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window behind monitors.... best way to treat this??

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Re: window behind monitors.... best way to treat this??

Postby Eric Desart » Wed Dec 29, 2004 6:46 pm

Sorry Hugh,

I just make it easy and leave. It's your home here and I respect that.

This was the request of Ethan (not to me)
Ethan Winer wrote: .... you'll be much more convincing if you explain why it's inaccurate.
Assuming normal 1/8 inch window glass as found in homes, I'd love to see some hard data from you showing the "crossover" frequency at which a window, versus a standard wall with sheetrock on both sides, transitions from reflecting to passing.


Even with the best of intents, and forgetting about exact use of notions, supported by close to 30 years of acoustics, I shouldn't have the slightest idea what to look for, even when I really should want to respond to this.
And the context why I explained.

But Eric gently disappears.
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Re: window behind monitors.... best way to treat this??

Postby Ido » Thu Dec 30, 2004 10:38 pm

Hugh et all,
Since I started this mess, I’d like to try and fix things up a bit.
Obviously the internet is an unlimited source of data and knowledge, but the downside for the non professional is the lack of overall “quality” supervision, both in qualifing the data itself (one may find contradicting sources) and in getting the right “feel” for the principles at work. Another problem I see is how does the amateur attain a perspective on the relative importance of things (as in “seperating the wheat from the chaff”).
The only reason I say this is to try and explain the basis for my approach.
Now Hugh, the way you last described window acoustic behaviour is fine with me, however, I think some misunderstandings might arise in certain settings (as in Doezer’s), to the effect of:
“hey, I’m not sure about this window thing, I think I might need to treat & absorb it, but then again, it might do some good for the bass. na, I’ll leave it be”.
Now please, I don’t want to argue, nor get into mechanisim disscussions. I want to keep it simple and straightforward for those who might be confused, so kindly hear me out, maybe we will all agree on the following:

1. It is preferabe to separate the inner acoustic treatment (mainly absorption) from noise isolation considerations. What I mean with this is that if you have an inner acoustic problem, treat it accordingly, and don’t rely on possible non-direct mechanisms stemming from isolation or others. I would only “rely” on such if I assuredly knew en-field that it works, that the problems are solved, and that no acoustic compromises are made.

2. To the best of my knowledge, in the average medium-small room (typical walls, one typical door, average/basic acoustic treatment), the “apparent absorption” of a 1 typical small window of ~1 sqr. meter would be insignificant.

3. I would consider the above to be the “default”.

4. Of course there are scenarios where windows or any other characteristic partitions will create variable degrees of absorption which could also benefit the inner-acoustics, there is no argument here, but this should be calculated, and preferably measured en-site.

Cheers,
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Re: window behind monitors.... best way to treat this??

Postby Ethan Winer » Fri Dec 31, 2004 8:03 pm

Ido,

> the “apparent absorption” of a 1 typical small window of ~1 sqr. meter would be insignificant. <

Sure, but the original point was not that a window absorbs some amount of bass energy. Rather, that it passes some of that energy to the other side. Energy that passes is not reflected, and less reflected sound equals less severe peaks and nulls within the room.

I think we can all agree that low frequencies pass through any boundary more than higher frequencies do. So at issue here is how much sound is passed, and how the amount varies at which specific low frequencies. Any absorption that may occur will further reduce the peaks and nulls, but that's in addition to how much sound passes through to the outside.

--Ethan
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Re: window behind monitors.... best way to treat this??

Postby Scott R. Foster » Sat Jan 01, 2005 2:18 am

I think the original question was how to treat the window with an inclination on the part of the person asking the question to cover it with absorption. As explained above, in harmony with the original queation, there is solid reasoning behind the idea of treating the entire front wall wih absorption. While of course this isn't actually necessary [after all what is?], there is a school of acoustic design that would advise this step.

So, doing nothing to the window is an option... but covering it with acoustic absorbent will have an effect, and follow a "known good" scheme of room design and treatment.

The flaw in reasoning that we seem to be stuck on is that you can do nothing to the window, and still have an absorber in that location... as explained at length above, doing nothing to the window does not render it into a practical absorbtion device for a number of reasons... the energies "tranmitted" are miniscule and therefore very little is absorbed at any frequency, the vibrations of the window's panes re-emit sound back into the room - this aint absorption, etcetera. Bottomline is windows make lousy absorbers.

