Absorption coefficient /Density? -- RFZ panels

[Gregwor]

I quickly drew this up for you because I thought it would be good to have anyway! This design could be used on walls or on the ceiling by just flipping which side has the fabric covering it. On the ceiling, the ribs would be towards the floor. On the wall, the ribs would be against the wall (providing an air gap and also preventing the insulation from being pushed in if someone leans against it). If you wanted an air gap on your ceiling panels, you could either use thinner insulation such as safe'n'sound which is 3" thick or else use a 1x8 for framing instead of 1x6.

Acoustic Panel.jpg

Greg

[musictracer]

Thanks so much for taking the time to Sketch it up, Greg!
I was confused in the beginning but it all cleared up a lot with your sketch. Got a few questions though...

First of all why is there a difference between dimensions and "real life" dimensions? I know this might be a silly question but I am not very familiar with construction... Sorry...

Also if used for the ceiling, why not place it with the ribs towards the ceiling? I mean, since it will be placed horizontally, while resting its weight evenly all across its length, would it still be subject to sag? On the other hand, it would it would benefit acoustically if the gap was on the ceiling side. Please, forgive me if I am getting something wrong.

So you mean that this construction is enough to prevent sagging, right? I am only asking because I am trying to understand how sagging is developing. So either this construction prevents sagging on any side, or it sags only to the side of the gap, thus not being noticeable on any of the two sides (front / back).

When you talked about layers, I thought you meant ones that extend all across the depth, so that the weight rests on them. I mean , ie. in my case, one of the two corner traps will be triangular, so I thought you meant creating triangular dividers between every few "leafs" of insulation.

I was also considering using some kind of thin mesh around the whole trap, right under the fabric, possibly made of thin metal or plastic. Do you think that might work instead?

Lastly, I got response from Knauf here in Greece. Luckily, they were very kind to inform me about the absorption coefficients of the Ultracoustic-p, but unfortunately they had no information about its density... That's too sad because I can't design anything without knowing how much weight it should handle.
Anyways, for anyone who's interested, I have attached the coefficient charts for the 45mm and 70mm Ultracoustic-p insulation. Personally I wasn't too amazed to be honest, but what do you think?

12 - Absorcion acustica Ultracoustic 45 mm.pdf

14 - Absorcion acustica Ultracoustic 70 mm.pdf

[Gregwor]

First of all why is there a difference between dimensions and "real life" dimensions? I know this might be a silly question but I am not very familiar with construction... Sorry...

Great question. Wikipedia says this:

"Historically, the nominal dimensions were the size of the green (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). ... After drying and planing, it would be smaller by a nonstandard amount."

Also if used for the ceiling, why not place it with the ribs towards the ceiling?

The ribs will prevent the insulation from sagging or falling out.

I mean, since it will be placed horizontally, while resting its weight evenly all across its length, would it still be subject to sag?

On the wall, it would be placed horizontally and in my experience, it does not sag.

On the other hand, it would it would benefit acoustically if the gap was on the ceiling side. Please, forgive me if I am getting something wrong.

100%. That's why I said it would be beneficial to frame it in a 1x8" instead when placed on the ceiling so that the ribs would hold the insulation up AND you would be able to have the gap above the ceiling. This would result in a loss of 7 1/4" visually (yes, once you hit 8" nominal boards, the finished wood is actually 3/4" less resulting in 7 1/4" inch lumber!).

Due to this extreme height loss (visually), this is one of the main reasons John's "inside out" ceiling is such an amazing concept!

So you mean that this construction is enough to prevent sagging, right?

In my experience, yes.

I am only asking because I am trying to understand how sagging is developing. So either this construction prevents sagging on any side, or it sags only to the side of the gap, thus not being noticeable on any of the two sides (front / back).

Even rigid insulation such as Owens Corning 703 is not a super rigid material. Heck, even drywall will sag if you don't follow the recommended screwing schedule. Having the ribs hold up the insulation from below will prevent the sagging.

When you talked about layers, I thought you meant ones that extend all across the depth, so that the weight rests on them. I mean , ie. in my case, one of the two corner traps will be triangular, so I thought you meant creating triangular dividers between every few "leafs" of insulation.

