3.5" Ultratouch or 2" Ecose on front wall? - AVS Forum
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post #1 of 57 Old 02-22-2012, 09:42 AM - Thread Starter
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I am ready to install front wall absorption in my theater room. I planned on using 2" Ecose rigid fiberglass but i can get 3.5" Ultratouch denim for 15% cheaper per sq ft.

Any downside to the thicker Ultratouch on the front wall? It has better specs for lower freq absorbtion (125hz and 250hz) and similar specs for everything else.
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post #2 of 57 Old 02-22-2012, 10:05 AM
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Im surprised that the Ultratouch is cheaper than the ECOSE. I used 2" of the ECOSE SONIC XP Duct liner. its only 1.5 lbs instead of the 3 lb rigid stuff. The duct liner works well because it comes in Black and doesn't need to be covered. I have enough left over that I could go 4 inches if I want.


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post #3 of 57 Old 02-22-2012, 10:20 AM - Thread Starter
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Quote:
Originally Posted by stockmonkey2000 View Post

Im surprised that the Ultratouch is cheaper than the ECOSE. I used 2" of the ECOSE SONIC XP Duct liner. its only 1.5 lbs instead of the 3 lb rigid stuff. The duct liner works well because it comes in Black and doesn't need to be covered. I have enough left over that I could go 4 inches if I want.

In Austin I can get 2", 3lb Ecose for $.91/sqft and 3.5" ultratouch for $.80/sqft. The Ecose is nice as it's a dark brown and no chemical smell like OC703. I've used it for my 2 rear superchunk traps so far.

Either will get covered since I don't have a baffle wall or AT screen.
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post #4 of 57 Old 02-22-2012, 10:52 AM
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I'm also using the 3# Ecose for my wall panels. I have a couple bags waiting in the garage. I would use the ultratouch since it is cheaper.


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post #5 of 57 Old 02-22-2012, 07:58 PM - Thread Starter
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So are there any concerns with too much absorption on the front wall or is that what we're shooting for?
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post #6 of 57 Old 02-22-2012, 08:02 PM
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Yes you can have too much high frequency absorption. Its hard to have too much low frequency though. You can always put plastic or paper over some of the wall later if you have too much high frequency. I'm nowhere near an expert on this though.


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post #7 of 57 Old 02-22-2012, 09:55 PM
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The front wall seems to be the one surface that there is consensus on completely deadening it.

(cue the dissenters)


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post #8 of 57 Old 02-23-2012, 12:34 AM
 
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Originally Posted by hoffmand34 View Post

So are there any concerns with too much absorption on the front wall or is that what we're shooting for?

Burn the witch! Heaven forbid that it takes 5 posts before the notion even surfaces, when it should have been consideration 1 or 2 in the process.

Quote:
Originally Posted by Brad Horstkotte View Post

The front wall seems to be the one surface that there is consensus on completely deadening it.

(cue the dissenters)

And of course we have the acknowledgment of the all too common common assumption (nay, mantra...) that has prevailed for the past 20+ years in sphere of among the more enlightened in consumer acoustics who astutely realize the importance of room treatment - not at all like those nabob buggers who have not progressed to the point of recognizing the importance of room treatment...

So...maybe we should subtitle this per the plaintive recurring mantra on this forum: "Isn't doing something better than nothing?"


First, the problem stems from the assumptions implied in the question.

Let me explain.

First, what would be the purpose and practical impact of "completely deadening it"?

I am going to assume that this implies exactly what it literally says. You are going to damp ALL reflections from the surface, be they low frequencies or gamma rays.

Do all reflections have the same affect on the system? Are all 'evil'.

(What follows is NOT aimed at anyone in particular - it is a summary of the all too common attitudes commonly expressed that have dominated the 'consumer audio' community for the past 20 years ever since a few read the early articles - (primarily the article by Don Davis published in Audio in 1987) where only PART of the message was absorbed, and the body of the piece totally ignored!) and proceeded to overly simplify and misrepresent what was actually said; and which has resulted in a consumer market that is literally 20+ years behind the pro market.

Unfortunately, this is the common misnomer that has resulted from well-meaning folks mis-interpreting acronyms and simple generalizations without bothering to read the body of the work and becoming aware of the critical 'rest of the story'... After all, you need panels to eliminate first reflections, right? And you need to establish a Reflection Free Zone, and the front of an LEDE is a "dead end". And we all know that "you can't have too much absorption", right? (and I can literally source this last quote on forums stated by principles of some of the popular commercial sources!)

Every common conclusion so often tossed about here and elsewhere to that effect is ABSOLUTELY WRONG!!!!!

Welcome to the modern popular commercial and online history covering the last 20 years that constitute a perversion of what was learned in the previous 20 years upon which so many claim to base their conclusions - but of which these conclusions are little more than the result of simply reading article titles, generalizing, and failing to read the critical qualifying details.

By the way, are you aware that NOT ONE major acoustic response model ever posited that the front of a room must eliminate all reflections? Not One! Not even the Non-environment room that is the closest thing to a 'dead room" format that we have!

So get you panties in a wad with what I say, and then get over it...as the fact is that it’s the truth! And it gets old reading the same nonsense again and again and again. (Again, no one needs to become personally upset. But folks should realize the reality of the situation and recognize the substantial schism in awareness that exists. And its each individual’s choice as to what they choose to do about it…And if you do nothing, at least understand the nature and source of the schism…)

And for the purposes of this post, the desired goal is an accurate, optimal result. One that maximizes the positive without introducing destructive elements that merely serve to move the problems around and associating that with "better".

And this has also caused a false (and very tired) debate between the so called 'advocates of early reflections" and those they falsely accused of being for the elimination of "early reflections" (aka the Toole debate). A debate the is only real if you start with the same mis-characterization based upon an incomplete understanding of what was originally posited.

So it sure would be nice if a baseline awareness was established to put an end to this perpetual straw man debate!

There - it’s been said...


So...Do all reflections have the same affect on the system? Are all reflections 'evil'. And if not, WHY would anyone want to damp all reflections?

I know, I know...but all the online forums and folks selling absorption all say that you need to apply "absorption"!!!

OK, what is really known?
In small spaces we DO need to control the low modal frequencies in order to damp resonances.

And we know that "high" gain early reflections interfere with localization, imaging, and intelligibility. We also know that SOME, but not all, later arriving high gain reflections interfere with localization, while still later high gain reflections can be perceived as discrete echoes. But we also know that later arriving reflections can add a pleasing sense of spaciousness making a very small room seem larger than it actually is.

So, suddenly, not All reflections are bad! Oh my!

I'll pause for a moment to allow the shocked and dismayed to recover a bit from the notion that SOME reflections can be good, to get a drink...

OK...

We can do several things.

First, while the mirror trick is a wonderful concept hung onto and advocated fervently by a few, it originated to illustrate a concept that specular reflections functioned like rays - virtual pool balls. But there is a reason that it was NOT posited as a substitute for the tool it was used to illustrate 44 years ago! And that reason is exactly what we are trying to deal with here!

The mirror only illuminated Some of the POSSIBLE vector paths early arriving energy MIGHT take. So, if you blindly follow the mirror, you will damp every possible low order reflective path. And if you damp every possible path of early low order reflections, and you then apply the proper amount and type of absorption, what is the logical result? You end up eliminating ALL early low order reflections (with the exception of diffractive sources of which the mirror is blind!).

