3.5" Ultratouch or 2" Ecose on front wall? - Page 2 - AVS Forum
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post #31 of 57 Old 02-24-2012, 09:10 PM
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I have always used to the term "intelligibility" instead of "quality" in the course of this discussion. That is the term you used when you first replied to my post to Brad, and I continued to stick with that term when replying to you.
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Originally Posted by dragonfyr View Post

The paper has Nothing whatsoever to do with a "recording studio" or a "recreational listening environment where you have multiple listening positions, like with a couch, let alone multiple rows".

Where did I say the paper had to do with those things? That comment was specifically in reply to localhost saying that his speakers tended to be on-axis to his listening position[singular] after I had mentioned listening off-axis (which happens when listeners are spread across a couch or multiple rows of seats).
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Originally Posted by dragonfyr View Post

Instead you might want to focus on why someone who feels "early reflections (without stated qualification) are beneficial to overall intelligibility"...

Who are you quoting? Search for the word "beneficial" in my posts (none have been edited). The reason I linked to the paper and subsequently mentioned other research was, ironically, in reply you making a general claim without stated qualification that:
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Originally Posted by dragonfyr View Post

We have already determined that high gain early reflections are detrimental to localization, imaging, and intelligibility.

[emphasis mine] All I did was present an exception.
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Originally Posted by dragonfyr View Post

And per the rule of logic, all we need do is present one exception to invalidate your overly general claims.


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post #32 of 57 Old 02-25-2012, 02:56 AM
 
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Quote:
Originally Posted by sdurani View Post

I have always used to the term "intelligibility" instead of "quality" in the course of this discussion. That is the term you used when you first replied to my post to Brad, and I continued to stick with that term when replying to you. Where did I say the paper had to do with those things? That comment was specifically in reply to localhost saying that his speakers tended to be on-axis to his listening position[singular] after I had mentioned listening off-axis (which happens when listeners are spread across a couch or multiple rows of seats). Who are you quoting? Search for the word "beneficial" in my posts (none have been edited). The reason I linked to the paper and subsequently mentioned other research was, ironically, in reply you making a general claim without stated qualification that: [emphasis mine] All I did was present an exception.


Blah blah blah.

Citing a paper dealing with the non sequitar focus on the non-applicable issue simply raising a direct signal above the noise floor is not an "exception", except as regards logic and parallel stricture.

And then saying nothing of substance.

Yes, the acoustics community (and in particular the participants in the SynAudCon colloquium) has long been well aware of the detrimental effects of early arriving HIGH GAIN reflections on intelligibility - moaning the QUALITY of the perceived signal. Editorially or literally, "We" is correct.

Oh, and for the record, participants in that colloquium were literally responsible for the development of precision microsecond delay and the need for precision signal alignment with respect to time as a result of such studies specifically in order to minimize such issues.
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post #33 of 57 Old 02-25-2012, 03:25 AM
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What's the best dampening material for gamma rays?

Well, for absorption I'd say a singularity like a Black hole would suffice, not sure how to answer your question on dampening...

btw tim, your sig "All advice, information, and instructions are subject to my legal disclaimer." "legal disclaimer" link is broken..I get the below
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My boys been sick since 2:30am with flu, so surfing avs while attending to him every 30 minutes..no REM sleep, ugh
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post #34 of 57 Old 02-25-2012, 04:29 AM
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Originally Posted by hoffmand34 View Post

Thanks for all the feedback and education. Maybe it would be less abstract to address this seemingly impossible topic in context of an actual theater room. I happen to have one handy

Take a 14x19x9 room with the seats 2ft from the rear wall and no false wall at the front. I already have 4ft long 17x17x24" 3lb/cuft superchunks in the upper rear corners. I will add full height 17x17x24" superchunks in the front two corners. I have not considered facing the superchunks because my room is still pretty "live". I have three 24x48x2" fiberglass panels spaced 2" off the rear wall and two 1" panels spaced 1" off the side walls.

I'm trying to get REW up and running but that has a bit of a learning curve.

What, if anything, should I do with the front wall? Is it all hopeless without actual ETC measurements? If I don't have that capability it seems like there should be some generally accepted treatments that are more effective than just doing nothing.

hoffmand34;
If you are adding superchunks to the front wall for broadband bass traps, consider making them bigger at 24" x 24" x 34", and using pink fluffy instead of OC703/705. There are multiple threads on that.
Also, consider to face the front side with reflective material, unless you have a specific issue that needs addressing by absorption of those reflections.