In a corner trap with a bunch of triangular batts of insulation stacked on top of one another, the weight adds up and can squish the bottom most batt. You could keep stacking them until there is some squishing starting to happen. Remove a few batts and then add a divider (thin wood mounted the wall for example) to prevent this from happening. Then, continue stacking the insulation on top of the newly placed divider. Maybe no noticeable/measurable squishing will happen... I think it all depends on the density/weight of the insulation and how much you use (taller ceilings = more batts of insulation required).

I was also considering using some kind of thin mesh around the whole trap, right under the fabric, possibly made of thin metal or plastic. Do you think that might work instead?

What for? Any material in front of the insulation will affect the performance of insulation at different frequencies. You could even put a thin layer of wood entirely covering the trap. This would reflect high frequencies back into the room but low frequencies would continue to be "trapped" so to speak. Here is a formula to calculate that:

F = 90 / m

F = The frequency at which the material transmits 80% of the sound
m = The surface Mass of the material in kg/m2

effect-of-plastic-sheet-foil-on-porous-absorber.jpg

I have attached the coefficient charts for the 45mm and 70mm Ultracoustic-p insulation. Personally I wasn't too amazed to be honest, but what do you think?

I'm not sure how they were mounted during testing because either it wasn't documented, or the fact that I can't read that language! However, it doesn't look great. The low end coefficients look closer to the performance of foam than a good acoustic insulation

Greg

[musictracer]

"Historically, the nominal dimensions were the size of the green (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). ... After drying and planing, it would be smaller by a nonstandard amount."

Ok, thanks for mentioning. I wasn't planning to plan anything in my case, but it's good to know.

Quote:
I mean, since it will be placed horizontally, while resting its weight evenly all across its length, would it still be subject to sag?

On the wall, it would be placed horizontally and in my experience, it does not sag.

Kind of confused with this... I meant the whole panel is placed horizontally when placed across the ceiling (which also lies across the horizontal imaginary axis), while it is placed vertically when placed against a wall (which lies across the vertical imaginary axis)

Even rigid insulation such as Owens Corning 703 is not a super rigid material. Heck, even drywall will sag if you don't follow the recommended screwing schedule. Having the ribs hold up the insulation from below will prevent the sagging.

Great, thanks for mentioning!

In a corner trap with a bunch of triangular batts of insulation stacked on top of one another, the weight adds up and can squish the bottom most batt. You could keep stacking them until there is some squishing starting to happen. Remove a few batts and then add a divider (thin wood mounted the wall for example) to prevent this from happening. Then, continue stacking the insulation on top of the newly placed divider. Maybe no noticeable/measurable squishing will happen... I think it all depends on the density/weight of the insulation and how much you use (taller ceilings = more batts of insulation required).

Ok, thanks for confirming my initial assumption on what you described in the first place. It makes perfect sense!

What for? Any material in front of the insulation will affect the performance of insulation at different frequencies. You could even put a thin layer of wood entirely covering the trap. This would reflect high frequencies back into the room but low frequencies would continue to be "trapped" so to speak.

Of course, I know this. But first of all in one of his comments in this thread, Stuart himself advised the use of a mesh in the case of first reflection panels to prevent sagging. Also, there is a great possibility that the room will sound quite dull after the cloud and the traps placement. So I thought I'd hit two birds with one stone: Deal with sagging and reflect a little bit of the mid/high frequency energy. In any case, the mesh would be quite thin, and at the same time it will have been placed behind the speakers (covering the corner traps), so there will be near zero chance of a direct reflection from speaker to mesh and subsequently to the sweet spot, eliminating the chance of comb filtering or stereo image distortion.

F = 90 / m

F = The frequency at which the material transmits 80% of the sound
m = The surface Mass of the material in kg/m2

Very interesting, but unfortunately I don't think I have the chance to know/buy specific surface Mass material where I live, but I will look for it if necessary. Thanks for mentioning anyways . . (By the way, is the image taken from the master handbook of acoustics? I think I have come across it somewhere in the past...)