Congratulations! You are now contributing to a problem, and not to the solution. (Unless your goal is to build an anechoic chamber - as even the non-environment room maintained a highly reflective front wall! Go figure!)

And in response to the oft cited mantra of "yeah, well if that is all someone can do, isn't that better than nothing?" Actually, no. Its different all right. And you might even learn to live with it.

But is it optimal? Have we maximized the positive while ALSO minimizing the negative?
NO, we have not.

(And we are also ignoring that fact that the front wall is mistakenly being addressed out of context to the larger room - which is a mistake. But we will focus simply on reflections to keep things simple...)

So, let's assume that we do want to control the Low frequency Modal resonances (and mitigate any potential related SBIR issues).

To that end, in addition to the physical aspects of room dimensions, wall construction, etc. which are beyond the scope of this post, we need bass trapping. And regardless of the type of bass trapping employed, be it passive or active, velocity or pressure based, or electronic, we need to insure that it is frequency specific...that it mitigates the bass frequencies but does NOT also damp the mid and high frequencies (for reasons apparent later...)

As most are limited to porous velocity based absorption that means we need to use LOTS of it. Not 2 or 3" thick panels stuck to a boundary.

But Substantial amounts of porous absorption placed as close to the 1/4 wave spacing distance from the boundary as possible. And you can then 'remove' 1/2 of the spacing worth of material closest to the boundary as it does little to help with the cause. And what little it does do is effective only against much higher frequencies that are not our goal to stop.

So, assuming we have established a sufficient amount of bass trapping, how do we control the frequencies absorbed and make it into a low pass filter that returns the mid an high frequencies back into the room, where they can be appropriately controlled?

We apply a reflective front facing barrier.
The MINIMUM barrier that becomes sufficiently effective from about 600 Hz up is 6 mil plastic. But this can easily be replaced with more substantial or rigid facings such a 1/8" thick MDF.

The caveat? We simply make sure the angle of the facing does not reflect high gain early reflections back-into the listening position, so angling this appropriately is a simple tool to insure this. (Gee, finally a legitimate use for your mirror!)

OK, and for those lamenting the fact that they cannot use sufficient porous trapping, well, you can treat additional corners and surfaces with LF oriented porous material as well, and if that's not enough, employ complimentary active or passive systems. And if that's not enough, well, it’s not enough.

So, we have addressed the modal frequencies.
What about the early arriving specular frequencies?

First, let's dispel the nonsense that we need to eliminate ALL reflections. We not only do not Need to, we don't Want to!

What we want to control are early arriving indirect HIGH GAIN reflections of sufficient gain to trigger the ear-mind psycho-acoustic imaging, localization and intelligibility capabilities. the reason is that in this time range, our ear-mind is simply not up to the task as this is beyond the ear-brain's limit of resolution, and the result is a smearing and over simplification of sensory triggers as well as a loss of intelligibility. Now this is even more important with spoken word, as articulation is important to intelligibility - and with music we can generally get away with more indistinct 'smearing' of signals - and given the content of most stuff available now, maybe even ALLOT of smearing...And if you listen to rap, perhaps you can ignore this altogether, as the context is nothing that need be understood.

But how do we identify the HIGH gain early reflections from the low gain non-destructive reinforcing reflections? Can we use a mirror that is unable to distinguish the real from the possible, or the low from high gain reflections, and misses the very early Very destructive diffractive reflections? Hardly. But if you do, just realize the fact that you are compromising the system as much as you are improving it...

The way one easily identifies the real from the possible, and the high gain from the low gain indirect signals including diffraction, is to use the ETC response. With this one can rather easily resolve the vector path and point of incidence for the ACTUAL REAL issues. And then you STOP!

(Oh, and we are assuming that your room has sufficiently adequate resistive walls that essentially reflect all of the specular energy!)

You surgically apply ONLY enough broadband absorptive panels sufficient to mitigate the FULL range of the incident reflective energy. That's it! No more, no less.

And for those who have any number of reasons for using less, understand that absorption that is not sufficient to damp the full specular bandpass will result in coloration of the first signal. Its that simple.

And a some point in the precess, hopefully earlier rather than later, one should stop and think: just where are the reflections off the front wall originating, and what is their nature? Are they direct first order reflections from a speaker featuring terrible pattern control? (If so, get new speakers!) Or are they higher order low gain semi-diffuse reflections that have bounced around the room that have somehow managed to avoid the 'kill all the reflections' routine that have managed to persist long enough to be incident on the front wall? And do we really want to get rid of semi-diffuse later arriving reflections????

So, do you still want to indiscriminately place absorption all over the front wall?

First, let’s examine the case for modal and ALL early arriving specular reflections, and then we will narrow the issue to the front wall…

And then, is it 'thick enough' to actually control modal frequencies?

If not, it is simply going to damp ALL of the early and late higher frequency (but not necessarily all of the indirect signal bandpass) specular reflections incident off the front wall. And do you really have that many early high gain reflections off the front wall that impede on the listening spot(s)? (If so, i would examine your speakers!!! as i would suggest that you could benefit from a speaker with more controlled dispersion...).

Is the front wall REALLY a prominent source of early arriving specular reflections? (Just out of curiosity, how many have tried using a mirror to see???? And how many using the ETC have identified front wall high gain early reflections??? Anyone? Is this a REAL problem, or an imagined problem?

And do you really want to damp all of the early low gain, as well as the later low gain reflections (that contribute to a positive sense of spaciousness to the room) off the front wall? What acoustical response model, aside from an anechoic chamber suggests that response?

And assuming the power response of most speakers, where the low frequencies tend to be more cardioid and the highs beam, what frequencies would comprise the majority of early incident energy. Here, let me help – it will be LOW frequencies. And how effective is 2-3 inch porous absorption applied directly to a zero velocity boundary against LOW_MID frequencies? But the 2-3” of absorption applied directly to the boundary is GREAT for eliminating the high frequency energy that is already in too short supply!

The result: we remove still more of the beneficial low gain high frequency energy and totally ignore the problematic low-mids.

So, is “doing something better than nothing” if we create more problems without resolving the imagined problem that we have let to even verify exists???? Namely, do we have a problem with early high gain reflections? (Just to clarify - we MIGHT, as who knows what degree of cabinet resonance or uncontrolled Q the speakers exhibit! So while a well controlled spatial dispersion speaker most likely will not, all bets are off for the majority of speakers out there!) But what does common sense, let alone measurements that will CONCLUSIVELY provide the answer – one that the mirror can’t even guess at?

You see, instead of beginning with the mistaken mindset that we must "eliminate reflections" and stopping to examine both the modal and specular regions, and also WHAT specular reflections are actually detrimental and which are reinforcing, the situation become both more complex, but actually simpler in many ways.

So what is the 'better way':

1.)One, we focus on addressing modal resonance with frequency selective high pass bass traps.*

2.) Using the ETC, we specifically identity ONLY the early high gain reflections that require treating and resolve their specific points of boundary incidence.

3.) and then we Surgically treat ONLY those limited regions with a sufficiently broadband absorptive panel**

- which saves you time, money and effort buying, building and installing all sorts of additional insufficiently broadband absorption that only makes the existing problems LARGER.


