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OC 703 faced? - Page 2

post #31 of 218
Quote:
Originally Posted by BIGmouthinDC View Post

First time I've been called a disrupter

are there any particular concepts presented in this thread that you are in disagreement with?
post #32 of 218
Consuming 12 to 16 inches of room width for first reflection absorbers is not feasible for many.
post #33 of 218
Just to rub some more salt around. A young guy goes to see a cardiologist and says what can I do now in my life so that I never have to see you again, the doctor says that is impossible , just live your life and come back when you have either shortness of breath or chest pain. We'll run a battery of tests, do a little surgery and prescribe some meds. Theater building is lot like that, we want clear dialog at all seating positions and lack of uneven or booming bass. What can we do now to avoid those problems once the room is completed.
post #34 of 218
Quote:
Originally Posted by BIGmouthinDC View Post

Consuming 12 to 16 inches of room width for first reflection absorbers is not feasible for many.

i asked you specifically what concepts you disagree with - not to present potential physical design constraints.

and there is no need to exaggerate -
post #4 of this very thread:

Quote:
Originally Posted by localhost127 View Post

4" OC703 (2x 2" unfaced batts stacked together) + 2-4" air-gap.


facts are facts and facts have been presented. facts and physics do not give a damn whether one is not able to give up X inches in their room, or what the wife says. if one is looking to attenuate an 'early reflection' then the ETC is utilized to measure (key word: measure) the gain of the reflection and such data is used to determine (for example) whether treatment even needs to be applied in the first place.

the fact remains that due to the inherent nature of many of us being constricted to an acoustically small space (dictated by physics) - that we are dealing with specular energy that may well behave down to ~300hz. as such, when one is looking to attenuate a reflection - the 'treatment' must be effective enough to fully attenuate the signal. otherwise, one is simply and effectively applying a 'filter' to the response at the listening position.
post #35 of 218
12-16" is exactly what 4" + 2-4" on both walls adds up to

Edit: "fully attenuate" seems to me a bit of a misnomer, in the sense that attenuate means "to lessen", not "eliminate", so how could it be "fully"? "sufficiently attenuate" (say -20 dB) might be more clear? In which case, the absorption need not reach 100% (at all frequencies)?
post #36 of 218
Quote:
Originally Posted by Brad Horstkotte View Post

12-16" is exactly what 4" + 2-4" on both walls adds up to

does the interpretation of his sentence alter the physics discussed??
post #37 of 218
Quote:
Originally Posted by localhost127 View Post

does the interpretation of his sentence alter the physics discussed??

Oh please local, you're just trying to be argumentative - carry on, I'm done
post #38 of 218
Quote:
Originally Posted by BIGmouthinDC View Post

I'm feeling chest pain, check please.

Quote:
Originally Posted by localhost127 View Post

are there any particular concepts presented in this thread that you are in disagreement with?


???
post #39 of 218
Quote:
Originally Posted by Brad Horstkotte View Post

Oh please local, you're just trying to be argumentative - carry on, I'm done

what have you presented in this thread?
what concepts, specifically, are you in contention with?

the fact remains you are going to great lengths to find any sort of contention instead of actually discussing the topic at hand. to me, this sort of behavior is the "wife factor".

please - dictate to me why you might recommend a thin absorber to a member of this thread that will essentially filter the response instead of appropriately attenuating the reflection.

im all the more curious to hear why you recommend applying a 'filter' when a member is looking to gain information on how to attenuate a reflection.
post #40 of 218
Quote:
Originally Posted by Brad Horstkotte View Post

Edit: "fully attenuate" seems to me a bit of a misnomer, in the sense that attenuate means "to lessen", not "eliminate", so how could it be "fully"? "sufficiently attenuate" (say -20 dB) might be more clear? In which case, the absorption need not reach 100% (at all frequencies)?

attenuation of a reflection such that it is below the human detection threshold.

do lower frequencies of the specular region not posses longer wavelengths than those above?
do lower frequencies of the specular region not contain more energy than those above?
post #41 of 218
let us not also consider the fact that not only do the lower frequencies of the specular region inherently contain more energy (thus, requiring more attention when 'treating') - but also that the lower frequencies have a higher potential to be 'off-axis' than the HF, highly directional content - precisely at side-walls and areas of 'early reflection'.
post #42 of 218
Not being able to give up 16" of your room is a design constraint. It can't just be ignored because it interferes with the ideal situation you want to achieve. If space and costs are not an issue, sure, we would all use that 16" to give us the best possible results. As it stands, most of us want to make the best use of the space and funds that we have. Even if that means we're limited to a couple inches of absorption.

