

Seeing as we do not smoke, a good thing. But I might suggest others lay off smoking stuff until they gain a more complete understanding of the causal relationship between gas flow resistivity and absorption, the behavior of perforated plates for use in noise abatement and control, and jettison the notion of density, which only accounts for how much stuff is available per unit volume but utterly fails to account for the critical factors of how such mass is distributed within said unit volume - unlike gas flow resistivity which via its focus on porosity and tortuosity, and their effects on the acoustical impedance of a material, does.


Do us all a favor, and before trotting out another ill-formed case for density being a determinant causal basis for evaluating the absorptive behavior of porous material, PLEASE read Acoustic Absorbers and Diffusers and learn a bit about the physics of how the material actually works. And then, if one is really brave, they can actually access the various studies and models upon which the prediction and modelling of the materials performance are based.

This topic is done.
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Do us all a favor, and before trotting out another ill-formed case for density being a determinant causal basis for evaluating the absorptive behavior of porous material,

If density doesn't matter, why do we put any absorptive material into the absorber at all?

Quote:


PLEASE read Acoustic Absorbers and Diffusers and learn a bit about the physics of how the material actually works.

If you made a credible argument, I'd plunk down the $80-160 in a heartbeat. Of course if you knew the topic as well as you seem to claim, you'd be able to cite a relevant online document in a relevant, believable way.

Quote:


And then, if one is really brave, they can actually access the various studies and models upon which the prediction and modelling of the materials performance are based.

Given how you blew off this one, what's the chance you being able to accomplish what you demand of others?

Quote:


This topic is done.

What's done is your credibility.

Clear points were made and you dismissed them all without any reference to any external support other than to drop their names.

You may feel that you're all the reference you need, but maybe not everybody agrees with you.

The interesting thing is that with all the smoke and mirrors, dogs and ponies, you never actually provided an apples-to-apples comparison or ran the item we are discussing through any of the software you said would resolve the question.

Tell me, do your fingertips get frostbit when you wave your hands this fast? ;-)
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post #75 of 146 Old 04-26-2012, 12:51 PM
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thanks for putting the Science back in AVS, dragon.

Quote:
Originally Posted by arnyk View Post

If density doesn't matter, why do we put any absorptive material into the absorber at all?

Quote:
Originally Posted by arnyk View Post

What's done is your credibility.

ignorance preserved. he still doesn't understand the topic of porous insulation, gas-flow-resistivity, complex impedance, etc.

im still waiting on the flow-resistivity values for OC705.

when can we expect any 'science' in your commentary?

there is NO meat in your response to dragon.
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Quote:
Originally Posted by localhost127 View Post

thanks for putting the Science back in AVS, dragon.

One dirty hand washes the other.



Quote:
ignorance preserved. he still doesn't understand the topic of porous insulation, gas-flow-resistivity, complex impedance, etc.

If either of you you had said something useful and instructive, the results may well be different, were different results reasonable.

What comes through well is that you are very pleased with yourself. Since that seems to be the most important thing to you, well done!
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Originally Posted by arnyk View Post

If density doesn't matter, why do we put any absorptive material into the absorber at all?

So now the substance of his reply fails to account for the NATURE of the material and instead focuses on the mere existence of material.

Density is a secondary term that has an extremely limited applicability in the realm of absorption. Its use as a derivative factor assumes that all of the structural material characteristics remain constant except for the degree of compression of the material structure. One could just as accurately say that the behavior of materials of similar construction but differing degrees of compression based upon the color of their wrapper, where the red one is more absorbent than the blue one which is more absorbent than the yellow one. But only a fool would mistake such a derivative attribute as exhibiting a casual absorptive nature.

Such a comparison is one of convenience and is NOT portable between materials whose internal structure varies Thus a semi-rigid bond fiberglass cannot be compared to a non bound fiberglass material, nor to another fiberglass material featuring differing porosity or tortuosity or strand orientation (anisotropism). And the critical factors that directly 'cause' the absorptive characteristics are the variance in the porosity (fraction of air volume in the material), material structure (anisotropism or orientation of fibers, tortuosity), both of which contribute to the characteristic known as gas flow resistance.

Quote:
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If you made a credible argument, I'd plunk down the $80-160 in a heartbeat. Of course if you knew the topic as well as you seem to claim, you'd be able to cite a relevant online document in a relevant, believable way.

I have a reference library of such materials. And they ALL deal with the material structure and rely on GFR rather than density. The fact is that you refuse to even read an overview of the concepts and now expect me to go and do YOUR work for you.