However, it doesn't look great. The low end coefficients look closer to the performance of foam than a good acoustic insulation

Yeah, like I mentioned before, I wasn't impress either.
Today, I found there is a dealer of Isover products nearby and I was surprised positively. So I searched about Isover alternatives to the knauf ultracoustic-p and I found there is a product called PIANO that is of impresively low density (15kg/m3 , GFR ≥ 5000mks Rayls) but the acoustic properties seem just a little bit more efficient than the knauf one.
I just don't understand why these companies rate these products as high efficient acoustically, and also give them such names (Piano, ultracoustic-p etc.) Maybe it's just a commercial trick... don't know....
https://saint-gobain.gr/sites/default/f ... -27-en.pdf.

So what do you think about this one? The depth is a little different, so there can't be direct comparison of the charts, but generally it doesn't seem to perform a lot different than the ultracoustic-p.
But on the other hand it's hard for me to believe that such behemoth companies don't make any products that would suit our acoustical needs...

Also I found this product, that seems to perform a bit better, but isn't the GFR a bit high for basstraps ? :

isover akustic ssp.jpg

What about you, Greg? Have you had any experience with Isover products? Anything you might recommend, to save me from this rough sea...

[DanDan]

I have had good success with Isover High Performance Duct Cladding. But at the time it was before the Ecose movement. Itchy and Scratchy.
In Europe Polyester Fibre is becoming more and more available. High absorption, hangs without sagging, fire certified, cosmetically finished- no fabric.
https://www.don-audio.com/Caruso-B100-B ... absorber_2

IMO it would take quite a thick plastic layer to reflect significantly, and there goes your fire insurance.
While fibre treatment will shorten and lessen the room tone, when it removes early reflections this results in less HF destructive comb filtering. Result, a very bright clear sound in the direct field.

[musictracer]

Oh, Dandan! One of the usual suspects!
Welcome and thanks for contributing!
The CARUSO-ISO-BOND you linked is an unbeatable product! But I'd rather give my money to a charity fund rather than spend 300 € for 6 leaves of polysterine.
Besides, I think I have already decided to use this product of polysterine :
https://balamoti.gr/domisi/domika-ylika ... 120x60x30/
The 50mm costs nearly 10 times less than the Caruso , while acoustically it seems that it can match the caruso with 2 or 3 leaves. I am thinking of using it for the cloud, 4 leaves on top of each other, maybe 3 stacks one next to the other.

While fibre treatment will shorten and lessen the room tone, when it removes early reflections this results in less HF destructive comb filtering. Result, a very bright clear sound in the direct field.

Yes but the absorption in the mid and high frequencies is always more than the lower ones and that might result in a dull room...

But what do you think of the products I presented before? Would they make any significant difference in my small room when placed in a 30X60X240 cm rectancular trap on one front corner as well as a 150cm high - 60cm deep triangular trap on the other ?

By the way, you are missed from the GS forum... I don't know what happened, but I hope you will be back soon

[Gregwor]

Kind of confused with this... I meant the whole panel is placed horizontally when placed across the ceiling (which also lies across the horizontal imaginary axis), while it is placed vertically when placed against a wall (which lies across the vertical imaginary axis)

Sorry, it's pretty hard to use proper descriptive words when referring to an object in the 3rd dimension
I'm going to try this method:

When looking at the cross sectional view of the placement,

On the ceiling, it would look like this --------- and the ribs would be on the bottom side holding up the insulation.

On the wall, it would either be like this:

-------
|%%%%%|
|%%%%%|
|%%%%%|
|%%%%%|
-------

or like this:

----------------
|%%%%%%%%%%%%%|
|%%%%%%%%%%%%%|
|%%%%%%%%%%%%%|
----------------

and the ribs would be on the "back" part of the panel as you look at it. The ribs would be "behind" the insulation which would both create the air gap and prevent the insulation from being pushed up against the wall if someone were to lean on it.

I hope that makes sense now. If not, I might have to sketch something up for you.

(By the way, is the image taken from the master handbook of acoustics? I think I have come across it somewhere in the past...)

I got it from our dear friend Stuart.

I just don't understand why these companies rate these products as high efficient acoustically, and also give them such names (Piano, ultracoustic-p etc.) Maybe it's just a commercial trick... don't know....

These products DO perform great acoustically. But only in the frequency range that MOST of their clients care about -- the vocal range.

So what do you think about this one? The depth is a little different, so there can't be direct comparison of the charts, but generally it doesn't seem to perform a lot different than the ultracoustic-p.