This thread has been painful to follow, I'll leave it with you.
post #43 of 218
Quote:
Originally Posted by J_P_A View Post

Not being able to give up 16" of your room is a design constraint. It can't just be ignored because it interferes with the ideal situation you want to achieve. If space and costs are not an issue, sure, we would all use that 16" to give us the best possible results. As it stands, most of us want to make the best use of the space and funds that we have. Even if that means we're limited to a couple inches of absorption.

This thread has been painful to follow, I'll leave it with you.

such commentary looks for any and all excuses to actually address a particular problem.

the 'catch-all' psychology is overwhelmingly predictable.

"most of us". .... yes - please, speak for the entire forum. anything except actually addressing the topic at hand.

Quote:
Originally Posted by localhost127 View Post

are there any particular concepts presented in this thread that you are in disagreement with?
post #44 of 218
You really want to argue that "most of us" want to make the best use of our space and money. OK. I give, you win
post #45 of 218
Quote:
Originally Posted by J_P_A View Post

You really want to argue that "most of us" want to make the best use of our space and money. OK. I give, you win

is there a particular concept presented in this thread that you do not agree with?

or are you looking for any excuse to argue... another "wife factor"
post #46 of 218
Quote:
Originally Posted by J_P_A View Post

Not being able to give up 16" of your room is a design constraint. It can't just be ignored because it interferes with the ideal situation you want to achieve. If space and costs are not an issue, sure, we would all use that 16" to give us the best possible results. As it stands, most of us want to make the best use of the space and funds that we have. Even if that means we're limited to a couple inches of absorption.

This thread has been painful to follow, I'll leave it with you.

it's unfortunate but also predictable via human nature that you also assume what the 'ideal' solution is. why would you make such assumptions that broadband absorption is the ideal solution with regards to attenuating early reflections ???

if one has such 'design constraints' and cannot effectively apply 'absorption', then one could just as easily apply a large (with respect to wavelength) reflector at 'early reflection points' to redirect the specular energy away from the listening position which will allow the finite energy to be maintained and preserved such that it can be properly presented back to the listening position at termination.
post #47 of 218
I'd have to do a quick sketch to be sure, but I suspect that in most all cases the depth of an angled reflector will be as least as great as the 8" of absorption being discussed due to angle of incidence requirements.

Space is a real problem for people. Designing a room from scratch, I'd leave about two feet around the room boundaries to give flexibility in implementing required acoustic treatments. Given the typical sized room people here start with, I'm not sure what compromise I would eventually make. I might well try the way less than ideal and potentially worse than nothing approach of thinner panels, and check out the results.

Nah, I'd just use speakers that minimized the issue from the get-go.
post #48 of 218
Quote:
Originally Posted by Bigus View Post

Nah, I'd just use speakers that minimized the issue from the get-go.

and a quick measurement via the ETC will eliminate any such 'guess-work' and clearly display how specular energy is impeding the listening position - gain with respect to time.

it's amazing the on-and-on discussions we have regarding this topic and yet the very tool for the job is rarely (if ever) mentioned. and not only does it clearly outline early arriving energies, but it also displays early-early arriving energy such as that via edge diffraction. it is also used for verification once an 'absorber' has been placed, as it will detail to the user how effective the absorber is at attenuation of the specular reflection, and whether the panel is properly placed such that the reflection is attenuated across the entire listening position. the "mirror-trick" does not provide you with any of this relevant data. and on the topic of the "mirror-trick" - as discussed, since the lower-mid range of the specular region inherently contains more energy, this is why it is important to look for the 'acoustic center' of the speaker in the mirror, vs the tweeter which is constantly and incorrectly promoted on this forum. but, as stated - the "mirror-trick" does not detail to you in any fashion the relevant data required for proper placement of the broadband absorber except for general areas of incident energy via large boundaries.

but of course, we seem to be stuck in the 'frequency domain' mentality within these forums - with many not understanding that in small acoustical spaces, the time-domain takes precedence (no pun intended).

