Cloud panel setup question...

[tnsngwtr]

Treatment of my room is an on going process. I've attatched a picture of my studio to help explain my questions...

I have some 703 panels covering the walls and a few first reflection points. My next project is to hang a couple cloud panels above my listening position. My first question is this:

I have nearly 12' ceilings. How low should the panels be hung? I know that space between panels is desired, but is there such a thing as too much space? is 4' or 5' of space too low to hang them?

Also, I hadn't thought of these panels necessarily as "bass traps". My goal was initially to kill reflections. The more I read, the more I hear people building and referring to them that way. My NEXT project is to hang 4" rock wool panels vertically in the corners and from the ceiling near the walls to help tame the low end issues. So my second question:

Should I concentrate more on the bass with the cloud panels? I had planned to use 2-2.5" 703 with FRK.

My room is small and oddly shaped, I've found my biggest problem is my stereo image. I don't have much coverage on the protruding closet to the right of the mix position, and I think that's where a lot of my problem comes from. I'll be fixing that very soon. Thid question:

Since I'm tight for space, will all the bass traps I'm placing up high in the room (11') be as effective as if they were lower?

Thanks in advance for the advice. It doesn't get said enough, but all the guys who have acoustical companies offering up their knowledge is incredibly helpful to guys like me

-Seth

[Glenn Kuras]

I have nearly 12' ceilings. How low should the panels be hung? I know that space between panels is desired, but is there such a thing as too much space? is 4' or 5' of space too low to hang them?

I would space them off the wall the thickness of the panel. So if the panel is 4" thick then hang them 4" down. You could go a bit more but to "play it safe" stick with the above.

Should I concentrate more on the bass with the cloud panels? I had planned to use 2-2.5" 703 with FRK.

My room is small and oddly shaped, I've found my biggest problem is my stereo image. I don't have much coverage on the protruding closet to the right of the mix position, and I think that's where a lot of my problem comes from. I'll be fixing that very soon. Thid question:

For the early reflection point panels it is not recommend to use FRK on the faces.

[tnsngwtr]

Originally Posted by Glenn Kuras

I would space them off the wall the thickness of the panel. So if the panel is 4" thick then hang them 4" down. You could go a bit more but to "play it safe" stick with the above.

just to clarify, you are recommending hanging the clouds the width of the panel from the ceiling? so rather than hanging them right above me 6 or 7 feet, they should be close to the ceiling?

[SAC]

Originally Posted by tnsngwtr

just to clarify, you are recommending hanging the clouds the width of the panel from the ceiling? so rather than hanging them right above me 6 or 7 feet, they should be close to the ceiling?

I need a bit of clarification as well, as I am quite confused by your description!


He is saying that, if the panels is 4 inches deep (for example), that you can obtain the behavior of a panel effectively ~8 inches thick, by suspending it about 4 inches from the boundary surface.

That is : boundary| 4 inch gap| 4 inch panel.

See D'Antonio & Cox: Acoustic Absorbers & Diffusers, 2nd ed. figure 5.20

[DanDan]

Surprisingly it appears that the notion that the gap is optimum when equal to the panel is simply not true.

Andre has explained this in detail over here. Post 5
Q 4 Avare

Here are a couple of extracts which should draw some interest.

gaps greater than the thickness of the porous material provide flat absorption.

Gapping is used to lower the effective frequencies of the sound absorption.

The efectiveness of a non thin absorber is not significantly reduced when located in the relatively low region of particle velocity

His post indicates that you may hang the cloud at any height you wish, the bigger the gap the better. I would go even further, if you create an extensive cloud with a huge gap, it should functions as an extremely broad band trap, possibly eliminating the need for much other trapping.

DD

[SAC]

No, it does not function literally as a panel twice as thick! The problem here is with the assumption.

The point is, the gap where the material is absent, is an area of lower velocity and hence less absorption relative tot he 1/4 wavelength frequency where the porous absorption is positioned. The absorptive porous material present is now physically positioned to an area of lower frequency (a longer 1/4 wavelength equals greater spacing!) where you now get to factor in just 'how much' effective porous material there is to mitigate the kinetic energy at that position in space - and in repositioning the material, modify the effective frequency of the porous absorber (and this is not a linear function).

Thus using the rule of thumb of double the thickness provides an effective range of absorption over a bandpass without radical non-linearities in the effective response relative to the incident boundary surface! But it is NOT a precise statement! The problem occurs when this is taken literally. But then an asymptote doesn't literally equal zero, but a generalization would say that it tends to zero, or even that it does approximate zero. Oh, but that invokes math, doesn't it - sorry, my bad.