And note that the finite set of broadband panels must be sufficient to absorb the full specular bandpass from about 300 Hz up or you will not eliminate the destructive effects of superposition that negatively affect imaging, localization and intelligibility, but you also ADD an additional problem called coloration to the mix. So if you are ready to scrimp on broadband absorptive panels (as opposed to employing other more advanced/complex treatment types of which little has been mentioned), you decide is 'something inadequate' is better than nothing...

So, you see... it’s really not that complicated. But the question and assumptions you begin with had better be well formed or the result, however well intentioned will not be optimal. And the result will be one of either a dead 'anechoic' claustrophobic environment where imaging cues are easily misinterpreted; or perhaps just as bad, a result where you have simply moved problems around in an environment that still suffers from modal resonance, as well as imaging, localization and intelligibility issues, along with the addition of coloration to the mix.

So you tell me, was "merely doing something (at a pretty fair expense in terms of material and time) better than doing nothing (that costs you nothing)?" That's for you to decide. Me, I suggest doing it properly.

And if you have compelling reasons why this cannot be done, and if you are going to spend the money, I would suggest calling a pro who is capable of possibly providing additional OBJECTIVELY verifiable alternative technologies that result in OBJECTIVELY verifiable measured results, be they passive, active, resonant, or whatever, to address the issues in the manner prescribed - being sure that you get a REAL return on your investment. (Or, failing that, you can convince yourself that fancy new expensive interconnects will make a real improvement and go out and buy and install them and sit back convinced that you just radically improved your system. And I dare say if you have already convinced yourself of their value, you will (most likely) at least feel like it sounds better!)


And beware of anyone who claims they can provide a solution that magically overcomes the issues mentioned (thin porous bass traps, thin non-spaced porous specular broadband panels, etc.) using traditional techniques.

And in the end, baring some really bizarre spatial dispersion characteristics of the speakers, I would suggest that the 2-3" of porous absorption applied directly to a zero velocity boundary will neither mitigate low frequency modes nor is it sufficient to mitigate any broadband (or the more likely low-mid) high gain specular reflections that most likely do not even exist off this surface And if that were not enough, it will be ineffectual against any low mid specular energy that may result from the speaker's uneven power response that can still detrimentally impact localization, imaging and intelligibility in addition to coloring the direct sound. And to think you spent time, energy and money to augment that! Congrats!.

And the net result will be allot of money, time and effort spent that will damp low gain ambient mid-high frequency energy that, depending upon its arrival time, is beneficial to the sense of envelopment and spaciousness while missing any high gain low mids specular reflections that will still cause the problems you originally imagined you would solve. Ouch!

But you will have a sense of accomplishment and the all important sense of "having done something" that a few have posited as being so important.

So, in the end I guess we can, without exceptional objective verification of a real problem to solve, better label the "doing something rather than nothing" approach a therapeutic exercise rather than an actual acoustical exercise. Hey, but that can be worth something...

* ...as well as other appropriate complementary methods aside from porous absorption.
**We have intentionally left out diffusion, simply to make the analysis simpler. But if the actual reflections meet the best practice standards for the use of diffusion without adversely impacting the listening spot, diffusion can certainly be properly employed. And the appropriateness of this option can be assessed with the ETC response.
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post #9 of 57 Old 02-23-2012, 02:35 AM
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Quote:
Originally Posted by Brad Horstkotte View Post

The front wall seems to be the one surface that there is consensus on completely deadening it.

Makes sense, since that is the direction where your brain is trying to create phantom images in order to form a coheisve soundstage, and the last thing you need is reflections from your surround speakers interfering with that process.

You and I both run 7.1 set-ups, which includes a pair of speakers behind and a pair of speakers along the sides. With the rear speakers pointed towards the front of the room, content from the surround-back channels is going to reflect off the front wall, muddying its intended directionality and messing with the front soundstage. It's even worse with the side speakers, since they are closer to the front wall AND it's their (often uneven) off-axis response that will be reflecting back. Absorb it.

Research done by Ando in the late 1970s tracked listener preference based on angle of early reflections. Listeners liked reflections from about ±40-140° from centre, with an especially strong preference from ±40-90° (spaciousness). Least preferred: reflections within ±30° from centre, coming off the front AND back walls. So good idea to deaden at least that portion of the front wall (and back wall), if not a little wider.

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Originally Posted by sdurani View Post


You and I both run 7.1 set-ups, which includes a pair of speakers behind and a pair of speakers along the sides. With the rear speakers pointed towards the front of the room, content from the surround-back channels is going to reflect off the front wall, muddying its intended directionality and messing with the front soundstage. It's even worse with the side speakers, since they are closer to the front wall AND it's their (often uneven) off-axis response that will be reflecting back. Absorb it.




Let's look at time relationships of the mentioned reflections.
And also note that the front wall is not much different from the other surfaces in this example...

The later reflections sourced by the front speakers that are incident off the back wall will arrive later than the direct and early first order reflections off the side walls floor and ceiling.

We have already determined that high gain early reflections are detrimental to localization, imaging, and intelligibility. While lower gain later reflections are advantageous in that the augment a sense of spaciousness.

And no one debates the research of Schroeder who identified the advantages of largely lateral arriving reflections.

As fa as surrounds interfering with the front speakers, their earlier arriving higher gain direct signals will account for a Much greater degree of any mentioned interference, where the later arriving surround signal incident of the front wall will be largely analogous to the later arriving rear wall reflection of the front speakers.

Unless either are of sufficiently high gain, they will add to the sense of spaciousness.

If anything, except for specific incidence of localized high gain reflections where the surgical application of absorption would be optimum, the rest of the surface would be fine assuming a sufficiently random distribution of ambient incident energy. Alternately, in order to increase the spatial and temporal randomization of the reflected soundfield while also reducing the gain of each arrival, diffusion would be appropriate.

Unfortunately, the surround format topology does not adequately address the issue of a later arriving exponentially decaying semi-diffuse soundfield. So the room remains the controlled source of this component.

In any case, the only issue that might require limited treatment is the control of any anomalous high gain specular reflections. And this treatment must be sufficient to control the lower reaches of the specular band=ass, meaning thicker porous absorption. ALL of the rest of the low gain reflections are desirable, and here one might consider additional diffusion dependent upon the actual distribution of he later arriving soundfield. -

So, assuming detrimental early arriving high gain reflections are controlled, the remaining choice remains in the degree of the sense of spaciousness one desires.

A good example of an option to simple thin absorption would be to use the hybrid 4" porous absorption faced with a Galois sequence BAD (binary amplitude diffusion) mask, that would serve to both reduce the level of specular energy while reflecting and diffusing lower gain energy back into the space. (In fact, except for specific control of anomalous high gain focused reflections requiring surgical treatment, one might do well with simply covering all other wail surfaces with sufficiently effective low frequency absorption in combination with a specularly diffusive mask such as the BAD panel.

And we are in any case still stuck with the fact that the specific treatment is insufficient for modal control, as well as broadband specular control. More limited targeted treatment sufficient for each problem would be advantageous.
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We have already determined that high gain early reflections are detrimental to localization, imaging, and intelligibility.