Pretending a window is an absorber will not make it one... OTOH opening the window so there is a hole in the wall where the window used to be... and then pretending it is still there would be a different matter.
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Re: window behind monitors.... best way to treat this??

Postby Hugh Robjohns » Sat Jan 01, 2005 12:03 pm

Foz wrote: So, doing nothing to the window is an option... but covering it with acoustic absorbent will have an effect, and follow a "known good" scheme of room design and treatment.

I would agree that placing absorption behind the monitors is often a useful and positive thing to do, but it certainly isn't mandatory, and in this case I'm not sure it is practical either.

There would probably be a far greater aesthetic advantage to retaining the view through the window and the daylight than to blocking it up for the sake of marginally improved acoustics.

Furthermore, I have been to far more professional studios and mastering rooms that have windows between the monitors than complete absorbing walls, and the majority sound very good. There is more than one way to achieve the desired goal of a good sounding room, and they don't all rely on complete absorbing walls behind the speakers. I wouldn't get to bothered about the window, but would put the effort into sorting out the acoustic treatment elsewhere to control side wall, ceiling and rear wall reflections.

The flaw in reasoning that we seem to be stuck on is that you can do nothing to the window, and still have an absorber in that location...

I agree that there is a 'flaw' is viewing the window as an 'absorber', which it clearly is not. However, it is inherently more 'leaky' at low frequencies than a solid wall and is thus retaining it is not entirely a 'bad thing'.

the energies "tranmitted" are miniscule and therefore very little is absorbed at any frequency

I'm open to persuasion here, but empiricle experience suggests to me that the LF energy passing through a simple window can be significant. For example, I have been in home studios with single-pane windows between control room and studio, and LF howlrounds are common -- so clearly significant LF energy from the monitors manages to get through to the mics to be a problem. If that LF energy is getting through the window, it must be leaving the room, and that is generally useful in small room situations. I'm not saying it is as good as a proper absorber, but it's not as bad as a solid wall either.

the vibrations of the window's panes re-emit sound back into the room - this aint absorption.

Surely, this is just reflection. I fail to see how (other than in pure resonance) the window's vibrations can re-emit more energy into the room than was there in the first place. Indeed, the inherent mechanical losses in the medium must surely mean that it re-emits (reflects) less energy than arrived on its surface in the first place.

Bottomline is windows make lousy absorbers.

Agreed...

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Re: window behind monitors.... best way to treat this??

Postby chrissyb » Sat Jan 01, 2005 4:18 pm

This is terribly confusing for the poor person who originally posed the question. The purpose of the window is largely psychological i.e. to see the performer and for the performer to engage with the control room, this is a very simple and gratifying thing to have, it feels professional and looks great. I've recorded in some first rate studios and whilst tracking is in progress it is unlikely monitoring in the control room will be that loud even if there is a rock band in the live room. Translate this to a smaller set up which may be handling only vocals and a bit of acoustic guitar it is unlikely that at THE TRACKING STAGE low frequency absorption is going to be much of an issue because monitoring levels are not going to be at mixing levels. I know this oversimplifies the relationship between amplitude (?) and frequency etc. but my end point is it is much nicer to have the visual communication coupled with a curtain absober (to pull across when mixing), than not to have any visual element at all.

DoeZer put a window in with my blessing - and enjoy the view :D
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Re: window behind monitors.... best way to treat this??

Postby Scott R. Foster » Sat Jan 01, 2005 7:24 pm

,
The purpose of the window is largely psychological i.e. to see the performer and for the performer to engage with the control room


Is that true in this case? I don't recall DZ mentioning a tracking room.... merely that he had a window, and that he supposed he wanted to explore how to make the area absorptive per the instructions provided with his foam treatment kit.... and asked how this might be done.

"Don't bother" is a reasonable response IMO [it aint a lot of SF and it is dead behind his monitors], but if DZ feels the window adds nothing useful, then following through with a complete LEDE treatment scheme is a pretty good idea IMO. Placing a couple of mineral fiber panels in the opening is trivial and would accomplish the expressed goal.