But we can also reliably state that a, say, 2" absorptive panel mounted directly to a boundary surface, will not be as effective in its lower range as the same panel mounted with a gap from the wall. And without a complex analysis of the relationship of panel thickness to gap, a panel thickness equal to the gap is a simple rule of thumb to follow to obtain a reasonable estimation of its range of effectiveness.

We could carry this to an extreme and place a 10 inch thick porous panel in the middle of the room, thus potentially corresponding to some 1/4 wavelength, but it means little if it is not mounted relative to an incident surface. And we now get to examine the effect of the thickness of the absorption alone sans its relationship with a boundary. In this scenario the gap becomes essentially meaningless!

Thus the attempt to equate the absorptive efficiency of a gapped panel with a panel literally the same thickness of the panel plus gap in a 1:1 relationship is erroneous and a straw man from inception. But it can be shown that the near equation of the effect - the generalization, is acceptable.

The primary reason for the gap and the resulting generalization is simply that filling the gap provides a diminishing return on investment in that the additional absorption provided by, say, a doubling of the absorptive material is NOT a doubling in the amount of energy absorbed! Thus you can get much of the desired absorption without using all of the volume of absorption! But no, it is, and never was, a 1:1 relationship where gap equals porous absorption! If such were the case, we could simply eliminate the absorptive material and allow air to function as an absorptive media and expect an efficiency equal to the same space filed with porous material! And I don't know of anyone who ever proposed such a scenario.

And we know this from various scenarios with straddled corner traps versus multiple layers versus superchunk corner traps. The increase in efficiency is NOT linear. And in fact, the largest ROI is in the straddled panel using the lease absorptive material. Note, that does not make it the most effective, but from a ROI on investment POV, it is most efficient.

It is NOT because we adhere to the fantasy that such a gap magically provides a doubling in the efficiency of the porous panel. It is because, in dealing with porous absorption, that the addition of such porous material in a region of low velocity provides reduced efficiencies that do not substantiate the ROI for the addition of porous material in the space. Its simply a matter of getting your larger return for the buck... Not some imagined equation of air being equal in absorptive efficiency for kinetic energy with porous materials.

If it were, I would be among the first to market my soon to be announced air absorber (patent pending) that not only is as efficient as a porous absorber, but it is easier to mount and excels with respect to the 'wife acceptance factor' for home theater applications. (My only surprise is that someone has not already done so!)

It is frustrating to deal with acoustics in a non-technical manner devoid of math where many object to its imposition upon the discussion while at the same time demanding that such issues be brought to bear on the generalized subject as an objection. But then, if we were to rigorously do so, we just might understand why the use of tuned resonant panels so dominate the professional markets for LF modal issues at the expense of porous LF absorption as is so adamantly stressed in such references as the D'Antonio & Cox Acoustic Absorbers and Diffusers and their and other prominent designers' various papers.

[DanDan]

Well stated by SAC, but possibly not entirely correct in many ways.
There is a very different view stated in Andre's post in that Q4 Avare thread.
Highly recommended.
I would have advised exactly as Glenn, John Brandt and many others do, i.e. A gap equal to the panel depth is best. Well, it looks right and in many situations is the most suitable choice. However, Andre has illustrated the we were quoting a myth. A bigger gap is better.
DD

[SAC]

The much larger issue is that we are using an inherently inefficient brute force method of absorption to mitigate LF that is effective only to mitigate high kinetic energy (velocity) sources in regions inherently characterized by low velocity and high pressure!

And larger gaps simply render the porous absorber more efficient at lower frequencies as its positioning is closer to the 1/4 wavelength of the low frequency desired!

This is like a discussion where we debate how much more efficient the use of a chisel would be compared to a screwdriver (mis)used as a chisel!

As such, a gapped absorptive panel is more efficient than a non gapped panel of the same thickness, and slightly less effective than a solid panel traversing the entire distance from wall to panel surface. But the gapped panel offers the largest ROI.

Its always fascinating to witness someone with little to no physics background assume the role of arbiter of other much more accomplished professionals' research. And citing what some are bold enough to label as incorrect, here is published measured data supporting the effectiveness of a gap equal to the thickness of the porous absorber from the apparently unreliable D'Antonio & Cox Acoustic Absorbers & Diffusers, 2nd ed.:

[DanDan]

Again from Andres post.

The effectiveness of a non thin absorber is not significantly reduced when located in the relatively low region of particle velocity.