How'd you determine the location of the side and back wall panels in your room presently?
Why do you think your front wall needs treatment?
In all the posts in this thread - some really good stuff in it all - simply its not clear to me that you do have a acoustic problem that you are addressing.

Can you take 5-10 minutes and look at this link, easy to see visually the various small room models, it's 7 pages from the book "Acoustics and Psychoacoustics Applied"
http://eetimes.com/design/audio-desi...n?pageNumber=0

You have REW, and a measurement Mic already?
So you've made some $ investment.
REW is your objective data toolset, my advice is don't give up.

I've had my learning curve on REW, but once you get past the initial set-up people will help with the graphs/measurements.
Look at this thread a dummy's guide on setting up REW

I also have a thread on ETC, Using energy time curve for acoustic analysis: developing a Home Theatre primer. , -that is NOT done yet.
Due to other "life stuff", like being cubscout leader for my boys group, my astrophotography hobby (lack of sleep), etc, that was put on Hold for a re-boot.

Come spring, when I re-do my 130" screen due to humidity induced warping of the screen, I will totally remove all my existing side wall/ceiling panels and start from baseline of no treatments on the room
(besides my corner superchunks, which all have front facing reflective treatment on them)

I also will do the following:
-Pure reflective room baseline
-baseline of "the mirror tricK", as I did, with side wall 2" panels + 2" air gap
-Pure ETC approach and using 4" panels + 4" air gap at specific locations verified by ETC
-compare and make objective and subjective assessment
All above is being done utilizing porous absorbers.

Come 2014/2015, when it's new PJ time (4k +LED light engine), and I go AT front screen - with DIY L/C/R main speakers in a baffle wall, then the whole HT acoustic treatment strategy will change; diffusion, membrane absorbers, etc....but that's topic for a different thread, not buried in yours.

Long winded post, I'm a learner in acoustics, but like to learn based on reading, taking objective data, etc.
Finally, I like to summarize all that for sharing, for me its the only way I can remember something, try to share with others.
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post #35 of 57 Old 02-25-2012, 07:21 AM
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Quote:
Originally Posted by dragonfyr View Post

Citing a paper dealing with the non sequitar focus on the non-applicable issue simply raising a direct signal above the noise floor is not an "exception", except as regards logic and parallel stricture.

The paper deals with high gain early reflections and intelligibility, like in your overly generalized claim.
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Originally Posted by dragonfyr View Post

Yes, the acoustics community (and in particular the participants in the SynAudCon colloquium) has long been well aware of the detrimental effects of early arriving HIGH GAIN reflections on intelligibility - moaning the QUALITY of the perceived signal.

But you just said that intelligibility should not be confused with quality.

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post #36 of 57 Old 02-25-2012, 07:46 AM
 
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LOL!

No genius, the resource presented drew a distinction in the realm of hearing aid research where THEY draw a common distinction between basic gain issues under the term "intelligibility" and additional qualitative aspects that directly affect the more common use of the term "intelligibility" in lAS/SAS acoustics.

In hearing aid research there is a significant difference and concern with distinguishing the signal of interest from background noise.

And with the exception of this forum where the effort is wasted, simple unsimplified S/N is not generally the focus in small room acoustics with the exception of board rooms and lecture halls. And it is generally only an issue on LAS when the program material dynamics drop below the ambient noise floor level generally defined by the reverberant noise floor.

So instead we are not concerned with simply being able to hear the program source, but instead we are focused on intelligibility used in a manner addressing the quality factors above and beyond mere gain - just as Peter Mapp refers to in the referenced source.

Your cited paper neither deals with that aspect, nor do any of the other subsequent comments offered in the non sequitar mistaken response done via the equation of research done for hearing aids that is not consequential to the amplified adequate gain sources to which we care concerned either in a applications about which we are here concerned ion the form of a HT or a critical surround or 2 channel listening room.

In fact, you have offered nothing to indicate that the insights you claim so pertinent are even applicable to the situation at hand, even as your own recommendations are completely opposite of the recommendations cited by the paper.

But that's not unexpected when a Google search produces an unread paper with a title mistakenly interpreted to apply to the problem at hand.