Its not up to me to convince you. I really don't care what what you fantasize. I merely have to mention the actual basis by which such behavior is gauged.

I have cited a prominent source that synopsizes of the major concepts, which also therein cites many of the pertinent source documents.

Maybe you can find a grade schooler who can help you navigate the scary library sufficient to access the reference desk in order to obtain the book via the inter-libary loan program without having to pay the money that others have had to in order to become more familiar with concepts about which you are obviously not familiar - and whom did not whine that it is others responsibility to read and learn for them.

Quote:
Originally Posted by arnyk View Post

Given how you blew off this one, what's the chance you being able to accomplish what you demand of others?

Clear points were made and you dismissed them all without any reference to any external support other than to drop their names.

LOL! Actually, you are wrong once again as I have made no recent reference to any of the models or to the actual researchers who have done the original research.

I merely referenced a source that does discuss many of the original sources. And I mentioned a few of the variables that are pertinent to their study, of which density is not a significant determinant factor. Get a copy of the book. I am not responsible for you doing your homework.


Quote:
Originally Posted by arnyk View Post

The interesting thing is that with all the smoke and mirrors, dogs and ponies, you never actually provided an apples-to-apples comparison or ran the item we are discussing through any of the software you said would resolve the question.

Yes, I can see where a complete read of the Ames study would confuse one seeing as they reference the behavior and implications of all of the factors you subsequently mischaracterize and dismiss without a single mention of "density".

And I have many advanced software packages that address the acoustical impedance of materials and boundaries as well as enable the actual measurement of absorption as well as diffusion that I had to save and buy based upon MY additional research and learning that I had to perform in order for them to be of use, as they are not substitutes for understanding the basic principles.

And here you sit on your posterior whining that others have not done YOUR due diligence that you now demand of them while absolving yourself of any and all responsibility, the least of which is to even discover the pertinence of a concept.

But its cute to see that you are now reduced to personal attacks devoid of any reference to any acoustical concepts.

You're done.

Ironically (unfortunately) our experience is not unique...
http://groups.google.com/group/rec.a...zkWdXVgvdvw?pl

Its also interesting that even commercial sites have noted this fact as well as the fact that OC has measured and determined that OC703 is a better absorber of LF energy than OC705 for some time as well...
http://www.readyacoustics.com/index....3_4&faqs_id=36

"Chapter 7: Sound Absorption
...
Primary material parameters affecting absorption:
• porosity (fraction of air volume in the material)
• structure factor (orientation of fibers, tortuosity)
• flow resistance"
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I dont see this argument as helping the OP, and Im not taking sides here at all. Ive enjoyed reading the parts of each response where there is some science to help me learn more about absorbtion techniques, but please dudes, start a new thread on this if you want to continue the banter. With the exception that the OP is ok with the pissing match going on in his thread, otherwise, carry on gents Oft times it is when two sides oppose, that the most is learned, and that goes for life in general, not just sound absorbtion...
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Quote:
Originally Posted by dragonfyr View Post

But its cute to see that you are now reduced to personal attacks devoid of any reference to any acoustical concepts.

basic human nature and easily identifiable.

i think the root of the contention is he has likely been recommending oc705 for LF porous absorption for some considerable amount of time. suddenly realizing that the misconception that 'denser is better' is invalid may be a tough pill to swallow! every other acoustical forum has gone through the same teething process regarding such facts.
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Quote:
Originally Posted by beastaudio View Post

I dont see this argument as helping the OP, and Im not taking sides here at all. Ive enjoyed reading the parts of each response where there is some science to help me learn more about absorbtion techniques, but please dudes, start a new thread on this if you want to continue the banter. With the exception that the OP is ok with the pissing match going on in his thread, otherwise, carry on gents Oft times it is when two sides oppose, that the most is learned, and that goes for life in general, not just sound absorbtion...

regarding the OP,
he's already been notified his surface coverage is NOT sufficient, period.

and also that since he is limited with respect to real estate of where he can place such absorbers, that he is better off building or procuring pressure-based absorbers that do NOT need to be thick as they are NOT required to be placed into areas of high particle velocity in order to be effective! ...but instead, placed against the boundary where pressure is maximum (and velocity approaches zero).

http://www.avsforum.com/avs-vb/showp...0&postcount=55

i even provided links to commercial pressure-based resonator absorbers for more information on actual products and their actual measured performance.

there is NOTHING else to say to the OP with respect to LF absorption unless he is able to add more surface coverage for his porous, velocity-based absorbers - or to source pressure-based resonator traps.

and there is no "pissing match" or "debate" going on - just the presentation of facts regarding porous insulation, and then the merciless blind contention of said facts via personal attacks lacking any scientific value. eg, "shoot the messenger".
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^^^

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Quote:
Originally Posted by localhost127 View Post

basic human nature and easily identifiable.