"We" have? http://asadl.org/jasa/resource/1/jas...s4?bypassSSO=1

"New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. The results confirmed that added early reflection energy is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signal‐to‐noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections, show that early reflections can increase the effective signal‐to‐noise ratio by up to 9 dB. The primary goal of room acoustics design should be to maximize early reflection energy to make possible increased effective signal‐to‐noise ratios."
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As fa as surrounds interfering with the front speakers, their earlier arriving higher gain direct signals will account for a Much greater degree of any mentioned interference, where the later arriving surround signal incident of the front wall will be largely analogous to the later arriving rear wall reflection of the front speakers.

Unless either are of sufficiently high gain, they will add to the sense of spaciousness.

They'd be arriving from the wrong direction (front and back) to add to the sense of spaciousness, which comes from lateral (sideways moving) sounds.
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Originally Posted by dragonfyr View Post

Unfortunately, the surround format topology does not adequately address the issue of a later arriving exponentially decaying semi-diffuse soundfield. So the room remains the controlled source of this component.

But that's not what surround sound is attempting to do, especially when it comes to discrete multi-channel music and modern movie soundtracks. For 2-speaker set-ups, like in a small recording studio, I can understand the room being the controlled source, since the room is essentially acting as a surround processor. But for current multi-speaker layouts, which have started incorporating Heights and Wides, that no longer has to be the case.
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Originally Posted by dragonfyr View Post

And we are in any case still stuck with the fact that the specific treatment is insufficient for modal control, as well as broadband specular control. More limited targeted treatment sufficient for each problem would be advantageous.

Sure, and that's where you come in: discussing surgically targeted approaches, based on certified small room acoustic models, that can be accomplished using a calibrated mic and measuring software. The OP's query in this thread is of much simpler scope (absortion on front wall), so I'm limiting my meager contributions to that.

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Originally Posted by sdurani View Post

"We" have? http://asadl.org/jasa/resource/1/jas...s4?bypassSSO=1

"New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. The results confirmed that added early reflection energy is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signal‐to‐noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections, show that early reflections can increase the effective signal‐to‐noise ratio by up to 9 dB. The primary goal of room acoustics design should be to maximize early reflection energy to make possible increased effective signal‐to‐noise ratios."

"Unamplified speech"
And I don't care about the S/N! Having a louder unintelligible source with less than accurate imaging isn't exactly my goal! But if you are at a football game and simply want to hear guys holler, it s great!

And "new results"??? You have got to be kidding! Sure it’s new if you've been oblivious to fundamental psycho-acoustics for ~175 years since Joseph Henry's work!

We have amplifiers and gain controls for loudness. That is not my concern. More important criterion such as localization, imaging, intelligibility and coloration exist that are detrimentally effected by early arriving high gain signals.

And this statement is simply false: "it is only possible to understand speech because of the presence of early reflections."

I will offer as evidence not only the tests we made on Bessels, but on the numerous listening tests to both a single source and a large variety of array s standing from 100-300 yards in a free field in a cornfield listening to speech specifically evaluating intelligibility and such factors as %AlCons (articulation loss of consonants) and STI and RASTI.All direct indicators of intelligibility! Additionally i will specifically cite Intelligibility Workshop at the University of Illinois fieldhouse - and the infamous encounter with Dr. Bose...

And the notion that early reflections are required for intelligibility is blatantly incorrect.In Some cases the additional loudness may be sufficient to make the difference between something being intelligible and unintelligible, but as in cases where there is already plenty of gain, such as in an auditorium, simply increasing gain does not necessarily result in increased intelligibility. So, while it makes near field listening louder, but it is NOT necessary for intelligibility. In fact, it denigrates the intelligibility if their gain is sufficiently high as the sources are merged into a less discrete stimulus. And I can assure you that one can easily understand someone when they speak in an anechoic chamber, assuming that you are in the direct path.

And lets take that still further - you are asserting that one cannot clearly hear a direct signal in a Hidley Newell non-environment studio where only the direct signal is desired. A completely ludicrous notion.

And its interesting to note that I can understand spoken word just fine in headphones - assuming the recording is clear..

And SURE such reflections make the unintelligible sound LOUDER!!! Anyone familiar with the Henry Precedence Effect and Haas corollary is intimate with this FUNDAMENTAL factor! And I say “we” as quite a few folks – well, unless you frequent this site - ARE readily familiar with the concept and have been working with it for a LONG time.

In the Haas interval all of the early arriving signals are "time smeared" into one LOUDER signal that seems to come from the direction of the first energy arrival and it features reduced intelligibility. Handy for basic survival needs too!. And gain can be critical for intelligibility provided that the sound is at or below a critical threshold of having sufficient gain to distinguish what is being said and where a noise floor might mask the direct sound - such as happens with a reverberant soundfield in a large auditorium during periods of very quiet dynamics where the direct signal is masked. But given that the source already exhibits sufficient gain, it is not a determining variable. And excessive early reflections are lousy for critical listening. If you still have doubts, let me refer you to a few high school gymnasiums. But I feel better knowing that, with luck, you won't need to employ your basic survival skills in the event someone sneaks up on you in your theater.

Geesh - and the paper goes on to point out that speech intelligibility is raised for OFF axis signals...!!!


Quote:
Originally Posted by sdurani View Post

They'd be arriving from the wrong direction (front and back) to add to the sense of spaciousness, which comes from lateral (sideways moving) sounds. But that's not what surround sound is attempting to do, especially when it comes to discrete multi-channel music and modern movie soundtracks. For 2-speaker set-ups, like in a small recording studio, I can understand the room being the controlled source, since the room is essentially acting as a surround processor. But for current multi-speaker layouts, which have started incorporating Heights and Wides, that no longer has to be the case. Sure, and that's where you come in: discussing surgically targeted approaches, based on certified small room acoustic models, that can be accomplished using a calibrated mic and measuring software. The OP's query in this thread is of much simpler scope (absortion on front wall), so I'm limiting my meager contributions to that.

Sorry, but front to back reflections do no harm (based solely on this one characteristic). But the lack of lateral reflections from the side result in reduced sound quality So there is no need to damp reflections from either the front nor back due to any problem they create based solely on direction of travel. But we do benefit if we (if you would have read further above!) increased the diffusion and thus redirected the incident energy to the sides and INCREASED the laterally arriving energy – unless you are proposing to damp those surfaces as well will similarly reduce the reflected specular energy in the room, making it dead!

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Originally Posted by sdurani View Post

But that's not what surround sound is attempting to do, especially when it comes to discrete multi-channel music and modern movie soundtracks. For 2-speaker set-ups, like in a small recording studio, I can understand the room being the controlled source, since the room is essentially acting as a surround processor. But for current multi-speaker layouts, which have started incorporating Heights and Wides, that no longer has to be the case.

I just said that they are not trying to do this! And as a result, the total soundfield suffers. Instead you effectively have multiple decorrelaed direct early arriving soundfields whose sense of envelopment comes only from the direct sources, its gain, and the fact that it originates from a particular limited orientation.

But accurate localization and imaging involves a bit more than that. And the sense of spaciousness in a tiny bounded space comes from the exponentially decaying later arriving semi-diffuse soundfield – which for quality purposes should include a large laterally arriving component! You know, the ones you just suggested be minimized by absorbing the finite available specular energy.