Nor does he lend any credence to the fact that your own earlier recommendations are completely in conflict with the source you yourself erroneously presented as a rebuttal.brought - with regards to which even you ignore.
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post #37 of 57 Old 02-25-2012, 08:08 AM
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Quote:
Originally Posted by dragonfyr View Post

So instead we are not concerned with simply being able to hear the program source, but instead we are focused on intelligibility used in a manner addressing the quality factors above and beyond mere gain

And that's what the paper deals with, intelligibility, which you are now trying to conflate with quality.

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post #38 of 57 Old 02-25-2012, 11:48 AM
 
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There is more to intelligibility than simple S/N, of which your cited paper is concerned with simply increasing the gain of the unsimplified source signal and hence the S/N. It is not a study of all the factors that play a role in the larger topic of intelligibility.

But its not my job to do the research that you should be doing, since you are not aware of this information.

You will see a few of the additional factors listed in segments posted on the attached PDF from Sound System Engineering by Davis and Patronis. Both authors of whom are prominent in the field.

And you will also see included a note regarding who aforementioned SOME of the "We" refer.
And considering the date of the publication of the material being from being 2006 for the 3rd edition of which this reference was current, there are at least 100 folks professionally involved with acoustics for whom the facts are "well known" and of whom all have complete data sets of all the compiled information.

 

Intelligibility1.pdf 157.6357421875k . file

 

Intelligibility2.s.pdf 409.0283203125k . file
Attached Files
File Type: pdf Intelligibility2.s.pdf (409.0 KB, 6 views)
File Type: pdf Intelligibility1.pdf (157.6 KB, 5 views)
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post #39 of 57 Old 02-25-2012, 02:48 PM
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Quote:
Originally Posted by sdurani View Post

And that's what the paper deals with, intelligibility, which you are now trying to conflate with quality.

the paper speaks for itself and i've already commented on the irrelevancy of it.

how loud is your hvac?
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post #40 of 57 Old 02-25-2012, 02:50 PM
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Originally Posted by dragonfyr View Post

You will see a few of the additional factors listed in segments posted on the attached PDF from Sound System Engineering by Davis and Patronis. Both authors of whom are prominent in the field.

no no, people prefer the mickey-mouse publications and papers to support their theory rather than the heavyweights who constructed the foundation for modern acoustics.
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post #41 of 57 Old 02-25-2012, 04:58 PM - Thread Starter
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Quote:
Originally Posted by mtbdudex View Post


hoffmand34;
If you are adding superchunks to the front wall for broadband bass traps, consider making them bigger at 24" x 24" x 34", and using pink fluffy instead of OC703/705. There are multiple threads on that.
Also, consider to face the front side with reflective material, unless you have a specific issue that needs addressing by absorption of those reflections.

How'd you determine the location of the side and back wall panels in your room presently?
Why do you think your front wall needs treatment?
In all the posts in this thread - some really good stuff in it all - simply its not clear to me that you do have a acoustic problem that you are addressing.

Can you take 5-10 minutes and look at this link, easy to see visually the various small room models, it's 7 pages from the book "Acoustics and Psychoacoustics Applied"
http://eetimes.com/design/audio-desi...n?pageNumber=0

You have REW, and a measurement Mic already?
So you've made some $ investment.
REW is your objective data toolset, my advice is don't give up.

I've had my learning curve on REW, but once you get past the initial set-up people will help with the graphs/measurements.
Look at this thread a dummy's guide on setting up REW

I also have a thread on ETC, Using energy time curve for acoustic analysis: developing a Home Theatre primer. , -that is NOT done yet.
Due to other "life stuff", like being cubscout leader for my boys group, my astrophotography hobby (lack of sleep), etc, that was put on Hold for a re-boot.

Come spring, when I re-do my 130" screen due to humidity induced warping of the screen, I will totally remove all my existing side wall/ceiling panels and start from baseline of no treatments on the room
(besides my corner superchunks, which all have front facing reflective treatment on them)

I also will do the following:
-Pure reflective room baseline
-baseline of "the mirror tricK", as I did, with side wall 2" panels + 2" air gap
-Pure ETC approach and using 4" panels + 4" air gap at specific locations verified by ETC
-compare and make objective and subjective assessment
All above is being done utilizing porous absorbers.