Exemplified by self-serving posts like this one!
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post #83 of 146 Old 04-26-2012, 02:19 PM
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Worked out examples relevant to the topic?

AFAIK, these equations are over your head to work with, except to post as graphics.
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Quote:
Originally Posted by arnyk View Post

Worked out examples relevant to the topic?

AFAIK, these equations are over your head to work with, except to post as graphics.

another post devoid of substance.
you have nothing of scientific value to offer here wrt: the subject of porous absorption.
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post #85 of 146 Old 04-27-2012, 03:10 AM - Thread Starter
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Alright guys, this has gotten WAY out of control. To the acoustic guru's that are posting in here, if you need to prove to others in an incredibly lengthy manner (other than me), that they're wrong about something, please keep it in PM's, or in another thread. If I'm wrong/mislead about a statement or an idea, keep your posts friendly and simple, I'm just trying to learn here, to an extent anyway. All of this technical data and "big words that I don't understand" talk is giving me a headache.

On the other hand, I do appreciate the vast amount of knowledge and vocabulary you guys have, honestly, I do, but you need to chill on the incredibly long replies, especially if they don't help me out directly. If you feel other replies are steering me in the wrong direction, you're welcome to offer your advice in a fairly simplistic and Layman's term manner, or even better, feel free to PM me if you are willing to offer advice that can relate to me and my room personally.

Thank you.
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Quote:
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another post devoid of substance.
you have nothing of scientific value to offer here wrt: the subject of porous absorption.

Just a humble little link that provides tools for designing porous absorbers with perforated fronts via a cookbook technique that many forum participants, perhaps even you, could benefit from:

http://www.iperf.org/pdfdownloads.html

more specifically: http://www.iperf.org/IPRF_DES.pdf
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Knock off the bickering guys...
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post #88 of 146 Old 04-27-2012, 06:29 AM
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Quote:
Originally Posted by Digital_Chris View Post

Alright guys, this has gotten WAY out of control. To the acoustic guru's that are posting in here, if you need to prove to others in an incredibly lengthy manner (other than me), that they're wrong about something, please keep it in PM's, or in another thread. If I'm wrong/mislead about a statement or an idea, keep your posts friendly and simple, I'm just trying to learn here, to an extent anyway. All of this technical data and "big words that I don't understand" talk is giving me a headache.

On the other hand, I do appreciate the vast amount of knowledge and vocabulary you guys have, honestly, I do, but you need to chill on the incredibly long replies, especially if they don't help me out directly. If you feel other replies are steering me in the wrong direction, you're welcome to offer your advice in a fairly simplistic and Layman's term manner, or even better, feel free to PM me if you are willing to offer advice that can relate to me and my room personally.

Thank you.

Ill continue to try and keep it up your alley, regarding your situation by asking if you have tried to pull that one peak down with your BFD yet? I still have a lot of work to do with mine, but at least down to 10hz, Im pretty close to ruler flat and it is just amazing what flat bass sounds like. I try and find my last sweep I ran.

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post #89 of 146 Old 04-27-2012, 06:35 AM
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Also, here is a link to how I managed to eq out my two XXX 18's. You can see with just a couple filters that I was easily able to get it near flat. Since then I have tweaked a little more and gotten it to sound even better, but im still concerned about the rolloff right before the 10hz line. You easily have the same capability with the BFD

http://www.avsforum.com/avs-vb/showt...2#post21819762

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post #90 of 146 Old 04-27-2012, 02:41 PM - Thread Starter
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Thanks for the link to your graphs. I haven't played around with the BFD yet, I'm going to get myself down there to run a few more graphs for both rows and see how much of a difference there is between the two. I'm afraid that if I EQ for one row, the other row will sound even worse and there will be no compromise

Do you have 1 or 2 rows of seating if your space?

EDIT: Just saw your construction pics, nice color :P Mine is just about the same. How did the wagner sprayer work out? Any streaks? How about overspray, did it cloud up the room while you were painting? I need to re-do my ceiling and was curious is the gun was the way to go
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