Quote:
Originally Posted by Bigus View Post

Space is a real problem for people.

but physics is physics - and the physics do not change based on space available, decor, wife-factor, etc. the fact remains that if one is looking to attenuate a specular reflection via broadband absorption, then the absorber must be effective down to the lower specular region. people can argue all they want about space constraints and look for any excuse for not addressing the problem properly - it doesn't change facts.

if i were attenuating an early specular reflection, i would prefer to attenuate it entirely vs what is essentially applying a 'filter' to the response via thin absorption. i, personally, do not care for my room to be an "FX generator"
post #49 of 218
Ok, back to facing.
If the facing is against the wall (drywall), no difference than without facing.
If the facing is toward the room, the facing will reflect a certain range of the HF component. At the same time, the facing is acting as a membrane and you have a pressure type absorber. The specific performance will be unknown until tested. Within the context of such products that have been tested, the general (not specific) effect is the performance of a 2" panel mimicks the performance of a 4" panel (lots of variables here...but that's the general idea).
post #50 of 218
Quote:
Originally Posted by localhost127 View Post

you could use faced and face it towards the wall, but then you're restricting yourself to a single, thin absorber of which you cannot utilize an air-gap.

Quote:
Originally Posted by Dennis Erskine View Post

Ok, back to facing.
If the facing is against the wall (drywall), no difference than without facing.

Quote:
Originally Posted by localhost127 View Post

if one is looking to reflect HF content from the rear wall, then used faced. but i am not sure why one would do that. you're still filtering the reflection from the rear wall.

Quote:
Originally Posted by Dennis Erskine View Post

If the facing is toward the room, the facing will reflect a certain range of the HF component.

...


Quote:
Originally Posted by BIGmouthinDC View Post

Localhost127: having read a number of your posts your advice is running contrary to a couple of Theater designers/audio advisers who have hung out here over the years, specifically Dennie Erskine and Brian Pape

sounds like we're in agree-ance with regards to this topic -

OP - does this clarify your questions regarding porous absorption to 'absorb' reflections and the difference in application between faced and un-faced OC703?
post #51 of 218
Quote:
Originally Posted by J_P_A View Post

Not being able to give up 16" of your room is a design constraint. It can't just be ignored because it interferes with the ideal situation you want to achieve. If space and costs are not an issue, sure, we would all use that 16" to give us the best possible results. As it stands, most of us want to make the best use of the space and funds that we have. Even if that means we're limited to a couple inches of absorption.

...You really want to argue that "most of us" want to make the best use of our space and money.

I agree. That's NOT the issue!

You can either do things that actually benefit the space and accomplish an objectively defined goal defined by physics, or you can offer aesthetic treatments that modify the space in an unintended and detrimental manner.

If that is what you going to settle for as you willfully ignore the real behaviors, you may as well simply hang a bunch of Spiderman beach towels around the space and enjoy the aesthetics as you try to convince yourself that it sounds "better" - and not simply "different".

And the next time you go to the doctor, tell him (her) that you don't want to spend the money necessary to accomplish an effective treatment, but instead suggest they offer a few chants and placebo sugar pills so that you can go home and imagine how effective the treatments are.

Funny, but why do I suspect in that regard you would refuse the equivalent to which you assert is acceptable acoustically.



And Dennis, with all due respect, its nice to see that you acknowledge that such a faced panel can act to a minuscule degree as a membrane absorber.

The problem is that it acts as a membrane to such a small degree that it is not considered a significant pressure based absorber anymore than a diffusor is considered to be an absorber - but its nice to see that one has the ability to recognize that no device is absolute in its nature and that all are characterized based upon the preponderance of their behavior and not upon the totality of heir behavioral characteristics. Just as all absorbers ofter a bit of reflectance and that all reflectors/diffusors offer a certain amount of loss.