Come 2014/2015, when it's new PJ time (4k +LED light engine), and I go AT front screen - with DIY L/C/R main speakers in a baffle wall, then the whole HT acoustic treatment strategy will change; diffusion, membrane absorbers, etc....but that's topic for a different thread, not buried in yours.

Long winded post, I'm a learner in acoustics, but like to learn based on reading, taking objective data, etc.
Finally, I like to summarize all that for sharing, for me its the only way I can remember something, try to share with others.

Thanks for staying on topic

I have heard people recommend pink fluffy traps but I haven't seen any test data on their performance. Just gas flow theorizing. I have seen before/after with 703 though. Do you know of any tests comparing the two?

I only have my RS SPL meter to use with REW so I can't do higher frequency measurements. I think I found a phase issue between my mains and subs so it's certainly helpful for a basic measurement setup.

My rear panels were pure guesses. My seats are only 2ft from the rear wall so I wanted to reduce reflections and provide some level of bass trapping. Everyone points out that seats close to boundaries are bad so I figured this was one case where something was better than nothing.

I'll read through the links you posted and try some more measurements.

Thanks for your help!
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post #42 of 57 Old 02-25-2012, 05:10 PM
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Quote:
Originally Posted by dragonfyr View Post

It is not a study of all the factors that play a role in the larger topic of intelligibility.

You keep erecting strawmen, based on things I didn't say, just so you can then tear them down pointlessly. Where did I claim the paper was a study of "all" the factors? It simply presents an exception to your overly generalized claim.

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post #43 of 57 Old 02-26-2012, 12:13 AM
 
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Nope. Sadly its a testimony to yur limited grasp of the subject.

I have from the start maintained that there are not only more, but more important factors than simply S/N, which is the ONLY issue your paper focuses upon - a factor that the is not even in question in the OP's room!

Your one trick pony response which you intended as a rebuttal, but in fact which simply missed the target entirely, is superfluous in the case at hand.
But you simply debate against me rather than address the issue.

In fact, you have not added ANY information addressing the actual issue since you posited the paper. You have nothing to say about the acoustical issue of any substance, and the paper you posted, thinking it would be sufficient as it mentioned a factor not at issue in the room, not only did not rebut the original large issues, it simply avoided them altogether as its scope was much more limited.

And then YOUR original proposed solution (utilizing absorption inadequate to adequately damp all reflected energy with the notable exception of the low and mid frequency reflected energy that would serve to color the direct signal!!!) totally contradicted the applied conclusion of the paper you presented, further rendering the point of the paper as a comedic prop rather than a serious addition to the discussion.

And since you have utterly failed to reconcile your response with the content of the paper you cling to so tightly that you introduced merely because it has the word "intelligibility" in its title without any understanding of its relationship to the issue at hand.

One hell of a strawman, huh, scarecrow? Which way to OZ?

So have fun with your personal debate, for as far as the acoustics are concerned, you have been done for quite a while.
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post #44 of 57 Old 02-26-2012, 12:32 AM
 
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Quote:
Originally Posted by hoffmand34 View Post

Thanks for staying on topic

I have heard people recommend pink fluffy traps but I haven't seen any test data on their performance. Just gas flow theorizing. I have seen before/after with 703 though. Do you know of any tests comparing the two?

I only have my RS SPL meter to use with REW so I can't do higher frequency measurements. I think I found a phase issue between my mains and subs so it's certainly helpful for a basic measurement setup.

My rear panels were pure guesses. My seats are only 2ft from the rear wall so I wanted to reduce reflections and provide some level of bass trapping. Everyone points out that seats close to boundaries are bad so I figured this was one case where something was better than nothing.

I'll read through the links you posted and try some more measurements.

Thanks for your help!

The pink fluffy traps are optimal for the large low frequency bass traps.

For absorption for specular reflections (those that occur from about 250-300 Hz on up), the optimal generally available material density characteristics are either ~3lb/ft^3 Fiberglass or ~4 lb/ft^3 mineral wool.

Note, it is not the density that is important, but the GFR characteristics of the material that has those densities - the densities are referenced as that is the figure you will find on the packaging, as you will find no reference to the gas flow resistivity. Does that make sense?

And the density is offered as you it affords you more choices than simply the OC semi-rigid material - so you can select the one most easily available and hopefully save money in the process.