When this thread touches about how useful a window might be if left uncovered, I am unsure that these statements are OT... I don't recall DZ pointing to any such utility as to this particular window [view to an aestheticly pleasing landscape, or tracking room]. For all we know the window provides a view of a brick wall... and in any event, one could provide the ability to have the option to easily switch between absorption or the view [shutters]. If the window IS useful, then by all means use it.. if not then go on with your bad self and go LEDE all the way.

The other main side track of the thread is the idea that a window is already an absorber.. it aint.

PS to Hugh:

Surely, this is just reflection. I fail to see how (other than in pure resonance) the window's vibrations can re-emit more energy into the room than was there in the first place


As explained above, it aint a matter of more energy... it is the fact that the energy re-emitted by a an excited panel is not absorbed - neither is this energy simply reflected - but rather the energy is displaced in time by the physical action of the vibrating panel - thus the room's sound is colored by the persistence of a particular set of frequency in the reverb tails. This does NOT happen with an effective absorber... nor does this occur with simple reflection from a stiff boundary.
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Re: window behind monitors.... best way to treat this??

Postby Paul Woodlock » Sat Jan 01, 2005 8:12 pm

Foz wrote:, .....

PS to Hugh:

Surely, this is just reflection. I fail to see how (other than in pure resonance) the window's vibrations can re-emit more energy into the room than was there in the first place


As explained above, it aint a matter of more energy... it is the fact that the energy re-emitted by a an excited panel is not absorbed - neither is this energy simply reflected - but rather the energy is displaced in time by the physical action of the vibrating panel - thus the room's sound is colored by the persistence of a particular set of frequency in the reverb tails. This does NOT happen with an effective absorber... nor does this occur with simple reflection from a stiff boundary.

Greetings :)

I hope you all had a good New Year Celebration :)

I also wondered where 'more energy' came from.

Take an infinitely stiff panel. Even without any mass it would provide 100% Isolation, and I would guess that 100% of the acoustic energy hitting it would be reflected off it.

but in the real world....

NO panel is infintely stiff, so any acoustic energy hitting it would excite the panel into vibration ( very easily at it's resonant frequencies ) and re-radiate it on BOTH sides of the panel, as well as absorption and reflection. It's this action that Soundproofing is all about stopping isn't it?

I think I'm right in saying an excited panel is a storage of energy. In a similar ( or same ) way as a room mode standing wave is also a storage of energy. i.e The standing wave has a rise and fall time that lags behind the excitation period and thus colours the rooms ambience. Another reason why EQ isn't that good for compensating for room mode problems :)

So... could you say room mode standing waves also re-radiate energy into the room?

Just some thoughts. Any corrections welcome :)


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Re: window behind monitors.... best way to treat this??

Postby chrissyb » Sat Jan 01, 2005 8:17 pm

There we go - I'm so immersed in buiding studios from scratch they I never realised DoeZer wasn't talking about a new studio build.

So this is just a normal window in a normal wall in a normal house - extraordinary? :ooo:
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Re: window behind monitors.... best way to treat this??

Postby Ido » Sat Jan 01, 2005 10:52 pm


Ethan,

1. I honestly don’t understand why you keep on with “LF energy passing through window” motif. It is very vague (“.. passes some of that energy..”), so that I fail to see any practical implication from it in this case:
If the specific window area creates reflections that need be treated, you treat them. If not, you don’t treat them.
If you’re not sure (which is common), take some absorbent of any kind, cover the window, and hear/measure if there is a difference/improvement.
If not, obviously no treatment is necessary.
If there is some difference, and you want the window visible, do the curtain.
How does the window’s “LF energy passing” as you call it, change this?

2. In any event, one can treat & absorb the window as is. I don’t think anyone thought of closing the window with bricks, right?

3 .
Ethan Winer wrote:Ido,

> the “apparent absorption” of a 1 typical small window of ~1 sqr. meter would be insignificant. <

Sure, but the original point was not that a window absorbs some amount of bass energy. Rather, that it passes some of that energy to the other side....
--Ethan

????
The “passing” is directly related to the “absorption”, hence I used the term “apparent absorption”.