You answered the question yourself. If the specs says it's similar, then it's similar!

But on the other hand it's hard for me to believe that such behemoth companies don't make any products that would suit our acoustical needs...

Most of these companies don't really care about low frequency performance. Their clients buy insulation for their thermal properties. It just so happens that insulation rocks for acoustic treatment!

What about you, Greg? Have you had any experience with Isover products?

I haven't ever used the brand (I believe Certainteed is the Canadian name for the product) for anything acoustic-related. I've seen some home builders use it for thermal purposes. That's all.

Greg

[musictracer]

I hope that makes sense now. If not, I might have to sketch something up for you.

No no, that's fine, you really don't have to, what you describe is exactly what I thought you meant in the first place. My concern regards the sagging possibility of the cloud when placed upside down. But yesterday I browsed a picture in the Gearslutz forum showing a sagging cloud, so I am convinced .

I got it from our dear friend Stuart.

Great! Another wonderful Sir who's always willing to help! I guess he presented it in a conversation, so this is why it ringed a bell to me.

Yesterday, while trying to find more info about the cloud design and placement, I found out that most people agree that it should be placed half way between the speakers and the sweet spot, absorbing the first relfections, kind of how the panels are placed on the walls, is that right? Of course I have seen others covering the whole area, all the way from speakers to the sweet spot.
I'd also like to mention that I have a bump around 123 Hz which by calculations I found it must be due to a vertical axial mode. If that's the case:
1. should I consider covering the speakers along with the first reflection point, or
2. should I prefer to cover the sweet spot along with it (the first reflection point) ? Or maybe
3. should I only cover the first reflection point

I am asking this because it is rather impossible to cover the whole area, all the way from speakers to the sweet spot.

Also I think I made a decision regarding the absorbing material of the cloud. And that would be this:
https://alphacoustic.com/wp-content/upl ... %CE%B1.pdf

My choice would be the one with the greatest absorption coefficient on the 125hz. But there is a misconception in this leaflet, I didn't notice until now. The first page graph which is refered to the 25/50 product is identical with the green line graph of the second page which is refered to the 38/50 product. I just can't believe how they missed that...I will call them again tomorrow to clear this up.

But what do you think of it? Would it be good enough for the cloud? I only hope it is the 25/50 (25kg/m3, 50mm) that corresponds to the greatest absorption coefficient on the 125 hz, since I want it to be as light as possible, and since there will be 12 pieces (2 stacks of 1,5 * 4 each) hanging from the ceiling, its weight - without the frame - will be limited to around 8,5 kg, which is quite reasonable for me. I will be making a sketch soon, but any recommendation is much appreciated.

[Gregwor]

1. should I consider covering the speakers along with the first reflection point, or

I would if possible because as frequencies get lower, they become more omnidirectional.

But what do you think of it? Would it be good enough for the cloud? I only hope it is the 25/50 (25kg/m3, 50mm) that corresponds to the greatest absorption coefficient on the 125 hz

I can't read it but I could make sense of the graph. I would go for the 25/50 one as it won't kill the high end as much and it has better performance down low.

its weight - without the frame - will be limited to around 8,5 kg, which is quite reasonable for me. I will be making a sketch soon, but any recommendation is much appreciated.

I've attached that quick panel .skp I drew up in case it helps you in any way (ignore/delete the silly floor I drew to shadow onto!).

Acoustic Panel.skp

Greg

[musictracer]

Thanks a lot for sharing the sketchup file, Greg. It might become really handy when designing the cloud...

So, here are my sketches for the rectangular trap as well as the triangular superchunk - with real dimensions. Any opinions, much appreciated!

rectangular bass trap - fixed.jpg

triangular bass trap - fixed.jpg

Also, after all this time researching on what insulation products that I could use are available in Greece generally, as well as speaking directly (phone / email) with the companies to get more info and recommendations on the products I made a little table gathering the most significant info, to be able to present here and choose from. As far as the response the companies gave me I have to say I was very pleased by most of them. Alpha Acoustiki, Fibran, as well as Knauf here in Greece responded directly and even on the phone they were very kind to assist me with my project no matter how low cost it seems in contrast with the projects they are dealing every day. Very impressed! The only company I haven't gotten response from yet is Isovar, but arguably they will respond within the next few days.