So to try to make the choices a bit easier...absorption on the front wall is definitely an option - just be sure to use enough to make it optimally effective. It would be a shame to go to all the trouble and have the material not be sufficiently effective and still have destructive artifacts.

The other option is a bit more involved up front as it uses REW and simple measurements. But thereafter it is actually easier...

That is to actually measure the ETC for each source (fronts and surrounds) and to identify any actual high gain early reflections. Then after identifying their paths and points of boundary incidence, simply place smaller localized absorbers at those locations. this offers the benefit of using much less absorptive material and it also allows the other beneficial lower level early reflections to remain in the room.

...And THOSE early reflections are desirable. As you see, our goal is NOT to eliminate all reflections, the proper goal is only to address the destructive high gain focused reflections.

And to take this one step further, the use of 1D QRD diffusors on the front wall scattering the energy in the horizontal plane directing more toward the sides would be advantageous as it would further reinforce the amount of later arriving diffuse lateral reflections.

Or, to take this still further, an angled front wall featuring an inverted V that extends into the room would serve to redirect all the energy incident on the front wall toward the side walls where it could be better processed into later arriving semi-diffuse lateral returns - thus turning lemons into lemonade. And such a wall would not be difficult to build, using the region behind it, filled with pink fluffy insulation, as a large bass trap, as the wall surface, properly constructed, would not be massive enough to stop the low frequencies - only to reflect the higher specular energy.
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post #45 of 57 Old 02-26-2012, 01:39 AM
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Quote:
Originally Posted by dragonfyr View Post

But you simply debate against me rather than address the issue.

My first post was on-issue (absorbtion on the front wall). Besides, you engaged me, not the other way 'round. Did you expect me not to reply?
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Originally Posted by dragonfyr View Post

And then YOUR original proposed solution (utilizing absorption inadequate to adequately damp all reflected energy with the notable exception of the low and mid frequency reflected energy that would serve to color the direct signal!!!) totally contradicted the applied conclusion of the paper you presented, further rendering the point of the paper as a comedic prop rather than a serious addition to the discussion.

My reply to Brad had to do with direction of reflections and listener preference, based on research done by Ando that confirmed what Brad had mentioned (absorbtion on the front wall, as the OP was intending to do). I linked to the paper because you brought up intelligibility, not because of my "original proposed solution". You're now trying to conflate the two in order to create a contradiction that doesn't exist. Yet another strawman.
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One hell of a strawman, huh, scarecrow?

Not really (too obvious, didn't work), like your fake quotes of things I never said.

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Your, and the original suggestion, were BOTH INADEQUATE to fully address the high gain early reflections which they merely EQ, and as such merely add to the problems in the form of coloration.

All the rest of your posts are merely noise as they fail to address that fundamental fact.

One might think that as a big supporter of things Harmon, that you would be intimate with that basic issue regarding inadequate absorption and its propensity to EQ rather than linearly control low-mid frequencies so dear to Toole and Olive.

And to the degree that you refuse to address that fact (with good reason, as you can't), your proposed solution then is just as flawed now.

But rather than address that fundamental acoustical limitation, you have apparently opted for Goebbels' strategy of simply persisting in repeating the assertion in the hopes that some will ignore the facts and believe it true.
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post #47 of 57 Old 02-26-2012, 02:27 AM
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Originally Posted by dragonfyr View Post

Your, and the original suggestion, were BOTH INADEQUATE to fully address the high gain early reflections which they merely EQ, and as such merely add to the problems in the form of coloration.

Where did I claim that my original suggestion would "fully address" high gain early reflections? In fact, my original suggestion boiled down to 2 words: "absorb it" (in reference to surround speaker reflections bouncing off the front wall).
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Originally Posted by dragonfyr View Post

One might think that as a big supporter of things Harmon, that you would be intimate with that basic issue regarding inadequate absorption and its propensity to EQ rather than linearly control low-mid frequencies so dear to Toole and Olive.

"Inadequate"? How much absorbtion did I suggest?

Oh, since you brought up Toole: http://www.aes.org/e-lib/download.cf...86&name=harman
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But rather than address the fundamental acoustical limitation, you have apparently opted for Goebbels' strategy...

Godwin's Law strikes again.

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post #48 of 57 Old 02-26-2012, 05:13 AM
 
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Another case where you fail to read and understand the very source you cite.