Hugh,


…I'm open to persuasion here, but empiricle experience suggests to me that the LF energy passing through a simple window can be significant. For example, I have been in home studios with single-pane windows between control room and studio, and LF howlrounds are common -- so clearly significant LF energy from the monitors manages to get through to the mics to be a problem. If that LF energy is getting through the window, it must be leaving the room, and that is generally useful in small room situations..


I thought Eric Desart explained that earlier very well, mainly, that this has to do with the logarithmic nature of acoustics:
The energy is of course getting through, and it can be significant on the outside, but this energy can be but a mere fraction of the energy inside.

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Re: window behind monitors.... best way to treat this??

Postby Ethan Winer » Sun Jan 02, 2005 6:55 pm

Ido,

> How does the window’s “LF energy passing” as you call it, change this? <

Any sound that passes through the window to the outside is not reflected back into the room. I don't know any way to state it more simply so you'll understand.

> The “passing” is directly related to the “absorption” <

No it's not! At any given frequency all materials absorb, reflect, and pass - all at the same time but in different proportions. Any LF energy that passes through to the other side it is neither reflected nor absorbed by the glass, though the net effect is similar to absorption.

--Ethan
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Re: window behind monitors.... best way to treat this??

Postby Eric Desart » Mon Jan 03, 2005 11:47 am

*** 0VU woz 'ere! ***

Hugh Robjohns wrote: I'm open to persuasion here, but empiricle experience suggests to me that the LF energy passing through a simple window can be significant.

Physics here is not a matter of being persuaded, but of acoustic math.
***and ere'!***
The question is not what's out there or what phenomena happen there, but what's the outside escaped energy ratio versus the energy inside in order to rate the influence on the sound inside.

Ethan Winer wrote:Ido,

Ido wrote: How does the window’s “LF energy passing” as you call it, change this?


Any sound that passes through the window to the outside is not reflected back into the room. I don't know any way to state it more simply so you'll understand.


Ido clearly refers to this ratio.
***and 'ere!***

Ido implies that this energy RATIO outside varies from low to high frequencies from about negligible to very negligible.
As such his question: "How does .... change this."

Ethan Winer wrote:
Ido wrote: The “passing” is directly related to the “absorption”


No it's not! ....


YES IT IS , and in more than one sense.
***and 'ere!***

This are NOT independent properties.

I told how TL works here.
http://www.soundonsound.com/forum/showf ... rt=1#67207
And TL is not only defined by mass, but VERY dependent on internal damping. And internal damping = dissipation of energy which equals absorption or transformation into heat.
The sound does not go through the object but brings it in vibration, making it a source in itself.
And this vibration is either dissipated in the single window pane and/or connected structure or radiated in both directions (in + out).
The strength and physical properties of this vibration is what causes the single window pane to act as a low quality absorber. And this vibration of this window pane is very related with this internal damping

Ido gave a careful correct summary.
Playing with words shouldn't substitute the core of things.

And this core is:
Loud outside noise should substantiate the statement that most or lots of the bass should have left the room and therefore prevent or strongly diminish internal low frequency problems.

THIS STATEMENT IS WRONG, PLAIN WRONG, in function of normal TL values to be found for standard building applications.

True is that low TL panels as drywall in double leaf systems will increase absorption in the room, increasingly towards lower frequencies, but limited by the MSM (mass-spring-mass) resonance were this phenomenon reverses again. In fact such a wall is a huge panel trap (more or less damped depending on construction).
The absorption difference with a concrete room is enhanced by the huge quantity (read surface) of such an application.
In itself it are low efficiency absorbers, it's the quantity compensating for that.

But even then the advice of diminishing insulation by using 1 layer instead of 2 to diminish low frequency problems is plain dangerous, when not executed very controlled.
This relates to the MSM (mass-spring-mass) resonance of the double leaf system.
Below this MSM the TL of the wall increases again towards the lower frequencies (read diminishing absorption) and such an application makes a more or less damped panel trap/resonator of the whole room, which can be tuned to a not desirable frequency or tuned to a useful disturbing frequency, but simultaneously creating an acoustic leak at this frequency caused by the amplification in this MSM range.