Also regarding the leaflet misconception of the izifon product I refered to previously, the company assured me that the right measurements are the ones on the second page, so the plot of the first place can be safely ignored. (They said that it refered to a previous test of the product, though personally I don't know if that makes any sense since it was included in the same leaflet with the "new" measurements. Anyways, it might just be a printing mistake or so...)

So, voila! (Greek guys you can thank me later ):

Porous Absortpion Products Data (m.tracer).jpg

And a couple of plots that might be handy as well. Thought to share since I have them:

fibran b-040.jpg

knauf ultracoustic - p.jpg

So, any ideas on what to choose ?

[Gregwor]

Nice work! And speaking on behalf of everyone using this forum, we appreciate your time and contribution!

So, any ideas on what to choose ?

Taking acoustic measurements will determine what product to use where/when. If you need to address high frequency issues, then use the product that has the best absorption coefficients in the high frequencies - of course check with the acoustic modeller as the depth of the insulation and configuration changes the performance as we've seen above. If you're targeting low frequencies, use the insulation that performs the best at low frequencies. I think it's that simple!

Greg

[musictracer]

Here are a few measurements I did some time ago including or excluding side / sbir panels in place.


Response (green is with panels in place) :

sbir + side.jpg

RT60 without panels in place:

rt60 - without.jpg

RT60 with panels in place:

rt60 with.jpg

Waterfall without panels in place:

waterfall - no treatment Panels.jpg

Waterfall with panels in place:

waterfall - with Side + SBIR Panels .jpg

Personally I am more tempted to tame the rt60 and response below 200, since it is where the greater issues appear (as usual in a small room). In addition I will be hanging a big cloud on the ceiling, so I don't worry much about the mid /highs at this stage.

But judging by the measurements, is there a product from the table you would recommend?

[Gregwor]

Could you upload your mdat file? The pictures you posted are somewhat hard to read as the min/max values on the X and Y axis aren't what I prefer.

As for the low end ring, again, treat that with a product that has the greatest absorption coefficients at 125Hz. For bass traps, you're going to want to retain high end because I believe you already have a low RT60 in the mids and highs. So you'll want to face the bass traps with something.

Greg

[musictracer]

Here is the .mdat :
https://www.dropbox.com/s/xzja3ay92fudh ... 9.rar?dl=0

Regarding the low rt60 of the mid and high end, I would like to mention that possibly I might have had a carpet on the floor when taking these measurements, I am not sure. I don't know how much that might have affected the results, but I thought it would be good to mention.

But there is another think you possibly could assist me with. With the cloud addition it is likely that the rt60 of the highs will decrease even more. So, it is more likely that I will need to add something on the face of the traps to reflect them (the mid / highs). My plan was to make the front fabric of the traps removable in the first place anyways , so that I could "edit" the panel if I wanted, ie. for replacing the insulation, or adding reflecting surface (the fabric would be attached on the front wood frame by using velcro tape).

BUT, in this latter case of adding a surface, I would probably need to have some space between the fabric (meaning the front face of the trap) and the insulation behind it, so that the reflecting surface (or slats) could fit in. So my question is how thick might the surface / slats might be so that I could calculate the gap I should leave between the front face fabric and the insulation ? (I hope I gave a could description of what I mean, but if it doesn't make sense to you I could try better in my next post)

Also, my panels use 4 inch 150kg/m3 insulation with an impressive absorption coefficient of 0.35 @125hz . It is this one:
http://www.metaxiotis.gr/xml/pdf/Navisi ... 0%20gr.pdf

Is it really performing the way it should? (Used 2 side panels on F R points as well as one for SBIR.)

[Gregwor]

Here is the .mdat :

The rar has no files to extract

I would like to mention that possibly I might have had a carpet on the floor when taking these measurements

That would make a huge difference!

So my question is how thick might the surface / slats might be so that I could calculate the gap I should leave between the front face fabric and the insulation ?

I would suggest just leaving the fabric framing until the end when you've got the room tuned to your liking. Then build the accordingly.

Is it really performing the way it should?

We would need to see a baseline measurement, and another one with the treatment in place so that we can compare the two.

I realized we don't have any SketchUp or real pictures for your room. Care to share something?

Greg