Here, to help you:

"From the perspective of the loudspeaker, the off-axis response of the tweeter has just been greatly attenuated—it will sound duller and less good. Obviously if the purpose of the absorbing material is to attenuate the reflection, the material should be equally effective at all frequencies. Given the duplex nature of sound fields in small rooms, it seems reasonable to expect similar performance at all frequencies above the transition region.

In their examination of the audibility of reflections, Olive and Toole looked at detection thresholds as high frequencies were progressively eliminated from the reflected sounds, as they might be by frequency-selective absorbers.

They found that only small to moderate threshold elevations occurred for low-pass filter cutoff frequencies down to about 500 Hz, where the investigation ended. Removing the high frequencies alone is not sufficient to prevent audible effects" [32]


Oh, but wait, there's more!

"Finally there are the indications that the precedence effect is maximally effective when the spectra of the direct and reflected sounds are similar [4], [18], [20]. If the spectrum of a reflection is different from that of the direct sound, the probability that it will be heard as a separate spatial event is increased—not a good thing."

EXACTLY what constitutes the problem with the original solution with applying absorption that is inadequate to absorb the full bandpass of the specular energy.

So, to return to my earlier suggestions relative to what the OP had suggested implementing, the choices are:

1. To apply ADEQUATE absorption to fully damp the full spectra of the specular bandpass.

Or,

2. Optimally, to utilize measurements to identify anomalous high gain sparse reflections and to surgically damp them,. while also allowing the predominantly oblique incident lower gain reflections to be preserved in the room - most of which, due to their oblique angle of incidence will continue to the side walls where they will subsequently become part of a desirable exponentially decaying laterally arriving semi-diffuse soundfield.

What is NOT desirable is the original proposal in which the application of absorption over the full surface is inadequate to control the full specular bandpass that will result simply in the effective EQing of the reflected energy that will result in the coloration of the direct signal.
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post #49 of 57 Old 02-26-2012, 08:06 AM
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Quote:
Originally Posted by dragonfyr View Post

Here, to help you:
"Removing the high frequencies alone is not sufficient to prevent audible effects"

Help me some more: quote where I suggested using just enough absorbtion to remove "high frequencies alone"?

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post #50 of 57 Old 02-26-2012, 08:28 AM
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post #51 of 57 Old 02-26-2012, 09:39 AM
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^^^ Classic. Its getting to the point where nobody is going to dare to ask an acoustics related question anymore. Every thread like this goes on for weeks.
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post #52 of 57 Old 02-26-2012, 09:49 AM
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I think we could save a lot of time if AVS would just create an activated warning sort of like the "old thread warning" that would look for certain acoustics related keywords. If a post contains those keywords a warning would come up and say - "Before asking this question you must have REW and already taken ETC measurements and have read Toole's book on acoustics and have a full understanding of the following acoustic related list of acoustics research. (list of articles and research follows). In addition if you are not ready to undertake a PhD level study of acoustics you should avoid asking this question.
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post #53 of 57 Old 02-26-2012, 10:21 AM - Thread Starter
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I realize now that I am not qualified to enjoy my theater. Listening in a totally untreated room would be foolish and anything short of a NASA-level dialogue is a waste of time.

Thanks to those who tried to provide practical suggestions. To those who wrecked my thread with acoustic masturb@tion, I hope you have implemented at least a fraction of what you religiously spout on this forum.
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post #54 of 57 Old 02-26-2012, 04:39 PM
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Quote:
Originally Posted by hoffmand34 View Post

I realize now that I am not qualified to enjoy my theater. Listening in a totally untreated room would be foolish and anything short of a NASA-level dialogue is a waste of time.

Thanks to those who tried to provide practical suggestions. To those who wrecked my thread with acoustic masturb@tion, I hope you have implemented at least a fraction of what you religiously spout on this forum.

When the thread started I was hoping to learn a bit more, as I have a similar decision to make...looks like I am now more confused than ever.

Bummer you really could not seem to get a straight answer.
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post #55 of 57 Old 02-26-2012, 04:53 PM
 
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Quote:
Originally Posted by toofast68 View Post

Bummer you really could not seem to get a straight answer.

The options have been presented at least 3 previous times!

Whether you want to completely deaden the wall or to surgically damp the actual problem reflections and maintain the energy, is your choice.