DD

[SAC]

A porous absorber is not efficient in a region of low (kinetic energy) particle velocity (and high potential energy/pressure) PERIOD!

It becomes a bit more difficult to dissipate kinetic motion as heat when there is little or no motion!
And at the boundary condition where particle velocity reaches zero, the porous absorption efficiency approaches zero!

Porous absorption achieves a maximum potential for kinetic energy dissipation at a distance from a boundary equal to 1/4 wavelength - and you will notice that there is NO mention of the thickness or amount of porous absorption specified. (Additional to the spacing relative to a boundary, the rule of thumb is that the efficiency of the absorptive panel is most effective when its porous thickness also correlates to a minimum of 1/4 wavelength of the lowest frequency to be absorbed.)

There is much more to be done if one chooses to employ only porous absorption as a one size solution for all situations regardless of the physics involved. And the last thing to be expected in such a situation is to expect some linear relationship between spacing or material and efficiency!

[DanDan]

Capitals won't alter the laws of physics.

The classic way that the effect of gaps is explained is by use of graphs of thin absorbent material spaced away from a wall. The graphs show high values of α where the distance from the wall is 1/4 wavelength and 0 when the wavelength is 1/2. In other words the porous material is effective only where the particle velocity is high. These graphs are appropriate for thin material. The porous materials that we consider when discussing the use of gaps are not thin at the wavelengths significant to us. Therefore the graph is not accurate for our use of gapping!

DD

[SAC]

Change the laws of physics???? Simply acknowledging them would be a fine start. And to that end here is a bit from P. D'Antonio, Phd.

But then, what do they know about absorption and diffusion?

[DanDan]

Avare has proven himself to be a very considered and careful scientist.
In the linked post he states that the typical panels and traps we use are not at all thin in context. As they are not 'thin' many of the typical 'rules' established with thin or hypothetical panels, simply no longer apply.
This is the new stuff.

The first one which bites the dust is the 'equal depth of airgap and panel is optimum, most linear'.

Acoustic celings show no non-linearity, with 16 inch gaps. The peak and ripple generated by the Porous Material Calulators simply doesn't happen.

703 on a surface, no gap, is shown to be extremely effective down to 125Hz.
This is entirely in the 'low velocity zone'

The vast majority of our treatments are on or close to the wall.
Given the low, and at the boundary, no, particle velocity/displacement, how or why do our treatments work?
Andre's piece is the first I have seen to provide some attempt at explaining this.

SAC, it is pointless us firing other peoples quotes back and forth here.
I strongly recommend that you at least read the post in question.
If he is correct, it would appear that the common understanding is not fully correct. No-one has so far challenged him, the post is that clear.
If you have a decent scientific challenge to any of his assertions, it would be great to see it, in that other post.

Back to the OP and Topic.

I have nearly 12' ceilings. How low should the panels be hung? I know that space between panels is desired, but is there such a thing as too much space? is 4' or 5' of space too low to hang them?

4-5 is not 'too low'. This is in fact vastly superior to a small gap.

Should I concentrate more on the bass with the cloud panels? I had planned to use 2-2.5" 703 with FRK.

Sounds like a good plan to me. If you are building a frame or chose to install a regular suspended grid, consider that fact that a thicker layer of lighter, much cheaper, fibre will perform much better. e.g. a foot or more of light attic insulation over fabric or acoustically transparent ceiling tiles would be mega.

Since I'm tight for space, will all the bass traps I'm placing up high in the room (11') be as effective as if they were lower?

If you provide dimensions and info as to what the walls etc. are made of we could predict modal buildup.
However, you can do this more certainly by triggering the modes directly using sine waves. Run a Mode Calc, find the likely modes. Sweep sines around those frequencies to exactly hit resonance. Listen or use an SLM to find the hot spots. Good locations for bass traps.
DD

[Glenn Kuras]

And the battle rages on!!!!!!!!

The best way to say this is your both right on many points but if you want to be safe then I would space it the thickness of the panel. If you space a 2" panels 5" from the ceiling your world WILL NOT COME to a end.

enough said

Acoustic celings show no non-linearity, with 16 inch gaps. The peak and ripple generated by the Porous Material Calulators simply doesn't happen.

There is lab testing on this, but it shows them as several panels put together to make one large panel. I question what might happen if you where to take them and spread them out.

[DanDan]

Hi Glenn, I am pretty sure the OP was referring to 4-5 FEET below his 12 foot high ceiling.