...To quote the illustrious Don Davis "If bad sound were fatal, audio would be the leading cause of death."
post #52 of 218
Dennis I'm helping someone in this area build a theater to your specifications with insul-shield and Quest Perfsorber. Could we save some money and just hang Spiderman Beach towels?
post #53 of 218
Quote:
Originally Posted by BIGmouthinDC View Post

Dennis I'm helping someone in this area build a theater to your specifications with insul-shield and Quest Perfsorber. Could we save some money and just hang Spiderman Beach towels?

the best way to 'save money' is to measure to identify whether an issue exists in the first place before 'treatment' is procured.
post #54 of 218
"I used to be embarassed of my three inches...





Until I found out they like it that thick."
post #55 of 218
Quote:


just hang Spiderman Beach towels

NO...we all know you must use Silver Surfer beach towels.
post #56 of 218
As an admitted "non-expert", I'm confused by one seemingly contradictory aspect of one part of this discussion. As I understand it, local and dragon seem to be advocating the need for thick absorbers and air-gaps at first reflection points; mainly to effectively absorb the lower-mid range, down to around 300hz. However, all the absorption coefficients I've ever seen for OC703 indicate that it absorbs pretty well down to about 250hz, with only a 2" thickness placed directly on the wall. Even adding just one more inch of glass, for a total of 3", brings the coefficient well above 1. Is there something else I'm missing that would require double the thickness plus the air-gap?

Rob
post #57 of 218
Quote:
Originally Posted by robbyc30 View Post

As an admitted "non-expert", I'm confused by one seemingly contradictory aspect of one part of this discussion. As I understand it, local and dragon seem to be advocating the need for thick absorbers and air-gaps at first reflection points; mainly to effectively absorb the lower-mid range, down to around 300hz. However, all the absorption coefficients I've ever seen for OC703 indicate that it absorbs pretty well down to about 250hz, with only a 2" thickness placed directly on the wall. Even adding just one more inch of glass, for a total of 3", brings the coefficient well above 1. Is there something else I'm missing that would require double the thickness plus the air-gap?

Rob

could you please detail how an absorption coefficient above "1.xx" is necessarily valid in small acoustical spaces that is of context?

perhaps one should pay attention to the commentary explicitly detailed on such pages:


http://www.bobgolds.com/AbsorptionCoefficients.htm
Quote:
Originally Posted by bob gold View Post

"The absorption coefficients that are typically published for acoustical materials are found using the reverberation chamber method. This method yields random incidence absorption coefficients, which are not percentages. Normal incidence absorption coefficients are percentages. The two are often confused in the literature. A material that has a random incidence absorption coefficient of 1.22 is simply a better absorber relative to a material with a random incidence absorption coefficient of 0.67 for the same frequency band, all other factors being equal. The numbers should not, however, be treated as an indicator of the percentage of sound absorbed by the material." by Savant aka Jeff D. Szymanski

http://downloads.bbc.co.uk/rd/pubs/reports/1982-04.pdf

but once again - an ETC response of the room would clearly dictate how specular energy was impeding the listening position - gain with respect to time. everything else is guess-work - INCLUDING the effectiveness of a porous, broadband absorber without measurements to verify a particular specular reflection has been attenuated (and attenuated across the entire listening position)
post #58 of 218
Thread Starter 
Wow, yeah I'm good.
post #59 of 218
local,
You said that thin absorbers are fine for upper frequencies, but not for lower frequencies. OC703 absorbs upper frequencies at around 1, give or take. Is that not good enough for lower frequencies?

Rob
post #60 of 218
Quote:
Originally Posted by robbyc30 View Post

local,
You said that thin absorbers are fine for upper frequencies, but not for lower frequencies. OC703 absorbs upper frequencies at around 1, give or take. Is that not good enough for lower frequencies?

Rob

you have not provided any physical dimensions in your statement regarding "OC703"

the absorber needs to be sufficient to attenuate down to the lower specular region.

the lower wavelengths of the specular region have inherently longer wavelengths and more energy than those above.

if you are using a thin absorber that merely attenuates the HF content, then you are essentially "filtering" the reflection.

this is why it is imperative to use the ETC response to actually measure the specular response at the listening position once an absorber ("treatment") has been placed - to verify that it has sufficiently addressed the inherent problem of which it was procured for.
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