The originally proposed absorption is equivalent of only 1/2 the thickness of material placed to a gap equal to 1/2 the total thickness. In other words, 3" of velocity based porous absorption placed against a boundary is equivalent to a 1.5" gap and 1.5" of absorption as the velocity goes to zero near the boundary..
This is inadequate to control the full specular bandpass (in particular the low-mids) of any gain reflections and as such will simply result in the effective EQing of the high frequencies of the reflected energy that will result in the coloration of the direct signal.

Thus, depending upon your preference, the options are:

1. To apply Adequate absorption to damp the full spectra of the specular bandpass.

(Applying it to the entire wall has the disadvantage of being overkill and unnecessary, as you only need to control the actual early arriving high gain reflections. Additionally it will reduce the available energy for a later arriving semi-diffuse soundfield, if such is desired. If you want a deader room and don't mind the extra material, labor, time and expense, go crazy and treat the entire wall with adequately thick absorption sufficient to stop the full specular bandpass. This can be accomplished with a minimum of 4" thick panels of either ~3lb/ft^3 Fiberglas or 4 lb/ft^3 mineral wool with a 4" gap from the boundary.)

Or,

2. Or, optimally, utilize ETC measurements for each speaker in order to identify actual anomalous high gain sparse reflections. Then determine their points of boundary incidence and to surgically damp them using sufficient absorption to adequately damp the full specular bandpass.

This will allow the lower gain predominantly oblique incident energy to be preserved in the room,which, due to their oblique angle of incidence will continue to the side walls where they will subsequently become part of a desirable exponentially decaying laterally arriving semi-diffuse soundfield.


It is up to you to determine the preference regarding the degree of damping in the room that you prefer.
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post #56 of 57 Old 02-27-2012, 05:50 AM
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Quote:
Originally Posted by dragonfyr View Post

The options have been presented at least 3 previous times!

Whether you want to completely deaden the wall or to surgically damp the actual problem reflections and maintain the energy, is your choice.

2. Or, optimally, utilize ETC measurements for each speaker in order to identify actual anomalous high gain sparse reflections. Then determine their points of boundary incidence and to surgically damp them using sufficient absorption to adequately damp the full specular bandpass.

This will allow the lower gain predominantly oblique incident energy to be preserved in the room,which, due to their oblique angle of incidence will continue to the side walls where they will subsequently become part of a desirable exponentially decaying laterally arriving semi-diffuse soundfield.


It is up to you to determine the preference regarding the degree of damping in the room that you prefer.

Ok, so all the back and forth this must have gotten buried

As a follow up, if we (or me for sure) does not have access to all the high end measuring equipment...then I have to use other measures (mirrors, etc. that I really need to learn more about)

Finally, based on all my research...it seems that perhaps corner bass traps in the front are REALLY the best bang for the bucks...especially since I (don't want to steal OP thread) am not a super pro, etc.
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post #57 of 57 Old 02-27-2012, 06:15 AM
 
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Quote:
Originally Posted by toofast68 View Post


As a follow up, if we (or me for sure) does not have access to all the high end measuring equipment...then I have to use other measures (mirrors, etc. that I really need to learn more about)

Finally, based on all my research...it seems that perhaps corner bass traps in the front are REALLY the best bang for the bucks...especially since I (don't want to steal OP thread) am not a super pro, etc.

First, the measurements described are actually rather simple. Seriously

The most 'difficult part is ordering an:
ART Dual USB Pre(amp) from B&HPhoto for $69 (which included shipping)
A Dayton EMM6 mic from Parts Express for $39 (with an individual downloadable calibration file)
a mic stand
And a mic cable, USB cable, RCA cable to the rcvr, and a loopback cable
And downloading REW free from the HomeTheaterShack.

Don't let the subject intimidate you. The level of measuremets we are discussing here are both very basic and easily performed.

Additionally, a mirror will not tell you if the real high gain reflections exist, and assuming they do, where their paths and points of incidence are actually located.


As far as corner bass traps - that is a totally different issue from what is being discussed.

Bass traps are intended to address low frequency room modes, while the treatment that was proposed in the thread is FAR too thin to be effective against modal energy. Such energy behaves as standing waves and requires VERY thick absorbent panels spaced far from the wall - so far that I would not recommend using porous velocity based bass traps.

Specular reflections, on the other hand, are how energy above about 250-300 Hz acts. This energy can be modeled as rays - think pool balls bouncing about.
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