Spaciousness does not come from high gain early arriving direct signals! And the sense of envelopment is NOT a substitution for the sense of spaciousness. And the highs and wides do not make the 3space localization significantly greater – it simply tends to increase the 2D forward oriented complexity and sense of envelopment.

Combine that with the fact that sound is specifically mixed so that acoustical cues are not sufficiently sophisticated to cause one to turn away from the front screen, and you see that accurate localization is NOT the driving force in surround. Rather your point misses the difference between a dead space and a sense of spaciousness, and a million sources simply offering more direct early arriving signals does not provide for an increased sense of spaciousness. That comes from time and decreased gain, with quality enhanced with increased diffuse lateralness.

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Originally Posted by sdurani View Post

Sure, and that's where you come in: discussing surgically targeted approaches, based on certified small room acoustic models, that can be accomplished using a calibrated mic and measuring software.

You’ll have to pardon me, as yes, my focus is on the acoustics, and the goal of accuracy and quality of the reproduced signal. And it does involve the use of about $100 worth of components (depending upon when and where you buy them). Components that total about equal to the least expensive piece of gear one has in their setup and yet can provide a more substantial increase in quality than almost any of them. A mighty bargain… The focus is not simply in how fast someone can connect and configure a theater in a box from WalMart.
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post #13 of 57 Old 02-23-2012, 10:34 AM
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Originally Posted by dragonfyr View Post

Having a louder unintelligible source with less than accurate imaging isn't exactly my goal!

Nor was it the goal of the paper, which dealt with intelligibility, not louder levels.
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Originally Posted by dragonfyr View Post

And "new results"???

Well, it's not that new, considering there has been research since the 1950s (Lochner & Burger) showing that early reflections improve intelligibility. Similar research from Soulodre in the '80s and Ando in the '90s. I was reading a recent paper on Dirac room correction, and even it mentioned "There seems to be consensus in the field that some early reflections actually help make speech more intelligible. Reflections from the front and the rear (within ±40º) are perceived as detrimental to sound quality..." I'd taken it for granted at this point, so I was a little surprised by your "we have already determined.." comment, since it goes against what I've read on the topic.
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Originally Posted by dragonfyr View Post

And I can assure you that one can easily understand someone when they speak in an anechoic chamber, assuming that you are in the direct path.

Sure, but it comes down to degree. If speech is intelligible in an anechoic chamber, will early reflections hinder or improve intelligibility? All the research I've seen points to the latter.
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Originally Posted by dragonfyr View Post

I will offer as evidence not only the tests we made on Bessels, but on the numerous listening tests to both a single source and a large variety of array s standing from 100-300 yards in a free field... If you still have doubts, let me refer you to a few high school gymnasiums.

Even in previous discussions with me on this topic, you keep resorting to counter-examples (gymnasium, airport PA system, etc) that are much larger than the typical home listening room. You even once linked to a video showing an example of an untreated room resulting in poor intelligibility. Upon closer examination, it turned out the microphone was 300 feet from the speaker, in a large enclosed warehouse. That's not what happens in a residential listening room.
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Originally Posted by dragonfyr View Post

Sorry, but front to back reflections do no harm (based solely on this one characteristic).

Sorry, but I'll take Ando's word over your's, since it jibes with my experince.
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Originally Posted by dragonfyr View Post

Rather your point misses the difference between a dead space and a sense of spaciousness, and a million sources simply offering more direct early arriving signals does not provide for an increased sense of spaciousness. That comes from time and decreased gain, with quality enhanced with increased diffuse lateralness.

7 or 9 speakers aren't "a million sources". The spaciousness you're talking about assumes using the room as a surround processor. Routing recorded ambience away from the front soundstage to speakers placed around you lessens the need to rely on the room itself to provide spaciousness and envelopment.
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Originally Posted by dragonfyr View Post

The focus is not simply in how fast someone can connect and configure a theater in a box from WalMart.

"The" focus? You mean your focus.

Remember the thread where some poor guy simply wanted to connect his receiver to a pair of Bose speakers, and half a dozen posters started bashing him for his purchase? I told him how to hook it up in two easy steps, and you actually praised me for helping him (before editing, then deleting those posts). My (mostly negative) views on Bose wasn't the focus of that thread; getting his 'theatre in a box' receiver to work with a pair of crappy speakers was, so I focused my comments to the help he needed and let others lecture him on good speakers vs bad speakers.

Personally, I have no problem with you wanting to lecture us on acoustics, since they tend to be informative (even when I disagree with you). But let's not pretend that your priorities are "the" focus of other posters.

Sanjay
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Originally Posted by sdurani View Post

Nor was it the goal of the paper, which dealt with intelligibility, not louder levels.

Try actually reading it. On axis the intelligibility does not improve. Only off axis does it improve. And as we are dealing with an environment with multiple amplified sources where we can adjust the gain of he carious sources and so are not constrained by the critical limitations imposed in the papers premise.

And as we will see again, I love how you treat "reflections" as simply "reflections" - as you totally ignore relative gain levels and arrival times as well as spatial and temporal qualties and treat all reflections the same.


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Well, it's not that new, considering there has been research since the 1950s (Lochner & Burger) showing that early reflections improve intelligibility. Similar research from Soulodre in the '80s and Ando in the '90s. I was reading a recent paper on Dirac room correction, and even it mentioned "There seems to be consensus in the field that some early reflections actually help make speech more intelligible. Reflections from the front and the rear (within ±40º) are perceived as detrimental to sound quality..." I'd taken it for granted at this point, so I was a little surprised by your "we have already determined.." comment, since it goes against what I've read on the topic.



It is NOT new! And again we simply get buried in amorphous references to "reflections". No relative levels or differences in time. They matter! So please condition your amorphous claims that are modified when one examines the pertinent time and gain levels.And not only do gain and time mater, but so does the quality of the reflected sound. Are the "reflections equal in gain?, are they sparse, or are they semi-diffuse.

The irony is that each of the various qualifying characteristics has a significant impact on your amorphous and overly generalized use of the term "reflections" sans any qualifying adjectives or adverbs. The fact is, there are myriad contradictory results to your claims once you quality the terms, some supporting and some invalidating them, depending upon the specific qualifications! And per the rule of logic, all we need do is present one exception to invalidate your overly general claims.The fact is the subject is much more complex than you have reduced it. And the notion that "reflections" used so generally do NOT necessarily augment the direct signal!

And as you apparently do not believe that, how about researching who two of the first prominent beauticians were the first to coin and study the term Initial Time Delay gap, later modified to Initial Signal Delay gap to distinguish its use in Small Acoustical Spaces by Don Davis. And then tell us why such a gap is deemed a characteristic of ht best halls and studios and listening rooms. (Hint, the first one's first name is "Leo", and the second's first name is "Manfred")

And don't you find it rather amazing that NO major accepted acoustical room response model advocated early arriving reflections at near the same gain as the direct signal? Not one! Not even the ambechoic that has gone to absurd lengths to create and utilize diffusors specifically to create and maintain an early arriving field of semi-diffuse reflections! An early arriving dense field of early reflections that are 30 dB down from the direct signal!!! And yes they ARE reinforcing. And NO, they are not at or near the same gain level as the direct signal.

And to add further irony, these diffusors in Blackbird, per George Massenburg, have lately fallen to folks preferring them covered with packing blankets causing them to act more like absorbers. Hmmmmm....confusing isn't it?