This kind of headliner acoustics, without knowing or understanding the consequences or basic underlying concepts are dangerous and can lead to wrong applications by people blindly trusting such [incomplete and over-generalised] (edited 0VU) advice.
They almost guaranteed have trouble with too low insulation, this MSM resonance can really be disturbing (+ increases in frequency with lowering panel mass) while the internal acoustics can as well be influenced in a questionable and uncontrolled manner.
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Re: window behind monitors.... best way to treat this??

Postby Guest » Mon Jan 03, 2005 1:03 pm

Any sound that passes through the window to the outside is not reflected back into the room. I don't know any way to state it more simply so you'll understand.
Ethan, the second part of that response is just patronising and rude. Given your own dislike of being on the receiving end of such remarks please think before you type.

> The “passing” is directly related to the “absorption” <

No it's not! At any given frequency all materials absorb, reflect, and pass - all at the same time but in different proportions. Any LF energy that passes through to the other side it is neither reflected nor absorbed by the glass, though the net effect is similar to absorption.

Selectively quoting someone to pick an argument with them is pointless. What Ido actually said was:

The “passing” is directly related to the “absorption”, hence I used the term “apparent absorption”.

Here and in his previous post he made it pretty clear that he was referring to the way in which one (in very simplistic terms), could consider to have been absorbed, sound which isn't reflected back into the room. In referring to it as "apparent absorption" he suggests that absorption isn't actually the whole story but he gives a good idea of the effects without needing to go into the actual mechanisms involved. I don't have a problem with Ido using the term - certainly not if others can say that windows have a "crossover frequency".

Incidentally, as Eric had already explained and has again, the absorption, transmission and reflection properties of a window are related. Yes, they all describe different parts of the mechanical behaviour of the window but they are all physically related.
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Re: window behind monitors.... best way to treat this??

Postby Guest » Mon Jan 03, 2005 1:41 pm

Eric, Ethan, Hugh, Ido (and me :roll:), whilst no-one is trying to stifle the technical discussions or avoid giving accurate advice, however important it is to get the facts right, I feel that we're going off topic again and should do this in another thread. One can always link to it as necessary when more in depth information is called for.

Eric, I know that in a detailed discussion, this stuff is very much on topic and you're trying to dispel some misconceptions and to correct innacurate statements/advice but this topic was started by someone looking for some straightforward, practical advice on how best to set up his acoustic treatment kit in his particular room. I can't speak for DoeZer (and if I'm wrong I hope he'll tell me) but I get the impression that all he wants to know are some ideas on how to get his room sounding decent without having to spend too much more money - not a detailed explaination of how acoustic barriers work. The barrier discussion is an important one that warrants detailed information but it's probably better done in a dedicated thread, leaving this one to it's original purpose.

Foz - thanks for trying to keep this on topic and trying to stop the technical details confusing straight answers to a straight question. (Something of which I'm as guilty as the others as I do actually find it interesting - sad isn't it!)

If I read it right, everyone agrees that, whatever the actual mechanisms involved, a window, whilst providing a degree of frequency dependent "absorption" (in the simplest use of the word!), does so in an inefficent and (for the purposes of this thread) unpredictable way and is therefor not worth considering as an absorber in the context of DoeZer's original question. Since DoeZer hasn't described the construction of the rest of his mix room (or the window), any discussion of the window effects out of context are a bit pointless. We don't have enough information about the construction of the rest of the room to make too many judgements on the potential problems of the window. I think we're assuming a normal house type construction but for all we know it could be a garden shed where the window already has better attenuation characteristics than the walls and roof!

I think that, as has already been said, it all comes down to whether or not DoeZer wants to be able to look out of his window whilst mixing. If yes then he lives with whatever acoustic effects the window will have on his sound or goes for either a simple curtain to tame HF reflections or Foz's much more effective option of some kind of "shutter" design. If he doesn't want to look out of the wnidow he can board/brick it up and treat the area as he would if it weren't there. I'm not forgetting about the potential for problems arising from any of these actions - I'm just ignoring them in the name of simplicity! If DoeZer wants more information on any of these than is already given elsewhere in this thread, he can always come back and ask.
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Re: window behind monitors.... best way to treat this??

Postby Guest » Mon Jan 03, 2005 1:47 pm

Oh yeah, Happy New Year, all. :)
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