Again, like you, I intuitively suggested that there must be some limit to this.
e.g. what happens when the panels are spread out, or if there is just one panel? Or put another way, what happens when the dimensions of the panel begin to appear small compared to the gap?

I think the topic does deserve teasing out, and again I recommend that
Q4 Avare is the best place to do it.

I suggest that the OP has been answered, no-one seems to suggest there is nothing but good to be had from a 4-5 foot drop, even with spread panels.

Low flying clouds are quite common IMHO ;-)

DD

[Glenn Kuras]

I not so secure on 4 to 5 feet with them spread out. If a customer was buying from me I would not recommend it. Though I would feel as it would serve the purpose of the early reflection point though (maybe).

[DanDan]

Me too, although on the other hand having the cloud close to the listener and speakers clearly has merits. It is difficult to shake the intuitive assumptions.
Gap = Panel just looks right. However Andre is very convincing, using simple physics. I have asked a couple of questions just now over at the other thread.
I am sure the answers will remove all doubts.
Interesting eh?
DD

[Glenn Kuras]

I will have to look at the thread but the wave going through the panel goes through twice, so if you space it that far off the wall it will only go through once. I know there are other factors though. If the panels are large (or grouped together) I can see how it would solve that problem. Spread out though I am not so sure.

[tnsngwtr]

I was referring to hanging the panels 4-5' below my ceiling, so that (which i could understand) is great advice and answers my questions thanks!

[DanDan]

The OP used a single comma, a 12' ceiling and 4'-5' drop.
I doubt that you have a 12 inch ceiling.
Just to be clear, in words only please, do you mean four to five feet or inches?

Note it would not change my recommendation. I reckon 4-5 feet is quite reasonable IMNO. I have however asked for clarification, so you might find it well worthwhile to view that other thread to see Andre's answer.

DD

[tnsngwtr]

Originally Posted by DanDan

The OP used a single comma, a 12' ceiling and 4'-5' drop.
I doubt that you have a 12 inch ceiling.
Just to be clear, in words only please, do you mean four to five feet or inches?

oops. yes. i edited the above post. i did mean hanging them 4-5' below my 12' ceiling. thanks!

[DanDan]

The effect of such a large gap and spread panels is unknown. How about hanging your panels at 9 feet? This should hit the second height mode, and will probably also benefit from gap effect.
DD

[tnsngwtr]

great. i can always move them, but that sounds like a good place to start. thanks!

[Glenn Kuras]

I would recommend if you go that route (I would not but hey that is me) I would group the panels together and make the area as LARGE as possible.

[Seamus TM]

A 12' ceiling would have the first mode 47Hz and the second at 94Hz.

So, 1/4 wavelength of 47Hz is 6' and the 1/4 wavelength would be 3'.

If the room has been measured, and there is actually a problem at 94Hz due to the height, maybe hang them 3' from the ceiling...
then fill all that space with R30 .

[avare]

DanDan brought me back to this thread. With ~2.5" FRK 703 doubled up to yield ~5" thick, space it 8" from the ceiling. This will give flat absorption down to ~50 Hz.

Andre

[Seamus TM]

Originally Posted by avare

DanDan brought me back to this thread. With ~2.5" FRK 703 doubled up to yield ~5" thick, space it 8" from the ceiling. This will give flat absorption down to ~50 Hz.

Andre

Let me guess...
5% of 50Hz wavelength is approximately 13".
Am I close?

[avare]

Originally Posted by Mumblesound

Let me guess...
5% of 50Hz wavelength is approximately 13".
Am I close?

Yes you are close, but not to what I think the question is.

I think what you are wanting to ask why did I write that the material/gap would be flat down to ~50 Hz. The answer is test results shown in fig 1 of BBC RD 1992/11
, modified by logical extrapolation of the differences in material.

In other words, test data realistically applied. No guessing or myths. thumbsup

Andre

[Glenn Kuras]

Originally Posted by avare

DanDan brought me back to this thread. With ~2.5" FRK 703 doubled up to yield ~5" thick, space it 8" from the ceiling. This will give flat absorption down to ~50 Hz.

Andre

I believe these are going in the early reflection point so FRK on the fronts is not recommend. Or did you mean the backs??

[avare]

Originally Posted by Glenn Kuras

I believe these are going in the early reflection point so FRK on the fronts is not recommend. Or did you mean the backs??

Oops, agreed that if it is for ISD control, then the FRK should not face the front. Thanks for catching that.

Edit: Thinking over the post, I may have made impression that FRK is prefered for this application. The reason I wrote about FRK material is because that is what OP asked about.

Andre