You know, if anyone wants to try this simple experiment, if done properly, you will experience a very dramatic affect regarding the VERY audible (and rather neat) impact of a near equal early arriving signal with respect to one designated the direct signal.

Take two small cube speakers like Auratones and align and stack them one atop the other. (If you have a measuring platform, you might also want to observe the frequency response as you do this.) Split a generated sine wave of equal gain and feed both speakers independently.Now, very slowly slide the top speaker backward. Those seated in front will experience what 'appears' to be a rotating horn - like a Lesli speaker or a rotating directional civil defense siren that slowly rotates about the room complete with Doppler shift and all. And on the screen if you are watching, you will see the increasing appearance of comb filtering and the nulls that shift in frequency as the offset increases - the same nulls and lobes that you are hearing as they shift spatially with the temporal shift in the relation of the direct and moving speaker - which functions just like a reflection. And gee, does it add to the intelligibility! LOL!

And should we delve into effects such as flanging and how they are created with early arriving spaced 'reflections'? Now that's a fun affect that adds to intelligibility! Not.

The fact being that high gain reflections are detrimental. But reflections sufficiently low enough in gain that they do not trigger the localization response described in the Henry Precedence Effect, can indeed be beneficial.

But to say "early reflections aid in intelligibility" is patently false, as high gain reflections do not, but lower gain reflections can.

So, take a lesson from the March Hare and 'say what you mean and mean what you say'. As your generalizations are false as supported by the rules of logic which require only one exception to the contrary.

SOME carefully qualified early reflections are quite desirable. But ALL early arriving reflections do not - especially those of similar gain (within ~10 dB) - that very often have Very detrimental affects.

And if you will note, NOWHERE have I denigrated low level reflections! In fact, I have gone to great trouble to note the exceptions lest generalizations be drawn that might exclude their beneficial influence. And in each instance the potential for the use of diffusion rather than absorption has been offered.

And that includes in the OP's case where we specifically exclude the use of absorption of them, preferring to maintain and support them.

And in ALL cases ONLY with respect to HIGH GAIN reflections have it been suggested that they be very selectively and surgically damped so as to RETAIN the other lower gain reflections.

But...but ..but... and you arrive here telling me that I don't appreciate the beneficial use of "reflections".

But it seems that you have interpreted that I have written in the same manner that you have treated the papers - treating all reflections as simply "reflections", without regard to their various qualities that make ALL the difference in how they interact with other signals.

And if that was not enough, one wonders why, if early reflections only function beneficially to increase intelligibility, why absorption is being used at all, instead of as the 'go to' medium of treatment by (too) many? HMMM?

After all, the OP is proposing the use of absorption to eliminate reflections, to which you agreed rather than of using a reflective/diffusive boundary that would augment and facilitate the premise you claim to advocate on the one hand when you are not negating it on the other!

But I guess that we are supposed to simply overlook and ignore that logical inconsistency. All the while I have made a very clear case for both cases, advoiating the control of high gain early reflections as well as advocating and supporting the augmentation of low gain reflections and diffuse soundfields.

Quote:
Originally Posted by sdurani View Post

The spaciousness you're talking about assumes using the room as a surround processor. Routing recorded ambience away from the front soundstage to speakers placed around you lessens the need to rely on the room itself to provide spaciousness and envelopment.


Sorry, but you can't have it both ways

And its apparent that you have never looked at the ETC of various surround sources where the room has been effectively removed from the measurements and compared it to a spacious sounding room. And certainly not compared to an ITE recording that retains ALL of the phase and level relationships of 3space as perceived in the pressure zone of the eardrum to note the dramatic difference and to discover why the ITE recording have a typical listen literally and physically responding 'automatically' to environmental cues as if they are real while no one gets up to answer the phone when it rings in a surround movie nor even turns around to view something that is supposedly arriving from the rear.

The fact is that surround is not a sufficiently complete psycho-acoustic model to pass for actual acoustical 3space. The surround cues suffer a type of schizophrenia (further exacerbated by each engineer treating them as they choose without a standard) in trying to determine exactly what they want to be as they are timed to arrive as direct signals rather than as part of the later arriving exponentially decaying semi-diffuse soundfield.

ESPECIALLY as one might note that the formats are scrambling to add, not more lateral sources, but beau coup more front and rear sources in difference to the case made that such cues are detrimental and that they must be laterally arriving.

But then its not really that surprising, as front and rear cues are NOT necessarily detrimental. They are just not enhancing in the same manner as is the portion of the later arriving exponentially decaying LATERALLY arriving soundfield that adds a pleasing sense of spaciousness.


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Personally, I have no problem with you wanting to lecture us on acoustics, since they tend to be informative (even when I disagree with you). But let's not pretend that your priorities are "the" focus of other posters.

I make no claim to simply limit what I say to the strict limitations of the OP! So tell me that your routine participation in cable threads that span weeks have much to do with what wire to buy that can be answered in one post.

Hell, my replies don't even need to be limited to ANY specific post or concept. They may be a reaction simply prompted by the topic or an expansion on a related tangent or a specific how to. Or they maybe about something that simply caught my fancy.

And I will admit that many topics bore me to tears (especially topics that ARE well understood in many acoustical circles, even if the concepts hae not trickled down to consumer electronics and audio! After all, why are we having to explain what an ETC response is that has literally been a fundamental tool for literally 40+ years??? And I have little interest in revisiting mundane topics that are akin to a physicist faced with a debate over the functional nature of an electron for the umpteen billionth time all the while being told that those debating have no time or interest in simply reading a chapter on the topic- ...But, oh, by the way, would you mind explaining everything about everything on a topic predicated on the compete understanding as well as implications of the nature and behavior of multiple models of an electron???? Yeah...right... And some things are answerable with with a "yes" or a "No",even if most have little or no understanding as to the why. -

And no, I regret to inform you that i won't be losing any sleep over whether or not you approve.

But its been fun, and hey, it killed another 20 minute break...
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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.
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post #16 of 57 Old 02-23-2012, 01:54 PM
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Quote:
Originally Posted by dragonfyr View Post

I love how you treat "reflections" as simply "reflections" - as you totally ignore relative gain levels and arrival times as well as spatial and temporal qualties and treat all reflections the same.

Speaking in more general terms than you when it comes to magnitude, timing and direction of reflections is not the same as "totally ignoring" those aspects of reflections. This isn't binary.
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And don't you find it rather amazing that NO major accepted acoustical room response model advocated early arriving reflections at near the same gain as the direct signal?

I don't find it amazing at all, since those models deal with control rooms, not recreational listening spaces for consumers.
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And if that was not enough, one wonders why, if early reflections only function beneficially to increase intelligibility, why absorption is being used at all, instead of as the 'go to' medium of treatment by (too) many? HMMM?

After all, the OP is proposing the use of absorption to eliminate reflections, to which you agreed rather than of using a reflective/diffusive boundary that would augment and facilitate the premise you claim to advocate on the one hand when you are not negating it on the other!

You're erecting a straw man claiming binary thinking when no one has said that all early reflections are only beneficial or only detrimental. For example, when replying to Brad I pointed out which early reflections were found to be preferable and which were not, giving a reason to absorb the latter. Nothing inconsistent about that.
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The fact is that surround is not a sufficiently complete psycho-acoustic model to pass for actual acoustical 3space. The surround cues suffer a type of schizophrenia (further exacerbated by each engineer treating them as they choose without a standard) in trying to determine exactly what they want to be as they are timed to arrive as direct signals rather than as part of the later arriving exponentially decaying semi-diffuse soundfield.

You can lament the current state of surround sound as implemented by electronics manufacturers, but that doesn't change what is available to consumers. If you're surgically tuning the room for envelopment and spaciousness, then to some extent you are using the room as your surround processor. If you are doing this with surround processing and additional speakers, then you are relying less on the room. That was my only point.
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So tell me that your routine participation in cable threads that span weeks have much to do with what wire to buy that can be answered in one post.

What "routine participation in cable threads that span weeks"? Apparently you have me confused with someone else.
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Hell, my replies don't even need to be limited to ANY specific post or concept.

No one was asking you to. I was simply explaining why *I* limit myself to more general comments, based on the scope of the OP's query.
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I will admit that many topics bore me to tears...

Oh come now. If you were truly bored, you wouldn't be addicted to posting at this forum.
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And no, I regret to inform you that i won't be losing any sleep over whether or not you approve.

You're confusing disagreement with disapproval. When I agree with you about something, that's not the same as me giving you approval to post it. And vice-versa.

Sanjay
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"We" have? http://asadl.org/jasa/resource/1/jas...s4?bypassSSO=1

[i]"New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. .

unamplified speech tests? ... this is what you present???

and tell me where within a small acoustical space will you ever have reflected energy being greater in magnitude than the direct signal.


Quote:


"The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. "

and when has this ever been a problem in home theaters/listening rooms?
im afraid i don't see how the unamplified speech test is relevant to this discussion.
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unamplified speech tests? ... this is what you present???

Yes, amongst other research that I listed.
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and tell me where within a small acoustical space will you ever have reflected energy being greater in magnitude than the direct signal.

When the reflections are made louder (hitting a concave surface or wall indent) and/or the source is made quieter (speaker toed away). The point isn't when or how often it happens, but what happens to intelligibility with high gain early reflections, hence the example of an even worse case scenario (reflected energy greater in magnitude than the direct sound).
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and when has this ever been a problem in home theaters/listening rooms?

I'm not the one saying high gain early reflections are a problem.
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im afraid i don't see how the unamplified speech test is relevant to this discussion.

Replace the person speaking with a loudspeaker playing dialogue at the same level.

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"The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. "

so basically a verification that off-axis signals arriving within the 'fused' haas interval perceive a louder direct signal, which under high-noise (low s/n) environments becomes more intelligible by virtue of being louder - not by being more distinct.

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Replace the person speaking with a loudspeaker playing dialogue at the same level.

my loudspeaker is not unamplified. i can control gain. i also do not orient the loudspeakers within my room such that they point away from the listening position in such an orientation that the reflected signals may arrive higher in gain than the direct signal. i tend to have the loudspeakers pointed towards the listening position.

again, this is for "off-axis, unamplified speech" in low s/n environments. how loud is your HVAC?
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Originally Posted by localhost127 View Post

my loudspeaker is not unamplified.

Nor is human speech, which can be adjusted to vary in level ("amplification" need not be electronic).
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Originally Posted by localhost127 View Post

i tend to have the loudspeakers pointed towards the listening position.

Easy in a recording studio. Harder to do in a recreational listening environment where you have multiple listening positions, like with a couch, let alone multiple rows.

Sanjay
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post #22 of 57 Old 02-23-2012, 05:31 PM
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Originally Posted by sdurani View Post

Easy in a recording studio. Harder to do in a recreational listening environment where you have multiple listening positions, like with a couch, let alone multiple rows.

this has nothing to do with studios. and control room studios are most certainly not limited to one seating location. couches are quite common!

where in your home theater with multiple listening positions do you have such a low s/n (high-noise) environment that you REQUIRE reflections to be fused with the direct signal such that the direct signal is perceived as louder as to be intelligible (by virtue of being louder). and who on this forum can provide an ETC where their home theater arrangement induces louder reflections than that of the direct signal ??

we do not need to worry about reflections fusing with the direct signal to provide a louder perceived signal in order for them to be "intelligible". we are NOT prone to low s/n environments within the context of these rooms. we control the gain as we have amplified sources. the referenced paper is not applicable to such environments here! it's for off-axis, unamplified speech in high-noise environments! it's about greater intelligibility by virtue of being louder with respect to the environment, not by being more distinct!

im curious to know what data can be provided that states that MULTIPLE copies of the same signal, of which the reflections arrive at a later time than the direct signal but still within the haas interval such that they are fused together can provide MORE intelligibility than the direct signal by itself. what "extra data" are these reflections providing the brain with to increase intelligibility of the direct signal? why don't i have such intelligibility issues when using headphones?
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post #23 of 57 Old 02-23-2012, 06:27 PM
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All I know is I when I treated my theater's front wall it sounded better. When I treated the side walls it got even better.

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post #24 of 57 Old 02-23-2012, 06:46 PM
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Originally Posted by BIGmouthinDC View Post

All I know is I when I treated my theater's front wall it sounded better. When I treated the side walls it got even better.

LOL ! I gave up trying to find a few words of actual practical advice in the thousands of words above.

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post #25 of 57 Old 02-23-2012, 06:49 PM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post

All I know is I when I treated my theater's front wall it sounded better. When I treated the side walls it got even better.

Thanks BIG. I tried to ask a specific question to avoid the urinary Olympics that these threads usually devolve into. Oh well.....
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post #26 of 57 Old 02-23-2012, 07:38 PM
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Quote:
Originally Posted by localhost127 View Post

couches are quite common!

Then, unlike you, people do listen off axis, like in the paper.
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Originally Posted by localhost127 View Post

it's about greater intelligibility by virtue of being louder with respect to the environment, not by being more distinct!

Then it shows that high gain early reflections aren't detrimental to intelligibility.

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post #27 of 57 Old 02-23-2012, 08:42 PM
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Quote:
Originally Posted by sdurani View Post

Then, unlike you, people do listen off axis, like in the paper.

the reflections are not louder in gain than the direct signal for those sitting "off-axis" on the couch.

it's also comical that within that very same paper, the authors refer to "reverberation time" @ 500hz for a conference room. must be quite a large conference room!

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Originally Posted by sdurani View Post

Then it shows that high gain early reflections aren't detrimental to intelligibility.

your logic isn't correct. the paper is with regards to high-noise environments where the increased gain of the fused indirect reflections with the (lower gain) direct signal allows the unamplified speech to become intelligible (as it is a GAIN, S/N issue). it doesn't state anything to the fact that in a high snr room (low noise), that the increase of high-gain early reflections are not detrimental to intelligibility. can you quote which part of the paper makes such a statement?


"The results confirmed that added early reflection energy
is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signalto-
noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that
for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early
reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections,
show that early reflections can increase the effective signal-to-noise ratio by up to 9 dB."
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post #28 of 57 Old 02-24-2012, 12:43 AM
 
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"speech intelligibility should not be confused with speech quality. Speech intelligibility is related to the amount of speech items that is recognized correctly while speech quality is related to the quality of a reproduce speech signal with respect to the amount of audible distortions."


(Note this qualification directly related to the type of research earlier cited. Also note that in general acoustics (as opposed to hearing aid research), that we use "intelligibility" in a broader sense incorporating both technical intelligibility and quality...)

Likewise, we are now to believe that signal alignment in the time domain, which effectively eliminates an early 'reflection(s)' (an out of sync arrival of the same material) does NOT increase the overall intelligibility of a soundfield.

And that flutter echo - a series of early arriving reflections - is not only beneficial but it adds to the intelligibility of a sound field.

Its one thing to quote research designed to increase the signal level (gain) relative to background noise (S/N) in order to make a signal more easily detected relative to the masking background noise floor noise that is important in hearing aid design, and it is quite another to reduce the amount of distortion and to maximize the quality of a perceived signal that is already of sufficient gain.


Sometimes there is value in understanding the purpose and context of a study, and understanding the goal in raising low level un-amplified sources to a level of sufficient gain so that they can simply be distinguished from the background noise. And there is no doubt that the sum of the direct and early reflections is indeed greater than that of the direct signal alone.

If that is actually the condition in your theater or critical listening room, that your program signal levels are inadequately loud that you cannot hear them above the background noise, and if you have some bias against simply increasing the gain of the system, then by all means increase early reflections in order to make your system easier to be heard and distinguished above the background noise floor!

If you want to optimize the audibility - the quality of a signal that is already adequately loud, then one needs to further control early reflections.

A better summary might be papers such as Peter Mapp's A World of Reflections. (I apologize that the online version is missing the critical diagrams) there are many more that are more technical, but this is a reasonable summary. And to repeat, it is ludicrous to take either position that all early reflections are 'bad' or that all early reflections are good. Reflections have characteristics relative to time, gain, orientation, temporal and spatial distribution and spectral content, and to ignore this is to misunderstand the nature and behavior of the behavior of reflections.

And to this end, high gain early reflections, those within about 10 dB of eh direct signal result in what Richard Heyser termed "time smear distortion". And anyone who has had the opportunity to align out of phase array elements will immediately know to what this refers. It is the same effect commonly heard in highly reflective gymnasiums where the PA is plenty loud, but the ability to distinguish what is said, is abysmal.

You see, here the solution is not to simply increase the gain of the direct and resultant early reflections - as the problem is not one of raising the program level above the background noise. Rather the goal is to optimize the quality of the perceived sound.

To revisit the OPs space, we have several options. None of which support an increase in high gain early reflections.

In fact, the choice is between reducing all* reflections to the maximal degree with absorption (which ironically the person advocating early reflections supported - having apparently little faith in the very paper that was cited out of context),

or,

to instead damp ONLY the high gain early reflections and to allow the lower gain reflected energy to continue in the room supporting a semi-diffuse decaying soundfield. And to the degree that we were not addressing perpendicular SBIR issues, such reflections would necessarily be oblique and would continue to the side walls where, at least potentially, they would become part of the beneficial later arriving laterally oriented semi-diffuse sound field.

You will note the only one position advocated the damping of essentially all reflections.

For you see, all reflections are NOT bad!
Only the early arriving high gain reflections contribute to the summing of the early events into a less distinct distorted perceived event. The lower gain reflections do not. Thus we are not worried about the low gain reflections, and we actually encourage them, as they are responsible for augmenting the desirable sense of spaciousness that makes a small space feel larger.

Thus the optimal approach would be to identify ALL incident points from ALL of the sources in the room and to very selectively damp them, either by absorption (if necessary) or with diffusion, thus reducing the gain and retaining the reflected energy in a more beneficially spatially and temporally diffuse manner.

This latter approach requires a bit more initial work via the use of the ETC response, while the brute force use of absorption adequate to actually damp the full specular band is a less elegant solution.

The problem here is that the proposed absorption is NOT adequate to control the full bandwidth of the reflected energy. So the problems that they want to resolve will in large measure remain - in addition to coloration of the direct signal due to the EQ'd reflection combining with it.

So, the actual choices are between:

1.) inadequate treatment insufficient to damp the full bandwidth of the high gain early reflections that will exacerbate the problems
2.) Adequate absorption able to control the full bandwidth of ALL boundary the reflections resulting in a dead boundary response
3.) Limited surgical use of adequate absorption targeted only to the high gain reflections while supporting the existence of a later arriving exponentially decaying laterally arriving diffuse soundfield (and diffusion is an additional option that can be used to augment this as well)

Each has varying degrees of difficulty and trade-offs, as does any choice. But those are the choices. And each involves a balance of time, energy, cost, hassle factor, response preference, and practicality.


But the advocacy that early arriving high gain reflections are beneficial to our purposes is simply erroneous. If such were the case, there would be no concerns with setting distance/time of the various speakers and signal arrival times. There would be no justified use for using absorption in boundaries in a small space at all. There would be no practical use for precision microsecond delay units that dominate the landscape and whose presence literally increased as EQs, which are unable to equalize the results of the combining of out of phase signals, decreased.

And if such were valid, one wonders why they support the application of absorption to the surface???



*Here we assume for the moment that thin absorption is sufficient to damp ALL reflections and not simply the higher frequencies
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post #29 of 57 Old 02-24-2012, 12:54 AM
 
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Quote:
Originally Posted by sdurani View Post

Nor is human speech, which can be adjusted to vary in level ("amplification" need not be electronic). Easy in a recording studio. Harder to do in a recreational listening environment where you have multiple listening positions, like with a couch, let alone multiple rows.

Sorry, but you are grasping for straws.

Un-amplified in the context of he paper you cited refers to the INABILITY to 'externally' adjust the gain EXCEPT via the incorporation of reflections..

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". It is a study done simply to determine passive means to increase the gain of a low level signal in a relatively high background noise environment. It is a topic common to hearing aid research.

Instead you might want to focus on why someone who feels "early reflections (without stated qualification) are beneficial to overall intelligibility" advocates the use of dead boundaries considering that the overwhelming majority of the reflections would predominately be oblique and would be directed to the lateral surfaces for return as lateral reflections.
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post #30 of 57 Old 02-24-2012, 01:07 AM
 
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Originally Posted by sdurani View Post

Then it shows that high gain early reflections aren't detrimental to intelligibility.

No it does not. It shows that early reflections are beneficial to increasing the GAIN of the OFF axis perceived signals relative to the background noise.

And their use of the term "speech intelligibility" relates not to overall speech quality, but specifically to the increase in the ability to distinguish the perceived signal relative to background noise - the signal to noise ratio.

It makes no conclusion regarding the sound quality of the increased gain signal.

Of course, if the results are as you have claimed, one would have to be a bit confused to advocate the absorption of such 'beneficial' early reflections?

And I am sure that the intentional offsetting of various sources in the system, rather than the calibration and setting of all sources in a signal aligned manner would be beneficial as well, as each similar spaced source would act as an indirect source relative to the others and increase the perceived gain, which if we ignore the quality aspect, would be beneficial according to your premise.

The selective attention on such a small aspect of the overall characteristics as an increase in summed gain and extrapolating that to the equivalence of an increase in overall sound quality is unfortunate, and one might be advised to hold off in the belief that we are on the cusp of yet another acoustic revolution.. ...however backwards...
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